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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Eons of a Cold, Dry, Dusty Mars
22 August 2003 (All day)
The trio of missions that will touch down on Mars this December and January are "following the water" as they search for signs of life. But new data from instruments orbiting Mars builds a case for a volcanic planet only gently touched by the chemical alteration that water has wreaked on Earth for billions of years.
In the latest development, reported in the 22 August issue of Science, a team led by planetary geologist and spectroscopist Philip Christensen of Arizona State University in Tempe finds much less of the mineral carbonate than would be expected on a wet planet. On Earth, water and atmospheric carbon dioxide combine to form carbonic acid that eats away at rocks and flushes their remains into lakes and oceans. There, dissolved carbonates eventually precipitate to form solid carbonate deposits like the White Cliffs of Dover. Geochemists imagined that wet weathering would produce something like 20% carbonate in martian dust.
Christensen and colleagues analyzed data from the Thermal Emission Spectrometer on the orbiting Mars Global Surveyor spacecraft to estimate the fraction of carbonate. The wiggles and squiggles of the spectrum are "consistent with a small amount of carbonate," Christensen says, about 2% to 3%. That's no more than might form over the eons by the dust's reaction with today's vanishingly low martian humidity, he notes, or the higher humidities possible during the ebb and flow of martian ice ages.
The work adds to growing evidence pointing to a colder, drier Mars (Science, 22 August, p. 1037). And other products of extensive weathering expected under a warm, wet climate, such as clays, are showing up in unexpectedly tiny quantities, if at all. Researchers have also found minerals long exposed on the surface that would have been quickly destroyed by liquid water. In the emerging view, a perpetually frigid climate has kept Mars's modest store of water locked up as ice most of the time. The surface may never have been particularly hospitable to life, at least not for long.
Yet even spectroscopists do not fully trust their squiggly lines to tell them all about Mars. Upcoming missions will take a closer look. Earlier this month NASA announced plans to land a soil and ice analyzer on the ice-laden northern plains of Mars in 2008 (Science, 8 August, p. 743). And three Mars landers--two NASA and one European--are now on their way to the planet. With luck, they'll have a firsthand chance to spy water's work on Mars.