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Space News Update — November 16, 2018 —

Contents

In the News

Story 1: International Team, NASA Make Unexpected Discovery Under Greenland Ice

Story 2: Scientists are using artificial intelligence to see inside stars using sound

waves

Story 3: How NASA Will Know When InSight Touches Down

Departments

The Night Sky

ISS Sighting Opportunities

Space Calendar

NASA-TV Highlights

Food for Thought

Space Image of the Week

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1. International Team, NASA Make Unexpected Discovery Under Greenland Ice

An international team of researchers, including a NASA glaciologist, has discovered a large meteorite impact crater hiding beneath more than a half-mile of ice in northwest Greenland. The crater — the first of any size found under the Greenland ice sheet — is one of the 25 largest impact craters on Earth, measuring roughly 1,000 feet deep and more than 19 miles in diameter, an area slightly larger than that inside Washington’s Capital Beltway.

The group, led by researchers from the University of Copenhagen’s Centre for GeoGenetics at the Natural History Museum of Denmark worked for the past three years to verify their discovery, which they initially made in 2015 using NASA data. Their finding is published in the Nov. 14 issue of the journal Science Advances.

"NASA makes the data it collects freely available to scientists and the public all around the world,” said Joe MacGregor, a NASA glaciologist at Goddard Space Flight Center in Greenbelt, Maryland, who became involved in the investigation in its early stages. “That set the stage for our Danish colleagues’ ‘Eureka’ moment."

The researchers first spotted the crater in July 2015, while they were inspecting a new map of the topography beneath Greenland's ice sheet that used ice-penetrating radar data primarily from NASA’s Operation IceBridge — a multi-year airborne mission to track changes in polar ice — and earlier NASA airborne missions in Greenland. The scientists noticed an enormous, previously unexamined circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northwestern Greenland.

Using satellite imagery from the Moderate Resolution Imaging Spectroradiometer instrument on NASA’s Terra and Aqua satellites, MacGregor also examined the surface of the ice in the Hiawatha Glacier region and quickly found evidence of a circular pattern on the ice surface that matched the one observed in the bed topography map.

To confirm their suspicions, in May 2016 the team sent a research plane from Germany’s Alfred Wegener Institute to fly over the Hiawatha Glacier and map the crater and the overlying ice with a state-of-the-art ice-penetrating radar provided by the University of Kansas. MacGregor, who is an expert in radar measurements of ice, helped design the airborne survey.

"Previous radar measurements of Hiawatha Glacier were part of a long-term NASA effort to map Greenland’s changing ice cover," MacGregor said. "What we really needed to test our hypothesis was a dense and focused radar survey there. The survey exceeded all expectations and imaged the depression in stunning detail: a distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris — it’s all there."

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The crater formed less than 3 million years ago, according to the study, when an iron meteorite more than half a mile wide smashed into northwest Greenland. The resulting depression was subsequently covered by ice.

"The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact," said Kurt Kjær, a professor at the Center for GeoGenetics at the Natural History Museum of Denmark and lead author of the study.

Kjær said that the crater’s condition indicates the impact might even have occurred toward the end of the last ice age, which would place the resulting crater among the youngest on the planet.

In the summers of 2016 and 2017, the research team returned to the Hiawatha Glacier to map tectonic structures in the rock near the foot of the glacier and collect samples of sediments washed out from the depression through a meltwater channel.

"Some of the quartz sand coming from the crater had planar deformation features indicative of a violent impact; this is conclusive evidence that the depression beneath the Hiawatha Glacier is a meteorite crater," said associate professor Nicolaj Larsen of Aarhus University in Denmark, one of the authors of the study..

Earlier studies have shown large impacts can profoundly affect Earth’s climate, with major consequences for life on Earth at the time. The researchers plan to continue their work in this area, addressing remaining questions on when and how the meteorite impact at Hiawatha Glacier affected the planet.

Source: NASA Return to Contents

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2. Scientists are using artificial intelligence to see inside stars using sound waves

As stars pulse, heave, and quiver from the complex physics in their interiors, their surfaces vibrate with standing sound waves, which we can see from a distance as tiny changes in brightness.

How in the world could you possibly look inside a star? You could break out the scalpels and other tools of the surgical trade, but good luck getting within a few million kilometers of the surface before your skin melts off. The stars of our universe hide their secrets very well, but astronomers can outmatch their cleverness and have found ways to peer into their hearts using, of all things, sound waves.

Starquakes “Sound waves in space” is a pretty confusing phrase, but don’t worry, these sounds waves stay strictly within their stellar spheres. Every star is a dynamic, vibrating maelstrom of intense frenetic activity. On the inside you have the insanity of the nuclear core, forging new elements by the second at temperatures of millions of degrees. On the outside you have the vacuum of space itself, colder than cold at a temperature barely above absolutely zero.

The job of the body of a star is to get all that heat from the inside to the outside, where it desperately wants to go. While throughout their lives stars exist in a state of equilibrium (they’re not exploding in a supernova or collapsing into a black hole right now), any slight disturbance can persist as slight bumps and wiggles throughout the bulk of the star – and on its surface.

“Bumps and wiggles throughout the bulk” are also known as sound waves.

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There are a few different ways that stars can start screaming. If a patch or entire layer of star-stuff just happens to be a little bit more dense than average, it can trap radiation underneath it, preventing it from escaping. This heats the layer abnormally, causing it to rise and expand, freeing the trapped heat and allowing the layer to cool back off and settle back to the way it started, resetting the entire process. As this cycle continues, sound waves emanate from the pulsation, temporarily encompassing the entire star.

The convection inside the star plays a role too, as giant blobs of stellar material make their way up to the surface, touch the coldness of space, release their heat, and slink back down into the fiery depths. This continuous stirring, like the boiling surface of a pot of water on the stove, resonates throughout the entire star.

Even a nearby companion can drive the creation of sound waves, as the gravity of the orbiting partner tugs and tweaks on the star, reaching out with invisible gravitational slaps and squeezes, igniting more quakes.

Simulation meets sound wave reality Stars host all sorts of vibrations inside them. Some only last for a little while, some stay for a long time. Some stick just to the surface or just below it, while others zip up and down, ricocheting off the dense core in the process. This means that the vibrations are very useful diagnostics into the conditions of the star. How old is it? What percentage of heavier elements swim around inside it? How are the various internal layers connected (or not) to each other?

The particular mix of ingredients that go into any particular star subtly changes the kinds of vibrations that live on the surface. It’s like stellar phrenology but actually science: studying the bumps and wiggles on the surface of a star reveals its character.

This is where computers come into the picture in a big way, and why asteroseismology is a relatively new field. We don’t have catalog upon catalog of dissected, displayed stars to compare against living specimens. Instead we have computers – lots of them. Model after model, we bake every possible kind of star in our silicon ovens, spanning the range of every kind of input parameter manageable.

And we tune the physics too, tinkering and toying with various theories on how stars work on the inside. How well are the cores connected to the atmospheres? How important are magnetic fields? What’s the relationship between rotation and heat transfer? Important questions with not a lot of answers.

Rise of the machines These extensive simulations of pretend stars give us the necessary “back catalog” to compare against observations. But the observations aren’t easy. We can’t observe the surface of most stars – we can only watch distantly as the light from the stars dims and brightens.

Some of that variation is due to random flare-ups or other temperamental activity. Some of that variation is due to an orbiting planet crossing the line of sight. And some of that variation is due to sound waves crashing through the star and bubbling up onto the surface, ever-so-slightly changing the brightness in the shine of the star.

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It’s here where theory meets reality, but the observations are extremely short (we don’t get to observe the stars for very long), and incomplete (we can’t see all the vibrations on the surface). To better make sense of it all, astronomers recently developed an entire machine learning pipeline to compare data with models.

In this pipeline, the scientists trained a neural network on the simulations, allowing it to discover all the subtle relationships between model input parameters (mass of the star, metallically, etc.) and vibration patterns on the surface. Then, using that sophisticated knowledge, the algorithm can look at real stars with real, messy data and find the best match in the models. This technique is still in its infancy when it comes to asteroseismology, but opens up a promising future for mining through stellar samples, understanding how stars work on the inside.

Source: Universe Today Return to Contents

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3. How NASA Will Know When InSight Touches Down

What's the sound of a touchdown on Mars?

If you're at NASA's Jet Propulsion Laboratory, it sounds like winning the Super Bowl: cheers, laughter and lots of hollering.

But in the minutes before that, NASA's InSight team will be monitoring the Mars lander's radio signals using a variety of spacecraft - and even radio telescopes here on Earth - to suss out what's happening 91 million miles (146 million km) away.

Because these signals are captured by several spacecraft, they're relayed to Earth in different ways and at different times. That means the mission team may know right away when InSight touches down, or they may have to wait up to several hours.

Here's how NASA will be listening for the next Mars landing on Nov. 26.

Radio Telescopes

As the InSight lander descends into Mars' atmosphere, it will broadcast simple radio signals called "tones" back to Earth. Engineers will be tuning in from two locations: the National Science Foundation's Green Bank Observatory in Green Bank, West Virginia and the Max Planck Institute for Radio Astronomy's facility at Effelsberg, Germany. Their results will be relayed to Mission Control at JPL and engineers at Lockheed Martin Space in Denver.

These tones don't reveal much information, but radio engineers can interpret them to track key events during InSight's entry, descent and landing (EDL). For example, when InSight deploys its parachute, a shift in velocity changes the frequency of the signal. This is caused by what's called the Doppler effect, which is the same

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thing that occurs when you hear a siren change in pitch as an ambulance goes by. Looking for signals like these will allow the team to know how InSight's EDL is progressing.

Mars Cube One (MarCO)

Two briefcase-sized spacecraft are flying behind InSight and will attempt to relay its signals to Earth. Belonging to a class of spacecraft called CubeSats, the MarCOs are being tested as a way for future missions to send home data during EDL.

The MarCOs are experimental technology. But if they work as they should, the pair will transmit the whole story of EDL as it's unfolding. That might include an image from InSight of the Martian surface right after the lander touches down.

InSight

After it touches down, InSight will essentially yell, "I made it!" Seven minutes later, the spacecraft says it again - but a little louder and clearer.

The first time, it will communicate with a tone beacon that the radio telescopes will try to detect. The second time, it will send a "beep" from its more powerful X-band antenna, which should now be pointed at Earth. This beep includes slightly more information and is only heard if the spacecraft is in a healthy, functioning state. If the radio telescopes or antennas at NASA's Deep Space Network pick up this beep, it's a good sign that InSight survived landing. Engineers will need to wait until early evening to find out if the lander successfully deployed its solar arrays.

Mars Reconnaissance Orbiter (MRO)

Besides the MarCO CubeSats, NASA's MRO will be soaring over Mars, recording InSight's data during descent.

MRO will hold on to the data it records during EDL as it disappears over the Martian horizon. When it comes back around from the other side, it will play back that data for engineers to study. By 3 p.m. PST (6 p.m. EST), they should be able to piece together MRO's recording of the landing.

MRO's recording is similar to an airplane's black box, which means that it could also prove important if InSight doesn't successfully touch down.

2001 Mars Odyssey

NASA's longest-lived spacecraft at Mars will also relay data after InSight has touched down. Odyssey will relay the entire history of InSight's descent to Mars, as well as a couple images. It will also relay confirmation that InSight's solar arrays, which are vital to the spacecraft's survival, fully deployed. Engineers will have this data just before 5:30 p.m. PST (8:30 p.m. EST).

Odyssey will also serve as a data relay for InSight during surface operations, along with MRO, NASA's Mars Atmosphere and Volatile Evolution mission (MAVEN) and the European Space Agency's Trace Gas Orbiter.

Source: JPL Return to Contents

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The Night Sky Friday, November 16

• Very high in the south is the Great Square of Pegasus. Its right-hand side points down toward the Moon. Closer to the right of the Moon is Mars, as shown here.

Saturday, November 17

• When you see the waxing gibbous Moon passing highest in the south in early evening tonight, it's straight below the Great Square of Pegasus, which is level and upright.

• The Leonid meteor shower, which has been very weak this decade, should be at its modest best late tonight during the three hours between moonset and the beginning of Sunday's dawn. Have patience.

Sunday, November 18

• Now the Great Square's left side points down toward the Moon.

• We're two thirds of the way through fall this week, so Capella shines in the northeast as soon as the stars come out. As night grows darker, look to its right by about three fists at arm's length for the frosty little Pleiades cluster. It's the size of your fingertip at arm's length.

Orange Aldebaran climbs up below the Pleiades. By about 8 p.m., depending on your location, Orion is clearing the horizon below Aldebaran.

Monday, November 19

• The asteroid 3 Juno is at opposition this week — and the closest to Earth it will come from 1980 to 2060! That means it's now as bright as magnitude 7.4, visible in large binoculars but still not very bright for such a low-numbered asteroid. Juno is substantially smaller than 1 Ceres, 2 Pallas, or 4 Vesta; only by a stroke of luck was it the third asteroid discovered.|Juno is in northern Eridanus south of Taurus, in high view by late evening. See the article and finder chart in the November Sky & Telescope, page 49.

Tuesday, November 20

• Whenever Fomalhaut is "southing" (crossing the meridian due south, which it does around 7 or 8 p.m. this week), the first stars of Orion are just about to rise above the east horizon. And the Pointers of the Big Dipper stand upright low due north, straight below Polaris.

Source: Sky & Telescope Return to Contents

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ISS Sighting Opportunities

For Denver: No sighting opportunities

Date Visible Max Height Appears Disappears

Fri Nov 16, 5:22 AM 2 min 16° 16° above SW 10° above S

Thu Nov 22, 6:22 PM 2 min 28° 10° above SSW 28° above S Sighting information for other cities can be found at NASA’s Satellite Sighting Information NASA-TV Highlights (all times Eastern Daylight Time) November 16, Friday 2 p.m., 6 p.m., 10 p.m. – Replay of Powering Exploration Mission-1 (All Channels) 3 p.m., 7 p.m. – Replay of “What’s on Board?” Briefing for Northrop Grumman Cygnus CRS-10 Cargo Flight to the International Space Station from Wallops Flight Facility (All Channels) 4 p.m., 8 p.m. – Replay of the Pre-launch Briefing for Northrop Grumman Cygnus CRS-10 Cargo Flight to the International Space Station from Wallops Flight Facility (All Channels) 5 p.m., 9 p.m. – Replay of the RS-25 Engine Test from Stennis Space Center (All Channels)

November 17, Saturday 1:30 a.m. – Replay of “What’s on Board?” Briefing for Northrop Grumman Cygnus CRS-10 Cargo Flight to the International Space Station (All Channels) 2:30 a.m. – Replay of the Pre-launch Briefing for Northrop Grumman Cygnus CRS-10 Cargo Flight to the International Space Station (All Channels) 3:30 a.m. - Coverage of the Launch of the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft to the Space Station; Launch scheduled at 4:01 a.m. (All Channels) 5 a.m. - Coverage of Solar Array Deployment on the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft (All Channels) 6:30 a.m. - Northrop Grumman “SS John Young” Cygnus CRS-10 Post-Launch News Conference from Wallops Flight Facility (All Channels) 9 a.m., 12 p.m., 4 p.m. - Replay of the Launch of the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft to the ISS - Johnson Space Center (All Channels) 10 a.m., 6 p.m., 10 p.m. - Replay of the International Space Station Expedition 58 Crew News Conference at the Gagarin Cosmonaut Training Center in Star City, Russia All Channels) 11 a.m., 5 p.m., 7 p.m. – Replay of the Northrop Grumman “SS John Young” Cygnus CRS-10 Post-Launch News Conference - Wallops Flight Facility, Virginia (All Channels) 2 p.m., 8 p.m. – NASA in Silicon Valley Live: The Wonder Women of NASA - Ames Research Center (Public Channel)

November 18, Sunday 7 a.m., 12 p.m., 9 p.m. - Replay of the Space Station Expedition 58 Crew News Conference at the Gagarin Cosmonaut Training Center in Star City, Russia (All Channels) 8 a.m., 6 p.m. – Replay of the NASA in Silicon Valley Live: The Wonder Women of NASA (Public Channel) 10 a.m., 5 p.m., 10 p.m. - Replay of the Launch of the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft to the Space Station (All Channels)

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11 a.m., 4 p.m., 8 p.m. – Replay of the Northrop Grumman “SS John Young” Cygnus CRS-10 Post-Launch News Conference (All Channels) 1:45 p.m. - Coverage of the Rendezvous and Docking of the ISS Progress 71 Cargo Craft to the Space Station; Docking scheduled at 2:30 p.m. EST (All Channels)

November 19, Monday 4 a.m. - Coverage of the Rendezvous and Capture of the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft at the Space Station; Capture scheduled at 5:20 a.m. EST (All Channels) 6:45 a.m. - Coverage of the Installation of the Northrop Grumman “SS John Young” Cygnus CRS-10 Cargo Craft to the ISS - Johnson Space Center (All Channels) 4 p.m. – Video File of the Space Station Expedition 58 Crew’s Departure from the Gagarin Cosmonaut Training Center in Star City, Russia for the Baikonur Cosmodrome in Kazakhstan (Media Channel)

November 20, Tuesday 10:55 a.m. – ISS Expedition 57 Facebook Live In-Flight Event for the 20th Anniversary of ISS with ISS Commander Alexander Gerst of the European Space Agency and Flight Engineers Serena Aunon-Chancellor of NASA and Sergey Prokopyev of Roscosmos (All Channels)

Watch NASA TV on the Net by going to the NASA website. Return to Contents

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Space Calendar

• Nov 16 - [Nov 11] Progress MS-10 Soyuz-2.1a Launch (International Space Station 71P) • Nov 16 - Moon Occults Mars • Nov 16 - Comet P/2017 R1 (PANSTARRS) At Opposition (3.003 AU) • Nov 16 - [Nov 15] Apollo Asteroid 2018 VT8 Near-Earth Flyby (0.026 AU) • Nov 16 - Amor Asteroid 2018 VS Near-Earth Flyby (0.065 AU) • Nov 16 - [Nov 13] Apollo Asteroid 2018 VS7 Near-Earth Flyby (0.082 AU) • Nov 16 - Asteroid 3140 Stellafane Closest Approach To Earth (1.791 AU) • Nov 16 - [Nov 13] Kuiper Belt Object 2012 VP113 At Opposition (82.801 AU) • Nov 16 - 45th Anniversary (1973), Skylab 4 Launch (Last Launch to Skylab)

• Nov 17 - [Nov 16] Cygnus CRS-10 (OA-10)/ Thinsat 1A-1L/ TechEdSat 8/ CAPSat/ CySat 1/ HARP/ KickSat 2/ SPACE-HAUC/ UNITE/ TJREVERB/ VCC A (Aeternitas) & VCC B (Libertas) & VCC C (Ceres)/ MYSAT 1Antares 230 Launch (International Space Station)

• Nov 17 - Leonids Meteor Shower Peak • Nov 17 - Asteroid 433 Eros Occults TYC 4078-00534-1 (10.1 Magnitude Star) • Nov 17 - [Nov 15] Apollo Asteroid 2018 VS8 Near-Earth Flyby (0.005 AU) • Nov 17 - Asteroid 2531 Cambridge Closest Approach To Earth (2.011 AU) • Nov 17 - Asteroid 447 Valentine Closest Approach To Earth (1.874 AU) • Nov 17 - Educators Workshop: Liftoff!, Downey, California • Nov 18 - Comet 373P/Rinner Closest Approach To Earth (1.537 AU) • Nov 18 - Comet 294P/LINEAR At Opposition (2.560 AU) • Nov 18 - Comet C/2017 S7 (Lemmon) At Opposition (7.507 AU) • Nov 18 - [Nov 10] Apollo Asteroid 2018 VT4 Near-Earth Flyby (0.028 AU) • Nov 18 - [Nov 12] Apollo Asteroid 2018 VY6 Near-Earth Flyby (0.066 AU) • Nov 18 - Apollo Asteroid 25143 Itokawa Closest Approach To Earth (0.706 AU) • Nov 18 - Asteroid 7016 Conandoyle Closest Approach To Earth (1.178 AU) • Nov 18 - Asteroid 15907 Robot Closest Approach To Earth (1.443 AU) • Nov 18 - Asteroid 51827 Laurelclark Closest Approach To Earth (1.736 AU) • Nov 18 - Plutino 455502 (2003 UZ413) At Opposition (43.043 AU) • Nov 18 - 5th Anniversary (2013), Mars Atmosphere and Volatile EvolutioN (MAVEN) Launch (Mars

Orbiter) • Nov 18 - Alan Shepard's 95th Birthday (1923) • Nov 19 - SSO-A/ SkySat 14 & 15/ Eu:CROPIS/ STPSat 5/ FalconSat 6/ NEXTSat 1/ KazSTSAT/ eXCITe

(PTB 1)/ SeeMe/ BlackSky Global 2/ HawkEye Pathfinder 1-3/ ORS 7A & 7B (Polar Scout 1 & 2)/ COPPER 2/ MinXSS 2/ Audacy Zero/ Fox 1C (Fox 1Cliff)/ KNACKSAT/Elysium-Star 2/ JY1-Sat Falcon 9 Launch

• Nov 19 - [Nov 11] BeiDou-3 CZ-3C/YZ-1 Launch • Nov 19 - [Nov 13] Comet 9P/Tempel At Opposition (3.654 AU) • Nov 19 - Apollo Asteroid 518735 (2009 JL1) Near-Earth Flyby (0.083 AU) • Nov 19 - Asteroid 4464 Vulcano Closest Approach To Earth (1.046 AU) • Nov 19 - Asteroid 3949 Mach Closest Approach To Earth (1.271 AU) • Nov 19 - Asteroid 14880 Moa Closest Approach To Earth (1.414 AU) • Nov 19 - Apollo Asteroid 3200 Phaethon Closest Approach To Earth (1.428 AU) • Nov 19 - Asteroid 91287 Simon-Garfunkel Closest Approach To Earth (1.453 AU) • Nov 19 - [Nov 13] Centaur Object 37117 Narcissus At Opposition (2.112 AU) • Nov 19 - Kuiper Belt Object 523645 (2010 VK201) At Opposition (47.139 AU) • Nov 20 - [Nov 13] Jiading-1 (OKW-1) CZ-2D Launch • Nov 20 - [Nov 12] Comet 130P/McNaught-Hughes At Opposition (1.943 AU)

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• Nov 20 - [Nov 13] Apollo Asteroid 2018 VP7 Near-Earth Flyby (0.020 AU) • Nov 20 - [Nov 11] Apollo Asteroid 2018 VQ6 Near-Earth Flyby (0.029 AU) • Nov 20 - Asteroid 3169 Ostro Closest Approach To Earth (0.977 AU) • Nov 20 - Asteroid 10183 Ampere Closest Approach To Earth (1.392 AU) • Nov 20 - Asteroid 2713 Luxemburg Closest Approach To Earth (1.917 AU) • Nov 20 - [Nov 12] Neptune Trojan 2007 VL305 At Opposition (27.264 AU) • Nov 20 - Neptune Trojan 2011 WG157 At Opposition (29.805 AU) • Nov 20 - Kuiper Belt Object 90377 Sedna At Opposition (83.975 AU) • Nov 20 - International Space Station Forum, London, United Kingdom • Nov 20 - Seminar: Counting Black Hole Microstates in AdS5/CFT4, Trieste, Italy • Nov 20 - 10th Anniversary (2008), Buzzard Coulee Meteorite Fall (Hit Barn in Canada) • Nov 20 - William Coblentz's 145th Birthday (1873)

Source: JPL Space Calendar Return to Contents

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Food for Thought

Evidence of aliens? What to make of research and reporting on 'Oumuamua, our visitor from space

As an astrophysicist, probably the most common question I get asked is: "Are we alone in the universe and do aliens exist?"

There is no doubt: people love to think and talk about aliens. Hence, stories about the search for extraterrestrial intelligence get picked up and reported with gusto in the media.

But what really lies at the heart of this complicated and popular topic is evidence – the nature of any evidence of alien life, how we view and respect this evidence, and how this is communicated to the public.

Nowhere is this more important than in the coverage of scientific studies of a mystery object – 'Oumuamua – that was recently discovered passing through our solar system. For example, two publications in two respected peer-reviewed journals prompted very different reactions.

Hello 'Oumuamua

'Oumuamua, meaning scout or messenger in Hawaiian, is the name given to the first detected interstellar object to visit our solar system. On discovery last year, 'Oumuamua was classified as a comet, but this was later withdrawn when no evidence for cometary activity was detected.

'Oumuamua was quickly found to have an orbit that does not belong to our solar system. It has an origin elsewhere in our galaxy, and a trajectory that saw it traverse the inner solar system over the course of a few months.

It passed close to the sun and to Earth, and was found to have an unusual geometry, about 200 metres long and some 35 metres wide, rotating every seven hours.

The discovery of 'Oumuamua generated a lot of attention in the scientific community, and in the media. Given its unusual geometry and its origin outside the solar system, questions were soon asked as to whether 'Oumuamua could be a spacecraft.

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Observations were made with radio telescopes to search for any direct evidence of transmissions indicating intelligent life, including by a team led by me using an Australian telescope (the Murchison Widefield Array). We listened around FM radio frequencies, on the basis that any intelligent life on 'Oumuamua may recognise FM frequencies popular on Earth.

No direct evidence of intelligent life was ever found in these searches.

Extensive and impressive observations with a range of telescopes, including the Hubble Space Telescope, were made to accurately determine 'Oumuamua's trajectory. Results of the study, by a team of astronomers led by the European Space Agency's Marco Micheli, were published in Nature in June.

These very careful observations showed that 'Oumuamua accelerated as it left the solar system, revealing the existence of "non-gravitational forces". This means that the trajectory of the object could not be explained just by the gravity of the sun and other major objects in our solar system.

A range of possible explanations for the acceleration exist. One is that heated gas escaping from 'Oumuamua (outgassing) could produce a force that caused the observed acceleration. This is commonly seen in normal comets.

But 'Oumuamua still shows no evidence for cometary activity. Micheli's team ran through six possible explanations and concluded that outgassing is the most likely option, even though there is no direct evidence that this is the case.

They showed that the acceleration of 'Oumuamua is unusual, but within the bounds of what has been seen previously for solar system comets.

One of the explanations discounted by the study team is that 'Oumuamua was accelerated by radiation pressure from our sun. Radiation from the sun can push objects away from it.

But they concluded that this explanation is not preferred, because it means that the density of 'Oumuamua would have to be very low. An object needs have a large surface area and low mass (low density) to be accelerated by radiation pressure.

Could it be aliens?

Another study by postdoctoral researcher Shmuel Bialy and distinguished astronomer Avi Loeb, from Harvard University, took a different approach.

Details of the study have just been published in November's The Astrophysical Journal Letters, but were available online earlier.

The authors chose to assume solar radiation pressure to be the cause of the acceleration, and then determined the properties of 'Oumuamua required to make this work. They require an object with thickness less than 1mm, an areal mass density of 1 to 2 grams per square centimetre, and a large area.

It is unlikely that nature would produce such an extreme geometry. The authors quickly mention this, before moving to a discussion that, under the assumption that solar radiation is the cause for the acceleration, 'Oumuamua is artificial—that means the product of an alien civilisation.

The properties the authors derive under their assumptions are similar to those of solar sails being designed and built by humans as a possible way to travel interstellar distances.

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Bialy and Loeb spend half of their article discussion section on the idea that 'Oumuamua could be a defunct or active solar sail belonging to an alien civilisation.

The nature and communication of evidence

Bialy and Loeb did not issue a press release about their study, but the media picked up the paper once it was accepted and available online, prior to this week's journal publication.

(This is something that happened to me in 2012, leading to my published non-detection of aliens being run on the front page of the BBC news website.)

Bialy and Loeb's publication attracted headlines such as this, for example: "Harvard astronomers claim Oumuamua is ALIEN PROBE - 'Nothing like we've ever seen!'". Most other reporting was more balanced.

This is pretty normal. A lot of the media jump to aliens in the reporting of space and astronomy, even when the original reported studies have never mentioned aliens. Recent reporting of Fast Radio Bursts (FRBs) is an example.

What surprised me was the reaction of some of my colleagues to Bialy and Loeb's paper. On social media, there have been some pretty personal attacks by scientists – on Loeb in particular – for being in the media for this work.

Both new studies lay out their assumptions, cite substantial evidence, and undertake rigorous calculations. Both were accepted by top-quality journals after independent peer review.

Both finish with bottom lines that the studies of 'Oumuamua are inconclusive and we will need to examine more such objects that come through the solar system in the future.

Both sets of authors also come up with different perspectives and motivate different questions. But Loeb has ended up in the media, talking about his paper, and is being panned by some colleagues for it.

Since the pre-journal paper was picked up he told me he has been swamped by media interest. "I use the discussions with the media as a platform for highlighting the standard scientific methodology: an anomaly is observed in data, the standard explanation fails to explain it, and so an alternative interpretation is proposed. I encourage anyone with a better explanation to write a paper about it and publish it. Wrong interpretations can be ruled out when more data will be released on 'Oumuamua or other members of its population in the future."

As for the negative reactions he has received, he referred to an article he recently published where he paraphrased another scientist known for his once-controversial theories. "As Galileo reasoned after looking through his telescope, 'in the sciences, the authority of a thousand is not worth as much as the humble reasoning of a single individual.'"

Let's talk about evidence

Given my work on observations of 'Oumuamua, a few journalists have contacted me for comment.

These have been great opportunities to discuss in depth with journalists the nature of evidence, the difference between something being consistent with observations and direct evidence for a conclusion, and the need for evidence to be commensurate with the impact of a claim.

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If aliens are claimed, direct and robust evidence is required – not a conclusion based on a few observations that are difficult to explain, plus a bunch of assumptions.

But no scientist has claimed 'Oumuamua is alien in this discussion – they have just raised questions and explored answers.

There is no point in shying away from a proper discussion on the search for extraterrestrial intelligence, or in being personally critical of colleagues.

Scientists should take every opportunity to engage with the public and the media on the topic, given the public's interest and the media's willingness to report.

It is interesting, fun, and scientific, and a great opportunity to discuss the scientific method and science in an engaging manner. The media reporting of 'Oumuamua shows that (aside from a few headlines), the content of reports is generally pretty good and responsible.

Whatever 'Oumuamua is (almost certainly not made by aliens, in my view), it is a fascinating object and presents lots of interesting scientific questions that will trigger further studies and observations.

We will never see 'Oumuamua again, and we may never know exactly what it is. But seeing 'Oumuamua in the news is likely to inspire some kids to take up a career in science.

Source: Phys.org Return to Contents

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Space Image of the Week

Comet 46P/Wirtanen Image Credit & Copyright: Alex Cherney (Terrastro, TWAN)

Explanation: Periodic Comet 46P/Wirtanen is now the brightest comet in the night sky, but too faint to be seen by eye. From dark sky sites it could just become naked-eye visible though, as its 5.4 year long looping orbit takes it closest to Earth and the Sun in mid December. Fluorescing in sunlight, its spherical coma is about half the angular size of a full moon in this southern hemisphere telescopic view from November 7. Then the comet was about 2 light-minutes away or 35 million kilometers from Earth-bound telescopes, so the pretty greenish coma seen here is around 150,000 kilometers across. That makes it about the size of Jupiter. The stack of digital images also reveals a very faint tail extending toward 4 o'clock with a distant background galaxy notable at the upper left. As a regular visitor to the inner Solar System, comet 46P/Wirtanen was once the favored rendezvous target for ESA's comet exploring Rosetta mission.

Source: APOD Return to Contents