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Rocks from Space

A series of articles published by Space.com between 1999 and 2004

By Michael Paine and Rob Roy Britt

All articles are copyright of Space.com

Rocks from Space

Contents Chicken Little Was Right: The Sky Is Falling........................................................ 3

Riches in the Rubble ............................................................................................ 6 Asteroids & Tsunamis ........................................................................................ 10

How an Asteroid Impact Causes Extinction........................................................ 15 Your Ancestors May Be Martian......................................................................... 19

Did Asteroid-Induced Firestorm Destroy the Dinosaurs? ................................... 24 Prospecting for Oil? Look In an Asteroid Crater ................................................. 28

Simulating Armageddon on Your PC: Asteroid Impacts with Earth .................... 33 Asteroid Hunters Downgrade Overall Threat to Earth ........................................ 42

Defending Earth: Fact Vs. Fiction....................................................................... 46 Fossilized Bacteria Found in Ancient Meteorite ................................................. 55

Saturn 5 Blueprints Safely in Storage................................................................. 57 Bigger Telescopes Seek Killer Asteroids............................................................ 59

Next: Space-Based Telescopes for Asteroids?.................................................. 69 Scientists Study the Effects of Comet Linear's Breakup..................................... 70

Killer Asteroid Hunt Reaches a Milestone .......................................................... 73 Meteor Showers and Shooting Stars: A Primer.................................................. 75

Hunt for killer asteroids is a global responsibility: UK Report ............................. 78 British Asteroid Report Takes Some of Shine Off the Sydney Olympics............ 81

Mars Explorers to Benefit from Australian Research.......................................... 83 Asteroid May Have Created Hawaii.................................................................... 87

Viking Data Still Cause Stir About Mars Life ...................................................... 91 Search for Large Asteroids Nears Completion, Experts Ponder Gaps in Program........................................................................................................................... 97 Reinventing Darwin Again: How Asteroids Impacted Human Evolution ........... 101

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Chicken Little Was Right: The Sky Is Falling By Michael Paine Special to space.com posted: 06:07 pm ET 05 November 1999 On a clear, dark night away from the city lights you might be lucky enough to glimpse a grain of sand colliding with the Earth at 15 miles per second. To our primitive ancestors, these "shooting stars" must have been the most interesting objects in the night sky -- brief flashes of light to break the monotony of the fixed stars. Of more practical concern to the ancients, however, was the passing of the seasons. The science of astronomy became a respected means of timing the planting of crops and hunting migrating herds. The elite practitioners of this science probably dismissed shooting stars as unimportant and this attitude persisted until just a few decades ago. From time to time, the peace and tranquillity was broken by violent events -- collisions with large chunks of rocks from space. Most of these collisions were destructive. Some may have pushed the human species close to extinction, but sometimes they brought a blessing, such as mysterious metals that could be pounded into weapons and tools. Violent cosmic collisions are inevitable events on a time scale of thousands of years, but not during a human lifetime. Without firsthand accounts of impacts there was no reason to suspect that a hazard existed. This changed in the 1960s. Robotic spacecraft sent back pictures of thousands of impact craters on most of the airless moons of our solar system, as well as on the planets Mercury, Venus and Mars, where craters are not obscured by plant growth or oceans. Hundreds of impact craters have since been discovered on the surface of the Earth. The scientific study of asteroids and comets became respectable.

Our neighbors in space

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The Earth and the other planets orbit the sun in near-circular paths and stay well away from one another in their respective "running lanes." Many asteroids and comets also orbit the sun in near circular orbits well away from the Earth. However, some of these objects are occasionally sent into elongated orbits and they venture into our region of the solar system. If their running lanes cross Earth's they become a threat. Comet Halley circles the sun every 76 years and spends most of its time out beyond the orbit of Saturn. But every year the Earth crosses Halley's running lane and collides with tiny bits of the comet. The results are the Eta Aquarid and Orionid meteor showers. If Halley's orbit stays the same then eventually, perhaps after hundreds of millions of years, the Earth and Comet Halley will collide at more than 100,000 mph. A "dirty snowball" ten miles across can make quite a mess at this speed -- just ask the dinosaurs. Comets, however, are not the greatest hazard to the Earth. We share our running lane around the sun with millions of asteroids. Most of these chunks of rock are less than 50 yards across and, if they collide with the Earth, will burn up in the upper atmosphere. Asteroids between 50 and 200 yards across will typically explode several miles up in an "airburst" -- much like a hydrogen bomb. One such event devastated 800 square miles of Siberian forest in 1908. Larger asteroids will reach the Earth's surface and, if they hit land, will form an impact crater. Asteroids and comets with orbits that come close to the Earth are known as Near Earth Objects. (Rather a dull name!) [image] The asteroid Ida is about 32 miles long. Above, Comet Halley. IMAGES: NSSDC/NASA

The odds of an impact Based on estimates of the number of objects out there, astronomers expect an asteroid 1 kilometer (1,100 yards) in diameter to collide with the Earth about once every 100,000 years, on average. Such an impact is thought to be at the threshold of global catastrophe. 100 million people could die, mainly from starvation due to global crop failures. It is also likely that the fragile global economy would collapse. Impacts by small asteroids occur more frequently but do much less damage. An asteroid 50 yards in diameter could easily devastate a

Rocks from Space

city. With asteroids more than 200 yards in diameter there is an additional risk to coastal cities from tsunami (tidal waves) caused by ocean impacts.

Looking out for NEOs The chances of an impact by a large asteroid or comet are very small, but the consequences for our civilization are very grave. After watching the movies "Deep Impact" or "Armageddon" you might have come away thinking that dozens of telescopes and hundreds of scientists are busy searching for "a big one with our name on it." But only a handful of professional searches are underway, and none of these cover the skies in the Southern Hemisphere. As it now stands, if a large asteroid is on a collision course with the Earth then the odds are 7 to 1 against that astronomers will detect it beforehand. In 1992 the "Spaceguard Survey" was proposed as an international search for large asteroids. The worldwide, ten-year budget was less than Americans spent watching the "Armageddon," but Spaceguard is not yet underway. We seem to be facing the dilemma of the ancient skywatchers -- those in power dismiss the issue as unimportant.

Saving the future If an object is discovered to be on a collision course, it is preferable that we have several decades warning (provided that the full Spaceguard Survey gets underway soon). Given enough advance notice, we have the capability to send spacecraft to rendezvous with an asteroid or comet and nudge it into a safe orbit. Current technology is certainly closer to the task than that available to NASA when President Kennedy announced the moon landing goal in 1961. On this theme of historic events another U.S. politician, Congressman George Brown Jr, who died recently, had this to say at the opening of a 1993 Congressional hearing into the asteroid threat: "If some day in the future we discover well in advance that an asteroid that is big enough to cause a mass extinction is going to hit the Earth, and then we alter the course of that asteroid so that it does not hit us, it will be one of the most important accomplishments in all of human history."

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Riches in the Rubble By Michael Paine Special to space.com posted: 06:07 pm ET 05 November 1999 Thirtyyears ago, when the Apollo astronauts brought rocks back from the Moon,nobody rushed to stake a mining claim. Only traces of useful materialswere found. The surface of the Moon turned out to be barren and unattractivefor commercial development. Asteroids, however, are anothermatter. Nearly all the raw materials needed to build a self-sufficientspace colony are available on the most common type of asteroid. NASA plansto land a small robotic spacecraft on an asteroid within a few years, justone example of the belief that asteroids are both accessible and worthexploring.

Recipe for a Solar System Most asteroids are made fromthe raw ingredients of the solar system, researchers believe. Those ingredientscame from supernova -- exploding overweight stars. The solidified debrisfrom these explosions contains mainly dust, rocks, water ice and iron (actuallyan alloy of iron, nickel and cobalt -- a natural stainless steel). Nearly 5 billion years ago, under the tug of gravity, debris from supernovas gatheredinto a spinning disk. Most of this material fell into the center of thedisk and formed our Sun. Further out the material formed many planets.As these planets circled the Sun they collided with each other and grewlarger, until just nine planets were left. The debris from these collisions,together with other leftover rubble, was either swallowed up in furthercollisions or was mostly herded into planet-free zones like the asteroidbelt between Mars and Jupiter.

Blast-furnace Planets The inner planets (Mercury,Venus, Earth and Mars) likely started off as hot balls of molten metaland rock. Like a blast furnace used for making iron, most of the metalsank to the center of each planet and a thin, rocky crust formed on thesurface. The crust material of these planets generally has much less metalthan the raw ingredients of the solar system. Most crust is the equivalentof the slag, or discard, from a blast furnace, and there are just a fewplaces near the

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Earth's surface where metal ores are concentrated enoughto make mining worthwhile. The good stuff is deep withinEarth's interior. What's in a Meteorite? Iron meteorite Stonymeteorite Earth'scrust Iron91% Nickel 8.5% Cobalt 0.6% Source: Encyclopaedia Britannica Oxygen36% Iron 26% Silicon 18% Magnesium 14% Aluminum 1.5% Nickel 1.4% Calcium 1.3% Oxygen49% Silicon 26% Aluminum 7.5% Iron 4.7% Calcium 3.4% Sodium 2.6% Potassium 2.4% Magnesium 1.9%

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Riches in the Rubble Solar system rubble still collideswith the Earth -- the smaller rocks reach the ground as meteorites. Somemeteorites are nearly pure stainless steel, born in ancient supernovas. Most of the asteroids aremade of the same stuff as meteorites. They too are rich in useful metalsand chemicals such as water and carbon, and hence their commercial potential. An example of the possibleriches amongst this rubble of the solar system is the asteroid Amun. Theorbit of this mile-wide object comes close to the Earth's orbit and, overmillions of years, it could be a threat to the Earth. Before then, however,it is likely that mankind will have visited the asteroid and mined it awayto nothing, because research indicates Amun is made from that primordialstainless steel. Planetary Scientist John Lewis, from the University ofArizona, estimates that the iron, nickel and cobalt in this single asteroidis worth about $20,000 billion at market prices. Amun is unusually rich inmetals and is typical of perhaps only 5 percent of asteroids. Most asteroidscontain more rock than metal, but at least half of the material in theseso-called stony asteroids could also be put to human use. Let the Asteroids Come toUs Some half a million asteroids100 yards across or larger orbit the Sun along paths that cross or comeclose to the orbit of the Earth. In principle, it is easier to reach about100,000 of these "Near Earth Asteroids" and return a payload to the Earththan it is to return the same payload from the Moon. Therecent Deep Space 1 flyby of asteroid Braille showed that we have the spacetechnology to reach Near Earth Asteroids. By using material mined in space,mission planners could avoid the very high cost of launching materialsfrom Earth. The biggest technical difficultyin mining solid metal asteroids such as Amun might be the task of choppingchunks of metal from the main block. On Earth we have never had the luxuryof mining a giant lump of pure stainless steel, so we don't even know howto do it. Still, there is plenty ofiron in common asteroids that could be mined using conventional techniques.These asteroids also contain water, which is not only

Rocks from Space

important for survivingand manufacturing in space but also has potential as a rocket propellant. A New Steam-powered "Rocket" In 1829 George Stephensen wonthe first ever railway competition with a steam engine called the "Rocket."Although steam engines have now gone out of style on the surface of theEarth, there is great potential for steam-powered rockets in space. In the vacuum of space acraft produces thrust by shooting matter at high speed out an exhaust portal.Conventional rockets burn exotic chemicals and the combustion productsare forced out of a rocket nozzle to produce thrust. An alternative to a chemicalrocket is to heat a volatile material (a material which readily forms agas) and expel the resulting superheated gas from the rocket chamber. Thenatural choice for this expendable material is water. Possible sourcesof heat are nuclear or solar power. The main obstacle to steampowered rockets is the cost of launching tons of water into space fromthe Earth's surface. At a current cost of thousands of dollars per poundlaunched, we might as well send exotic chemicals into space -- the costof the material becomes irrelevant. But what if we could obtainwater in space? The Moon's polar regions are suspected of holding frozenwater, but the lunar poles are difficult to reach and launching payloadsfrom the Moon is technologically and economically difficult. The obvioussource of water is Near Earth Asteroids, because asteroids typically contain10 to 20 percent water in the form of permafrost or saturated minerals.Dormant comets also orbit the Sun near the Earth, and these "dirty snowballs"likely contain more than 50 percent water. There is another advantageto using water in space rockets. A thick layer of water ice around a mannedspacecraft makes an excellent shield from radiation and small meteoroids.Water storage tanks could surround the habitable modules of spacecraft,like igloos in space. The Next Giant Leap for Mankind Our Earth-based technology formining and processing raw materials needs to be adapted for use in space-- for mining the asteroids. If the dreams of science fiction writers areto become a reality and humans are to colonize space, then the next stepis to tap into the vast resources of the rubble of the solar system.

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Asteroids & Tsunamis By Michael Paine Special to space.com posted: 06:07 pm ET 05 November 1999 Bigasteroids can be extra deadly when they strike the ocean, carving aquaticcraters and sending huge waves in all directions. These tsunami can wreakdestruction on shores thousands of miles away. Bad news for people livingin coastal areas, but it could be a lucky break for the rest of mankind:The same impact on land would throw dust high into the atmosphere and couldblock sunlight for many months, possibly causing global starvation andmass extinctions.

Dangerous waves The surface of water is verygood at transferring energy, in the form of waves, across great distances.In 1960, for example, an earthquake near Chile created a series of wavesthat crossed the Pacific Ocean and killed several hundred people 10,000miles away in Japan. These waves, which are generatedfrom a major disturbance to the water surface, are known as tsunami. (Mostscientists don't like the popular name "tidal wave" because tsunami havenothing to do with the tides. However, tsunami sometimes surge ashore likea huge, fast-moving tide rather than breaking like a classic surfing wave.) Tsunamican travel at around 400 mph in deep water. When they reach shallow waterthey slow down, and that's when the real danger begins. The front of thewave slows first and the effect is like a pile-up on a freeway, with therear of the wave catching up to the front. The wave increases in heightfrom this bunching effect. The final height of the wave depends on severalfactors, but the shape of the sea floor has the greatest impact. Estuaries,harbours, cliffs, reefs, and the topography of the continental shelf allplay a role. For a typical shoreline,the final tsunami height is usually about three times its height in deepwater, but in some locations the ratio (known as "run-up factor") reaches40. In other words, a 1-foot wave in deepwater can amplify to a 40-footwave at a shoreline that is exceptionally vulnerable to tsunami, as aresome parts of Hawaii.

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Splashdown Ifan asteroid collides with the Earth there is a good chance it will hitan ocean, simply because two-thirds of the Earth's surface is covered bywater. A gigantic explosion occurs and the asteroid is pulverised and vaporised,along with a huge volume of water. This creates a crater in the water surfacethat quickly fills. The filling process generates a series of tsunami thatradiate across the ocean. The effect is similar to a pebble thrown intoa pond, though with a 50,000-mph impact, we're not talking ripples here. Based on NASA estimates,about once every 2,000 years an asteroid with a diameter of about 100 yardscan be expected to hit one of Earth's oceans. Larger asteroids collidewith the Earth much less frequently -- a 500-yard rock from space mighthit an ocean once every 80,000 years and a 1,000-yard (1 k) asteroid perhapsonce every 200,000 years.

Atomic bombs and oceanimpacts The largest aboveground H-bombtest by the United States was like a firecracker compared to an asteroidimpact. That "Bravo" explosion at Bikini Atoll in 1954 was equivalent tofifteen megatons (million tons) of TNT but was only about one-thousandthof the energy of a 500-yard asteroid moving at 50,000 mph. The Bikini Atoll H-bomb testsenabled scientists to develop computer models of the destructive effects(on shipping) of explosions at the water surface. In the early 1990s thesemodels were applied to asteroid impacts. Initial results suggested thateven relatively small impacts could pose a grave tsunami threat over largeareas of ocean. More recent modelling indicatesthat the tsunami generated by an asteroid impact tend to dissipate, ordie out, rapidly (the computer program, developed by Sandia National Laboratories,accurately predicted the consequences of the plummet of Comet Shoemaker-Levy9 into Jupiter in 1994). According to this work, a500-yard-diameter asteroid is predicted to generate a water crater nearly3 miles in diameter. At a distance of 10 miles from "ground zero" the resultingdeepwater tsunami will be about 200 yards high, but by the time the wavehas travelled 100 miles it will be reduced to a height of about 14 yards.After 1,000 miles it will have dropped to less than 1 yard in height. Dueto the amplification in shallow water, however, this size tsunami couldstill become a 120-foot wave at a vulnerable shore.

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Extra hazard to coastal areas Due to the extra hazard of tsunami,locations such as Hawaii are at much greater risk from asteroid impactsthan inland areas. Rough calculations suggest that a coastal location witha typical tsunami run-up factor of three has about three times the riskof devastation from an asteroid-generated tsunami than the risk of a directblast to an inland location. Locations with an extreme tsunami run-up factorof 40 have about 70 times the risk compared with an inland location. People in these vulnerablelocations need not lose sleep, however, because the odds of a major asteroid-generatedtsunami in any one year are about one in 200,000. On the other hand, asastronomer Duncan Steel has pointed out, asteroid impacts don't run toa timetable like busses. The estimate of impact tsunamirisk is based on the limited search for Near Earth Asteroids carried outso far and assumes that impacts are randomly distributed in time. Thereis some evidence that impacts may come in clusters (some busses seem todo the same). If this is the case, then it is well worth finding out ifwe are approaching the next barrage so that coastal areas can be betterprepared.

Climate disruption The comparison between coastaland inland locations is not entirely fair because the biggest danger froman asteroid impact is not from the direct blast but from the after-effects.In particular, the temporary cooling of the Earth due to huge quantitiesof dust released into the atmosphere from a land impact can disrupt cropproduction and lead to global starvation. The giant plumes from theJupiter impact of Comet Shoemaker-Levy 9 clearly showed how a comet orasteroid tunnels through the atmosphere and creates a temporary chimney.This draws the impact debris into the upper atmosphere. Scientists areonly beginning to understand this effect in the case of an impact intoEarth's oceans. An ocean impact by a 500-yard-diameterasteroid will vaporise about 20 cubic miles of water. At first sight thisappears to be insignificant since it is less than one tenth of the totalamount of water that evaporates from the world's oceans every day (assuming1 inch of rain over 10 percent of the Earth's surface each day).

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Scientists caution, however,that an ocean impact would send the water vapour high into the atmosphere,compared with the lower atmosphere, or troposphere, in the case of evaporation.The upper stratosphere is normally extremely dry and the effects of a suddeninjection of a large quantity of water vapour are simply unknown. Othereffects of concern are greenhouse warming (water vapour is a strong greenhousegas) and ozone depletion. Unlike evaporation, an ocean impact would sendsalt (sodium chloride) into the air. The chlorine in the salt may affectupper atmosphere ozone levels in the same way as chlorofluorocarbons. The same impact on land wouldpulverise an equivalent amount of rock (20 cubic miles -- about 1,000 timesthe volume of the asteroid) and send much of it into the upper atmosphere,where it would circulate around the globe and disrupt agriculture for manymonths. A lesson from violent volcanoes In 1815 a volcano on the Indonesianisland of Tambora exploded and produced a crater similar in size to thatfrom a 500-yard asteroid. About 20 cubic miles of ejecta was released (forcomparison, the Mount St. Helens explosion in 1980 released about a quarterof a cubic mile of ejecta). In the case of Tambora, ithas been estimated that 10,000 people died directly from the explosionand 80,000 more died in the region from indirect effects, such as starvation.In addition, the ash is thought to have caused the "year without a summer"in 1816, when there were widespread crop failures across North America.The final death toll was probably in the hundreds of thousands. A similarevent today might kill millions. Because of the chimney effect,an asteroid impact is much more efficient at sending dust into the upperatmosphere than a volcanic explosion, and the climatic disruption is probablymuch greater with an asteroid impact. Even so, the events of 1815 serveas a clear warning of the global danger from land impacts by asteroids. With much less dust releasedinto the atmosphere, an ocean impact will have very different, and perhapsless damaging, effects than a land impact. If an asteroid struck thickice formations, such as Antarctica or the extensive ice sheets of the lastIce Age, the result would likely be similar to a water impact. It's possible that our specieshas been saved from extinction several times because a large asteroid hitthe ocean or ice rather than the land. Every million years or so it canbe expected that a mile-wide asteroid will hit the Earth. A land impactwould probably cause severe climatic disruption and regional

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extinctions.Ifthe global effects of an ocean/ice impact are less severe than one on land,then the impact by a mile-wide asteroid into the ocean might not be ashazardous to life.

Evidence of ocean impacts Past impacts with water or iceare very difficult to detect, because they leave very little evidence.One such impact is known to have occurred in the South Pacific Ocean, nearChile, about 2 million years ago. This event -- known as "Eltanin" afterthe ship that discovered the deposits -- involved an asteroid between 1and 3 miles in diameter that would have created a water crater at least40 miles across. Tsunami would have swamped coasts around the Pacific andwould even have reached some Atlantic coastlines. Assuming a typical run-upfactor of three, the coast of Chile would have been inundated by 250-yard-hightsunami. Likely results for other locations: Hawaii 90-yard tsunami (probablyhigher due to the greater run-up factor); California, 60 yards; Japan andAustralia, 25 yards; New Zealand; 120 yards. Despite this presumed destructionto coastal areas, there is no evidence of global climate change or regionalextinctions around this time, when our early ancestors, Australopithecus,were roaming Africa. We don't know whether they would have been wiped outif the Eltanin asteroid had struck land in South America or Africa, insteadof splashing into the ocean. To solve that puzzle, to understand whichtype of impact most threatens our existence, we need a much better understandingof the consequences of asteroid impacts. Acknowledgements I am grateful to the followingscientists for providing comment on this article: Erik Asphaug, Universityof Southern California, Elisabeth Pierazzo, University of Arizona, DavidCrawford, Sandia National Laboratories. This article does not necessarilyrepresent their views. -- Michael Paine

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How an Asteroid Impact Causes Extinction By Michael Paine Special to space.com posted: 06:07 pm ET 05 November 1999 Imagine: NASA scientists announce they have detected a 10-mile-wide asteroid on a collision course with the Earth. They calculate it will hit Southeast Asia in two weeks. There is no chance of Bruce Willis being sent on a beefed-up space shuttle to blow up the asteroid. Earthlings will have to ride out the impact. The Tunguska event in 1908 flattened 800 square miles of Siberian forest -- and the object didn't even reach the ground. The world economy grinds to a halt as people take to the hills. Anarchy sets in, civilization breaks down. Accusations fly over the lack of warning -- where was Spaceguard, the proposed international search effort for large asteroids? People in Brazil feel less vulnerable than most of the world's population. They are on the opposite side of the Earth from the predicted impact point. But one hour after the impact Brazilians notice some brilliant meteors. Then more meteors. Soon the sky gets brighter and hotter from the overwhelming number of meteors. Within a few minutes trees ignite from the fierce radiant heat. Millions of fragments of rock, ejected into space by the blast, are making a fiery return all over the planet. Only people hiding underground survive the deadly fireworks display. Within three hours, however, massive shock waves from the impact travel through the Earth's crust and converge on Brazil at the same time. The ground shakes so violently that the ground fractures and molten rock spews from deep underground. Maybe Brazil wasn't the best place to be after all. The survivors of the firestorms, tsunami and massive earthquakes emerge to a devastated landscape. Within a few days the Sun vanishes behind a dark thick

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cloud -- a combination of soot from the firestorms, dust thrown up by the impact and a toxic smog from chemical reactions. Photosynthesis in plants and algae ceases and temperatures plummet. A long, sunless Arctic winter seems mild compared to the new conditions on most of the planet. After a year or so the dust settles and sunlight begins to filter through the clouds. The Earth's surface starts warming up. But the elevated carbon dioxide levels created by the fires (and, by chance, vaporization of huge quantities of limestone at the impact site) results in a runway greenhouse effect. Those creatures that managed to survive the deep freeze now have to cope with being cooked. Many species of plants and animals vanish. The few hundred thousand human survivors find themselves reverting to a Stone Age existence. Is it fiction? Computer modeling of asteroid impacts and climatic effects suggest that this devastating sequence of events could happen. Fortunately it is extremely unlikely that this scenario will occur in our time. No known asteroids are on a collision course with Earth. However, every 50 to 100 million years the Earth collides with a comet or asteroid of sufficient size to cause planet-wide devastation. Evidence of past impacts has only been recognized in recent decades and is pointing to the conclusion that big impacts have caused major disruptions to the development of life on Earth. Known impact craters. IMAGE: Canadian Geological Survey

The end of the dinosaurs In 1980 Scientists Luis and Walter Alvarez claimed they had found evidence of a huge impact event 65 million years ago. This age corresponded with the demise of the dinosaurs at the end of the Cretaceous Period. The evidence included a worldwide layer of clay with high levels of the rare element iridium, usually the signature of an impact.

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The search was on for a giant crater associated with this impact. Hopes weren't high because in 65 million years the Earth's surface has changed dramatically -- nearly all of the present ocean floor is younger than 50 million years. Some great scientific detective work pointed to an impact somewhere in Central or North America. Finally, in 1990, the buried remains of a 150-mile-diameter crater were discovered near the town of Chicxulub on the Yucatan Peninsula in Mexico. A crater this size would have been blasted out by a 10-mile-wide comet or asteroid colliding with the Earth at some 50,000 mph. The "smoking gun" had been found.

Impact, volcanoes, or both? The debate continues on whether the Chicxulub impact caused the mass extinction at the end of the Cretaceous Period or whether it was one of a sequence of disasters. The Deccan Traps of India are the remnants of a massive upwelling of molten rock from deep within the Earth 65 million years ago. The toxic fumes and dust from the eruption have been put forward as a possible alternative cause of climate change that led to the extinction of the dinosaurs. A possible link between impacts and volcanism became evident in 1974 when the Mariner 10 spacecraft flew past the innermost planet Mercury. The planet was found to be covered with impact craters like the moon. One giant impact crater on Mercury was particularly interesting. Directly opposite the impact point, on the other side of the planet (called the "antipodal point") was a region of highly disrupted terrain with no evidence of an impact. The shock waves from the impact on one side of Mercury had traveled around the surface and met simultaneously at the antipodal point to create the chaotic features. Similar features have since been detected on several moons of the giant planets. Astronomer Duncan Steel has suggested that the same occurred with the Chicxulub impact and that the shock waves caused the Deccan Traps. Taking into account millions of years of continental drift, this region would have been at the antipodal point to Mexico at the time of the impact. Although the eruption may have contributed to the suffering, it now seems more likely that the Deccan Traps were just a consequence of the catastrophic initial event, the Chicxulub impact. More craters are there to be found A meteorite dug the misnamed Meteor Crater in Arizona. IMAGE: NASA

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As a tourist destination, impact craters on Earth are virtually unknown. Americans might know of Meteor Crater in Arizona. Australians planning an Outback tour may have heard of Wolfe Crater in Western Australia. American geologist/astronomer Gene Shoemaker (of Comet Shoemaker-Levy 9 fame) spent many "holidays" touring the Australian Outback looking for impact craters. He and his wife Carolyn helped to identify some of the twenty or so Australian impact craters that are now known. Tragically, in 1997, Gene died in a car crash during one of these searches. It is only in the past few decades that scientists have learnt how to clearly identify impact craters on the surface of the Earth. In that time they have found more than 150 craters. Most are heavily disguised by siltation, erosion and vegetation. There are relatively few places on Earth where any geological features can be expected to survive beyond tens of millions of years. Impact craters have been found on most of the rare ancient landforms. In several cases the estimated age of a large crater appears to match that of a mass extinction event, as told in the fossil record. Although the picture is still fuzzy -- due to the time scales involved -- massive impacts by comets and asteroids deserve serious consideration as an explanation for some of these extinction events.

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Your Ancestors May Be Martian By Michael Paine Special to space.com posted: 09:58 am ET 08 November 1999 Suppose that billions of years ago life developed on Mars. Primitive, tiny organisms that thrived deep within rocks and made a living from water and chemicals seeping through those rocks. Now imagine that a huge asteroid collided with Mars. Millions of martian rock fragments were thrown into space by the force of the impact. Tough martian organisms hitchhiked on some of this ejecta. Many pieces went into orbit around the sun and, after hundreds of thousands of years, some of these collided with the Earth. Of those rocks, a few reached the surface. Some hardy martian organisms survived the journey, colonized the Earth and eventually evolved into the huge variety of life that we know today. Just a few years ago this scenario would have been dismissed as wildly imaginative and highly improbable. Though still highly speculative, recent discoveries in several fields of science have shown that it is far from impossible -- our ancient ancestors might have been martians.

Enter the nanobes It is not every day that a scientist discovers a possible new life form. Dr. Phillipa Uwins works in the Center for Microscopy and Microanalysis at Queensland University, Australia. Last year she was asked to analyze some rock samples taken from several miles under the seabed in a drilling operation off the coast of western Australia. The temperature at this location was around 300 Fahrenheit (150 Celsius) and the pressure was an incredible 2,000 times normal atmospheric pressure at sea level. During an electron microscope examination, Uwins found what appeared to be tiny, dormant organisms only 20 nanometers across. (A nanometer is one -billionth billionth of a meter.) She named them "nanobes."

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To Uwins' surprise, filaments grew when samples of the nanobes were given some food and exposed to normal temperatures and pressures. She was also surprised because the cell walls of the nanobes survived the intense radiation and vacuum of the electron microscope. Uwins teamed up with two microbiologists to further investigate the nanobes. A range of chemical tests indicated that the tiny objects contained DNA. This finding challenged the notion that a "cell" 20 nanometers in diameter was too small to have room for this essential ingredient of life as we know it (it is also one of the arguments against the "nanofossils" in martian meteorites -- discussed below). Here was a tough little critter that was able to survive the heat and pressure deep underground and, possibly, the vacuum and radiation of an electron microscope. The Queensland team may have found an organism that can survive a ride between the planets aboard a meteorite. Creatures don't have to be as small as nanobes to survive space-like conditions. Several other examples of "extremophiles" (organisms that can survive very hostile conditions) have been found by other researchers in recent years, including bacteria that live inside nuclear reactors.

Meteorites from Mars Rocks from Mars have made it to the Earth. Remember the fuss in 1996 when NASA scientists claimed they had found possible fossil evidence of ancient life in a meteorite from Mars? (That debate is still not settled.) After being blasted from the surface of Mars, one small chunk of rock spent 16 million years in orbit around the Sun. Then some 13,000 years ago it collided with the Earth and landed in the icy Antarctic. In 1984, scientists searching for meteorites found it and named it ALH84001. Ten years later researchers figured out that ALH84001 had come from Mars. This was based partly on an analysis of the Martian atmosphere by the Viking spacecraft in 1977 -- but that is another detective story. A dozen or so other meteorites are now known to have come from Mars. In 1911 one of them fell to Earth in Egypt and killed a dog. It took almost 80 years to recognize that the unlucky dog had been killed by a rock thrown from Mars. Planetary scientist and crater expert Dr. Jay Melosh, from the University of

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Arizona, has estimated that about half a ton of martian material falls to Earth each year. Melosh observed that some of the martian meteorites showed no evidence of a violent shock when they were blasted into space from the surface of Mars. This meant "back to the drawing board" for theories about rocks ejected into space by impacts -- they were supposed to be partly melted by the intense heat from the shock wave. Melosh worked out a theory that rocks near the surface could be launched into space without "shock heating." The effect is something like crumbs being flicked from a shaken picnic blanket. The discovery meant that organisms hiding within ejected rocks could survive the blast from a nearby asteroid impact. There are, however, many other hazards in a flight from Mars to Earth. Melosh investigated these hazards and was able to show that some organisms had a fighting chance of making the trip between the planets.

Surviving space flight In his classic 1865 novel From the Earth to the Moon, science fiction writer Jules Verne wrote of a piloted space capsule being launched by a gigantic cannon. Verne was aware of the scientific error with this idea -- the astronauts would be crushed by forces thousands of times greater than the pull of gravity (1 G or an increase in speed of 32 feet per second every second). Verne knew that the steady and comparatively gentle rocket was the way to reach space, but his audience of the day was more likely to believe the cannon story. For most creatures on Earth, exposure to several hundred Gs would be fatal. They have no hope of surviving the Jules Verne cannon blast, or a ride on a rock blasted into space by an asteroid impact. But some very primitive forms of life are so small and simple that they can survive enormous accelerations -- 10,000 G or more. One way that scientists can test the ability of organisms to survive very high G forces is to fire them out of a cannon. This was recently done in Sweden and a substantial proportion of dormant organisms survived the launch conditions. Jules Verne had the right idea but the wrong organism.

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Of all the rocks blasted from the surface of Mars into orbit around the sun, about one in 15 will eventually collide with the Earth. Some make it in thousands of years. Others may take millions of years. For organisms aboard these rocks the journey would be extremely hazardous, with freezing temperatures, deadly cosmic rays and ultraviolet radiation. But the rock spaceship provides some protection from radiation and cosmic rays, and the deep freeze may actually help some organisms survive the tough conditions. Next, the organisms would have to survive the rigors of colliding with the Earth. The outside of a meteorite glows white-hot as it plunges into the atmosphere at 25,000 mph or more. Many burn up completely and never reach the ground. However, a small percentage survive and make it to the surface. The inside of a meteorite is protected from the heat of re-entry because rock is a very good heat insulator. People who have come across a freshly fallen meteorite sometimes report that a layer of frost has formed on its surface. The inside remained at the freezing temperature of space even though the outside glowed white-hot during reentry. Any organisms within the meteorite could therefore -- in theory -- survive to reach the surface of the Earth. Finally, the organisms would have to make a home for themselves on their new planet. Billions of years ago the conditions on Earth might have been similar to those on Mars, so colonizing this planet may not have been difficult, compared with the hazards of getting here. Of course, this scenario all depends on Mars having some tough forms of microscopic life billions of years ago. Maybe the exciting space missions to Mars planned over the next few years tell us whether this was the case or not.

Lifeboats in space Another intriguing possibility is that meteorites may have acted as lifeboats ("escape pods" for Star Wars fans). Giant asteroids and comets bombarded the planets up until the time that life is first thought to have arisen. Following some of these impacts the surface of the Earth would have been sterilized by temperatures much hotter than an oven, and any oceans would have boiled away. Perhaps the only escape for organisms was

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to be blasted into space and the really lucky ones returned to the Earth when things cooled down. The same rescue system could have worked for any life on Mars.

Maybe martians came from Earth Even if the scenario of Mars life seeding the Earth is not correct, the reverse seems quite likely. Rocks all over the surface of the Earth have been found to contain microscopic life. It is hard to find places that don't have life. Hundreds of huge asteroid impacts have occurred on Earth since life first began. Without doubt some of these impacts would have launched rocks bearing microscopic life. In his book "The Fifth Miracle," physicist Paul Davies discusses the origins and development of life on Earth. He pays great attention to the possibility of life being exchanged between Earth and Mars and concludes "It is therefore inevitable that life from Earth has reached Mars ... that is why I am certain that there was life on Mars in the past, and may well be life there today". Paul Davies also notes that, 4 billion years ago, Mars may have been more suitable than Earth for the development of life. He argues that we should be prepared for the possibility, remote though it may seem, that we are descended from martians.

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Did Asteroid-Induced Firestorm Destroy the Dinosaurs? By Michael Paine Special to space.com posted: 03:10 pm ET 18 November 1999 Dinosaurs may have met their demise in a global firestorm of methane gas triggered by an asteroid impact, a team of scientists reports in the latest issue of Geo-Marine Letters. The methane gas was released from the Earth by the asteroid collision and ignited by lightning, says Naval Research Laboratory scientist Barton Hurdle. Hurdle told space.com that he and several colleagues put forth the idea -- a fiery end to Earth's greatest land creatures -- before various teams of researchers in 1991 and 1992 theorized that a crater discovered in Mexico was the site of an asteroid impact responsible for the mass extinctions. "It shook up the ocean, generated tsunamis that ruptured pockets of methane that were trapped under gas hydrates, and it also created slumping -- a sliding down of the ocean bottom -- that released (the methane) too," Hurdle said. "This stuff came out, lightning set it afire, and it burned," Hurdle explained. "There were fantastic quantities of this stuff." The theoretical fire would have burned near the ground and high into the atmosphere, Hurdle said, enveloping much of the planet as shock waves from the impact moved through the planet and dislodged methane around the globe. "The atmosphere itself would have been on fire," Hurdle and his colleagues wrote in the paper. The fire would have incinerated land creatures, he said, while decreasing oxygen supplies and increasing the amount of carbon dioxide in the atmosphere. "There was a lot of soot, and that soot has been found," Hurdle said.

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The theory, also featured in this week's issue of New Scientist magazine, stems from the discovery of vast deposits of methane, a carbon-based molecule, under the sea floor that are locked in crystals of water ice, forming "methane hydrate." Marine geologist Erwin Suess and co-workers from the Research Center for Marine Geosciences in Germany estimate the total amount of carbon locked in these deposits exceeds the amount in all of the known coal, oil and gas reservoirs. What is more, methane hydrate is very unstable and releases methane if the temperature or pressure rises slightly above that existing under the seafloor.

Interest, and skepticism Brown University's Peter Schultz, who studies impact craters and the processes that create them, says Hurdle's idea definitely merits further study. "The observation that there are these methane traps on the bottom of the ocean is pretty well established," Schultz told space.com. He said that while an ocean impact could certainly release this methane, he's not sure if the affect would be over a large enough area to release enough methane to cause the scenario Hurdle describes. "My reservation is whether or not the shock wave could have released as much methane as they say," Schultz said. And as planetary scientists John Lewis and Sidney van Den Bergh point out, there are several other dire consequences of the impact, (the site is known as the Chicxulub crater), that could explain the extinction of the dinosaurs. The methane hydrate proposal is seen by many researchers as credible, but may in fact have been a nail in the coffin rather than the exact cause.

Evidence and likelihoods There is ample evidence of a global firestorm at the time of the Chicxulub impact. Iridium-bearing clay in the boundary layer between the Cretaceous Period (a time when dinosaurs roamed) and Tertiary Period (the subsequent geologic time frame when dinosaurs seem to have disappeared) contains soot.

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The quantity and composition of the soot corresponds to the burning of at least 50 percent of the world's forests. Although Hurdle's idea that methane fires were responsible for this firestorm is plausible, there is another simpler explanation. The Chicxulub impact would have launched millions of tons of rock into ballistic space flight. Over the following hour this debris would have re-entered the Earth's atmosphere at high speed, causing millions of brilliant "shooting stars." The radiant heat from these meteors alone would have been sufficient to ignite the trees around the world. This idea is supported by the discovery of charcoal in tsunami deposits near the impact site. The best explanation may be that the trees were ignited by radiant heat, then swamped soon after by the waves. The shock wave from the impact would indeed have triggered massive earthquakes in the region and indirectly triggered other earthquakes around the globe. A tsunami would have formed from the impact, which occurred in a shallow sea. The giant waves would also have been generated by the earthquakes and undersea landslides triggered by the shock wave. "Megawaves emanating from an impact site would circuit the earth at high speeds and cause worldwide disruption in the entire ocean in a single day," Hurdle and his colleagues wrote.

Acid rain and a long, long winter Researchers say the impact fireball and the forest fires would have created huge quantities of nitrogen oxides, which react with water vapor to form acid rain. By chance, the Chicxulub asteroid struck rocks with an unusually large proportion of calcium sulfate. This would have generated sulfur dioxide -- another source of acid rain. There are several signs of a massive dose of acid rain at the time, including sudden weathering of continental rocks. The dust thrown up by the impact, the soot generated by the firestorms and the smog formed from the oxides of nitrogen and sulfur particles would have blocked sunlight for many months. The surface of the Earth would have plunged to freezing conditions -- typically 70 degrees Fahrenheit below normal -- and

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photosynthesis would not have been possible, even if plants had survived the fires and acid rain.

Global warming After several months the dust would have settled and sunlight would have begun heating up the land. Now the greenhouse effect would have taken over due to the excess of carbon dioxide created by the fires and the melting of limestone rocks at the impact site. Methane released from ocean sediments could have added to the greenhouse effect. It has been estimated that the surface temperatures on Earth were at least 10 degrees Fahrenheit above normal for hundreds of thousands of years after the impact. So dinosaurs, if they were not consumed in a firestorm, would have had to live through a torturous sequence of events -- from the barbecue to the freezer, to a dip in acid and then a hothouse baking. Regardless of whether Hurdle's idea is correct, it agrees with mounting evidence that suggests how a massive asteroid impact at Chicxulub may have been the fatal blow to the dinosaurs, as well as 50 percent of all the Earth's species. space.com's Robert Roy Britt contributed to this report

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Prospecting for Oil? Look In an Asteroid Crater By Michael Paine Special to space.com posted: 07:27 am ET 14 December 1999 The Earth has suffered thousands of violent collisions with asteroids and comets over the last four billion years. The scars from these collisions are impact craters. But the Earth hides its wounds well -- less than two hundred impact craters have been discovered. Many are buried deep below the surface. They were only found by accident during geological surveys that were part of the massive, ongoing effort to find oil for an energy-dependent world. Now it seems that the link between impact craters and oil is not accidental. Buried impact crater formations make excellent underground traps for oil, but these craters rarely seem to be above the types of rocks that are supposed to contain oil. New thinking changes all that. If Russian theories about the non-biological origin of much of our oil prove to be accurate, then there may be good reasons for oil prospectors to go searching for impact craters.

Where does oil come from? "Rock oil originates as tiny bodies of animals buried in the sediments which, under the influence of increased temperature and pressure acting during an unimaginably long period of time transform into rock oil" -- M.V. Lomonosov 1757AD.

Maybe it's time to change the textbooks. For two centuries Lomonosov's simple and compelling theory on the origin of oil went unchallenged. It meant, of course, that the world would run out of this fuel once the rare sedimentary rocks that contained the bodies of animals were drained of oil. It also meant that so-called basement rocks, which had never been near the surface of the Earth, would not bear oil.

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The Russians decided to try something different. In the 1950s, perhaps due to the pressures of the Cold War, they started to hunt for oil according to a new theory -- most oil occurred naturally, deep within the Earth's crust, and had nothing to do with rotting organisms. That hunt has been highly successful, and the former Soviet states have many commercial oil wells apparently producing from deep basement rocks. Tom Gold, Professor Emeritus of Astronomy at Cornell University, supports the Russian idea. In his book The Deep, Hot Biosphere, Gold discusses the discovery of life deep within the Earth' s crust. He argues that most oil and gas could only have come from non-biological sources much deeper underground. According to this theory, the natural traps formed by impact formations will be even more promising as places to look for oil because the "source rocks" containing the oil are everywhere.

Liquid gold in the rubble of an impact crater Wham! 65 million years ago a huge asteroid hit the Earth in a shallow sea off the coast of Mexico. A crater perhaps 150 miles or more across was briefly formed in the seafloor and chunks of rock were scattered in mile-thick layers for hundreds of miles in all directions. Tsunami from the impact churned up more piles of broken rocks on coastlines thousands of miles away. Over time, layers of sediment covered the impact scars and they lay undisturbed for millions of years. Then, only several decades ago, prospectors started looking for oil in the region, unaware that the Chicxulub crater lay buried deep beneath them. They were very successful, and commercial oil production began. But it was not until 1990 that the signs of a crater were recognized. The rubble from that impact is now thought to be the source of most of Mexico's vast oil reserves. Geologists are beginning to see that impact crater formations make good traps for oil.

How it gets there Oil from deep underground gradually works its way upward through cracks and fissures in rocks. Oil prospectors get excited if the "reservoir rocks" that contain the oil are covered by a contorted layer of "cap rocks" because this can confine

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oil in natural reservoirs. An oil well is usually drilled until it breaks through the cap rocks and reaches the oil-saturated reservoir rocks below. The rubble from an impact often forms a porous rock known as breccia that is full of cracks and fissures -- making it excellent for extracting oil through a well. Domes, basins, deep cracks, along with crumpled, folded landforms are other typical features of an impact crater that make them promising for oil prospectors. There are hundreds of thousands of oil wells in the United States, but only a dozen or so are known to be associated with impact structures. Like Chicxulub, none of the craters were discovered until after commercial production of oil began. Geologist Richard Donofrio of Oklahoma City points out that drilling an impact structure is much more likely to be successful than drilling other types of formations. Deep under the layers of sedimentary rocks that cover most of the United States there should be at least 20 undiscovered impact craters. Canada's geology is different and most craters are on or near the surface. Donofrio therefore went through the exercise of randomly superimposing the distribution of known Canadian impact craters on a map of the U.S. Using conservative assumptions he came up with an estimate of the oil-producing potential of undiscovered impact craters in the U.S. His conclusion is staggering -- 50 billion barrels -- double the current proven American reserves. Geoscientist John Gorter from Perth, Western Australia has studied the petroleum potential of Australian impact structures. He also believes that impact craters make very promising sites for oil exploration. The most interesting, and speculative, of the Australian sites is the Bedout Structure some 200 miles off the coast of Broome. There are tentative signs that this was originally a crater 160 miles in diameter -- perhaps bigger than Chicxulub. If it does turn out to be a large impact crater, there could be huge reserves of oil in the region. The Bedout Structure could also be of interest to paleontologists -- its possible age of 250 million years corresponds with the great mass extinction at the end of the Permian period.

Tar-coated comets and oily asteroids The idea that complex hydrocarbons (the main components of petroleum oil) are a natural part of the Earth's crust should come as no surprise to scientists who

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study comets and asteroids. Some of the meteorites that fall to Earth are rich in tar-like hydrocarbons. Comets such as Halley and Hale-Bopp are thought to have a skin of tar-like material covering a "dirty snowball" -- like an ice cream dipped in chocolate. The early Earth was made of the same stuff as comets and asteroids, so the presence of hydrocarbons deep within the Earth is to be expected. It used to be thought that the fierce heat deep underground was sufficient to break up any hydrocarbon molecules. However, Russian scientists have demonstrated that the enormous pressures prevent this. Even if the Earth did not manage to retain its original supply of hydrocarbons it is likely that the rain of comets, space dust and asteroids over billions of years would have kept the crust of the Earth topped off with the raw ingredients for oil.

Could there be too much oil? Oil is best found near impact structures. Oil forms deep underground from non-biological processes. If these ideas prove correct then Donofrio's estimates for the United States should apply to other parts of the world. For areas of similar size there are possibly 20 buried impact craters with perhaps half having commercial oil reserves. The search for these elusive craters could be very rewarding. It may turn out that there is too much oil for our own good. A massive increase in known oil reserves could lower oil prices and drastically devalue existing reserves. A longer-term problem is that an unchecked increase in oil consumption could place untenable strain on the global environment. Already human activities in our oil-dependent society have led to alarming species extinction rates. An oil glut could accelerate this problem. It would be ironic if the Chicxulub impact event turned out to be a time bomb that was not only associated with the extinction of the dinosaurs and other species at the end of the Cretaceous Period, but also with another mass extinction resulting from human activities some 65 million years later. Glossary

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Basement rocks are rocks that have never been near the surface of the Earth. They lie under the top layer of rocks, most of which are sedimentary and have been recycled many times by erosion. Cap rocks are rocks that are impervious -- they resist the flow of fluids such as water, oil and gas and trap these fluids in rocks below. Organic molecules are simply molecules that contain carbon. This does not mean that they have anything to do with organisms or life. As Carl Sagan pointed out in his book "Comet," astronomers tend to be nervous about the word organic because of concern that it might be misunderstood as a token of life. So they use the term "carbonaceous" to describe meteorites that are rich in carbon compounds. Kerogen is a tar-like organic compound found in some meteorites (and in over-cooked hamburgers on Earth). Reservoir rocks act as reservoirs for oil. They have sufficient cracks and fissures to allow the oil to flow into the well. Reservoir rocks must be covered by cap rocks to prevent the oil seeping up to the surface and escaping. Source rocks are those in which oil is generated. The classical view is that source rocks must have layers containing the bodies of dead plants and animals and that these gradually change to oil. The controversial view is that all basement rocks have the potential to be source rocks because oil has non-biological origins deep within the Earth.

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Simulating Armageddon on Your PC: Asteroid Impacts with Earth By Michael Paine Special to space.com posted: 09:00 am ET 10 January 2000 Millions of non-catalogued space rocks careen through interplanetary space, and Earth is one of the many sitting ducks in the cosmic shooting gallery. Although centuries can pass on Earth without a catastrophic strike, waiting impassively to be hit is seen by many experts as a clear and possibly deadly gamble. But what are the odds? And what would happen under different types of impacts? As with almost anything that can be simulated, the odds and consequences of an asteroid strike are now programmed into a computer software package. I ran some scenarios on the new software, created by planetary scientist John Lewis from the University of Arizona. The results, described below, are not official predictions. But they do present some frightening possibilities that put the threat of rocks from space into tangible terms, while at the same time pointing to the need to search for the uncharted asteroids and comets (known as Near Earth Objects or NEOs) that threaten our civilization. Lewis' software uses a Monte Carlo analysis to calculate the human fatalities resulting from impacts. This works by generating random numbers for the size and type of NEO and the human population density at the impact site. The process is based on the actual distribution of these factors. It includes fatalities from "airbursts," where the NEO explodes in a devastating fireball several miles from the ground. The consequences are similar to those from a nuclear bomb and estimates of fatalities are based mainly on research with nuclear weapons. Another danger modeled by the program is the risk of a tsunami swamping coastal cities hundreds or thousands of miles from the site of an ocean impact.

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A million years of bombardment In one run I simulated a total of one million years, looking at the worst event in each of 10,000 centuries. I want to stress that these are not predictions and that no known NEOs are on a collision course with Earth. Although one million years seems a very long time, bear in mind that impacts do not run like clockwork -- they could occur at any time. An event that happens once in one million years of the simulation has a one-in-a-million chance of happening in the next twelve months. This should not be dismissed as unimportant, particularly if it could involve billions of deaths and the end of civilization. After all, many optimistic people around the world regularly buy lottery tickets where the chance of winning first prize is one in 30 million or less. The chance of being dealt a royal flush in 5-card poker is about one in half a million. In my simulation the total death toll during one million years was 7.5 billion. This represents an average of 7,500 fatalities per year and is higher than the 3,000 fatalities per year generally quoted by scientists. However, nearly half of these fatalities occurred in one devastating event that wiped out half of the world's population -- a possible outcome in the real-life gamble with rocks from space. To put the NEO death toll in perspective, it lies somewhere between that of airline crashes (700 per year) and earthquakes (10,000 per year). Fatalities by size of NEO in the simulation Asteroid/Comet Diameter (yards) Annual Fatalities

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Fatal Events % Fatal (for group)* 25 to 99 yards 236 2,664 31% 100 to 199 231 736 69% 200 to 499

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532 295 95% 500 to 1000 618 44 98% 1000 yards to 1 mile 788 10 100% 1 mile to 1.3 miles

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2,064 5 100% More than 1.3 miles 3,060 1 100% Total 38% *Percentage of events in this size group that cause fatalities. Looking at the results

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Fatalities topped 1 million in 2% of the centuries. Nearly two-thirds of centuries had no fatalities. In another 5 percent of centuries, the worst event happened in a remote location and caused less than one thousand fatalities. Such events would probably not been blamed on NEOs, for lack of being spotted. An additional 5 percent of centuries had only had tsunami fatalities, with an average of 100,000 fatalities per tsunami event. Many of these tsunami events would not have been linked to a NEO since the ocean impact happened well away from eyewitnesses. Overall, some 70 percent of centuries may have had no reported fatalities from NEOs. This may help to explain the general lack of awareness of the NEO threat by the public and politicians. Surprisingly, 1,207 fatal impacts involved NEOs with a diameter less than 50 yards. Most did their damage in an airburst of around 10 megatons -- like that of a "small" H-bomb. There were several sobering impact events in the simulation. They are described below. Geographic names are arbitrary and are intended to give an indication of the population density and landforms of the impact site (as well as dramatic effect).

Big blasts First the really big ones -- asteroids or comets a mile or more across. These are civilization-destroying events that leave little opportunity for disaster recovery. Estimates of the NEO population suggest that, over a period of one million years, about 5 such impacts can be expected. By chance, this is the number produced in the simulation. * During the 133rd Millennium a 1.3-mile-wide comet hits the American Midwest at a speed of 100,000 mph. The blast, equivalent to 3 million megatons of TNT or 60,000 H-bombs, kills 7 million instantly and makes a crater 20 miles across. Within days the skies around the globe darken from the dust injected into the atmosphere. Sunlight is blocked. Crops fail and, over the next year, half of the Earth's human population dies, mainly from starvation.

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* In the 621st Millennium a mile-wide comet slams into Mongolia. "Only" 300,000 people die instantly, but the dust from a crater 13 miles across darkens the skies around the globe. Some 900 million die from starvation. * In the 952nd Millennium a 1.2-mile-wide comet hits central Africa. About 3 million people are killed instantly. An 11-mile-wide crater is formed. Later, 500 million starve to death around the globe. * During the 11th Millennium a 1.2-mile asteroid hits the southern Atlantic Ocean 400 miles off the coast of southern Argentina. A tsunami 250 yards high sweeps 50 miles inland and kills 300,000. The climatic effects are less severe than with a land impact, but 400 million still die from starvation due to these effects. * An almost identical event, this time off the northern coast of Russia, occurs in the 699th Millennium.

Quirky blasts There were several events that were unusually deadly -- a matter of bad luck for 54 million people: * 136th Millennium: A 200-yard-wide asteroid hits the South China Sea just 300 miles from Hong Kong. A 40-yard-high tsunami sweeps the coast and kills 18 million people. * 20th Millennium: An asteroid just 70 yards across explodes in the skies 14 miles above London. 10 million are killed in the 80-megaton blast and firestorm. * 273rd Millennium: A 50-yard-wide comet travelling at an unusually fast 150,000 mph explodes in the atmosphere 25 miles above Mexico City. 14 million are killed by the 110-megaton blast and firestorm. * 721st Millennium: An almost identical event occurs over Manila, killing 12 million.

The lessons from the simulation Comets accounted for three-quarters of the fatalities, due mainly to the event in the midwestern United States. That event was caused by a long-period comet that spent tens of thousands of years out beyond the orbit of Neptune before diving into the inner solar system.

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The simulations show that unusual events can be killers. In his book, Lewis points out that the simulations generally produce a greater number of casualties from small NEOs than would be expected from calculations involving "typical" values. Unfortunately, it would be extremely difficult for current technology to reliably detect such small, but deadly, objects. The situation is very different for the civilization-destroying giants because most can be easily spotted from Earth using existing technology. Given decades of warning, we can develop the space technology to nudge them into a non-threatening orbit. But the current odds are that a large NEO will strike with little or no warning because the world-wide search for NEOs is grossly under-funded and under-staffed (as one frustrated scientist put it -- less than the number of staff at a typical McDonald's restaurant). Lewis sums up the situation succinctly: "Of all the natural hazards facing Earth, impacts are the most dangerous. Unlike native hazards of the Earth's surface, impacts know no size limit. Their effects can be devastating over the entire surface of the planet. They are the only credible natural threat to human civilization. But impacts, especially those of large bodies, are both predictable and avoidable. "The Near Earth Object (NEO) population constitutes both an unprecedented hazard and an unparalleled opportunity," Lewis said. "It is sometimes said that there is a fine line that separates a threat from an opportunity. The near-Earth asteroids present us with just this dilemma. They present us with an intelligence test of the highest order, with the highest possible stakes for the human race."

Notes about the computer program The computer program is available on diskette distributed with the book "Comet and Asteroid Impacts on a Populated Earth" by John S. Lewis, Academic Press. It was released late in 1999. Due to its random nature, each time the program is run it generates a completely different set of results. The overwhelming influence of a few horrendous events means that the total number of fatalities can vary considerably between successive runs. Only the worst event in each century was considered in my simulation. Other fatal events may occur but are not included in the death toll.

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The original program uses a tsunami runup factor of 30 (the height of the wave at the shoreline was assumed to be 30 times the height of the wave in deep water). A more conservative runup factor of 5 was used in the simulation. The program is mainly intended for runs covering several thousand years. In these time periods, impacts massive enough to cause global climatic trauma are extremely rare and the program did not fully account for these effects. Lewis and others suggest an explosion equivalent to one million megatons of TNT would be sufficient to cause over a billion human fatalities, mainly due to global starvation. A typical asteroid about 1 mile across would do the trick. Global climatic effects probably become insignificant for asteroids smaller than 500 yards across, with a typical explosion of 10,000 megatons of TNT (some 200 times larger than an H-bomb). The potential fatalities from these climatic effects have been included in the above fatality estimates. A constant world population of 5 billion people is assumed. It is also assumed that impacts occur without warning (the current situation) and that there is no time for evacuation or preparation, such as stockpiling of food supplies.

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Asteroid Hunters Downgrade Overall Threat to Earth By Michael Paine Special to space.com posted: 12:21 pm ET 12 January 2000 A handful of professional astronomers regularly search the night skies for asteroids or comets that may eventually slam into Earth. Their main quarries are objects about 1,000 yards (one kilometer) or more across -- rocks capable of severe destruction. Until recently most scientists thought there were about 2,000 of these Near Earth Objects (NEOs). Now the astronomers who operate the Near Earth Asteroid Tracking (NEAT) project have come up with a lower estimate: 700. If accurate, the new number would reduce the odds of a civilization-destroying impact in any one year from about one in 100,000 to about one in 300,000, something still more likely than being dealt a royal flush in five-card poker. "I think the new estimates are plausible and that many colleagues are accepting them," said the Minor Planet Center's Brian Marsden, who was not involved in the research but who collates and analyses information about known asteroids and comets. In the study, David Rabinowitz of Yale University and Eleanor Helin and her colleagues, who operate NASA's telescope in Hawaii, analyzed results for the amount of sky covered by their project. The results are described in the January 13 issue of the journal Nature.

Uncertainty remains Like all NEO estimates, the new one is an educated guess based on the amount of sky searched so far and backed up by counts of craters on the Earth, as well as on the moon, Venus and Mars, where the scars of past impacts do not erode so quickly.

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"The real comfort is that we are on track to finding most of the hazardous asteroids before they find us." The actual number of 1-kilometer NEOs could range from about 500 to 900, Rabinowitz said. These objects are so small and distant that their size cannot be measured directly -- the task is equivalent to using a telescope to gauge the girth of ant a hundred miles away. Instead, scientists consider the brightness of the object, assuming that the larger objects will appear brighter in the sky. The NEAT team, like most other groups, assumes a typical space rock reflects 10 percent of the sunlight that hits it. This is based mainly on the characteristics of meteorites and a few large asteroids that are well studied. A trap with this method is that space rocks come in different shades of gray -- some reflect more sunlight than others.

In the dark Last summer NASA scientists who operate the Deep Space 1 spacecraft were taught a lesson about dark asteroids. Their pioneering spacecraft was supposed to spot and photograph asteroid Braille which, coincidentally, was discovered by Helin and a colleague in 1992. Braille is some 1.5 miles (2.4 kilometers) end to end, and the spacecraft passed within 10 miles of it -- a brilliant feat of auto-navigation. But the elation of the scientists was dampened when no close-up pictures were beamed back to Earth. It turned out Braille was much darker than anticipated, and the imaging system of Deep Space 1 could not lock onto the asteroid. It's possible that these dark objects are more common than previously thought and they have eluded Earth-based asteroid search programs.

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Other threats Researchers study Near Earth Objects that are 1 kilometer and larger because they pose the most significant risk to the planet for global devastation. There are other threats that this study does not consider, such as long-period comets that return to the inner solar system only rarely and could only be detected a couple of years before impact. "Comets are also a significant global hazard, and we are fortunate that they impact less frequently, presumably about 10 times less frequently," Rabinowitz said in an e-mail interview. "Smaller NEOs don't have a global effect. Though hazardous on a local level, they are not as important in the long run." A subclass of objects, called Potentially Hazardous Asteroids, includes 200 rocks in space that are expected to pass within 5 million miles (about 8 million kilometers) of Earth and are estimated to be more than about 600 feet (183 meters) across. More sensitive equipment will be needed to detect a reasonable proportion of these objects, experts say. "The real comfort is that we are on track to finding most of the hazardous asteroids before they find us," Rabinowitz said.

Another search effort In the early 1990s an international group of scientists proposed the Spaceguard Survey -- a global search that would find 90 percent of the potential civilization destroyers over ten years. Current efforts have fallen far short, but the NEAT scientists point out that their reduced estimates mean the Spaceguard goal will be easier to reach. Marsden, of the Minor Planet Center, agrees, but he cautions that there is much more to the task than just finding an object. Follow-up observations are needed to pin down the orbit, he said.

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At the current rate of discovery -- about 50 to 110 per year -- it will take about two decades to find all the 1-kilometer NEOs, Rabinowitz and his colleagues calculate. space.com's Robert Roy Britt contributed to this report.

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Defending Earth: Fact Vs. Fiction By Michael Paine Special to SPACE.com posted: 06:23 am ET 11 February 2000 First, the good news: Asteroid 433 Eros is not on a collision course with the Earth. At roughly twice the size of Manhattan Island, Eros is huge compared with other known near-Earth asteroids. A collision by an object this size would be more devastating than the impact that is thought to have finished off the dinosaurs 65 million years ago. Eros is in the news because, on Monday, after a torturous four-year journey, the NEAR spacecraft will attempt to become an artificial moon of Eros. A successful NEAR mission to Eros will show that we have the ability to rendezvous with an asteroid, and to orbit it. This ability is crucial if -- some scientists would say "when" -- an asteroid is discovered to be on a collision course with Earth. Space missions to asteroids and comets might not seem as exciting as a landing on Mars, but the social, scientific and commercial benefits from these missions could be great. An asteroid or comet impact with Earth is the only type of natural disaster that could instantly wipe out human civilization, and yet -- unlike earthquakes, floods and volcanoes -- it is within our grasp to prevent the collision. The know-how needed to protect Earth from collision could also be used for commercial mining in space. Comets and asteroids are packed with useful raw materials. Eventually, space prospectors might want to rendezvous with them and, perhaps, change their orbit.

Catching Comets; Angling Asteroids

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To learn more about the physical properties of asteroids we first have to reach them with spacecraft. The NEAR mission is the first attempt to rendezvous with an asteroid. A rendezvous involves carefully maneuvering the spacecraft so that it follows nearly the same orbital path as the asteroid. The spacecraft (pictured below) slowly approaches the object, then adjusts its speed so that the spacecraft and asteroid follow the same path around the sun. In the case of NEAR, a further maneuver will put the spacecraft into orbit around the asteroid. Previous spacecraft missions to asteroids and comets have involved quick flybys with no attempt to match the speed of the object. These missions were important steps in our exploration of these bodies, but improved technology was needed to achieve a rendezvous. One recent space mission was designed to test new technology. In July last year the Deep Space 1 spacecraft passed within 10 miles (16 kilometers) of Asteroid Braille. This mission successfully tested two important new technologies -- auto-navigation and the ion drive. Auto-navigation means that the robot spacecraft worked out its own location in space and plotted the course to the target object. The ion drive (pictured below) is an advanced form of propulsion where particles coming out of the exhaust are electrically charged (ions) that are accelerated by electrical means to very high speeds. Solar cells or a nuclear generator could provide electrical power. (Credit: Johns Hopkins University) Deep Space 1 used an advanced solar collector to generate a stunning 2,500 watts of power. By using a steady, reliable power source, the ion drive can gradually accelerate the spacecraft to interplanetary speeds. Within 12 months Deep Space 1 will have consumed all of its 180 pounds (80 kilograms) of xenon propellant, having achieved a speed of 9,000 m.p.h. (4 kilometers per second). Dr Marc Rayman from the Deep Space 1 mission team explained that the Braille flyby was a bonus for the primary mission, which was mainly designed to test new technology. The experience gained at Braille will help them plan an encounter with Comet Borrelly -- the main target of the extended mission. He added that the failure, last November, of the spacecraft's "star tracker" navigation

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aid meant that they had to drop plans to reach a second comet, but otherwise, the failure would not seriously hamper the extended mission. (Credit: NASA/JPL) Slingshots from planets Many recent interplanetary space missions have involved a gravity-assist Earth flyby. This slingshot technique (illustrated below) can produce substantial reductions in the size of the rocket needed to reach a planet or asteroid. For example, in January 1998 the NEAR spacecraft whizzed within 340 miles (550 kilometers) of Earth's surface. (Credit: Johns Hopkins University) This planned encounter changed the course of the spacecraft so that it would reach Eros one year later. (Unfortunately a technical bug had prevented it from going into orbit and the mission scientists had to wait an additional year for the next opportunity, which is on February 14, 2000.) Of course, an Earth flyby would be very difficult to sell to the world's population if the spacecraft was carrying nuclear weapons intended to deflect an asteroid. Adding further to the difficulties, the best time to nudge an asteroid is when it is closest to the sun, but this can make the mission much more challenging. Alan Harris, senior research scientist with the Jet Propulsion Laboratory in California, points out a mission to rendezvous with the asteroid 1999 AN 10 -- which is in an orbit that is typical of a "potentially hazardous asteroid" -- would involve a space mission that is formidable with current rocket technology. They run out of fuel well before the necessary speeds are achieved. Maybe we should be dusting off the blueprints for the giant Saturn 5 rockets that were used for the Apollo moon landings -- just in case we need to quickly intercept an asteroid or comet on a collision course with Earth. This may not be that easy -- in his book "Mining the Sky", planetary scientist John Lewis reports that he went looking for the Saturn 5 blueprints a few years ago and concluded, incredibly, they had been "lost".

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Harris cautions that even the mighty Saturn 5 could only deliver a few pounds/kilograms of payload to land on, or orbit, an asteroid such as 1999 AN 10. He adds, "Ion drive is probably the most feasible way out of this quandary." To Nuke or To Nudge An asteroid is heading for Earth. With just days to go before the collision a beefed-up space shuttle is sent to intercept it. A brave team of astronauts and oil-rig workers drills deep into the space rock, plants a nuclear bomb and blows it in two. The two halves fly apart and miss the Earth. Dream on! The idea of blowing up an asteroid makes for good movie scripts, but is not the way to do it in the real universe. Many of the fragments would remain on a collision course and like the blast from a shotgun; the fragments can do up to ten times as much damage as the original, intact object. In any case, Erik Asphaug from the University of Southern California has modeled "rubble-pile" asteroids and finds that blowing them up with bombs may be much more difficult than with asteroids made of solid rock. It is a bit like the difference between hitting a sandbag and a solid sandstone block with a sledgehammer -- the sandbag absorbs the impact with little disruption but the sandstone block shatters.

Applying a nuclear "nudge" "Stand-off" nuclear explosions are favored by some scientists (see below) and might work with both solid and rubble-pile objects. A nuclear bomb is detonated several hundred yards away from the object. Surprisingly, it is the intense radiation generated by the explosion that does the job. In one scenario, the radiation grills one half of the asteroid and causes a very thin surface layer to vaporize and fly off into space. "Yippee-Ki-Yay …Hmmm, maybe not." Bruce Willis meant well in "Armageddon" but he could have doomed us all Tens of tons of material blasting off the asteroid at high speed would be sufficient to jolt the asteroid in the opposite direction. The effect is like the recoil of a rifle --

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a small bullet moving at high speed causes the heavier rifle to recoil at low speed. One thing most scientists agree on is there is no need to maintain an arsenal of nuclear weapons in space ready to intercept rogue asteroids. They also point out that there are ways to deflect asteroids that don't require nuclear explosions and we should be looking at these methods more closely. In theory, an asteroid that is found to be on a collision course with our planet can be deflected to avoid an impact. The deflection involves changing the asteroid's course with a sideways push or, preferably, changing its orbital speed so that it arrives before or after, rather than when Earth crosses its path. In either case the deflection is far more effective if it can be carried out years or decades ahead of the predicted collision. For example, after twenty years, a nudge of just 1 m.p.h. (1.6 kilometers per hour) would change an asteroid's location in space by about 170,000 miles (273,500 kilometers). That is more than halfway to the moon. Recent discoveries suggest that deflection of some Earth-threatening asteroids may be easier than first thought. Most schemes for nudging asteroids into a safer orbit assumed a single catastrophic encounter with Earth. This meant changing the course of the object by at least 4,000 miles (6,300 kilometers) -- the radius of Earth.

Nuclear Deflection: A safer, more effective procedure Alan Harris, from NASA's Jet Propulsion Laboratory, explains that scientists now realize an asteroid will usually make several close passes by the Earth before a collision occurs. The recently discovered 1000-yard (1-kilometer) wide asteroid designated 1999 AN 10 provides an instructive example. It will make a close pass of Earth every few decades. During each pass the asteroid is deflected slightly by the Earth's gravity.

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Astronomers in Italy have calculated that a critical deflection could occur in 2027. This would involve the asteroid passing through an imaginary hoop in space they call a "keyhole". If the asteroid were to pass through this keyhole, which is only about 60 miles (100 kilometers) across, then it would collide with the Earth on its return in 2039. When the initial calculations were made, astronomers didn't know the orbit well enough to determine if it might pass through the keyhole. After important follow-up observations were made they have now pinned down the orbit enough to be sure that it will not pass through any keyhole in 2027 and there is no chance that it will collide with Earth in the next century or so. If, however, they had determined instead that there was a chance it would pass through a keyhole in 2027, then a mission to place a transponder, like a radio homing device, on the asteroid would have been wise so that its orbit could be determined precisely. Harris explains that such a high level of precision would likely be required to determine for sure if the asteroid were on a course through a keyhole and, if it came to be, to measure the success of any deflection efforts. In this case a deflection of just a few hundred miles prior to the 2027 keyhole event would be all that was needed to avoid the 2039 collision. Deflection of dangerous asteroids that are not in a "keyhole" orbit is more difficult because a larger change in course is required. The task is still feasible provided that sufficient warning time is given. If a serious global effort is made to discover most large near-Earth asteroids within the next decade, then we should have decades, or even centuries of warning before a devastating impact. With such lead times only a relatively small nudge is required to change an asteroid's course so that, decades later, it will miss Earth.

Sailing with Sunlight: Non-nuclear Asteroid Deflection Asteroid expert Jay Melosh from the University of Arizona has looked at a range of ideas for deflecting asteroids without resorting to nuclear weapons. They include:

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* Deploying a giant parabolic mirror to concentrate the sun's rays and vaporize rock on the surface of the asteroid. The vaporized material flies off at high speed and generates a re-coil action that pushes the asteroid, slowly but surely, in the opposite direction. * Landing cannon-like devices on the surface to fire asteroid material into space. This also depends on re-coil action. An ion drive, as used on the Deep Space 1 spacecraft, might also do the trick. * Attaching a giant solar sail to the asteroid The solar sail (pictured below) uses the small, but constant pressure of sunlight acting over a large area to steadily move the asteroid. Melosh points out that the sail needs to be steerable, like those on a modern yacht, to tug the asteroid in the right direction: "An along-orbit push (at right angles to the sun) is by far the most effective in changing a collision into a miss," Melosh says. There are two other ideas related to the solar sail concept: a giant silvery balloon, which in theory would be easier to deploy than a sail and wrapping the asteroid in foil (or painting it) to increase its reflectivity. Melosh explains, "with such a reflector it is hard to steer -- it can only apply a force directly away from the sun, which is the least helpful direction". (Credit: NASA/JPL) Melosh is cautious about techniques that depend on being attached to the asteroid. "The asteroid is rotating and perhaps tumbling -- a hard object to tie anything up to," he says. "It would probably have to be enclosed by a system of gimbals anchored to the asteroid surface: a mechanical nightmare begging for a catastrophe." The solar mirror scheme, preferred by Melosh, has the advantage that it could avoid the need for physical attachment to the asteroid. During the 1960s NASA did some work on solar mirrors for use in space, but little has been done since then.

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Space Missions: Chasing Comets and Asteroids Several researchers are using supercomputers to predict the effects of asteroid-deflection techniques. One day these simulations may be needed to plan a mission to save Earth from a collision. But the physical properties of asteroids and comets are poorly understood, and so the information gathered from space missions to these objects is crucial for these simulations. Several challenging missions to asteroids and comets are underway or are planned. Space Missions to Asteroids and Comets Deep Space 1: NASA. Launched in 1998. DEEP SPACE 1 flew within 10 miles (16 kilometers) of Asteroid 1992 KD Braille on July 28, 1999. The mission is mainly a test of new propulsion and navigation technology. The extended mission was to include flybys of two comets, Wilson-Harrington and Borrelly, but a problem with the tracking system meant that priority is now being given to Comet Borrelly. NEAR: NASA. Launched in 1996. NEAR flew within 753 miles (1,212 kilometers) of Asteroid Mathilde in June 1997. Earth swing-by January 1998. Planned Eros rendezvous in January 1999 failed. Next attempt February 14, 2000 when NEAR will go into orbit around Eros. MUSES C: Japanese Space Agency. Launch planned for 2002. MUSES C is a mission to the asteroid, Nereus. This mission will return fragments of Nereus' surface to the Earth for detailed analysis. CONTOUR: ASA/JPL Launch planned for 2002. The CONTOUR spacecraft will study three: Encke, Schwassmann-Wachmann 3 SW3 and d'Arrest. Rosetta: European Space Agency (ESA). Launch planned for 2003. ROSETTA is designed to land and remain on comet Wirtanen as it tours the inner solar system.

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Stardust: NASA. Launched 1999. STARDUST will fly past comet Wild 2 and capture dust grains blown from the comet's surface. These will be returned to Earth for analysis. NEAP: Spacedev Corp. SpaceDev is a publicly owned company. With the assistance of the science community, SpaceDev has selected 4660 Nereus, possibly a carbonaceous near-earth asteroid, as its NEAP mission target. To reach Nereus, NEAP is currently scheduled to launch on April 3, 2001 (possibly put back nine months to simplify the mission). It will land a payload on the surface of the asteroid and will be a demonstration of the potential for commercial mining of asteroids. Deep Impact: NASA/University of Maryland. Launch planned for 2005. A University of Maryland proposed space mission to penetrate deep into the nucleus of a comet. The launch of the DEEP IMPACT mission is planned for January 2004. The schedule calls for the mission to reach its target, Comet Tempel 1, at the beginning of July 2005, with impact on July 4. Although knowledge about asteroids is important for protecting Earth from collisions, it is more likely to be used, ultimately, for commercial purposes. Over the next few decades an impact by a large asteroid is highly unlikely (but cannot be ruled out). During that time commercial mining of asteroids may become commonplace. Many asteroids are rich in the raw materials needed for manufacturing in space, and some are easier to reach than the moon. Of course, one way to deal with an Earth-threatening object is to mine it away to nothing.

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Fossilized Bacteria Found in Ancient Meteorite By Michael Paine Special to SPACE.com posted: 07:51 am ET 21 February 2000 Russian scientists claim to have discovered fossils of primitive extraterrestrial organisms in a meteorite thought to be a leftover from the formation of the solar system. Similar theories have met with skepticism in the past and there are doubts about the latest claims. It seems that garden-variety microbes love to feast on these carbon-rich meteorites. "Since these objects look so much like the remains of terrestrial organisms, it seems most likely that they are remains of terrestrial organisms." Last year, at a conference on Astrobiology held in Denver, Dr Stanislav Zhmur and colleagues from the Russian Academy of Sciences revealed that they had found what looked like fossilized microorganisms in fragments of several meteorites that fell on the rural town of Murchison in South-East Australia in 1969. Their electron microscope pictures and comments were recently posted on the web pages of "Cosmic Ancestry" -- part of the Panspermia website, devoted to research and conjecture about the spread of life between star systems. Even to the un-trained eye the objects in the pictures look like organisms. "Since these objects look so much like the remains of terrestrial organisms, it seems most likely that they are remains of terrestrial organisms," said Allan Treiman from the Lunar and Planetary Institute in Houston. "Terrestrial bacteria and fungi infest meteorites almost immediately on landing on Earth, take up residence and consume whatever they can. The fungi worm their way into the meteorites along cracks and pores, and 'burrow' into the carbonaceous material as they eat it".

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Treiman has also been critical of the claims about microfossils in the famous martian meteorite ALH84001. Dr Andrew Steele from the University of Portsmouth told SPACE.com "meteorites become contaminated with Earth life within days of landing, yet some of the Murchison meteorites were in the open for four to five months before being collected." Added Steele, "electron microscopes and morphology [comparing the shape of organisms] are powerful tools, but they are not conclusive. More detailed biological tests of other meteorite specimens point in one direction -- terrestrial microbial contamination." Last year Steele found evidence of infestation by fungi and bacteria in another piece of Murchison meteorite. Crystals had even started to grow over some of the microbes while the rocks had been in storage. In more extreme cases this mineral growth could possibly be mistaken for fossils. Dr Matthew Genge, a meteorite researcher from the Natural History Museum in London, is also skeptical. "Murchison meteorites are even more likely than most to have experienced contamination since they fell in a farmyard and, reputedly, at least some of the stones had to be recovered from a ditch filled with manure," Genge said, adding that "any meteorite recovered outside Antarctica has had ample opportunity to become contaminated. Those in museum collections have furthermore been handle many times." Treiman wrapped up the case for the negative: "my opinion [for what its worth] is that the meteorites are infested with Earth bacteria -- the meteorites are not infested with extraterrestrial bacteria. The issue of life in the solar system is fascinating, but [like all good detective stories] will have lots of false leads."

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Saturn 5 Blueprints Safely in Storage By Michael Paine Special to SPACE.com posted: 06:34 am ET 13 March 2000 A NASA official has denied a claim made by a book author that blueprints for the mighty Saturn 5 rocket used to push Apollo astronauts to the moon were lost. The denial came in response to a recent story in SPACE.com that reported on a claim John Lewis made in his 1996 book, Mining the Sky, that he went looking for the Saturn 5 blueprints a few years ago and concluded, incredibly, they had been "lost." Paul Shawcross, from NASA's Office of Inspector General, came to the agency's defense in comments published on CCNet -- a scholarly electronic newsletter covering the threat of asteroids and comets. Shawcross said the Saturn 5 blueprints are held at the Marshall Space Flight Center on microfilm. "There is no point in even contemplating trying to rebuild the Saturn 5 ... The real problem is the hundreds of thousands of parts that are simply not manufactured any more." "The Federal Archives in East Point, Georgia, also has 2,900 cubic feet of Saturn documents," he said. "Rocketdyne has in its archives dozens of volumes from its Knowledge Retention Program. This effort was initiated in the late '60s to document every facet of F 1 and J 2 engine production to assist in any future restart." Shawcross cautioned that rebuilding a Saturn 5 would require more than good blueprints. "The problem in recreating the Saturn 5 is not finding the drawings, it is finding vendors who can supply mid-1960's vintage hardware," he wrote, "and the fact that the launch pads and vehicle assembly buildings have been converted to space shuttle use, so you have no place to launch from.

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"By the time you redesign to accommodate available hardware and re-modify the launch pads, you may as well have started from scratch with a clean sheet design," he wrote. In years past, rumors have abounded that in the 1970s the White House or Congress had the Saturn 5 plans destroyed "to prevent the technology from falling into the wrong hands". That seems doubtful -- it would be a formidable terrorist group that decided to build a Saturn 5 to wreak havoc on the world, or build a lunar base. Also, by the1970s, the Soviets apparently had given up on the race to the moon. Geoffrey Hughes from the Rotary Rocket Company supported Shawcross's view. "There is no point in even contemplating trying to rebuild the Saturn 5," he said. "Having a complete set of Saturn 5 blueprints would do us no good whatsoever. True, we would still be able to bend the big pieces of metal fairly easily. But they are not the problem. "The real problem is the hundreds of thousands of other parts, some as apparently insignificant as a bolt or a washer, that are simply not manufactured any more. Everything would have to be redone. So a simple rebuild would be impossible. The only real answer would be to start from scratch and build anew using modern parts and processes. Yet another immense challenge!" It turns out that NASA is taking on that challenge, but not necessarily to chase asteroids. Engineers at NASA's Marshall Space Flight Center are working on designs for a new giant launch vehicle called Magnum. It would use a curious mix of Russian rocket engines -- derived from the abandoned Soviet Energia rocket program -- and newly developed strap-on, liquid-fueled boosters that would first be tested out on space shuttles. The Magnum would use the space shuttle launch facilities at Cape Canaveral and could launch 80 tons (81,280 kilograms) of payload into low Earth orbit (LEO). This compares with around 20 tons (20,320 kilograms) for the piloted space shuttle, and for un-piloted vehicles like the U.S.' Titan 4-B and the European Space Agency's Ariane 5. Its lift capacity, however, would be less than the 100 tons (101,600 kilograms) that the Saturn 5 and Energia could manage.

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Bigger Telescopes Seek Killer Asteroids By Michael Paine Special to SPACE.com posted: 03:17 pm ET 26 April 2000 An Earth-bound asteroid or comet could still kill us but thanks to powerful telescopes slated for addition to the worldwide detection effort, we may be able to actually see it coming. In Japan, a telescope at the Bisei Spaceguard Center (BSGC) came online in February. Its mirror is only 20 inches (a half meter) in diameter, but scientists plan to upgrade to a larger 40-inch (1-meter) diameter scope in September. And a couple months ago, the long-running Near-Earth Asteroid (NEA) Tracking project at NASA's Jet Propulsion Laboratory upgraded to a larger telescope that also makes monthly observations three times more often than before. Also, in terms of sheer mirror width, the Spacewatch asteroid-seeking team at Kitt Peak in Arizona is about to bring down the house. Later this year the team hopes to start using a 6-foot (1.8-meter) telescope, along with a 0.9-meter telescope already in use. The bigger telescope will help scientists search for fainter objects and cover greater areas of sky. Thanks to those changes, scientists soon will be one scope away from a "magic number" total of six telescopes with mirrors at least 1 meter across in use for detecting asteroids. In 1992, the "Spaceguard Report" recommended that six telescopes with mirrors 2.5 meters across be built to discover within 10 years about 90 percent of large asteroids with orbits approaching Earth. Bisei will bring the total to five. Efforts were falling quite short of that goal, while movies such as Deep Impact and Armageddon publicized the threat of "killer" asteroids and comets. But two years ago, NASA scientist Alan Harris said the 90 percent in 10 years goal could be achieved with six scopes as small as 1 meter across. So now a decent shot at forecasting our demise is on the horizon, though how fast we'll find all those rocks and what we'd do about it both remain unclear.

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Busy at Bisei Syuzo Isobe of the Japan Spaceguard Association (JSA) described to SPACE.com the $7 million Bisei Center, operated by the JSA and funded by the Japanese Space and Technology Agency (STA). "It will have two telescopes and six full-time staff," Isobe said. "The running cost this fiscal year is about $600,000. The center also would find space debris that could pose a hazard to Japan's STA's science satellites currently orbiting Earth." Bisei Spaceguard Center in Japan. Credit: Syuzo Isobe The Bisei Spaceguard Center's second telescope will have similar capabilities to the Lincoln Near-Earth Asteroid Research (LINEAR) asteroid-detecting telescopes in New Mexico. LINEAR, which also uses two 1-meter telescopes, is by far the most successful asteroid search program to date. According to NASA, during 1999 LINEAR accounted for more than 70 percent of the discoveries of large asteroids. Discovery of large asteroids by the major observatories Credit: NASA LINEAR now faces tougher competition from Bisei, Spacewatch and NEAT (Near Earth Asteroid Tracking), which upgraded from a 1-meter telescope to a 4-foot (1.2-meter) telescope at the Maui Space Surveillance Site in Hawaii. (NEAT temporarily closed during 1999 and this boosted LINEAR's proportion of discoveries).

Japan bonus The entry of Japan into the search for killer rocks helps geographically, said Don Yeomans, manager of NASA's Near-Earth Asteroid (NEA) program office.

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"The entry of the Japanese search effort is a very welcome one for a couple of reasons," Yeomans said. "It will add longitude diversity for the ongoing search efforts so that weather problems in the U.S. Southwest (where most U.S. search programs are based) will not be such a problem. "Also, a discovery of a near-Earth object (NEO) [from] the [continental] U.S. or in Hawaii could be followed up easily by the Japanese site, which is several hours to the west," he said. "A very close, fast moving object can be quickly lost unless followed up immediately." Follow-up observations are needed to track an asteroid over several days or weeks. They enable the orbit to be calculated. In 1998 a "potentially hazard asteroid" called 1998 OX-4 was detected by the Spacewatch team, but was lost due to the lack of follow-up observations. Another benefit of a non-U.S. search team is "political diversity," Yeomans added. "NEOs are an international problem and they require an international solution. The more international partners that are involved, the less the entire effort need depend upon NASA-supported programs."

Project Spaceguard In his 1973 novel Rendezvous with Rama, Arthur C. Clarke describes a fictitious asteroid impact in Europe in 2077. This event forces Earthlings to create a "Spaceguard" system to detect and deflect Earth-threatening asteroids and comets. So far, most scientists and politicians, not to mention the public, have embraced such an approach. For now, NASA has embraced the recommendations of the Spaceguard Report, named for Clarke's vision, and is aiming to find most of the large rocks. The report identified asteroids 1 kilometer or larger as the main risk to civilization. The group acknowledged that comets and small asteroids also posed a threat but felt that less priority should be given these objects. Debate continues over the risk from these other objects but there is general agreement that the large rocks, at least, should be found. For now, there is no international commitment or cooperation to achieve the Spaceguard goal.

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Recent downward revisions to the estimated number of large near-Earth asteroids will not make much difference to the required survey effort. The odds of a collision with the Earth might be reduced but the same amount of sky still needs to be searched each month -- there will simply be fewer large asteroids to find because they will be spread more thinly across the sky. There is an unexpected benefit with a scheme to detect large asteroids. Harris's calculations suggest that an ongoing search using six telescopes will also detect many of the most threatening smaller NEOs because, before hitting us, they are likely to buzz the Earth during several orbits of the sun. Being close to the Earth means they are likely to be picked up by a vigilant Spaceguard program.

International efforts Spaceguard efforts have had ups and downs in other countries. Jin Zhu runs the Schmidt CCD Asteroid Program (SCAP) asteroid search project at Beijing Observatory in China. He told SPACE.com that the time allocated to asteroid detection at the observatory had reduced considerably during 1999. In Australia Rob McNaught reports that he plans to have the 0.6-meter Uppsala telescope operational early in 2001. McNaught runs the only professional search program in the southern hemisphere and this is regarded as particularly important for follow-up observations.

Taking the Search to Space A couple groups advocate searching for asteroids with space-based telescopes to solve the trouble of astmospheric glare. The project is mostly funded under NASA's NEO Observations Program and is associated with the Catalina Sky Survey in Arizona. Between 1990 and 1996 McNaught was part of the "Spaceguard Australia" team looking for NEOs from the Anglo-Australian Observatory in Australia. That search effort found 30 percent of all new NEOs up to 1996, when the Australian government withdrew funding. The news from Europe is not good. The OCA-DLR Asteroid Survey (ODAS) asteroid tracking project, located near Nice in France, stopped observing in April

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1999 so it could be refurbished. Alain Maury, ODAS' technical project manager, told SPACE.com that, following management changes the telescope had closed down. "I am currently looking for a new job," Maury said. "I don't think the Schmidt telescope will reopen anytime soon." Still, assuming that the latest systems can be configured to detect sufficiently faint objects, only one more dedicated telescope with a diameter of 1 meter or larger would be required to achieve the Spaceguard goal within a decade. However, given the uncertainties with near-Earth asteroid search programs in recent years, perhaps it would be wise to have a few more telescopes spread around the world. Arthur C. Clarke may prefer to be known as a visionary rather than a prophet of doom. Major Programs Searching for Near Earth Asteroids and Comets Name and location Equipment Status Bisei Spaceguard Center (BSGC) http://noewg.mtk.nao.ac.jp/ Okayama, Japan 1-meter telescope & 0.5-meter telescope, both used for detecting NEOs and space debris

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0.5-meter telescope commissioned in February 2000. 1-meter should be ready September 2000. Catalina Sky Survey (CSS) http://www.lpl.arizona.edu/css/ Mt Bigelow, Arizona 0.7-meter telescope, dedicated to NEO work Magnitude 19.2 Pays greater attention to objects high in the northern sky than other surveys. Plans to upgrade a 1.5-meter telescope at Mt. Lemmon. Lincoln Near-Earth Asteroid Research (LINEAR) http://llwww.mit.edu/LINEAR/ White Sands, New Mexico 1-meter telescope originally developed for tracking satellites. Two are now mainly doing NEO work. Magnitude 19 (maybe 20.5) Responsible for 70 percent of large near-Earth asteroid discoveries in 1999.

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Second telescope began in October 1999.. Lowell Observatory Near Earth Object Search (LONEOS) http://www.lowell.edu/users/ elgb/loneos_disc.html Flagstaff, Arizona 0.6-meter telescope dedicated to NEO work Magnitude 18.5. Concentrating on detecting large NEOs. Near Earth Asteroid Tracking (NEAT) http://huey.jpl.nasa.gov/ %7Espravdo/neatintr.html Maui, Hawaii 1.2-meter telescope dedicated to NEO work. Recently upgraded from a 1-meter GEODSS telescope, magnitude 19. OCA-DLR Asteroid Survey (ODAS)

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http://earn.dlr.de/odas/odas.htm Nice, France 0.9-meter telescope Closed down in April 1999. Schmidt CCD Asteroid Program (SCAP) http://vega.bac.pku.edu.cn/ %7Ezj/scap/scap.html Beijing Astronomical Observatory, China 0.6-meter telescope. NEO work is secondary. Telescope time reduced during 1999 due to other demands for the telescope. Southern Hemisphere Survey http://www.lpl.arizona.edu/ css/csssouth.html Siding Spring, Australia 0.6-meter Uppsala telescope will be dedicated to NEO work

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Plans for commissioning early in 2001. The only professional search in the southern hemisphere. Spacewatch http://www.lpl.arizona.edu/ spacewatch/ Kitt Peak, Arizona 0.9-meter telescope dedicated to NEO work Magnitude 21.5 A 1.8-meter telescope is under construction Notes: Magnitude is essentially a measure of the faintness of an object. The higher the magnitude, the fainter the object. Magnitude 21, which is a typical upper limit for the above surveys, is exceedingly faint. Background light such as the Milky Way or moonlight will swamp any objects of this magnitude. A typical 1-kilometer asteroid would have a magnitude of 18 when observed about 100 million miles (160.9 million kilometers) from Earth, in the opposite direction to the sun. Spaceguard scientists need to detect these objects at larger distances and at less favorable angles, where they will appear fainter. Magnitude 20.5 has been suggested as an appropriate limit for reaching the Spaceguard goal of detecting 90 percent of these large asteroids within a decade. All the above systems use CCD detectors for recording the images. These are similar to the devices used in camcorders to collect light digitally. To eliminate the effects of random bright spots in the images (mostly caused by cosmic rays) the

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usual procedure is to take between three and five shots of the same portion of sky. Sophisticated computer programs have been developed to scan the resulting images for signs of NEOs.

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Next: Space-Based Telescopes for Asteroids? By Michael Paine Special to SPACE.com posted: 07:17 pm ET 26 April 2000 Several scientists have pointed out limitations to the observation of asteroids and comets using only Earth-based telescopes, but Japanese and European scientists are offering a solution. Without the atmosphere's glare, a telescope based on the moon or elsewhere in space could search the region between Earth and the Sun, says the Japan Spaceguard Association. Infrared detectors on space-based telescopes would be better at determining the physical properties of asteroids and comets than ground-based equipment. A consortium of European scientists also has proposed a space-based telescope called Spaceguard. 1. The project recently missed out on being selected by the European Space Agency (ESA) for a low-budget "flexi-mission." "It is encouraging that the ESA Working Group that selected the missions recognized the wide intrinsic interest of our mission [the risk to the planet]," said Alberto Cellino, a consortium member. "We will continue to explore all the possibilities to develop this space-based observatory." Don Yeomans of NASA's NEO (Near-Earth Object) office said he is unaware of any U.S. plans to launch a space telescope to look for asteroids and comets. But he said space-based telescopes already up could contribute. "Space-based surveys in the optical and infrared will observe countless asteroids," he said, "whether they wish to or not. And perhaps this is the most cost-effective method for space-based near-Earth asteroid research -- to ride on the coattails of programs designed for observing objects other than NEOs."

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Scientists Study the Effects of Comet Linear's Breakup By Michael Paine Special to SPACE.com posted: 04:03 pm ET 04 August 2000 The break-up of Comet Linear as it swept past the sun last week has shocked astronomers into rethinking theories of the origins of such rocky ice balls in ways that could reduce the threat of a collision course with Earth. Though astronomers say they need more time to analyze Hubble Space Telescope and Jacobus Kapteyn Telescope images of the disintegrating Linear, they hope to soon have a greater understanding for how cometary nuclei are put together. Far beyond just the interests of academia, this knowledge could affect all of humankind. If, for example, a different comet were found to be directly en route to Earth, would the rogue comet withstand a nuclear-bomb blast that would deflect it away from our planet? Earth-defense deflection methods such as nuclear blasts might not work on something as fragile as Comet Linear. Blasting a more solid object, like an asteroid or even a smushy comet, could have serious repercussions. Many of the fragments could remain on a collision course and, like the blast from a shotgun, the fragments could do up to 10 times as much damage as the original, intact object.

Comet Linear Linear comes from the outer reaches of the solar system -- a quarter of the distance to the nearest star. Analysis of its orbit suggests it has been plunging toward the sun for millions of years. Last September, the LINEAR telescope in New Mexico detected the comet out beyond the orbit of Jupiter. With its highly sensitive automated search system, the scope is designed to detect near-Earth asteroids and observe their behavior. Occasionally, it also picks up a comet.

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Strange behavior Comet Linear's behavior is very strange. As it moved closer to the sun, chunks of the comet started flying off. By then, many large telescopes were pointed at the object, including the Hubble Space Telescope. ~ Earlier in July, LINEAR (which stands for Lincoln Laboratory Near-Earth Asteroid Research) was about 74 million miles (120 million kilometers) from Earth. Scientists say the side-splitting event started on July 5 as LINEAR began spitting out a large amount of dust, increasing the comet's brightness by more than 50 percent in just four hours. Last week, as Linear swung around the sun, the heating effect from the solar radiation, perhaps along with solar gravity, seems to have been too intense for the fragile object, breaking it apart. Astronomer Mark Kidger was observing Linear with the Jacobus Kapteyn Telescope at La Palma in the Canary Islands. Over several nights he watched the comet elongate into a "cigar" shape. At first he thought he was seeing the development of a "string of pearls," similar to Comet Shoemaker-Levy 9, which broke up into smaller pieces before plunging into Jupiter in 1994. But Kidger soon realized that Linear was catastrophically fragmenting -- turning to dust and gas. In fact, by next week it might disappear completely, he said.

A fragile comet Don Yeomans, a cometary specialist with NASA, said Linear's break-up pointed up its contrast with Shoemaker-Levy and the diversity of comets in the solar system.

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"The primary lesson to be learned from this one is that it was an incredible wimp -- so fragile it made Shoemaker-Levy 9 look like at tower of strength," Yeomans said. "Just goes to show you that Mother Nature's got a wide variety of comets to display -- from hard-packed iceballs [perhaps] to fragile, wimpy fluff balls like Linear." The demise of Linear may be a disappointment for amateur astronomers who were looking forward to the comet passing in front of the Sombrero Galaxy late in August. This is turning into a great year for asteroid and comet research. In addition to the Comet Linear event, the NEAR Shoemaker spacecraft continues to send detailed images and data while orbiting Asteroid Eros.

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Killer Asteroid Hunt Reaches a Milestone By Michael Paine Special to SPACE.com posted: 07:00 pm ET 07 August 2000 According to NASA scientists, the hunt for large asteroids that might collide with Earth has reached a milestone -- it is estimated that about half of these giant space rocks have now been found. NASA's goal is to find 90 percent of "Near Earth Asteroids" larger than 1000 yards (1 kilometer) by 2009. In recent years the discovery rate has improved dramatically. In figures just released by NASA, the LINEAR system in New Mexico still dominates the discovery statistics. Near Earth Asteroids (NEA) orbit the sun in the same region as Earth. But in most cases, the orbits are highly elongated and stretch out to the asteroid belt between Mars and Jupiter. Recent estimates suggest there are about 900 of these objects larger than 0.6 mile (1 kilometer) in diameter. A collision with a space rock of this size could destroy civilization. In an e-mail newsletter posted this week, David Morrison from NASA reports that 410 large NEAs have now been found. He points out that this is just past the halfway mark -- assuming that the 90-percent goal is achieved when 810 large NEAs have been found. This may be a halfway point when measured by the number of objects discovered, but this is not the same as measuring the time it takes to reach the goal. Although the graph of discovery rate suggests this goal can be achieved by 2009, the task will become more difficult once the remaining easily-detected NEAs have been found. More telescopes will probably be needed to keep the graph on target. The claim that a milestone has been reached is expected to draw a mixed reaction from scientists. Also, smaller NEAs and fast-moving comets are also still a threat. A collision by a NEA just 200 yards (180 meters) across could devastate a small country, disrupt global weather for months and, perhaps, bring down the global economy.

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Earlier this year NASA's Don Yeomans told SPACE.com: "The current [NASA] plan is to find the big ones first, then as the detection technology improves, extend the search to smaller and smaller objects." But it would likely take a major international effort to find a good proportion of the remaining threatening objects. Scientists are concerned about a lack of a major international program to follow-up on discoveries and to ensure they are not lost. In the words of astronomer Duncan Steel, "It is like throwing the needles back into the haystack."

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Meteor Showers and Shooting Stars: A Primer By Michael Paine Special to SPACE.com posted: 07:00 am ET 10 August 2000 Shooting stars are a bonus of stargazing. If you watch the sky on a dark night for half an hour you should spot several brief streaks of light -- meteors. All you need is a blanket to lie on, a clear view of the sky on a dark, a moonless night and patience. Of course, kids dont usually have much patience, but it is amazing how they react when they see their first shooting star. So be prepared with a few things to talk about while the family is lying down staring up at the sky. Here are some "facts" that you can throw into the conversation.

What are shooting stars? Shooting stars are mostly grit from space colliding at very high speed with air molecules high up in the sky. As Earth travels in its orbit around the sun it runs into clouds of grit generally pulverized rock that also orbits the sun. Many shooting stars are produced by grit no larger than a grain of sand. Some of the more spectacular ones are pea-sized and the really stunning (but very rare) fireballs are the size of an orange or larger. These objects collide with air molecules some 60 miles (95 kilometers) above Earth's surface and, due to their very high speed, they begin to glow white hot. We see a streak of light as they burn up. The scientific name is meteor but shooting star will do fine (just tell the kids that they are not really stars). As Earth slowly rotates, the side facing the direction of its orbit around the sun tends to run into more grit. This direction is directly overhead at dawn (at right angles to the sun) and this is why there tends to be at least twice as many shooting stars observable in the few hours before dawn, compared with just after sunset. Occasionally a lump of rock survives the fiery journey and reaches the ground. These rocks are known as meteorites. They tell us a lot about the composition of the solar system.

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How many are there? Millions of shooting stars occur each day, including during daylight hours. When you stare up at the night sky, however, you can only see about 0.005 percent (one twenty-thousandth) of the total area of the sky. This translates to just a dozen or so shooting stars per hour.

Meteor showers and storms On a typical night a shooting star can be seen every 10 to 15 minutes, but on some nights of the year a spectacular "meteor shower" occurs and shooting stars can be seen every few minutes or less. The peak of the next "shower" the Perseids -- occurs on August 12. Incredibly, the grit that forms the Perseid meteors comes from a comet. Though it happens less frequently, a "meteor storm" occurs when space debris falls at an even greater rate per hour.

How does a comet produce shooting stars? Comets have been described as giant, dirty snowballs a mixture of grit and ice. Comet Swift-Tuttle orbits the sun once every 134 years and last visited our region of the solar system in 1992. Its orbit stretches from near Neptune to inside the orbit of Earth. Around August 12 each year the Earth crosses the comets path. (Fortunately, the Swift-Tuttle wont be at the same point at the same time in the foreseeable future, so a collision is very unlikely!) Each time that a comet like Swift-Tuttle comes close to the sun, the ice on its surface starts to boil and chunks spurt into space. The ejected ice turns to vapor that is blown out of the solar system by the solar wind, along with very fine dust -- the source of a comet's "tail". But the larger grains are gradually spread around the comets orbital path. Each year our planet crosses the path of several comets and runs into grit, giving us periodic meteor showers and storms. The grit that forms the Perseid meteor shower comes from Comet Swift-Tuttle and is travelling at 140,000 miles. (225, 300 kilometers) per hour when it collides with Earth. That is about 60 times faster than a bullet from a rifle. No wonder the collisions are seen as brief streaks of light. It is all over so quickly that you dont have time to say to others "Look! Over there." The usual expression is more like

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"Did you see that?" The speed of meteors is also a reason why telescopes and binoculars are not much help for casual observations. By the time you point the instrument in the right direction it is all over.

Why "Perseids"? The Perseid meteor shower is named after the constellation Perseus. This is because the meteors from this particular shower appear to radiate from that constellation. This is an optical illusion, much like driving through a snow storm makes the snow flakes appear to be radiating from a point on the road up ahead.

How to observe the Perseids from the Northern Hemisphere The bad news this year is that there is a full moon on August 15. This means that when the Perseids shower peaks on August 12, the moon will be visible for most of the night and the moonlight will swamp all but the brightest meteors. The best time might be the few hours before dawn, between August 10 and 12, when the moon will have set or be low in the west . At that time the constellation Perseus will be high in the eastern sky, near the bright planets Jupiter and Saturn. Look straight up and you should see the Perseid meteors streaking from the east towards the west and south.

Contributing to scientific research If you become enthusiastic about observing meteors then you can become an official meteor spotter. The International Meteor Organization coordinates sightings and scientists, using multiple sightings of the same event to estimate the height, speed and other characteristics of meteors.

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Hunt for killer asteroids is a global responsibility: UK Report By Michael Paine Special to SPACE.com posted: 12:22 pm ET 18 September 2000 Scientists who hunt down asteroids and comets that pose an impact threat to Earth should focus on even smaller space rocks and add a British telescope facility in the Southern Hemisphere, according to a report released Monday. [NASA search programs currently focus on finding asteroids more than 1 kilometer (0.62 mile or 1,091 yards) in diameter, but the British government report recommends giving priority to finding near-Earth asteroids (NEA) as small as 300 yards (275 meters) in diameter.] The report, which describes the devastating effects of an asteroid or comet impact with Earth and the inadequacy of current international efforts to detect them, also made the following points: * Impacts by asteroids and comets present a real and * significant risk to humans and other life on Earth. Means now exist to avoid or reduce the fatalities caused by such impacts but only if the threatening objects are detected well in advance of the collision. * Earth-based telescope systems can carry out most of the necessary detection and follow-up work but they will need to be larger than those of current NEA-detection systems. These are the main conclusions of a report released today by the British Government. The report describes the devastating effects of an asteroid or comet impact with Earth and the inadequacy of current international efforts to detect these deadly objects. The report was prepared by three eminent British scientists and was released on the internet by Science Minister Lord Sainsbury.

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A copy of the report released Monday The task force reviewed the latest information about the impact risk and met with scientists from the United States and Europe. The potential death toll from an impact is much higher than any known artificial or natural disaster. For example an asteroid 1 mile (1.6 kilometers) across could explode with the force of more than 25,000 H-bombs. It would blanket the Earth in a dark dust cloud for months and cause freezing conditions and crop failures. One-quarter of the human population could die in the resulting global famine. Astronomer Duncan Steel commented on the report, saying that by the safety guidelines normally used for hazardous industries, a massive asteroid impact is "super-intolerable -- the government must act." Similarly, Alain Maury, a French astronomer who works at an observatory in Chile, told SPACE.com: "We have learned that sometimes, rarely, Mother Nature behaves like a terrorist, dropping 400-megaton bombs on us, and clearly we need to know her intentions for the coming century. In France today, nobody dares to think that looking for asteroids is useful. Reminds me of a time when nobody in the same country cared for Quebec or Louisiana."

U.S. asteroid search slipping behind The British report was finalized before a recent meeting of the International Astronomy Union (by coincidence, held in Manchester, England). Astronomers at that meeting heard that current discovery rates will need to double to reach NASA's "Spaceguard" goal: to find 90 percent of near-Earth asteroids 0.62 mile (1 kilometer) or more in diameter by the year 2009. The meeting was told that, with no further telescopes, the target would probably slip to 2015. Current search efforts are dominated by the U.S. This effort will be boosted in October by the new Japan Spaceguard 40-inch (1-meter) telescope at Bisei. However, the Japanese contribution is unlikely to be enough to reach the 2009 target.

Bigger telescopes needed to protect Earth

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The shortfall in Spaceguard telescopes would be addressed by the recommendations in the British report. Indeed, the authors recommend bigger telescopes than those currently used in the U.S. They see a need for a worldwide effort to find a good proportion of NEAs that are 300 yards across. The current detection technology would find less than 50 percent of these objects during a 10-year search. Although a collision with one of these asteroids would be unlikely to cause severe global climatic disruption, it would still cause regional devastation -- possibly leading to tens of millions of deaths.

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British Asteroid Report Takes Some of Shine Off the Sydney Olympics By Michael Paine Special to SPACE.com posted: 05:26 pm ET 18 September 2000 As an Australian I was very proud of the Opening Ceremony of the Sydney Olympics. As a taxpayer I was not too concerned about more than $1billion being spent on the Games. However, my pride in Australia was dampened today when I read the British NEO Task Force Report on the threat of asteroids hitting the Earth. It ignores any potential contribution from Australia! The U.S. and Japanese governments are funding several asteroid-search programs (about $3 million and $1 million per year respectively). If the recommendations of the report by British scientists are implemented then Britain will also be spending several million dollars per year. Only one national government has cancelled a successful asteroid-search program. You guessed it -- Australia. The current Australian Prime Minister (he is the person you might notice standing next to every successful Australian Olympic competitor) withdrew funding for "Spaceguard Australia" in 1996. From its unique location in the Southern Hemisphere this low-cost program was responsible for 30 percent of near-Earth asteroid discoveries. Since 1996 there has been no professional asteroid search in the Southern Hemisphere and this is raised as a concern in the latest British report. I am informed that, due partly to recent dismal performance (in astronomy -- not the Olympics), Australia currently rates a poor third to Chile and South Africa for locating the all-important Southern Hemisphere Spaceguard Telescope. Adding to the woes for Australian astronomers, the British Task Force report could tip the balance and push Britain into joining the European Southern Observatory (based in Chile). They would then have little choice but to pull out of the long-standing Anglo-Australian Observatory.

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Physicist and author of popular books on cosmology and the origin of life, Paul Davies, shares my sentiments about the Australian government. Davies now lives in South Australia and over the past few years he has been pointing out the asteroid impact hazard to Australian politicians. He told SPACE.com "Britain's enlightened attitude to the impact threat stands in stark contrast to the policy in this country. Australia scrapped its inexpensive and highly successful asteroid research project just as the rest of the world was waking up to the importance of tracking the dangerous asteroids." "There is an urgent need to reinstate an observational program in the Southern Hemisphere. I sincerely hope that the Australian government will for once remove its blinkers and cooperate with other nations to help protect the planet from the worst ecological threat we face." Michael Paine is a mechanical engineer based in Sydney, Australia. His main line of work is automotive safety. He has an amateur interest in astronomy and maintains the web pages of The Planetary Society Australian Volunteers.

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Mars Explorers to Benefit from Australian Research By Michael Paine Special to SPACE.com posted: 07:15 am ET 15 May 2001 MELBOURNE -- At the annual Australian Mars Exploration Conference (AMEC) in Melbourne last weekend, Australian researchers outlined some exciting projects designed to help with the exploration of Mars in coming decades, which coincided with National Science Week The conference, organized by the Mars Society of Australia (MSA), brought together specialists in geology, astrobiology, microbiology, robotics, vehicle design and Antarctic research to discuss exploration of Mars with space enthusiasts.

Water on Mars? On June 20, 2000 SPACE.com reported that NASA had found evidence of water on Mars. The tremendous discovery has fueled hope for microbial life on the Red Planet. It also makes a human mission to Mars more practical. For SPACE.com's special report, CLICK HERE. Although Australia is not planning any missions to Mars, its researchers are keen to help other countries with the design of their missions. The conference came just days after NASA chief Dan Goldin announced that a human mission to Mars was likely within 20 years.

Life on Mars Professor Malcolm Walter of the Australian Centre for Astrobiology Institute, explained that the most likely place to find evidence of life on Mars was around hydrothermal vents similar to those found in Yellowstone National Park. Hydrothermal vents are cracks of fissures in the ocean floor through which hot water and minerals are ejected.

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Walter said that although there might not be any active hydrothermal vents on Mars, ancient or dormant ones could have fossil evidence of life. He is currently studying a region of the Flinders mountain range in South Australia that used to be a huge hydrothermal system. His techniques for searching for fossil evidence of life could well be repeated on Mars within a few decades. Walter was enthusiastic about a new Australian invention, the PIMA spectrometer, for determining the mineral content of rocks -- a very important clue to their history. He said this was a great breakthrough for planetary exploration because the instrument was far superior to the one fitted to the Sojourner rover that landed with the Mars Pathfinder spacecraft in 1997. During a panel discussion Malcolm Walter was asked at what stage would he be prepared to declare Mars dead. He said that if we go to Mars and find an ancient, active hydrothermal system and there were no signs of life then the chances of finding life on Mars would be "pretty bleak." Dr. Philippa Uwins from Queensland University gave a gripping update on her pioneering work on nanobes. Four years ago she reported that she had found tiny organisms within a rock sample drilled from 3 miles (4.8 kilometers) underground. Many scientists thought that "life" could not be so small but the latest research has strengthened her claim that nanobes are alive. Snapshots of nanobes pushing apart layers of mineral crystals and a video of larger versions of the nanobes in motion fascinated the audience at the conference. Uwins' work may support claims by some U.S. scientists that the controversial features in Martian meteorite ALH84001 are fossilized life forms. Those claims can no longer be dismissed on the basis that the objects are too small to have been alive. It seems that searchers for life on Mars will need to be equipped with devices that can detect organisms as small as nanobes.

Robotic exploration of Mars Professor Ray Jarvis from the Intelligent Robotic Research Centre of Monash University described his experiments with a Russian-built miniature Marsokod rover using simulated Mars terrain.

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The center is applying recent advances in computer science to control the rover, which is a proven robust mechanical design. Jarvis said that it would be useful to send robots to Mars for scouting purposes but "in the end we have to go. Robots are no substitute for a human on Mars."

Lessons from Antarctica Environmental geologist Dr. John Webb, of Latrobe University spoke of his experiences in Antarctica. He showed photographs of gullies caused by the melting of permafrost in Antarctica that look like gullies on Mars. Webb cautioned about the psychological stresses on people living in harsh, remote environments. People start out as friends but often tensions build up after weeks of isolation. He pointed out that scientists typically "don't respond well to orders and do not mix well with military types." There may be social lessons for Mars mission planners from experience at Antarctica research bases.

At odds with NASA Dr. Nick Hoffman, also from Latrobe University added to the controversy in a "gloves-off" talk. He described his "White Mars" theory, where many of the geological features seen on Mars can be attributed to carbon dioxide and not water. Furthermore, he said this went against the official NASA line that there are signs of recent water flow on Mars. Hoffman said that carbon dioxide exists as a liquid some 80 yards (73 meters) beneath the surface of Mars and that if it comes into contact with the thin atmosphere it explodes and causes a massive flow of dust, rocks and gas. Hoffman has modeled the effects of these outbursts and finds they produce gullies and canyons similar to those seen on Mars. He also warns that explorers drilling for water from the surface of Mars had better be prepared for the explosive effects of striking liquid carbon dioxide instead of water.

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Hoffman also stunned the audience with the suggestion that maybe human missions to Mars should be one-way trips. He said that the resources needed for the return trip would be better spent on establishing a permanent base. On the topic of space tourism, Hoffman said "Dennis Tito has probably done more for space exploration than NASA has in the last 20 years" and that "Bill Gates could buy a seat to Mars".

Mars Society activities Jason Hoogland from the Mars Society of Australia described the Society's research projects. These draw on the expertise and unique conditions available in Australia. Society volunteers are building a Human Operations Prototype (HOP) rover that will be used in Mars-like terrain in the "Red Center" of Australia. Based on the chassis and engine of a four-wheel-drive passenger van, the HOP will be fitted out as a fully self-contained habitat, like a small motor home. Two people will drive the vehicle into remote areas. They will simulate the operational difficulties of rover expeditions on Mars. A "Mars Skin" suit is also being developed to simulate the difficulties of using a spacesuit on Mars. The "Red Center" of Australia could also be used for a Mars habitat research station, similar to the research program that the Mars Society is currently operating on the uninhabited Devon Island, located in the Arctic Circle. A telephone conference with the Mars Society in the U.S. confirmed that Australia was a likely location for a second habitat station. The Mars Society of Australia is also participating in a Mars rover design project and a series of radio communications experiments in remote areas.

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Asteroid May Have Created Hawaii By Michael Paine Special to SPACE.com posted: 09:04 am ET 01 August 2001 It's bad enough when, every few million years, an asteroid rocks our planet. It's worse if the impact triggers regional or global volcanic activity, which is not only hazardous to nearby plants and animals but can choke Earth's atmosphere with deadly gases for months or years. But there's also a possible bright side, like the birth of nice places like Hawaii. For more than three decades, scientists have explored the question of whether an asteroid impact could cause significant volcanic eruptions, hot spots that spring up out of nowhere and create new landforms or rearrange old ones. The process might have given birth to the Hawaiian islands, for example. The idea of linking space rocks and lava goes back to at least the 1960s, and in recent months the debate has heated up like a volcano ready to erupt. Though no firm answers have emerged, controversial computer modeling in recent years has shown what might happen, and why.

Old and buried Andrew Glikson from the Australian National University makes a living by hunting for signs of ancient impact craters, many of which are not readily visible, some of which are buried under oceans that didn't used to be where they are now. In several recent papers, Glikson maintains that the large craters found so far on Earth only account for about one-fifth of the actual number of major impacts predicted over the past 3.8 billion years. These impact predictions are based on a number of factors, including the vast numbers of craters on the Moon, which don't disappear on the geologically dead and atmospherically challenged satellite.

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During these billions of years it is likely that there were at least 10 impacts producing craters more than 125 miles (200 km) in diameter and 30 impacts producing craters more than 60 miles (100 km) in diameter, Glikson figures. And he argues that at least 50 percent of these impacts would have struck locations in ancient oceans where the Earth's crust was much thinner than continental crust and, in particular, some 10 percent would have struck the thin crust adjacent to mid-ocean ridges. A volcanic eruption is much more likely to occur if an impact occurs at one of these sites and, paradoxically, evidence of the impact is likely to be buried under the eruption and lost forever if that area is later folded, or subducted, into the Earth's crust. But Jay Melosh, a crater expert from the University of Arizona, doubts this and other links between asteroids and volcanoes. Melosh presented his views last July at a conference on catastrophic events in Vienna. "There is not a single clear instance of volcanism induced by impacts, either in the near vicinity of an impact or at the antipodes (opposite side) of the planet," Melosh concluded. "The possibility of impact-induced volcanism must therefore be regarded with extreme skepticism." Researchers who are independently working on various impact mechanisms say Melosh's reasoning is flawed. Hermann Burchard is a mathematician at from Oklahoma State University. He notes that there are several examples where either a volcanic eruption is speculated to be associated with a known impact or an undiscovered impact is speculated to be associated with a major eruption. Again the problem is that such eruptions tend to obliterate evidence of an impact.

Rocking the other side of the planet Mark Boslough and his colleagues at Sandia National Laboratories have modeled asteroid impacts. In a 1996 paper, they predicted that the seismic energy from an impact travels through the Earth and is strongly focussed at the antipode to the impact, near the boundary of the crust and the hot, molten mantle.

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This, they argue, generates instability in the upper mantle that can produce a "hot spot" under the surface, like the one that continues to form the Hawaiian Islands. They also claim that geologists have no satisfactory explanation for the generation of hot spots by other means, other than that they arise "spontaneously." Melosh expressed skepticism about the focussing idea after calculating that the seismic energy delivered to the antipode would be insufficient to melt the rocks. Boslough counters that melting is not needed to generate an instability -- the increased temperature of the region may be sufficient to trigger the start of a hot spot.

Clues on the Moon Dallas Abbott from Columbia University, New York has taken a different approach to the whole question. Using terrestrial evidence and crater evidence from the Moon, which retains a record of bombardment going back nearly 4 billion years, Abbott has analyzed the timing of large impacts compared with major volcanic eruptions, or mantle plumes. She found a strong correlation between the two and speculates that large impacts strengthen existing mantle plumes. She describes the ancient and dormant Deccan Traps volcanism, an area that is presently part of India. At the time of the Chicxulub asteroid impact, which occurred in Mexico 65 million years ago and likely led to the demise of the dinosaurs, the Deccan Trap region was near the antipode of the impact. Others have suggested this coincidence could be possible evidence that impact antipode effects initiated the Deccan Traps. However, Boslough says the Deccan Traps would have been several thousand kilometers away from the antipode to Chicxulub. Abbott says the Deccan Traps were active well before the Chicxulub impact, and so could not have been initiated by that event, but she observes that the Deccan plume was strongest immediately after the impact and this phase lasted less than one million years. At the least, it appears to be a strange coincidence.

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Despite advances in computer modeling, there is no clear physical evidence of a link between space rocks and lava, but the models are coming up with mechanisms by which an impact could cause, or at least speed up, a volcanic eruption. And proponents of the idea are quick to point out that geologists have not come up with a better explanation for how the Earth's hot spots got started. Michael Paine is a member of the Planetary Society Australian Volunteers. Information related to this story and the threat of asteroids can be found at his web site.

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Viking Data Still Cause Stir About Mars Life By Michael Paine Special to SPACE.com posted: 01:00 pm ET 05 September 2001 NASA recently posted on its Web site detailed data collected at Mars 25 years ago by life-detection experiments aboard the Viking spacecraft. The scientific community's judgment on those findings is one of the longest running and most contentious debates in space science. In 1976, two ingenious spacecraft soft-landed on Mars. Each was equipped with a miniature biology laboratory packed into less space than a domestic microwave oven. The three biology experiments within the package each produced some positive results that might have been associated with living organisms but the overall verdict at the time was that these results were caused by chemical rather than biological processes. All these years later, scientists continue to glean information from the Viking data and still debate whether the results indicate life in the soils of Mars. The pendulum has swung back and forth between chemical and biological explanations for the Viking results.

The experiment The Labeled Release (LR) experiment produced the most tantalizing results. Like most forms of life on Earth, when we consume food, some is processed and combined with oxygen to produce energy. The gas carbon dioxide is a product of that process and is present in our expired air. The clever idea with the LR experiment was that the carbon atoms in the food were radioactive and therefore could be detected in the air if a creature in the Martian soil processed the food and generated carbon dioxide (or some other gas containing carbon). In the LR experiment a radioactive broth was added to a sample of Martian soil in a closed chamber. A detector in a side chamber measured the amount of radioactivity in the air. A series of experiments was conducted to help eliminate non-biological processes. For example, some involved heating the soil to high temperature to sterilize any micro-organisms.

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Viking scientists back on Earth got very excited when the first results from both Vikings were received. There was a burst of gas production when the broth was first added to the soil. This did not happen when the soil was sterilized -- as might be expected if micro-organisms had died. However, when the unheated sample was measured over several weeks the gas production levelled off, suggesting that any micro-organisms, if present, had failed to survive and grow. Also when more broth was added there was no substantial release of gas. These conflicting results, coupled with the results of other Viking experiments led most scientists to conclude that the LR results were produced by non-biological reactions due to (unknown) chemicals in the Martian soil.

The players Harold Klein was Biology Team Leader for the Viking Project. He has been described as the father of exobiology -- the study of life beyond the Earth. Despite his strong desire to find life on Mars he understood the rigorous evidence that would be needed to convince the scientific world that non-terrestrial life had been discovered. Since the 1970s he has expressed skepticism about further claims of evidence of life in the Viking data. Sadly, Klein died in July this year. Gilbert Levin was involved in the design of the LR experiment and the analysis of the results. For 25 years he has labored to show that the best explanation for the results is that they were produced by Martian organisms. He has collected microbes from Alaska and Antarctica and subjected them to the LR experiments with results that match some of the Viking results. He has experimented with a range of non-biological chemicals see if they can produce the same results. He has questioned assumptions about the absence of liquid water on Mars and the chemical effects of bombardment of the soil by ultraviolet radiation. Levin has made a tremendous contribution to the study of extra-terrestrial life and he has designed new experiments for future Mars missions that could resolve the ambiguous Viking results. Unfortunately his enthusiasm for the issue has put off some scientists who regard his claims about the Viking experiments extravagant and unfounded. Levin has pushed the pendulum towards a biological explanation for the Viking results but, as Klein pointed out, this as a long way from unambiguous evidence of life on Mars. In a 1998 paper Klein questioned whether there were, as claimed by Levin, terrestrial organisms that could produce the LR results under the conditions encountered on Mars. If organisms were present in the Martian soil they came from extremely cold, dry conditions with no atmospheric oxygen. They were heated to about 10 degrees Celsius and held at that temperature for several days before a small amount of broth was added. Radioactive gas was detected almost

Rocks from Space

immediately and increased quickly before tapering off after about two hours. After the initial reaction died down a second quantity of broth was added. There was an initial drop in radioactive gas readings -- possibly the moistened soil reabsorbed it. After this no substantial release of radioactive gas was observed. These were not results that are usually associated with micro-organisms on Earth. Klein also pointed out that the process which produced the gas was highly selective in the type of carbon compounds that it consumed -- a result that was more likely with a selective chemical reaction than a biological process. From experience on Earth, if organisms were present in the Martian soil samples they were either dormant, and waiting for the "right" conditions to start the life processes, or they were extremely hardy organisms that managed to live normally in the harsh Martian conditions. If dormant, it seems surprising that they "awoke" so quickly when the nutrient was added. Levin refers to tests of Earthly lichen that gave a vigorous initial response and then apparently died from too much water. He suggests this might have occurred with Martian organisms. However, Klein noted that only a small quantity of broth was added in the Viking experiment so that a large portion of the soil was not drenched with the broth. Why didn't micro-organisms in the unaffected soil survive to produce gas in later experiments? The other puzzle is that the surface of Mars typically has not changed for millions of years so where did the dormant spores come from? If the organisms were adapted to the Martian conditions it is surprising that they also found the much warmer and wetter conditions in the Viking chamber comfortable. Most organisms on Earth do not respond well to being heated to more than 40 degrees Celsius above their usual temperature. This does not rule out a remarkably tough Martian organism but is another reason to be cautious about the Viking results. The other lingering question is the composition of the gas that was released. Radioactive carbon was present. This was probably carbon dioxide but could have been methane, some other gas or a mixture of gases. Earthly organisms generally require atmospheric oxygen to produce carbon dioxide but other sources of oxygen would be needed on Mars.

Later acts Rick Cavicchioli of the University of New South Wales studies extremophiles from Antarctica, including an organism called Methanogenium frigidum. It only grows in very cold oxygen-free conditions and makes a living by combining hydrogen and carbon dioxide to produce methane. Other Methanogens have been found in warmer conditions such as deep sea hydrothermal vents but the Antarctic bugs will die if exposed to oxygen or to temperatures higher than 18

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degrees Celsius. They stop growing at temperatures below -10 degrees Celsius but might do quite well in the soils of Mars on a warm day, if they could find a source of hydrogen and protection from UV rays. Cavicchioli points out that M. frigidum do not require a source of carbon, other than carbon dioxide in the air. They are therefore unlikely to have been interested in the offer of carbon-containing broth in the LR experiments. Joe Miller of the Keck School of Medicine at the University of Southern California has taken a different approach to analysis of the Viking LR data. He noticed that the radioactivity readings had a small but persistent sawtooth pattern that matched the length of the Martian day. This caught his attention because he had observed similar "circadian rhythms" in Earthly microorganisms. Careful analysis revealed that the fluctuations matched those of the temperature in the test chamber. The Viking laboratory was designed to hold the samples at near constant temperature despite the fluctuations of more than 50 degrees Celsius outside between the Martian day and night. The equipment managed a creditable 2 degrees Celsius fluctuation but Miller points out that this was still sufficient to cause some of the observed oscillation in radioactive gas due to reabsorption of carbon dioxide when the soil cooled slightly. He claims that this effect, together with other sources of variation such as equipment effects, can, at best, account for between 55 percent and 78 percent of the observed LR oscillation. He suggests that a biological response best explains the remaining component of the oscillation and several other characteristics of the experiments. Miller is conducting further analysis of the Viking LR data to look for circadian rhythms that do not match the length of the Martian day, and therefore the temperature fluctuations in the chamber. He notes that Earthly organisms that are held under constant conditions develop rhythms that are out of step with day and night on Earth. Miller is particularly excited about the possibility of organisms that process methane on Mars because methane is not easily absorbed by soil. The sawtooth pattern would need to be explained by other means. Also, from Earthly findings, it now seems possible to have an ecology of methane producers and methane consumers that live in a symbiotic partnership in the absence of oxygen. While the work of Miller and Levin, if confirmed, might push the pendulum further towards biology it is unlikely that the Viking data will ever fully eliminate the possibility that the strange results were caused by exotic chemical reactions. It seems that we will need to wait for further spacecraft missions to Mars to resolve the question of whether the Viking experiments detected life. Hopefully the designers of those spacecraft are looking at the lessons learned from the stunning Viking project.

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Bibliography Cavicchioli, R., Thomas, T., Saunders, N., Curmi, P., Kuczek, E., Slade, R., Davis J. and Mattlick, J. (2000) :Towards the genome of the psychrophilic archaeon Methanogenium frigidum', Proceedings of the 8th International Conference on Small Genomes, 2000. http://www.micro.unsw.edu.au/rick/arrowhead.html Horowitz, N. (1977) 'The Search for Life on Mars', Scientific American, November 1977. Kimball, J. (2001) Is (Was?) there life on Mars, http://www.ultranet.com/%7Ejkimball/BiologyPages/M/Mars.html Klein, H.P. (1996) 'On the Search for Extant Life on Mars', Icarus 120, 431-436, 1996. Klein, H.P. (1998) 'The Search for Life on Mars: What we learned from Viking', J. Geophysical Research Vol 103, No E12 28463-28466, 25 Nov 1998. Klein, H.P. (1999) 'Did Viking discover life on Mars?', Origins of Life and Evolution of the Biosphere, 29: 625-631, 1999. Levin, G.V. (1997) 'The Viking Labeled Release Experiment and Life on Mars', Proceedings of SPIE Conference, 1997. Levin, G.V. and Straat, P.A. (1977) 'Recent results from the Viking Labeled Release Experiment on Mars', J. Geophysical Research Vol 82 No 28, 30 Sep 1977. Levin, G.V., Kuznetz, L. and Lafleur A. (2000) 'Approaches to Resolving the Question of Life in Mars', Proceedings of SPIE Conference, 2000. Madigan, M.T. and Marrs B.L. (1997) 'Extromophiles', Scientific American, April 1997.

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Miller, J.D., Straat, P.A. and Levin G.V. (2001) 'Periodic Analysis of the Viking Lander Labeled Release Experiment', Proceedings of SPIE Conference, 2001. Scientific American, editors (1977) 'Science and the Citizen: Ambiguities of Mars', Scientific American, February 1977. Space Studies Board (2000) Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies, http://www.nas.edu/ssb/sssbch1.htm

Rocks from Space

Search for Large Asteroids Nears Completion, Experts Ponder Gaps in Program By Michael Paine Special to SPACE.com posted: 09:37 am ET 21 July 2003 SYDNEY, Australia -- A stated goal of finding 90 percent of all large Near Earth Asteroids (NEAs) by 2008 is more or less on target, leading experts said last week at the General Assembly of the International Astronomy Union (IAU) in Sydney, Australia. The goal, originally outlined by NASA and mandated by the U.S. Congress, is designed to insure that space rocks in the vicinity of Earth's orbit, and larger than 1 kilometer (0.62 miles), are found and tracked. An object of this size could cause global destruction if one were to hit Earth. An international affiliation of groups, collectively called Spaceguard, carries out the search and follow-up observations needed to purse the targets. NASA funds much of the work. No asteroids are presently known to be heading toward the planet. The global experts gathered here reiterated a common concern among asteroid scientists: When the current goal is reached, there will still be many unfound smaller objects that are easily capable of destroying a large city. Yet present technology is somewhat limited in its ability to find the thousands and perhaps millions of smaller asteroids that could potentially threaten the planet. The search for Earth-threatening asteroids was described by three international experts at a public forum Thursday: David Morrison from NASA's Ames Research Center; Alan Harris of the Space Science Institute in Colorado, and Andrea Milani from the University Pisa, Italy.

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Bigger, better telescopes are on the drawing board for finding these smaller asteroids, the scientists said. Meanwhile, images of the sky taken by current programs could be crucial to future attempts to find and track small asteroids using the new telescopes. Determining an asteroids exact trajectory and potential future danger requires observations across time, so the object's movement can be plotted. Importantly, there are no large telescopes devoted to the task of hunting asteroids from the Southern Hemisphere. A major search program down under would help in this task, the panelists said. The forum, "The danger from space: Are Near Earth Objects a catastrophe waiting to happen?" was moderated by Australian science celebrity Karl Kruszelnicki. NASA's Morrison described the consequences of an asteroid colliding with Earth. The larger NEAs, bigger than a half mile (1 km), would cause global environmental disaster, he said. Smaller objects are still a danger to cities and regions and Spaceguard will eventually be expanded to cover these smaller objects. Harris, from the Space Science Institute, showed the progress made with Spaceguard and described new telescopes that, within the next decade, could be used for detecting and tracking NEAs. He cautioned, however, that these new telescopes would have competing demands and most would be devoted to Spaceguard on a part-time basis. Harris said the lack of a major asteroid search program in the Southern Hemisphere was limiting the pace of new discoveries. A specialized Schmidt 1.2-meter (4-foot) telescope at Siding Spring in Australia is under-utilized and could be upgraded to search for near-Earth asteroids, he said. This would involve replacing a large photographic plate holder with a modern CCD camera (like those in video cameras). With new technology involving multiple CCDs, the Siding Spring telescope could be better at searching for asteroids than any current Spaceguard telescopes, Harris said. Australian astronomer Duncan Steel pointed this out in a science paper written in 1995, shortly before the Australian Spaceguard program was terminated as government funding was dropped.

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Milani, from the University Pisa, described the computations necessary to establish an asteroid's orbit around the Sun and to calculate whether it would hit the Earth in the future. He suggested that it was not very useful searching for new near-Earth asteroids if the extra work was not also done to check whether there was a risk of a collision. This usually involves alerting astronomers around the world to conduct follow-up observations. Much of the asteroid tracking effort involves amateurs who volunteer their time. Asteroids are sometimes initially found to have remote risks of hitting Earth. The additional observations are included in revised computations that, so far, have resulted in an impact risk being downgraded to zero in all cases that have been studied over time. Milani and his colleagues recently developed computer programs to generate numerous possible paths for a newly discovered asteroid. If any of these "virtual impactors" is found, by computation, to be on a collision course, then mathematicians can describe its predicted orbit and astronomers can carefully check whether the actual asteroid is on the same path. Just as important in this process is the checking of old sky images. The mathematicians can run a predicted orbit back in time and old images can be checked for signs of the object. Harris explained that not finding an object in old images could be used to eliminate the possibility an impact. The approach illustrates the importance of archiving astronomical observations -- a blank area on a picture could be just as important as a small white dot. It is also a good reason to immediately start taking images of southern skies, researchers say. After the public forum a discussion ensued about ways to deflect an incoming asteroid. The work by Milani and others has demonstrated that, if an asteroid is determined to be on a collision course, the most likely scenario is that over

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several decades it will perform multiple close approaches to the Earth before the impact. During these close encounters the asteroid must pass through a window, or "keyhole" in space if it is to continue on its collision course. In these cases it only takes a deflection of a few hundred kilometers (miles) to force a rock to miss the keyhole and therefore avoid Earth impact in a subsequent orbit. This compares with an object heading directly for an impact that must be deflected by thousands of kilometres (miles) so that it misses the Earth. Because they pass close to the planet on several occasions before impact, it should be possible to detect quite small keyhole asteroids with current telescope technology -- but only if scientists are effectively looking for them. A keyhole deflection is only possible if the threatening asteroid can be detected decades ahead of the impact and if sufficient sightings have been made to pin down its orbit. This was cited as another good reason for stepping up the Spaceguard effort and adding a southern sky search. On July 25, the Australian Minor Planet Workshop will take up discussion of how to jump-start asteroid searches in Australia and New Zealand.

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Reinventing Darwin Again: How Asteroids Impacted Human Evolution By Robert Roy Britt Senior Science Writer posted: 07:00 am ET 24 April 2001 In the 5 million years or so that it took for apes to become human, many human-like branches of the evolutionary tree were lopped off. Scientists have long wondered why these other hominid species, estimated to number a dozen or more, didn't make it. A newly presented mathematical argument suggests that the birth of Homo sapiens was guided by catastrophic asteroid or comet impacts, which created climate conditions that competing species, frankly, couldn't handle. It also holds that our human ancestors avoided early elimination by the statistical skin of their rotting teeth. "The reason that Homo sapiens have survived in spite of these global disasters has little to do with the traditional explanations given by neo-Darwinists," said Benny Peiser, a social anthropologist at Liverpool John Moores University. "It is sobering to realize that we are alive due to cosmic luck rather than our genetic makeup." Peiser bases his argument on the fact that populations of hominids and early modern humans were extremely small. "Had any of these impacts occurred in the proximity of these population groups, we might also have gone the way of the dodo," he said. The study's assumptions and calculations have met with strong caution and even sharp criticism among scientists who specialize in evolution, as well as asteroid experts. Adaptive advantage

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David Balding, a professor of applied statistics at University of Reading in the U.K., said the idea that human survival is due to "cosmic luck" does not compute: "Perhaps we were lucky in avoiding a massive impact, but perhaps it was our adaptive advantage that helped us survive modest regional impacts whereas our hominid cousins did not," said Balding, whose own research focuses on human evolution. But some called the new scenario plausible. It has not been published in a peer-reviewed journal but it is based on impact estimates that are generally accepted by the asteroid research community, though there are disagreements over the precise number of times a large asteroid or comet has struck our planet. Peiser laid the idea out earlier this month at a conference, "Celebrating Britain's Achievements in Space." He worked with Michael Paine, a volunteer for the Planetary Society in Australia who ran impact scenarios through a computer program. (Paine has written freelance stories for SPACE.com in the past.) The researchers concluded that there would have been 20 "globally devastating" impacts during the past 5 million years, with effects strong enough to have had "a catastrophic and detrimental effect" on human evolution. Five million years ago is roughly the time when hominids diverged from other apes, though some recent controversial evidence puts the split as far back as 6 million years ago.

Did space rocks set the human stage? No one argues that asteroids can be devastating when they tangle with Earth. An impact 65 million years ago is widely believed to have spurred the demise of the dinosaurs and many other animals and plants. But efforts to tie other, more ancient mass extinctions to impacts remain inconclusive. While extinctions are clearly identifiable in fossil records, impact evidence seems not to survive the millennia as well. So impact estimates are based largely on the Moon -- a nearby archive of countless craters that have not eroded much over time. Still, because scientists have not witnessed a severe impact, the presumed effects are speculative.

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If an asteroid larger than a kilometer (0.6 miles) hit the planet, it would cause instant death across a wide area near the site of impact, and researchers generally agree that drastic climate changes could last a year or more. Even our protective ozone layer could be damaged, studies have shown. But the precise consequences of these effects are not known. It is thought that long-term climate change could make life impossible for many species, which in turn would cause mass death that might move up entire food chains. Peiser suggests another possible effect: "The abrupt loss of the ozone layer and the sudden release of toxins may even affect the DNA in some unknown manner, thus triggering macro-mutations, including the sudden reorganization of entire genomes." Ellen Thomas, a Wesleyan University research professor who examines how climate change affects evolution, said few evolutionists would by this argument of quick, significant changes in the genetic blueprints. Instead, macro-mutations are seen by many as a genetic dead end. "Macro-mutations can hardly ever lead to evolution," Thomas said. "They lead to non-viable organisms."

Basic numbers questioned Of course to affect human evolution in any fashion, a space rock first has to hit Earth. But "no one knows how many impacts took place, or when, or with what severity, over the past 5 million years," said David Morrison, an asteroid expert at NASA's Ames Research Center in California. Morrison told SPACE.com that instead of the 20 potentially devastating impacts assumed by the study, he expects there were probably only five or 10 with enough energy to create global environmental effects. "But we know very little about specific impacts in this time frame, and virtually nothing at all about their actual environmental effects," Morrison said, adding that there is "no evidence of an impact associated with a hominid extinction."

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Morrison did not discount the whole idea, however. "I would be surprised if impacts had not had some influence on early hominid populations and perhaps evolution," he said. "On the other hand, I am not convinced that impacts led to numerous extinctions in the past 5 million years. This is all interesting speculation, but specific data are lacking on either impacts or extinction events and there is no known correlation between the two." Peiser counters that the estimates used in the study are "very conservative." He acknowledges that shortcomings in the human fossil record (fossils on land erode more easily than those in the oceans) "are far too big to allow any direct correlation between impact catastrophes and hominid extinction." But he said that the study shows that "impact catastrophes that occurred during the crucial period of human evolution should no longer be ignored." Still, it is clear that more research will be needed before any consensus emerges. "What [Peiser and Paine] may have added," said Balding, the statistics professor, "is some quantitative simulations to make more precise some well established speculations." Speculation about evolution is nothing new. And the more one delves into the nitty-gritty of our own past, the stronger the criticism gets over Peiser's attempt to reinvent Darwin. Followers of Charles Darwin have long believed that failed branches of our ancestry reflect a common mode of evolution, whereby species are gradually replaced by more advanced species that adapted because of their superior genetic fitness. But in recent decades, a different view called punctuated equilibria has taken hold. This theory, first put forth in the 1970s by Stephen J. Gould and Niles Eldredge, expects sharp changes in evolution. In either scenario, luck plays a role. And both fit within the most famous of Darwinian themes, survival of the fittest. But the rapid shifts assumed in punctuated equilibria, be they caused by sudden disasters or other means, are thought to be the mechanism by which one species replaces another.

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"There has been debate for over 100 years on whether evolution is gradual or punctuated," said Balding. And the debate continues. Recent fossil findings have some researchers leaning back toward the gradual approach to human evolution. Peiser said his study supports punctuated equilibria, and helps explain why "almost all hominids, i.e. the 14 known species of human ancestors, have become extinct during the last 5 million years." But Wesleyan's Ellen Thomas said it is not even known that there were 14 species. "The human fossil record is incomplete, and it is not easy to agree on which fossils belong to different species," Thomas said in an e-mail interview. "The experts disagree wildly." Thomas echoed other scientists in pointing out that there is no fossil evidence -- neither of human remains in Africa nor marine organisms, which leave a much more complete record -- that reveal any mass die-offs during the 5 million-year period covered in Peiser's study. "And if the extinctions affected humans, they should show up in the extinction record of other organisms as well," Thomas said. "The paper just shows that many impacts, many of which could have been damaging, possibly occurred." But Peiser argues that no expert on near-Earth asteroids, the space rocks known to exist in our region of the solar system, questions that "many such global disasters must have occurred." Yet he said "all textbooks on human evolution completely ignore the occurrence of catastrophic impacts."

Other forces of evolution While Peiser and Paine suggest that comets or asteroids are a driving force behind evolutionary change, it is the climatic consequences of impacts that are the would-be crushing mechanisms for fledgling species. Other researchers have long debated possible links between climate change and human evolution.

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For example, cold periods are suspected of forcing migrations that created small, isolated groups that could have evolved significantly but then died out. One such period may have occurred as recently as 71,000 years ago. But firm links between climate and serious evolutionary changes elude researchers. One recent international study, released earlier this year and led by Jeremy Marlow of Newcastle University, showed evidence of a significant cooling of the climate 2 million years ago that the authors said "adds weight to the theory that climate change played a significant part in the evolution of early humans." Further clouding the possibilities, recent findings have hinted at the possibility that the worst extinctions might require multiple killing mechanisms, such as when an impact, or perhaps several, happens to occur during a time of heavy volcanic activity.

Irony in our existence In an ironic preface to the whole argument, it's possible that asteroids and comets were responsible for life in the first place. A growing movement among astrobiologists suggests that rocks from space brought critical building blocks that stimulated the initial biological activity in the earliest primordial soup billions of years ago. But regardless of whether cosmic messengers helped make us who we are, there is one thing researchers seem to agree on: Given the evidence that our ancient ancestors were clustered in a relatively small area (in Africa) you are somewhat lucky to be reading about all this. "Asteroids certainly had the opportunity to wipe out man at his roots," said Jack G. Hills, an asteroid specialist at Los Alamos National Laboratory. "Only good luck prevented it." The following details of the new idea were provided by Benny Peiser and Michael Paine and appear here with only minimal editing for style and clarity: The findings are calculated on the basis of the generally accepted "impact rate" (i.e. the rate of cosmic impacts calculated from terrestrial and lunar impact craters together with the currently observable flux of asteroids and comets in the solar system). A computer simulation of cosmic impacts over a 5 million-year

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period was chosen to give an indication of the environmental disruptions that have occurred during the evolution of our species. These consequences can be categorized into: A. Local -- devastation over a radius of tens of (miles) kilometers. No serious regional or global consequences B. Moderate regional -- devastation over a radius of hundreds of miles (kilometers) -- the size of a small country. Short-term regional climatic problems. C. Severe regional -- devastation over 600 miles (1,000 kilometers) (the size of a large country). Severe regional climatic disruption. Mild, short-term global climatic disruption -- year without summer. D. Moderate global -- devastation over thousands of miles (kilometers) -- continental. Severe global climate disruption lasting several years. Global food chain failures E. Severe global -- global firestorms from ballistic entry of impact debris. Extreme worldwide climate disruption for decades to centuries. Extinctions. For everything except the last category, the effects on early human populations depend on proximity to the impact -- a matter of luck. In addition to climate disruption (mainly darkness and cooling), the larger impacts could lead to global warming due to the greenhouse effect (water and carbon dioxide), loss of the ozone layer (particularly with ocean impacts that propel chlorine into the upper atmosphere), acid rain and toxins. The simulation looked at the worst event in each of 5,000 millennia. It therefore gives an underestimate of the total number of impacts. The program recognizes five outcomes of an asteroid or comet colliding with Earth: * The object skims the atmosphere and flies harmlessly back into space. This happened in 2 percent of the millennia.

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* The object explodes above land in an airburst similar to an atomic explosion. This happened in 17 percent of the millennia. * The object impacts the land and forms a crater. This happened in 11 percent of the millennia. * The object explodes in an airburst above an ocean. This was the most frequent outcome, accounting for 41 percent of millennia. Fortunately, until recently, most of these impacts would have been harmless to land dwelling creatures. * The object impacts the ocean, forming tsunami and, possibly, ejecting vast quantities of water and salt into the atmosphere. This happened in 28 percent of the millennia. (Larger impacts may also reach the ocean floor and cause similar effects to a land impact) Over the period of the simulation some 57 percent of millennia suffered an impact that would potentially have consequences for land-dwelling creatures. In most cases they would only be affected when they were close to the impact site. The situation is different now with significant human populations living in low-lying coastal areas. Size impactor (The letters refer to the typical environmental consequences.) 1,650 to 2,950 feet (500 to 900 meters) (C): 108 events 0.6 to 0.9 miles (1 to 1.5 kilometers) (C/D): 24 events 1 mile (1.6 kilometers +) (D/E): 13 events Craters (The letters refer to the typical environmental consequences.) Over the 5,000 millennia a total of 552 craters were formed on land. Of these: * 477 were less than 3 miles (5 kilometers) in diameter (A); * 64 were between 3 and 6 miles (5 and 10 kilometers) in diameter (B); * nine were between 6 and 12 miles (10 and 20 kilometers) in diameter (C); * two were more than 12 miles (20 kilometers) (D).

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There were also six ocean impacts that could be expected to produce moderate-to-severe global climate disruption (D/E), particularly destruction of the ozone layer. Three of these involved transient craters more than 31 miles (50 kilometers) in diameter and would probably have penetrated to the ocean floor. Therefore, during this simulation severe climate disruption occurred, on average, every million years (i.e., two land impacts and three ocean impacts). The findings by Peiser and Paine are underpinned by a significant number of large impact craters. So far, 32 impact craters have been discovered that are younger than 5 million years. One is 32 miles (52 kilometers) in diameter, three are between 6 and 12 miles (10 and 20 kilometers), one is between 3 and 6 miles (5 and 10 kilometers) and 25 are less than 3 miles (5 kilometers) in diameter. However, it should be noted that it takes very unusual conditions to preserve craters of this size for more than a few hundred thousand years.

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