Monday, December 1, 2008

Vast underground glaciers reported on Mars

NASA's Mars Reconnaissance Orbiter has detected vast glaciers of water ice under Martian ground, researchers say. The findings could present new avenues for the search for life on Mars, they add, or provide water to support future human exploration. Scientists analyzed data from the spacecraft's ground-penetrating radar and report in the Nov. 21 issue of the research journal Science that buried glaciers extend for dozens of miles (kilometers) from the edges of mountains or cliffs. A layer of rocky debris blanketing the ice may have preserved the underground glaciers as remnants from an ice sheet that covered middle latitudes during a past ice age, scientists said.

This finding is similar to massive ice glaciers that have been detected under rocky coverings in Antarctica. "Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps," said John W. Holt of the University of Texas at Austin, lead author of the report. "Just one of the features we examined is three times larger than the city of Los Angeles and up to half a mile thick."

Scientists have puzzled over what are known as aprons -- gently sloping areas containing rocky deposits at the bases of taller geographical features -- since NASA's Viking orbiters first observed them on the Martian surface in the1970s. One theory has been that the aprons are flows of rocky debris lubricated by a small amount ice. Now, the shallow radar instrument on the Mars Reconnaissance Orbiter has offered "the smoking gun pointing to the presence of large amounts of water ice at these latitudes," said Ali Safaeinili, a shallow radar instruments team member with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Radar echoes received by the spacecraft indicated radio waves pass through the aprons and reflect off a deeper surface below without significant loss in strength, he explained; that would be expected if the apron areas consisted of thick ice under a relatively thin covering. The radar doesn't detect reflections from the interior of these deposits as would occur if they contained significant rock debris, he continued. The apparent velocity of radio waves passing through the apron is consistent with a composition of water ice, he said.

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