[meteorite-list] Mars Rovers Find New Evidence of 'Hapitable Niche'; Perilous 3rd Winter Approaches

[Ron Baalke]

http://www.news.cornell.edu/stories/Dec07/Rover.update.html

Chronicle Online e-News

Mars rovers find new evidence of 'habitable niche'; perilous third 
winter approaches

Dec. 21, 2007

By Lauren Gold
LG34 at cornell.edu

Inch by power-conserving inch, drivers on Earth have moved the Mars 
rover Spirit to a spot where it has its best chance at surviving a 
third Martian winter -- and where it will celebrate its fourth 
anniversary (in Earth years) since bouncing down on Mars for a 
projected 90-day mission in January 2004.

Meanwhile, researchers are considering the implications of what 
Cornell's Steve Squyres, principal investigator for NASA's Mars 
Exploration Rover mission, calls "one of the most significant" 
mission discoveries to date: silica-rich deposits uncovered in May by 
Spirit's lame front wheel that provide new evidence for a 
once-habitable environment in Gusev Crater.

Squyres and colleagues reported the silica deposits at the annual 
meeting of the American Geophysical Union in early December in San 
Francisco.

On the other side of Mars, Spirit's still-healthy twin Opportunity is 
creeping slowly down the inside of Victoria Crater, where layers of 
exposed rock are confirming findings made at the much smaller Eagle 
and Endurance craters -- and where deeper layers could offer new 
insight into the planet's history.

Spirit, which has been driving backward since its right front wheel 
stopped turning in March 2006, was exploring near a plateau in the 
Gusev Crater known as Home Plate when scientists noticed that 
upturned soil in the wake of its dragging wheel appeared unusually 
bright.

Measurements by the rover's alpha particle X-ray spectrometer and 
mini-thermal emission spectrometer showed the soil to be about 90 
percent amorphous silica -- a substance associated with 
life-supporting environments on Earth.

"This is one of the most powerful pieces of evidence for formerly 
habitable conditions that we have found," said Squyres, Cornell's 
Goldwin Smith Professor of Planetary Science, in a Dec. 11 interview 
with the BBC.

On Earth, silica deposits are found at hot springs, where hot water 
dissolves silica in rock below the surface, then rises and cools, 
causing the silica to precipitate out near the surface; and at 
fumaroles, where hot acidic water or vapors seep through rock, 
dissolving away other elements but leaving silica behind.

"Either place on Earth is teeming with microbial life," said Squyres. 
"So this is, either way, a representation of what in the past was a 
local habitable environment -- a little habitable niche on the 
surface of Mars."

The discovery was reminiscent of Spirit's journey to winter safety 
last year, when it uncovered (and briefly got mired in) patches of 
bright soil that contained high levels of sulfur -- another possible 
indicator of past hydrothermal activity.

Unlike last year, though, Spirit enters this Martian winter 
handicapped by dusty solar panels -- the result of giant dust storms 
in June and July. So the rover's power levels, which currently range 
between approximately 290 and 250 watt-hours (100 watt-hours is the 
amount of energy needed to light a 100-watt bulb for one hour; full 
power for the rovers is 800-900 watt-hours) -- could drop to 
dangerous levels in the dwindling winter sunlight.

Spirit's perch is currently at a 15-degree tilt on the north-facing 
slope of the Home Plate plateau, said Jim Bell, Cornell associate 
professor of astronomy and leader of the mission's Pancam color 
camera team. As the sun moves lower in the Martian sky, drivers will 
nudge the rover to a steeper angle.

"The fact that we've gotten to a good tilt, and we're going to get to 
a better tilt, is a good sign," said Bell. Still, he added, any work 
the rover does over the winter -- collecting Pancam images of its 
surroundings, for example -- will be strictly low-exertion.

"Most of 2008 is going to be a quiet time for Spirit," he said. "It's 
really about survival."

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