Houston, November 26: The deposit ranges in thickness from about 80 metres to about 170 metres, with a composition that is 50 to 85 per cent water ice, mixed with dust or larger rocky particles.
Scientists using data from NASA's Mars Reconnaissance Orbiter have found a huge reservoir of water frozen beneath a region of cracked and pitted plains of the red planet, which may prove to be a vital resource for astronauts in future.
Researchers examined part of Utopia Planitia region on Mars, 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 unveil a deposit more extensive in area than the state of New Mexico, which could hold about as much water as in Lake Superior, largest of the Great Lakes of North America.
The deposit ranges in thickness from about 80 metres to about 170 metres, with a composition that is 50 to 85 per cent 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 vapour in the planet's thin, dry atmosphere. The Utopia deposit is shielded from the atmosphere by a soil covering estimated to be one to 10 metres thick.
"This deposit probably formed as snowfall accumulating into an ice sheet mixed with dust during a period in Mars history when the planet's axis was more tilted than it is today," said Cassie Stuurman from the University of Texas, Austin in the US.
Mars accumulates large amounts of water ice at the poles. In cycles lasting about 120,000 years, the tilt varies to nearly twice that much, heating the poles and driving ice to middle latitudes.
Climate modeling and previous findings of buried, mid-latitude ice indicate that frozen water accumulates away from the poles during high-tilt periods.
The newly surveyed ice deposit spans latitudes from 39 to 49 degrees within the plains.
It represents less than one per cent 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.
"This deposit is probably more accessible than most water ice on Mars, because it is at a relatively low latitude and it lies in a flat, smooth area where landing a spacecraft would be easier than at some of the other areas with buried ice," said Jack Holt of the University of Texas.
The Utopian water is all frozen now. If there were a melted layer - which would be significant for possibility of life on Mars - it would have been evident in the radar scans.
"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 3,300 kilometres, resulting from a major impact early in Mars' history and subsequently filled.
The study was published in the journal Geophysical Research Letters.