All the worlds may be ours except Europa but that only makes the ice-covered moon of Jupiter all the more intriguing. Beneath Europa’s thin crust of ice lies a tantalizing global ocean of liquid water somewhere in the neighborhood of 100 kilometers deep—which adds up to more liquid water than is on the entire surface of the Earth. Liquid water plus a heat source(s) to keep it liquid plus the organic compounds necessary for life and…well, you know where the thought process naturally goes from there.
And now it turns out Europa may have even more of a heat source than we thought. Yes, a big component of Europa’s water-liquefying warmth comes from tidal stresses enacted by the massive gravity of Jupiter as well as from the other large Galilean moons. But exactly how much heat is created within the moon’s icy crust as it flexes has so far only been loosely estimated. Now, researchers from Brown University in Providence, RI and Columbia University in New York City have modeled how friction creates heat within ice under stress, and the results were surprising.
Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.
Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.
All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.
Two members of the Antarctic Search for Meteorites 2012-2013 team use tongs to collect a meteorite near the Transantarctic Mountains. Credit: Katherine Joy, University of Manchester / Antarctic Search for Meteorites Program
In the category of why-didn’t-I think-of-that ideas, Dr. Geoffrey Evatt and colleagues from the University of Manchester struck upon a brilliant hypothesis: that a layer of iron meteories might lurk just below the surface of the Antarctic ice. He’s the lead author of a recent paper on the topic published in the open-access journal, Nature Communications.
A possible stony meteorite found during the ANSMET 2014-15 expedition in Antarctica. Credit: Antarctic Search for Meteorites Program
Remote Antarctica makes one of the best meteorite collecting regions on the planet. Space rocks have been accumulating there for millennia preserved in the continent’s cold, desert-like climate. While you might think it’s a long and expensive way to go to hunt for meteorites, it’s still a lot cheaper than a sample return mission to the asteroid belt. Meteorites fall and become embedded in ice sheets within the continent’s interior. As that ice flows outward toward the Antarctic coastlines, it pushes up against the Transantarctic Mountains, where powerful, dry winds ablate away the ice and expose their otherworldly cargo.
Meteorite recovery sites in the Transantarctic Mountains. Credit: NASA
Layer after layer, century after century, the ice gets stripped away, leaving rich “meteorite stranding zones” where hundreds of space rocks can be found within an area the size of a soccer field. Since most meteorites arrive on Earth coated in a black or brown fusion crust from their searing fall through the atmosphere, they contrast well against the white glare of snow and ice. Scientists liken it to a conveyor belt that’s been operating for the past couple million years.
Scientists form snowmobile posses and buzz around the ice fields picking them up like candy eggs on Easter morning. OK, it’s not that easy. There’s much planning and prep followed by days and nights of camping in bitter cold with high winds tearing at your tent. Expeditions take place from October through early January when the Sun never sets.
The U.S. under ANSMET (Antarctic Search for Meteorites, a Case Western Reserve University project funded by NASA), China, Japan and other nations run programs to hunt and collect the precious from the earliest days of the Solar System before they find their way to the ocean or are turned to dust by the very winds that revealed them in the first place. Since systematic collecting began in 1976, some 34,927 meteorites have been recovered from Antarctica as of December 2015.
A team of scientists document the find of a small meteorite found among rocks on the Antarctic ice during the ANSMET 2014-15 expedition. Credit: Antarctic Search for Meteorites Program / Vinciane Debaille
Meteorites come in three basic types: those made primarily of rock; stony-irons comprised of a mixture of iron and rock; and iron-rich. Since collection programs have been underway, Antarctic researchers have uncovered lots of stony meteorites, but meteorites either partly or wholly made of metal are scarce compared to what’s found in other collecting sites around the world, notably the deserts of Africa and Oman. What gives?
This fragment of the massive Sikhote-Alin meteorite that fell over eastern Russia (then the Soviet Union) on Feb. 12, 1947 is a typical iron-nickel meteorite. Another specimen of this meteorite was used in the experiment to determine how quickly it burrowed into the ice when heated. Credit: Bob King
Dr. Evatt and colleagues had a hunch and performed a simple experiment to arrive at their hypothesis. They froze two meteorites of similar size and shape — a specimen of the Russian Sikhote-Alin iron and NWA 869, an ordinary (stony) chondrite — inside blocks of ice and heated them using a solar-simulator lamp. As expected, both meteorites melted their way down through the ice in time, but the iron meteorite sank further and faster. I bet you can guess why. Iron or metal conducts heat more efficiently than rock. Grab a metal camera tripod leg or telescope tube on a bitter cold night and you’ll know exactly what I mean. Metal conducts the heat away from your hand far better and faster than say, a piece of wood or plastic.
Antarctic researchers carefully pack meteorites found along the Transantarctic Range into collection boxes. Looks cold! Credit: Antarctic Search for Meteorites Program / Vinciane Debaille
The researchers performed many trials with the same results and created a mathematical model showing that Sun-driven burrowing during the six months of Antarctic summer accounted nicely for the lack of iron meteorites seen in the stranding zones. Co-author Dr. Katherine Joy estimates that the fugitive meteorites are trapped between about 20-40 inches (50-100 cm) beneath the ice.
Who wouldn’t be happy to find this treasure? Dr. Barbara Cohen is seen with a large meteorite from the Antarctic’s Miller Range. Credit: Antarctic Search for Meteorites Program
You can imagine how hard it would be to dig meteorites out of Antarctic ice. It’s work enough to mount an expedition to pick up just what’s on the surface.
With the gauntlet now thrown down, who will take up the challenge? The researchers suggests metal detectors and radar to help locate the hidden irons. Every rock delivered to Earth from outer space represents a tiny piece of a great puzzle astronomers, chemists and geologist have been assembling since 1794 when German physicist Ernst Chladni published a small book asserting that rocks from space really do fall from the sky.
Like the puzzle we leave unfinished on the tabletop, we have a picture, still incomplete, of a Solar System fashioned from the tiniest of dust motes in the crucible of gravity and time.
Europa’s water exists in a layer around the planet, encased in a layer of ice. Could there be life down there?
Hooray! Welcome to the 200th official episode of the Guide To Space!
First off, thank you. Thank you for watching, liking, sharing, subscribing and being a patron of our show. Yes, you. Thank you.
So to celebrate, a few weeks ago we invited the members of the Weekly Space Hangout Crew Google+ Community to suggest topics for episodes, and the winner would receive a precious iron-nickel meteorite. Congratulations Andres Munoz, this meteorite is for you.
This episode, chosen by Andres, is for everyone.
The search for life in the Solar System is about the hunt for water. Wherever we find liquid water on Earth, we find life. I’m talking everywhere. In the most briny, salty pools in Antarctica, in the hottest hot springs in Yellowstone, under glaciers, and kilometers deep underground.
So we go searching for liquid water in the Solar System.
You might be surprised to learn that Jupiter’s moon Europa has the most water in the entire Solar System. If you took all the water on Earth, collected it into a big sphere, it would measure almost 1,400 kilometers across.
Europa’s water would measure nearly 1,800 kilometers.All that water exists in a layer around Europa, encased in a layer of ice. How thick? We don’t know.
Is there life down there? We don’t know.You can say there might be, and it wouldn’t be untrue. However, if you say there isn’t, that’s way less interesting for clickbait purposes. Whenever we don’t know the answers to fundamental and intriguing questions like that, it’s time to send a mission.
Good news! An actual mission to Europa is in the works right now. In 2015, NASA approved the development of an orbiter mission to Europa. If all goes well, and nothing gets cancelled…
And nothing will get cancelled, right? Right? I heard Firefly. Which one of you said Firefly?!?
According to the plan, a spacecraft will launch in the 2020s, carrying 9 instruments to Europa. Most will be familiar cameras, mass spectrometers, and the like, to study the surface of Europa to a high level of resolution. Over the course of 45 flybys, the spacecraft will get down as close as 25 kilometers and capture it with incredible resolution.
A “colorized” image of Europa from NASA’s Galileo spacecraft, whose mission ended in 2003. The whiteish areas are believed to be pure water ice. Credit: NASA/JPL-Caltech/SETI Institute
Perhaps the most exciting, and controversial instrument on board the new Europa Orbiter mission will be its ice-penetrating radar. Mission planners battled over installing a radar this sophisticated, as it will be an enormous drain on the orbiter’s power.
This for us is incredibly exciting. It will allow the spacecraft to map out the depth and thickness of Europa’s icy exterior. Is it thick or thin? Are there pockets of water trapped just below the surface, or is it tough shell that goes on for dozens of kilometers?
The worst case scenario is that the shell goes thicker than the radar can reach, and we won’t even know how far it goes.
Whatever happens, the Europa orbiter will be a boon to science, answer outstanding questions about the moon and the chances of finding life there.
We’re just getting started. What we really want to send is a lander. Because of the intense radiation from Jupiter, the Sun, and space itself, the surface of the ice on Europa would be sterilized. But dig down a few centimeters and you might find life that’s protected from the radiation.
A future Europa lander might be equipped with a heated drill attached to a tether. The lander would be have with a heat-generated radioisotope thermoelectric generator, like most of NASA’s big, outer Solar System spacecraft.
Artist illustration of a Europa probe. Image credit: NASA/JPL
But in addition to using it for electricity, it’ll use the raw heat to help a tethered drill to grind through the ice a few meters and sample what’s down there.
Drilling more than a few meters is probably the stuff of science fiction. Russian scientists in Antarctica drilled for almost two decades to get through 4,000 meters of ice above Lake Vostok. Imagine trying to get through 100 kilometers of the stuff, on a distant world, with a robot.
But, since I’ve talked about moving the Sun, and terraforming the Moon, maybe I shouldn’t put any bounds on my imagination. Nuclear-powered Europa submarines will get us swimming with the singing Europan space whales in no time.
Europa is the best place to search the Solar System for life, and I’m excited to see what the upcoming Europa Orbiter mission turns up. And I’m even more excited about the possibility of any future lander missions.
It was a lot of fun wrapping my brain around a topic chosen by the fans. What topic would you like us to cover next? I’ve got a whole pocket of meteorites here. Put it in the comments below.
First, I want to thank everyone. It’s been a crazy race getting up to 200 episodes, but it’s been a blast all the way through. Thanks again for all your support and here’s to 200 more!
The crater that contains those puzzlingly bright spots on Ceres may harbor an equally puzzling haze. Or not. The hints of haze on the dwarf planet, seen in some of the images coming from NASA’s Dawn spacecraft, add another intriguing twist to Ceres’ mysteries.
The hubbub over haze arose this week during the Exploration Science Forum at NASA’s Ames Research Center in California. For months, Dawn’s scientists have been observing – and trying to make sense out of – unusually reflective spots within Ceres’ craters that show up when the asteroid turns into the sunlight. The team has speculated that they could be frozen pools of water ice, or patches of light-colored, salt-rich material.
The brightest spots are known collectively as Spot 5, and sit inside Occator Crater on Ceres. Dawn’s principal investigator, Chris Russell of the University of California at Los Angeles, told the forum that some type of haze could be seen inside the crater at certain times of Ceres’ day, according to reports from Nature and the Planetary Society. Nature quoted Russell as saying the bright spots “could be providing some atmosphere in this particular region of Ceres.”
Last year, scientists with the European Space Agency’s Herschel mission reported detecting signs of water vapor rising from Ceres’ surface, and it would be tempting to suggest that the water vapor is emanating from bright icy spots and creating the haze. That would strengthen Ceres’ status as the only asteroid with a significant atmosphere and a subsurface reservoir of water, and stoke speculation about life on Ceres.
However, Russell told Universe Today that it’s way too early to give in to temptation.
“I was speaking from less than a handful of images, and the interpretation of the images is disputed by some team members,” Russell said in an email. “I would like the debate to go on internally before we make a pronouncement one way or the other. I of course have my personal opinion, but I am not always right.”
Russell said the ice-vs.-salt debate is continuing. “I originally was an advocate of ice, because of how bright the spots seemed to be,” he said. However, the bright material’s albedo, or reflectivity factor, is about 50 percent – which is less than Russell originally thought. “This could be salt and is unlikely to be ice. I think the team opinion is now more in line with salt,” he said.
Either way, Russell doesn’t see any way for the spots to form without internal activity on Ceres. “Thus, the very existence of the spots tells us that there is some active process going on,” he told Universe Today.
Will we ever know if the haze is for real? Or what the spots are made of? As the Magic 8-Ball might say, “Ask again later.” The Dawn spacecraft recently recovered from a mechanical glitch and is gradually descending to a closer mapping orbit, around an altitude of 900 miles (1,500 kilometers). That will provide a much better look at Occator Crater and what lies within.
“Eventually I am expecting the spectral data will unambiguously tell us what has happened to the surface,” Russell said, “but it is a little too soon to be sure.”
Comet 67P/C-G may be tiny at just 2.5 miles (4 km) across, but its diverse landscapes and the processes that shape them astound. To say nature packs a lot into small packages is an understatement.
In newly-released images taken by Rosetta’s high-resolution OSIRIS science camera, the comet almost seems alive. Sunlight glints off icy boulders and pancaking sinkholes blast geysers of dust into the surrounding coma.
Examples of six different bright patches identified on the surface of 67P/C-G in images taken last September when Rosetta was 20-50 km from the comet. The center panel points to the broad regions in which they were discovered (not specific locations). 120 bright regions, including clusters of bright features, isolated features and individual boulders, were seen. The false color images were taken at different times and have been stretched and slightly saturated to emphasis color contrasts so that dark terrains appear redder and bright regions appear significantly bluer compared with what the human eye would normally see. Credit: SA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
More than a hundred patches of water ice some 6 to 15 feet across (a few meters) dot the comet’s surface according to a new study just published in the journal Astronomy & Astrophysics. We’ve known from previous studies and measurements that comets are rich in ice. As they’re warmed by the Sun, ice vaporizes and carries away embedded dust particles that form the comet’s atmosphere or coma and give it a fuzzy appearance.
Examples of icy bright patches and clusters seen in September 2014. The two left hand images are crops of OSIRIS narrow-angle camera images acquired on September 5; the right hand images are from September 16. During this time the spacecraft was about 19-25 miles (30-40 km) from the comet center. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Not all that fine powder leaves the comet. Some settles back to the surface, covering the ice and blackening the nucleus. This explains why all the comets we’ve seen up close are blacker than coal despite being made of material that’s as bright as snow.
True brightness comparisons of four different Solar System bodies. At top are Saturn’s moon Enceladus and Earth. At bottom are the Moon and Comet 67P. Enceladus’ ice-covered surface makes it one of the brightest objects in the Solar System. In contrast, 67P is one of the darkest, its icy surface coated in dark mineral dust and organic compounds. Credit: ESA
Scientists have identified 120 regions on the surface of Comet 67P/Churyumov-Gerasimenko that are up to ten times brighter than the average surface brightness. Some are individual boulders, while others form clusters of bright specks. Seen in high resolution, many appear to be boulders with exposures of ice on their surfaces; the clusters are often found at the base of overhanging cliffs and likely got there when cliff walls collapsed, sending an avalanche of icy rocks downhill and exposing fresh ice not covered by dark dust.
An individual boulder about 12 feet across with bright patches on its surface in the Hatmehit region. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
More intriguing are the isolated boulders found here and there that appear to have no relation to the surrounding terrain. Scientists think they arrived George Jetson style when they were jetted from the comet’s surface by the explosive vaporization of ice only to later land in a new location. The comet’s exceedingly low gravity makes this possible. Let that image marinate in your mind for a moment.
All the ice-glinting boulders seen thus far were found in shadowed regions not exposed to sunlight, and no changes were observed in their appearance over a month’s worth of observations.
“Water ice is the most plausible explanation for the occurrence and properties of these features,” says Antoine Pommerol of the University of Bern and lead author of the study.
How do we know it’s water ice and not CO2 or some other form of ice? Easy. When the observations were made, water ice would have been vaporizing at the rate of 1 mm per hour of solar illumination. By contrast, carbon monoxide or carbon dioxide ice, which have much lower freezing points, would have rapidly sublimated in sunlight. Water ice vaporizes much more slowly in comparison.
Lab tests using ice mixed with different minerals under simulated sunlight revealed that it only took a few hours of sublimation to produce a dust layer only a few millimeters thick. But it was enough to conceal any sign of ice. They also found that small chunks of dust would sometimes break away to expose fresh ice beneath.
“A 1 mm thick layer of dark dust is sufficient to hide the layers below from optical instruments,” confirms Holger Sierks, OSIRIS principal investigator at the Max Planck Institute for Solar System Research.
Comet 67P/C-G on June 21, 2015. The nucleus is a mixture of frozen ices and dust. As the comet approaches the Sun, sunlight warms its surface, causing the ices to boil away. This gas streams away carrying along large amounts of dust, and together they build up the coma. Copyright: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0
It appears then that Comet 67P’s surface is mostly covered in dark dust with small exposures of fresh ice resulting from changes in the landscape like crumbling cliffs and boulder-tossing from jet activity. As the comet approaches perihelion, some of that ice will become exposed to sunlight while new patches may appear. You, me and the Rosetta team can’t wait to see the changes.
High-resolution view of an active pit photographed last September from a distance of about 16 miles (26 km) from the comet’s surface in the Seth region. The image scale is about 45 cm a pixel. The Seth_01 pit measures approximately 720 feet (220 m) across and 605 feet (85 m) deep. Note the smooth deposits of dust around the pit. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Ever wonder how a comet gets its jets? In another new study appearing in the science journal Nature, a team of researchers report that 18 active pits or sinkholes have been identified in the comet’s northern hemisphere. These roughly circular holes appear to be the source of the elegant jets like those seen in the photo above. The pits range in size from around 100 to 1,000 feet (30-100 meters) across with depths up to 690 feet (210 meters). For the first time ever, individual jets can be traced back to specific pits.
In specially processed photos, material can be seen streaming from inside pit walls like snow blasting from a snowmaking machine. Incredible!
Active pits detected in the Seth region of the comet. The contrast of the image has been stretched to reveal the details of the fine-structured jets against the shadow of the pit, which are interpreted as dusty streams rising from the fractured wall of the pit. The image was acquired on October 20, 2014 from a distance of 4.3 miles (7 km) from the surface of the comet. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,” said Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.
Similar to the way sinkholes form on Earth, scientists believe pits form when the ceiling of a subsurface cavity becomes too thin to support its own weight. With nothing below to hold it place, it collapses, exposing fresh ice below which quickly vaporizes. Exiting the hole, it forms a collimated jet of dust and gas.
Pits Ma’at 1, 2 and 3 show differences in appearance that may reflect their history of activity. While pits 1 and 2 are active, no activity has been observed from pit 3. The young, active pits are very steep-sided; pits without any observed activity are shallower and seem to be filled with dust. Middle-aged pits tend to have boulders on their floors from mass-wasting of the sides. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The paper’s authors suggest three ways for pits to form:
* The comet may contain voids that have been there since its formation. Collapse could be triggered by either vaporizing ice or seismic shaking when boulders ejected elsewhere on the comet land back on the surface.
* Direct sublimation of pockets of volatile (more easily vaporized) ices like carbon dioxide and carbon monoxide below the surface as sunlight warms the dark surface dust, transferring heat below.
* Energy liberated by water ice changing its physical state from amorphous to its normal crystalline form and stimulating the sublimation of the surrounding more volatile carbon dioxide and carbon monoxide ices.
Graphic showing how pits may form through sinkhole collapse in the comet’s dusty surface layer covering a mixture of dust and ices. 1. Heat causes subsurface ices to sublimate (blue arrows), forming a cavity. 2.When the ceiling becomes too weak to support its own weight, it collapses, creating a deep, circular pit (orange arrow). Newly exposed material in the pit walls sublimates (blue arrows). Credit: ESA/Rosetta/J-B Vincent et al (2015)
The researchers think they can use the appearance of the sinkholes to age-date different parts of the comet’s surface — the more pits there are in a region, the younger and less processed the surface there is. They point to 67P/C-G’s southern hemisphere which receives more energy from the Sun than the north and at least for now, shows no pit structures.
The most active pits have steep sides, while the least show softened contours and are filled with dust. It’s even possible that a partial collapse might be the cause of the occasional outbursts when a comet suddenly brightens and enlarges as seen from Earth. Rosetta observed just such an outburst this past April. And these holes can really kick out the dust! It’s estimated a typical full pit collapse releases a billion kilograms of material.
With Rosetta in great health and perihelion yet to come, great things lie ahead. Maybe we’ll witness a new sinkhole collapse, an icy avalanche or even levitating boulders!
Those bright mystery spots aren’t the only ones on Ceres. Recent photos posted on JPL’s Photojournal sitefeature a spectacular rayed crater resembling the familiar lunar craters Kepler and Copernicus.
Unique view of the lunar crater Proclus showing an extension system of bright rays taken from Apollo 15. Credit: NASABright dots and patches of material are seen in this photo taken by Dawn on May 22, 2015 from 3,200 miles (5,100 km) away. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDATaken back on May 4 from 8,400 miles (13,600 km), this photo shows the rayed crater (bottom) and another bright spot above center. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Lunar rays are bright because they contrast with their older surroundings which have been darkened by exposure to solar and cosmic radiation. Impacts expose fresh material from below the surface that settles into a spider web of rays around the newly excavated crater. Huge boulders lofted above the Moon’s surface during the impact slam back into the crust to create secondary craters also crowned with bright dust and rock.
Based on Ceres’ density, it contains a large fraction of low density materials including clays, water ice, salts and organic compounds. This schematic gives a general idea of the dwarf planet’s makeup. Credit: NASA/ESA/STScI
Most models of Ceres depict a rocky crust, mantle of ice and a rocky inner core. This makes us wonder if the bright material unearthed might be ice. If so, it would gradually vaporize on the virtually air-free dwarf planet.
Dawn will spend through early 2016 at Ceres during its primary mission and then remain in orbit there perpetually. We should be able to cipher the composition of the white material during that time with the spacecraft’s Gamma Ray and Neutron Detector and Visible and Infrared Mapping Spectrometer, but a lengthy stay might allow us to see changes in the extent of any ice exposures as they gradually vaporize away.
Uncropped, untoned view of the rayed crater seen in the earlier image. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
One thing we know for certain about Ceres are its dimensions. Dawn observations have revised the size to be about 599 miles (963 km) across at the equator with a polar diameter of 554 miles (891 km). Like Earth and other planets, Ceres is a slightly flattened sphere wider at the equator than from pole to pole. The temperature there ranges from about -100°F (-73°C) during the day and dips to -225°F (-143°C) at night. That makes its daytime high about 28° warmer than coldest temperature ever recorded on Earth.
We’ve subsisted for months on morsels of information coming from ESA’s mission to Comet 67P/Churyumov-Gerasimenko. Now, a series of scientific papers in journal Science offers a much more complete, if preliminary, look at Rosetta’s comet. And what a wonderful and complex world it is.
Scientists have defined 19 regions on Comet 67P/Churyumov-Gerasimenko’s nucleus according to terrain and named for Egyptian deities like Imhotep, Aten and Hathor. Credits: ESA/Rosetta/MPS/OSIRIS Team/UPD/LAM/IAA/SSO /INTA/UPM/DASP/IDA
Each of the papers describes a different aspect of the comet from the size and density of dust particles jetting from the nucleus, organic materials found on its surface and the diverse geology of its bizarre landscapes. Surprises include finding no firm evidence yet of ice on the comet’s nucleus. There’s no question water and other ices compose much of 67P’s 10 billion ton mass, but much of it’s buried under a thick layer of dust.
Despite its solid appearance, 67P is highly porous with a density similar to wood or cork and orbited by a cloud of approximately 100,000 “grains” of material larger than 2 inches (5 cm) across stranded there after the comet’s previous perihelion passage. Thousands of tiny comet-lets! Continue reading “Latest Research Reveals a Bizarre and Vibrant Rosetta’s Comet”
It’s always good to get a little change of perspective, and with this image we achieve just that: it’s a view of Mercury’s north pole projected as it might be seen from above a slightly more southerly latitude. Thanks to the MESSENGER spacecraft, with which this image was originally acquired, as well as the Arecibo Observatory here on Earth, scientists now know that these polar craters contain large deposits of water ice – which may seem surprising on an airless and searing-hot planet located so close to the Sun but not when you realize that the interiors of these craters never actually receive sunlight.
The locations of ice deposits are shown in the image in yellow. See below for a full-sized version.
Perspective view of Mercury’s north pole made from MESSENGER MDIS images and Arecibo Observatory data. (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
The five largest ice-filled craters in this view are (from front to back) the 112-km-wide Prokofiev and the smaller Kandinsky, Tolkien, Tryggvadottir, and Chesterton craters. A mosaic of many images acquired by MESSENGER’s Mercury Dual Imaging Sustem (MDIS) instrument during its time in orbit, you would never actually see a view of the planet’s pole illuminated like this in real life but orienting it this way helps put things into…well, perspective.
Radar observations from Arecibo showing bright areas on Mercury’s north pole
Radar-bright regions in Mercury’s polar craters have been known about since 1992 when they were first imaged from the Arecibo Observatory in Puerto Rico. Located in areas of permanent shadow where sunlight never reaches (due to the fact that Mercury’s axial tilt is a mere 2.11º, unlike Earth’s much more pronounced 23.4º slant) they have since been confirmed by MESSENGER observations to contain frozen water and other volatile materials.
Similarly-shadowed craters on our Moon’s south pole have also been found to contain water ice, although those deposits appear different in composition, texture, and age. It’s suspected that some of Mercury’s frozen materials may have been delivered later than those found on the Moon, or are being restored via an ongoing process. Read more about these findings here.
In orbit around Mercury since 2011, MESSENGER is now nearing the end of its operational life. Engineers have figured out a way to extend its fuel use for an additional month, possibly delaying its inevitable descent until April, but even if this maneuver goes as planned the spacecraft will be meeting Mercury’s surface very soon.
An uncontrolled, chaotic landing. Stuck in the shadow of a cliff without energy-giving sunlight. Philae and team persevered. With just 60 hours of battery power, the lander drilled, hammered and gathered science data on the surface of comet 67P/Churyumov-Gerasimenko before going into hibernation. Here’s what we know.
Despite appearances, the comet’s hard as ice. The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument hammered a probe as hard as they could into 67P’s skin but only dug in a few millimeters:
Close-up of the first touchdown site before Philae landed (left) and after clearly shows the impressions of its three footpads in the comet’s dusty soil. At the final landing site, it’s believed that Times are CST. Philae’s 3.3 feet (1-m) across. Credit: ESA
“Although the power of the hammer was gradually increased, we were not able to go deep into the surface,” said Tilman Spohn from the DLR Institute of Planetary Research, who leads the research team. “If we compare the data with laboratory measurements, we think that the probe encountered a hard surface with strength comparable to that of solid ice,” he added. This shouldn’t be surprising, since ice is the main constituent of comets, but much of 67P/C-G appears blanketed in dust, leading some to believe the surface was softer and fluffier than what Philae found.
This finding was confirmed by the SESAME experiment (Surface Electrical, Seismic and Acoustic Monitoring Experiment) where the strength of the dust-covered ice directly under the lander was “surprisingly high” according to Klaus Seidensticker from the DLR Institute. Two other SESAME instruments measured low vaporization activity and a great deal of water ice under the lander.
As far as taking the comet’s temperature, the MUPUS thermal mapper worked during the descent and on all three touchdowns. At the final site, MUPUS recorded a temperature of –243°F (–153°C) near the floor of the lander’s balcony before the instrument was deployed. The sensors cooled by a further 10°C over a period of about a half hour:
The location of Philae’s first touchdown on the surface of Comet 67P/C-G. Although covered in dust in many areas, Philae found strong evidence for firm ice beneath the comet’s surface. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“We think this is either due to radiative transfer of heat to the cold nearby wall seen in the CIVA images or because the probe had been pushed into a cold dust pile,” says Jörg Knollenberg, instrument scientist for MUPUS at DLR. After looking at both the temperature and hammer probe data, the Philae team’s preliminary take is that the upper layers of the comet’s surface are covered in dust 4-8 inches (10-20 cm), overlaying firm ice or ice and dust mixtures.
The ROLIS camera (ROsetta Lander Imaging System) took detailed photos during the first descent to the Agilkia landing site. Later, when Philae made its final touchdown, ROLIS snapped images of the surface at close range. These photos, which have yet to be published, were taken from a different point of view than the set of panorama photos already received from the CIVA camera system.
During Philae’s active time, Rosetta used the CONSERT (COmet Nucleus Sounding Experiment by Radio wave Transmission) instrument to beam a radio signal to the lander while they were on opposite sides of the comet’s nucleus. Philae then transmitted a second signal through the comet back to Rosetta. This was to be repeated 7,500 times for each orbit of Rosetta to build up a 3D image of 67P/C-G’s interior, an otherworldly “CAT scan” as it were. These measurements were being made even as Philae lapsed into hibernation. Deeper down the ice becomes more porous as revealed by measurements made by the orbiter.
Rosetta’s Philae lander includes a carefully selected set of instruments to analyze a comet’s surface. Credit: ESA, Composite – T.Reyes
The last of the 10 instruments on board the Philae lander to be activated was the SD2 (Sampling, Drilling and Distribution subsystem), designed to provide soil samples for the COSAC and PTOLEMY instruments. Scientists are certain the drill was activated and that all the steps to move a sample to the appropriate oven for baking were performed, but the data right now show no actual delivery according to a tweet this morning from Eric Hand, reporter at Science Magazine. COSAC worked as planned however and was able to “sniff” the comet’s rarified atmosphere to detect the first organic molecules. Research is underway to determine if the compounds are simple ones like methanol and ammonia or more complex ones like the amino acids.
Stephan Ulamec, Philae Lander manager, is confident that we’ll resume contact with Philae next spring when the Sun’s angle in the comet’s sky will have shifted to better illuminate the lander’s solar panels. The team managed to rotate the lander during the night of November 14-15, so that the largest solar panel is now aligned towards the Sun. One advantage of the shady site is that Philae isn’t as likely to overheat as 67P approaches the Sun en route to perihelion next year. Still, temperatures on the surface have to warm up before the battery can be recharged, and that won’t happen until next summer.
Let’s hang in there. This phoenix may rise from the cold dust again.
