posted                   

quote:

---

Satellite Discovers Ice Cap At the South Pole of Mars
Scientists Discount Likelihood of Finding Liquid Water

By Guy Gugliotta
Washington Post Staff Writer
Thursday, March 18, 2004; Page A12

Instruments aboard a European satellite orbiting Mars have confirmed the presence of a vast expanse of water ice at the planet's south pole, overlaid in a small area by a veneer of frozen carbon dioxide, scientists reported yesterday.


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 carbon dioxide, or CO 2, 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 .6 percent as much as Earth -- is mostly carbon dioxide, but not enough for a warming effect. The Mars Express findings show that the poles are not a "carbon sink" holding dry ice that may once have been gas blanketing the planet.

"Obviously, the CO 2 reservoir at the south pole is not a major CO 2 reservoir," said astrophysicist Jean-Pierre Bibring, of France's Institut d'Astrophysique Spatiale, who led the Mars Express research team. "We'll have to find another reservoir, if there is one."

The European Space Agency's Mars Express entered Mars's orbit on Christmas Day, eight days before the first of two NASA rovers, Spirit and Opportunity, landed on the planet. A third Mars probe, Europe's Beagle 2, landed on Dec. 24 but never established communications with Earth.

Early this month, NASA announced that Opportunity, drilling and photographing a rock outcrop near its landing site, had found minerals and geological features common in Earth rocks that have 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, in a telephone interview from 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 will drive out of this sandy depression and head for another crater about 750 yards away -- perhaps no more than a 10-day trip over a gentle landscape.

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 extending back to 1984.

Bibring said Mars Express's OMEGA instrument determined the composition of the polar ice cap by analyzing the light glinting off it at the end of Mars's 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 found that the cap was about 250 miles wide and extends northward to about 50 degrees latitude, which on Earth would include the southern tail of South America. Most of the cap, with the exception of a small layer of carbon dioxide at the pole itself, is composed of "dirty ice," Bibring said -- water mixed with dust.

Of equal interest, said space scientist Timothy Titus, of the U.S. Geological Survey, is what Mars Express did not find. "The OMEGA result shows that we do not have a whole lot of CO 2 ," said Titus, who wrote an article accompanying the Mars Express report. "Like the north pole, we have a water ice cap."

Titus explained that if Mars ever had liquid water on its surface, there must have been a way to keep it from freezing -- impossible in the frigid wilderness of modern Mars. One way to warm up, he said, would have been for carbon dioxide in the atmosphere to have trapped the sun's heat close to the surface. The same phenomenon on Earth is widely believed to contribute to the current global warming.

"The likelihood is that the ground is a larger reservoir of CO 2 ," Titus said, but there is little evidence so far of the carbonate rocks that scientists would expect to see.

"Or maybe [the gas] was lost in space," Titus added -- knocked out of the atmosphere by solar radiation over billions of years. "Mars had a thicker atmosphere in the past, but was it thick enough to be a balmy place like the Earth? Probably not. It was probably never a nice place to live."

© 2004 The Washington Post Company

---

Posts: 22497 | Registered: Sep 2000  |  IP: Logged |