Snowbanks found in warmer areas of Mars, scientist says


Cheer up, Baltimore. There's a place where they've waited 100,000 years for grimy heaps of snow to melt away. And there's still no sign of a plow.

Just ask your favorite Martian. "Mars seems to have quite a bit of snow," said Philip Christensen, a principal investigator for NASA's Mars Odyssey spacecraft, which has been orbiting the Red Planet since October 2001.

Christensen braved Washington's towering snowbanks and gurgling meltwater to announce at NASA headquarters yesterday that he had found what looks pretty much like the same mess in places on Mars.

Astronomers have known for decades that there is water, ice and snow near the Martian poles. And more recent data has detected abundant buried ice as far from the poles as 60 degrees north and south latitude.

But Christensen said the smooth, dirty snowbanks he thinks he has spotted in photographs from Odyssey are on a few shady, protected crater slopes and ridges in the planet's relatively warm mid-latitudes - analogous to north-facing hillsides in snowbound Baltimore, Philadelphia and New York.

The snowbanks appear to be remnants of more widespread, ancient snowfalls. Christensen believes a Martian snowpack has been melting and reappearing in what others have said is a 100,000-year cycle of climate warming and cooling driven by a wobble in Mars' tilt toward the sun.

Snowmelt could explain the water-carved gullies seen for years in many ridgelines and crater slopes. Even better, snowbanks could provide enough sunlight, liquid water and shelter to sustain microbial life.

"The real kicker is finding that liquid water, and very tiny amounts would be enough," said Lynn Rothschild, an ecosystems researcher at NASA's Ames Research Center.

Scientists have had a difficult time in recent years explaining the source of the water that appeared to have carved the fresh-looking gullies seen in photos taken in 2000 by NASA's Mars Global Surveyor spacecraft.

Some of the first theories suggested that groundwater etched the gullies as it emerged from springs on the exposed slopes. But geologist Bruce Jakosky of the University of Colorado said those theories failed to explain adequately how groundwater could cut the gullies seen on some high Martian terrain.

Then infrared photos from the Mars Odyssey spacecraft revealed some gullies emerging from within and beneath shrinking blankets of what appeared to be dust-covered snow.

As the Martian climate warmed, snow cover would thin and meltwater would begin to carve gullies in the dirt beneath the snow, where it would be protected from evaporation in Mars' thin atmosphere. In warmer, less protected spots, the snow vanished, and all that was left were the gullies.

"That explains seeing gullies in very unusual places, such as isolated hills, sand dunes and the crests of ridges where it would be very difficult to have ... groundwater," Christensen said.

University of Rhode Island geologist John Mustard called Christensen's theory "compelling," and said it gets around some of the problems with the groundwater theories. "But does it explain all the gullies we see?" That may require more evidence from Mars orbiters.

The prospect of snowbanks in mid-latitudes of Mars offers an opportunity for future explorers, Christensen said. "If ever there was a place where life might appear on Mars, these are incredible candidates to go and look," he said. Just one caution: If there is a pair of chairs there when they arrive, better find another place to park.

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