Satellite confirms Mars ice, discounts 'greenhouse'

By Guy Gugliotta
The Washington Post

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The small amount of carbon dioxide found by the Mars Express satellite eliminates one possible answer to the question of whether Mars ever had sufficient CO2 to foster an atmospheric "greenhouse effect" strong enough to have warmed the planet so liquid water could have formed on the surface — and possibly supported life.

What atmosphere Mars now has — about 0.6 percent as much as Earth — is mostly carbon dioxide, but not enough for a warming effect, and the Mars Express findings show the poles are not a "carbon sink" holding dry ice that may once have been gas blanketing the planet.

The European Space Agency's Mars Express entered Mars orbit on Christmas Day, eight days before the first of two NASA rovers, Spirit and Opportunity, landed on the planet.

Rovers' finds

Early this month NASA announced that Opportunity, drilling and photographing a rock outcrop near its landing site, had found both minerals and geological features common in Earth rocks that have either been leached by groundwater or formed by sediment in ancient lakes or ponds.

A few days later — and 6,600 miles away in an ancient lake bed — Spirit drilled into a volcanic rock with fissures filled with material that may have crystallized from water, NASA announced.

Spirit has since spent several days reconnoitering the edge of a crater and is heading for an outcrop known as "Columbia Hills" about 1.5 miles away — "a long drive" expected to take two months over rock-strewn terrain, said Mars project manager Richard Cook at NASA's Jet Propulsion Laboratory, in Pasadena, Calif.

Cook said Opportunity is still taking soil samples near where it landed, but in about a week it will drive out of the sandy depression and head for another crater about 750 yards away.

Polar evidence

The European Space Agency reported in January that Mars Express had discovered the first direct evidence of water ice at the south pole, confirming prior analyses and indirect observations going back to 1984.
 
Mars Express research team leader Jean-Pierre Bibring, of France's Institut d'Astrophysique Spaciale, said Mars Express' OMEGA instrument determined the composition of the polar ice cap by analyzing the light glinting off it at the end of Mars' southern summer, when only permafrost remained. Results of their findings are being reported today in the journal Nature.

Besides confirmation that the south pole had water ice, the European team also found that the cap was about 250 miles wide and extends northward to about 50 degrees latitude. Most of the cap, with the exception of a small layer of carbon dioxide at the pole, is composed of "dirty ice," Bibring said — water mixed with dust.

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