Mars may not be as dry as it looks. NASA and the United States Geological Survey (USGS) have used instruments onboard the Mars Reconnaissance Orbiter (MRO) to analyze the vertical structure and thickness of buried ice sheets, which preserve a detailed record of the Red Planet's past and could provide future human explorers with an easily-accessible water supply.

The underground water ice deposits were previously mapped out by the MRO's Shallow Radar (SHARAD) instrument, but there were limits to what could be learned from those scans. The new study focused in on eight spots around the middle latitudes of Mars where these ice sheets were exposed to the surface as eroded slopes, called scarps. Using the MRO's High Resolution Imaging Science Experiment (HiRISE) camera, the team was able to get a cross sectional look at the ice to learn more about its composition and depth.

"The discovery reported today gives us surprising windows where we can see right into these thick underground sheets of ice," says Shane Byrne, co-author of the study. "It's like having one of those ant farms where you can see through the glass on the side to learn about what's usually hidden beneath the ground."

Some of these exposed sections of ice are more than 90 m (295 ft) thick, and the researchers used this window to determine that the ice is relatively pure, with little contamination by dust and rock in the water. That bodes well for thirsty future explorers, as does the fact that this resource is generally much closer to the surface than previously believed. In many areas, it lies beneath just a meter or two of dirt.

"Astronauts could essentially just go there with a bucket and a shovel and get all the water they need," says Byrne.

These ice sheets have scientific value beyond just hydrating the first Martian settlers. Here on Earth, ice cores drilled from the polar regions and places like Greenland provide invaluable insights into the history of the climate, so the ice sheets on Mars are likely to be just as useful as time capsules of the Red Planet's past.

"If you had a mission at one of these sites, sampling the layers going down the scarp, you could get a detailed climate history of Mars," says Leslie Tamppari, Deputy Project Scientist on MRO. "It's part of the whole story of what happens to water on Mars over time: Where does it go? When does ice accumulate? When does it recede?"

The research will help NASA and other agencies focus on landmarks of interest for upcoming rover and eventual human missions to Mars.

The study was published in the journal Science.

Sources: NASA, USGS

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