ASTR 330: The Solar System

ASTR 330: The Solar System

Lecture 16 - Quiz

Dr Conor Nixon Fall 2006

1. Are there canals on Mars? How did the idea start, and how was the issue resolved?

2. What features were discovered by Mariner 9?

3. What was the greatest accomplishment of the Viking missions?

4. Does Mars have any large impact basins?

5. Describe the main geologic features of the Tharsis uplift. How was Tharsis produced?

6. Compare Martian volcanoes to terrestrial and Venusian mountains.

7. Are the Valles Marineris on Mars bigger versions of the Earth’s Grand Canyon?


Lecture 17:

Mars II

Dr Conor Nixon Fall 2006Picture credit: NASA/JPL - MER Mission Team


Mars: up-close and personal


• In this lesson, the main theme is the in-situ exploration of the Martian surface.

• We will begin by looking at the landing sites of Viking, continue with the Sojourner Rover, and finish right up at the present day with the Spirit and Opportunity Rovers.

• We will consider the detailed information returned by these explorers regarding rock and soil, sediments and water.

• We will also examine the atmosphere and polar caps.

• Finally, we look at some of the planned missions to Mars in the next few years.


Viking 1: Chryse


• Chryse Planitia (The Plains of Gold) is a rock-strewn plain, originally volcanic in nature like the lunar maria, but modified by water and wind erosion.

• The rocks appear to be igneous, ejected from nearby impact craters.

Viking 2: Utopia

Image credit: NASA/JPL and Calvin Hamilton

• The Utopia, like Chryse, was intended to be flat landing site, but ended up being even rockier. Viking 2 ended up with one leg on a boulder, tilting at 8 degrees.

• Most of the rocks are ejecta from the 90-km crater Mie, 200 km away.


Viking: Rock and Soil


• The Viking landers were able to find the cause of Mars’ red coloring: iron oxides in the surface soil.

• Their chemical analysis showed that the soil was similar to some iron-rich clays we see on Earth.

• The Vikings were not equipped to analyze rocks, unlike the later rovers, however they did attempt to search for the presence of life in the soil using two experiments.

• We will return to these in a later lecture when we discuss the emerging field of astrobiology and the search for life outside the Earth.


View from Orbit: Dunes


• Most of the fine dusty surface material is light in color.

• After a major dust storm, dark surface rocks can be covered up by light-colored wind-blown sand.

• Later on, other winds or dust-devils can blow the sand away again, re-exposing the darker surface.

• This is the true explanation for the observed ‘seasons’ on Mars, the shifting light and dark coloration originally thought to be due to vegetation.

• The image (right) is of ‘cemented’ sand dunes in the Herschel crater of the Terra Cimmeria, taken by MGS/MOC. Image credit: MSSS/NASA/JPL.


Successes and Failures


• The Viking landers of 1976 were hugely successful: so successful in fact (in showing the apparent lifelessness of Mars) that NASA neglected the Red Planet for over a decade.

• From the late 1980s to the present day, the road has been littered with causalities:

Mission Country Year Outcome

Phobos 1 USSR 1988 Lost contact en-routePhobos 2 USSR 1988 Entered orbit and returned data for brief timeMars Observer US 1992 Lost contact before arrivalMars Global Surveyor US 1996 Successful orbiter - still operatingMars 96 Russia 1996 Launch FailureMars Pathfinder US 1996 Rover lasted for 90+ daysNozomi/Planet-B Japan 1998 Never entered orbitMars Climate Orbiter US 1998 Crashed into planet due to units errorMarsMars Polar Lander US 1998 Lost contactMars Odyssey US 2001 Successful orbiter - still operatingMars Express Europe 2003 Successful orbiter - still operatingBeagle 2 Europe 2003 Lander - crashedSpirit Rover US 2003 Successful rover - still operatingOpportunity Rover US 2003 Successful rover - still operatingMars Recon Orbiter US 2005 Successful orbiter - still operating


What Really Happened?

Dr Conor Nixon Fall 2006Cartoons: New Orleans Picayune (Handelman), Detroit Free Press (Thompson).

Mars Climate Orbiter 1998

Mars Polar Lander 1998?


Successful Surface Explorers


• The surface of Mars has been explored more thoroughly than any other planet outside the Earth and Moon.

• We have a multitude of information from at least 5 landing craft:

• Viking 1: landed on the Chryse Planitia, July 1976.

• Viking 2: landed on the Utopia Planitia, September 1976.

• Pathfinder/Sojourner: landed on Ares Vallis, July 1997.

• Spirit: landed at Gusev Crater, Jan 4th 2004.

• Opportunity: landed at Terra Meridiani , Jan 24th 2004.


US Return to Mars 1996-1997: Pathfinder


• After the costly M.O. failure, NASA opted for a scaled-down approach and had success with the Mars Global Surveyor (MGS) and Pathfinder missions in 1996 and 1997.

• While MGS orbited the planet, Pathfinder landed and became a weather station, returning 16,000 images and 8.5 million measurements of atmospheric pressure, temperature and wind speed.

• The battery, which kept the lander warm at night, was designed to only recharge about 40 times - to keep costs down. On Day 83 (‘Sol’ 83) after landing, the lander ceased communicating with the Earth - probably due to cold nighttime temperatures.

• The lander by that time had been renamed ‘Sagan Memorial Station’ after planetary scientist and writer Carl Sagan who died in 1996.


Pathfinder at Ares Vallis

Dr Conor Nixon Fall 2006Image credit: NASA/JPL

• Pathfinder landed in the Ares Vallis region - a location where scientists hoped to find a variety of rocks carried from the southern highlands to the northern lowlands by floodwaters.


Pathfinder Rover: ‘Sojourner’


• The Pathfinder mission included a small rover, Sojourner, which roamed the surface for 3 months before the lander failed and communication with the Earth was lost. It was the first ever rover on another planet.

Picture credits: NASA/NSSDC

• Sojourner weighed just 10 kg and was the size of a microwave oven. It’s maximum speed was just 1 cm/s (0.02 mph).

• Sojourner successfully demonstrated many technologies used in subsequent missions, including obstacle avoidance and airbag landing on Mars, as well as completing real science.


Sojourner Science


• The chemical analysis showed that all the rocks were igneous, but surprisingly they were not the expected basalts (volcanic), but rather silicon-bearing granites, similar to the continental crust on Earth created by tectonics.

Image credit: NASA/JPL

• Sojourner’s sole scientific instrument (besides cameras) was an Alpha-Proton X-Ray Spectrometer (APXS) - an instrument designed to analyze the elements of rock composition.

• In this image, the Sojourner rover examines a rock nick-named ‘Yogi’.


Mars Rocks on Earth


• Do we have samples of Mars rocks on Earth?

• We have never in fact sent a mission to return samples, however, we do have around 20 meteorites which have been positively confirmed to be of Martian origin. How do we know?

• Tiny bubbles of gas trapped in the rocks trapped inside the rocks perfectly match the atmosphere of Mars, as sampled by Viking.

• However, these rocks are basalts, with solidification ages mostly around 1.3 Gyr. One is as old as 4 Gyr.

• But we just said that Sojourner found only granites, no basalts! This mystery would have to wait for a new generation of explorers…


Mars Exploration Rovers 2003-2006


• Pathfinder paved the way for a much more ambitious (and expensive) duo of rovers: the Mars Exploration Rovers Spirit and Opportunity.

Picture credit: JPL/NASA/PDS

• These are larger, faster, smarter and better equipped with many more scientific tools than Pathfinder/Sojourner (see scale comparison, right).

• Each rover weighs 185 kilos: 18 times the little Sojourner Rover.

MER - First Year Movie


Mars Landing Sites 1976-2003

Dr Conor Nixon Fall 2006Map: NASA/JPL/GSFC


MER Science Instruments


• Each Rover is equipped with the following:

1. Panoramic Camera (Pancam): for determining the mineralogy, texture, and structure of the local terrain.

2. Miniature Thermal Emission Spectrometer (Mini-TES): for identifying promising rocks and soils for closer examination and for determining the processes that formed Martian rocks. The instrument will also look skyward to provide temperature profiles of the Martian atmosphere.

3. Mössbauer Spectrometer (MB): for close-up investigations of the mineralogy of iron-bearing rocks and soils.

4. Alpha Particle X-Ray Spectrometer (APXS): for close-up analysis of the abundances of elements that make up rocks and soils.

5. Magnets: for collecting magnetic dust particles. The Mössbauer Spectrometer and the Alpha Particle X-ray Spectrometer will analyze the particles collected and help determine the ratio of magnetic particles to non-magnetic particles.

6. Microscopic Imager (MI): for obtaining close-up, high-resolution images of rocks and soils.

7. Rock Abrasion Tool (RAT): for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments onboard.

Instrument descriptions from: marsrovers.nasa.gov


Spirit at Gusev Crater


• Spirit landed as planned inside a large (150 km) impact crater named Gusev, which probably formed 3-4 billion years ago.

• This area was targeted because orbital pictures starting with Viking had shown Gusev to have been likely flooded at some point in the past.

• Note the Ma’adim Vallis to the south, which looks like a dry riverbed or water channel.

Image credit: NASA


Where’s the water?


• Spirit’s initial science findings were somewhat disappointing: nearly all the rocks investigated were plain old basalt: thrown up in the impact which formed the giant crater.

• Where were the water-bearing minerals that that the orbital reconnaissance had suggested?

Image credit: NASA/JPL/Cornell


Spirit of Adventure


• Spirit spent much of its travels driving to, and then climbing the ‘Columbia Hills’ - a range of low peaks named for the Columbia Shuttle Crew.



Spirit - Sol 986

(6.9 km on odometer)



Perseverance pays off…


• At last, Spirit hit ‘paydirt’ in the hills. Examination of a rock named ‘Clovis’ showed the signature of a mineral called Goethite, which contains water in the form of hydroxyl: OH.

• Spirit was at last finding water, but Gusev crater had turned out to be much different to expectations.

• Scientists still believe that Gusev was flooded in the past, but the picture is more complex than anticipated and the process of unraveling the clues continues.



Opportunity at Eagle Crater


• Opportunity had landed in a small crater on the Meridiani Planum,


• The 22-meter depression proved to be a rich hunting ground for water-deposited minerals.

• Opportunity used its RAT to grind away the surface of a rock dubbed ‘El Capitan’. The Mossbauer spectrometer then showed evidence for Jarosite: another type of water-bearing rock.


Munching On Blueberries


• On analysis, the ‘blueberries’ turned out to be rich in haematite, an iron-bearing mineral which often forms in the presence in water.

• Along with the jarosite, the blueberries were telling a story of a watery past in this region.

• Much of the terrain inside Eagle crater was covered in scattered small spherules (2-4 mm in size), dubbed ‘blueberries’ by the science team.



‘Martian’ meteorite!


• On Sol 339 Opportunity chanced upon the last thing anyone expected: a object which was clearly not from Mars!

• The nickel-iron meteorite is about the same size as basketball, and would be a valuable find on Earth.

• This was the first ever meteorite found on another planet.



Opportunity

(9.0 km on odometer)



Victoria Crater


• Opportunity has now reached the 800m wide Victoria Crater, much larger the the Eagle and Endurance craters explored to date.

• This photo was taken from orbit, by the HiRISE camera system on Mars Reconnaissance Orbiter, showing a dune field inside.

• Animation of Victoria Crater

Image credit: NASA/JPL/UA


Victoria Crater


• Opportunity is currently exploring the rim of Victoria Crater, photographing the terrain and scouting for a way to descend inside.

• The image (below) superimposing a scale image of the rover on an actual photo to show scale - the rover was actually taking the picture at the time!

• The promontory is called ‘Cape Verde’ and is about 6 m in height, showing layered terrain.

Image credit: NASA/JPL/Cornall


Opportunity - spotted!


• Opportunity has even been photographed from orbit! This image was taken by HiRISE on MRO at the start of October.



MER Rover Status


• Both rovers continue to function, well beyond their designed lifetime: as Steve Squyres, the Rover PI likes to joke: the are 900 days into their 90-day mission!

• Spirit’s right front wheel ceased working on March 13th 2006: the drivers thereafter managed to make some progress by alternating forward motion with reversing the rover and dragging the wheel behind.

• Since April, Spirit has been parked on a south-facing slope to maintain power through the winter solstice (Aug 8th). The rover is now waiting for optimum power to be restored before setting off again.

• Spirit will need to stay clear of deeper sand, where it could become stuck.


Polar Caps


• Mars possesses two types of polar caps:

1. Seasonal Polar Caps: these are composed of CO2 frost (dry ice) which condenses and evaporates seasonally. In the south, these reach to 55° latitude, though only to 65° in the north. (Southern winters are more severe than northern, due to Mars’ elliptical orbit which brings it closer to the Sun in the northern winter than the southern one.)

2. Permanent Polar Caps: until several years ago, the residual ice at both poles in summer was believed to be CO2 ice also, however it has now been showed to be mainly water ice instead. The northern and southern permanent polar caps show some surprising differences.


Permanent South Polar Cap


•The southern residual or permanent polar cap is only 350 km across, and composed of two layers:

1. An 8m-thick covering of CO2 ice.

2. A much deeper layer of water ice.

•The south polar cap is at a temperature of 150 K, the freezing point of CO2 ice, even during the warm southern summer.



Permanent North Polar Cap


• The north polar cap is much larger (1000 km) and also warmer during summer (200 K) than the southern one. During northern summer, the the amount of water vapor rises sharply above the cap.

• Therefore most of the cap is water ice: perhaps the main repository on Mars.

Image credit: NASA/JPL/MSSS

• It is covered in a much thinner layer of CO2 ice than the southern cap: only 1 meter thick.

• This is an effect of the warmer temperatures.


Polar differences


• It is somewhat baffling that the southern cap remains colder in summer (150K) than the northern one (200K), although southern summers are warmer!

• The explanation may lie with the global dust storms which occur during southern summer, blanketing the northern cap with dust as it is forming.

• This in turn makes the northern cap darker, and more able to absorb sunlight.

• Therefore in the northern summer, the northern cap absorbs a lot of light and evaporates all its CO2 and some of the water too.



North Polar Laminated Terrain


• This image from a Viking orbiter shows laminated, or layered terrain where the northern ice has melted.

• This is caused by successive years of freezing and melting, leaving the dust behind in the summers.

• Each layer is 10 to 50m thick, showing cyclical climatic, rather than annual changes.

Image credit: solarviews.com


North Polar Dune Fields


• Yet another north-south difference is the existence of large dunefields, encircling the north pole for a distance of 500 km.

• This is another Viking image, showing two types of dunes: transverse at left, and barchan on the right, with a transition zone in the center.

Image credit: solarviews.com


Atmosphere


• Indirect evidence for an atmosphere on Mars was long ago determined: including the seasonal ice caps, dust storms, and even clouds. But how much atmosphere, and of what?

• The Viking landers carried out the first definite test of the atmosphere, and found:

• 95.4% carbon dioxide CO2

• 2.7% nitrogen N2

• 1.6% argon Ar-40• 0.13% oxygen O2

• 0.07% carbon monoxide CO• 0.03% water H2O

• The first three gases also exist in the atmosphere of Venus, and in almost the same proportions. But the atmosphere of Mars is much thinner, by about 10,000 times, at 0.007 bar.


Atmosphere and Temperature


• The minor constituents of Mars’ atmosphere are much different from Venus however, especially as Argon-40, a radiogenic isotope, is more prevalent than Ar-36, the original cosmic isotope.

• We also find no sulfur compounds, or acids.

• Mars has a troposphere and stratosphere, similar to Earth and Venus. The troposphere is about 10-20 km thick and does have convection in the day, but practically disappears at night.

• The surface temperature reaches a maximum of -30°C – on a summer afternoon! Night-time temperatures can dip to -100°C.

• The overall air pressure can vary by as much as 20%, due to the seasonal exchange of CO2 between the atmosphere and the polar caps.


Methane Surprise


• In 2004, scientists using infrared spectroscopy were surprised to discover small amounts of CH4 in the atmosphere of Mars.

• Methane is destroyed in about 300 years by sunlight, so the presence of even trace quantities (10 ppb - parts per billion) indicates that the gas must be being released somewhere at the present day.

• Possible sources include:

• Volcanic activity (as on the Earth)• Reactions in the soil• Methane-releasing bacteria.

• Hence, the presence of methane has added to the debate on whether there is life on Mars. Scientists are currently split, with the majority espousing a ‘wait and take more data first’ attitude.


Mars Science Laboratory


• MSL is a new rover currently under development by NASA for probable launch in 2009. It is twice as long and four times the weight of the MER rovers. It may be nuclear powered rather than solar powered.

• MSL carry new tools for scientific investigation, including:

• a laser for vaporizing the rock surface

• full soil chemistry and biology analysis package, to search fpr organic material (amino acids etc).



Mars Science Laboratorry

Dr Conor Nixon Fall 2006Image credit: NASA/JPL


Dr Conor Nixon Fall 2006Cartoons: Des Moignes Register ‘Duffy’, Richmond Times Dispatch (Brookins).

The source of all the Mars mishaps?

What really happened to pathfinder?


Lecture 17 - Quiz


8. Are craters on Mars the same as those on the Moon and Mercury? If not, what differences are there?

9. What differences are there between the northern and southern hemispheres on Mars?

10. What types of rocks were found on Mars. Is this what we expected?

11. What three types of channels are found on Mars, and what caused them?

12. Is there liquid water on the surface of Mars today?

13. Compare the Martian atmosphere to that of (i) Venus (ii) the Earth.

14. What missions are currently underway to explore Mars?

ASTR 330: The Solar System

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