Frozen beneath a region of cracked and pitted plains on Mars lies as much water as what’s in Lake Superior, largest of the Great Lakes, researchers using NASA’s Mars Reconnaissance Orbiter have determined.
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 to about 560 feet, 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 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 of the Institute for Geophysics at the University of Texas, Austin. She is the lead author of a report in the journal Geophysical Research Letters.
Mars today, with an axial tilt of 25 degrees, 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 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.
“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, a co-author of the Utopia paper.
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, 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.