spacetoday.net: Martian south polar cap made of water

Posted: Fri, Feb 14, 2003, 10:35 PM ET (0335 GMT)
Hubble image of Mars

The south polar cap on the planet Mars consists primarily of water ice, and not carbon dioxide as previously believed, scientists reported this week. In a paper published in Friday's issue of the journal Science, Caltech planetary scientists reported that they believe that most of Mars' south polar cap is made of water ice, hidden below a layer of carbon dioxide ice. They base their conclusion on an analysis of pits observed in the polar cap by the Mars Global Surveyor and Mars Odyssey spacecraft. Those images show the pits getting wider at the rate of one to three meters per year, but the pits never get deeper than eight meters despite being up to 1,000 meters across. They concluded that the pits were forming in an outer layer of frozen carbon dioxide which is no deeper than eight meters; below it is a much thicker layer of water ice that, unlike carbon dioxide, does not sublimate during the summer. This finding means that Mars has even more water that previously thought, but has less carbon dioxide. The latter could cause problems for models of an early Mars warmed by the greenhouse effect of a thick carbon dioxide atmosphere; it could also pose problems for possible techniques to terraform the planet in the distant future. In a separate study, scientists at NASA's Ames Research Center modeled the flow of water on the early Mars, matching it with known channels and lakebeds.