Erosion on Mars has uncovered large subterranean ice

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Fri Jan 12, 2018 9:26 am

The ice deposits in Utopia Planitia aren’t just an exploration resource, they’re also one of the most accessible climate change records on Mars. We don’t understand fully why ice has built up in some areas of the Martian surface and not in others. Sampling and using this ice with a future mission could help keep astronauts alive, while also helping them unlock the secrets of Martian ice ages.

In this false color image captured by NASA's HiRISE camera, one of eight recently discovered stripes appears dark blue against the Martian terrain. (Source / Credit : NASA/JPL/UNIVERSITY OF ARIZONA/USGS)

Locked away beneath the surface of Mars are vast quantities of water ice. But the properties of that ice—how pure it is, how deep it goes, what shape it takes—remain a mystery to planetary geologists. Those things matter to mission planners, too: Future visitors to Mars, be they short-term sojourners or long-term settlers, will need to understand the planet's subsurface ice reserves if they want to mine it for drinking, growing crops, or converting into hydrogen for fuel.

Trouble is, dirt, rocks, and other surface-level contaminants make it hard to study the stuff. Mars landers can dig or drill into the first few centimeters of the planet's surface, and radar can give researchers a sense of what lies tens-of-meters below the surface. But the ice content of the geology in between—the first 20 meters or so—is largely uncharacterized.

Fortunately, land erodes. Forget radar and drilling robots: Locate a spot of land laid bare by time, and you have a direct line of sight on Mars' subterranean layers—and any ice deposited there.

At this pit on Mars, the steep slope at the northern edge (toward the top of the image) exposes a cross-section of a thick sheet of underground water ice.
(Source / Credits: NASA/JPL-Caltech/UA/USGS )

Researchers using NASA's Mars Reconnaissance Orbiter (MRO) have found eight sites where thick deposits of ice beneath Mars' surface are exposed in faces of eroding slopes.

These eight scarps, with slopes as steep as 55 degrees, reveal new information about the internal layered structure of previously detected underground ice sheets in Mars' middle latitudes.

The ice was likely deposited as snow long ago. The deposits are exposed in cross section as relatively pure water ice, capped by a layer one to two yards (or meters) thick of ice-cemented rock and dust. They hold clues about Mars' climate history. They also may make frozen water more accessible than previously thought to future robotic or human exploration missions.

This vertically exaggerated view shows scalloped depressions in a part of Mars where such textures prompted researchers to check for buried ice, using ground-penetrating radar aboard NASA's Mars Reconnaissance Orbiter. They found about as much frozen water as the volume of Lake Superior.
(Source / Credits: NASA/JPL-Caltech/Univ. of Arizona)

Scientists examined part of Mars' Utopia Planitia region, in the mid-northern latitudes, with the orbiter's ground-penetrating Shallow Radar (SHARAD) instrument. Analyses of data from more than 600 overhead passes with the onboard radar instrument reveal a deposit more extensive in area than the state of New Mexico. The deposit ranges in thickness from about 260 feet (80 meters) to about 560 feet (170 meters), with a composition that's 50 to 85 percent water ice, mixed with dust or larger rocky particles.

At the latitude of this deposit -- about halfway from the equator to the pole -- water ice cannot persist on the surface of Mars today. It sublimes into water vapor in the planet's thin, dry atmosphere. The Utopia deposit is shielded from the atmosphere by a soil covering estimated to be about 3 to 33 feet (1 to 10 meters) thick.

Martian Water as a Future Resource

The name Utopia Planitia translates loosely as the "plains of paradise." The newly surveyed ice deposit spans latitudes from 39 to 49 degrees within the plains. It represents less than one percent of all known water ice on Mars, but it more than doubles the volume of thick, buried ice sheets known in the northern plains. Ice deposits close to the surface are being considered as a resource for astronauts.

The Utopian water is all frozen now. If there were a melted layer -- which would be significant for the possibility of life on Mars -- it would have been evident in the radar scans. However, some melting can't be ruled out during different climate conditions when the planet's axis was more tilted. "Where water ice has been around for a long time, we just don't know whether there could have been enough liquid water at some point for supporting microbial life," Holt said.

Utopia Planitia is a basin with a diameter of about 2,050 miles (3,300 kilometers), resulting from a major impact early in Mars' history and subsequently filled. NASA sent the Viking 2 Lander to a site near the center of Utopia in 1976. The portion examined by Stuurman and colleagues lies southwest of that long-silent lander.

SHARAD is one of six science instruments on the Mars Reconnaissance Orbiter, which began its prime science phase 10 years ago this month. The mission's longevity is enabling studies of features and active processes all around Mars, from subsurface to upper atmosphere. The Italian Space Agency provided the SHARAD instrument and Sapienza University of Rome leads its operations. The Planetary Science Institute, based in Tucson, Arizona, leads U.S. involvement in SHARAD. JPL, a division of Caltech in Pasadena, manages the orbiter mission for NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems of Denver built the spacecraft and supports its operations.

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Sat Jan 13, 2018 11:20 pm

Very interesting. Terraforming Mars is definitely a ways away, but this makes it a bit more feasible.

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