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Monday, February 17, 2003

Ardour for Martian Colony Cools

After years of speculation over the possibilities of making Mars habitable, new findings reported in Science show that while there may be plenty of water locked away in the form of ice, there is not enough carbon dioxide to ever warm the planet enough to make it drinkable. "There's definitely not liquid water" Caltech researcher Shane Byrne is quoted as saying "There's just a three-kilometre thick ice sheet, like Greenland." Apparent indications of surface water, including features that look like river valleys, suggest Mars might once have been warm and wet enough to sustain liquid water, and therefore allow for the possibility of life as we know it on Earth. However it is now thought that the water ice would never warm up enough to melt, being dozens of degrees below freezing, and this opinion, if sustained, certainly will be bad news for the idea of 'terraforming', a visionary approach to colonising Mars by heating it up enough to unlock the frozen water. All in all, it seems hopes of ridding ourselves of a certain group of super-numery politicians by sending them off on a colonisation mission are begining to fade.

Mars' polar ice caps are mostly frozen water, say researchers in California. Their calculations help to resolve a long-standing debate about whether or not the red planet's poles are coated with frozen carbon dioxide. Shane Byrne and Andrew Ingersoll of the California Institute of Technology in Pasadena have worked out what the martian south pole would look like for various different combinations of frozen water and carbon dioxide. The only arrangement consistent with satellite observations, they find, is a thin layer of dry ice coating a thick cap of water ice. Even if the south pole's solid carbon dioxide veneer were to turn to be entirely gas, the martian atmosphere wouldn't get much thicker — it is currently around 95% carbon dioxide anyway. Since the 1960s, some have thought that Mars' atmosphere is controlled largely by the freezing and thawing of large carbon dioxide reservoirs in the ice-caps.It has been known for a long time that this picture doesn't hold true at the north pole. Here the ice-cap shrinks each summer as a veneer of carbon dioxide burns off, revealing plenty of less volatile water ice beneath.

But the south pole is different. The ground is higher and the ice-cap is more constant. It seemed possible, then, that this cap might be mostly dry ice, kept frozen by its greater elevation. Not so, say Byrne and Ingersoll — the notion doesn't fit the latest findings of NASA's Mars Odyssey satellite, which has orbited the planet since late 2001. The ice-cap at the red planet's south pole is covered with strange pits, called Swiss-cheese features. They have flat bottoms and steep sides; some are more than a kilometre across and about 8 metres deep.The edges of these pits can expand by several metres each year, showing that they must be holes in a thin layer of volatile carbon dioxide ice. But does this rest on a slab of water ice or dry ice? Either situation could produce steep-sided pits. Carbon dioxide ice on the pit floors could resist sublimation if it is brighter — less contaminated with dust — than the veneer of dry ice on top. The pit floors are too warm to be frozen carbon dioxide, reveal measurements taken by Odyssey's Thermal Emission Imaging System. In other words, the layer of dry ice on the south polar cap of Mars is only around 8 metres thick.
Source: Nature

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