Mars would make a lousy host for the Winter Olympics. Yes, there's the lack of air to consider. But more important, Martian snow turns out to be rock hard. Worse, it is melting away at an alarming rate.
In fact, Mars may be in the midst of a period of profound climate change, according to a new study that shows dramatic year-to-year losses of snow at the south pole.
It is not yet clear, though, if the evidence of a single year's change represents a trend. But the study provides a surprising new view of the nature of the southern ice cap, said Michael Caplinger of Malin Space Science Systems.
"It's saying that the permanent cap isn't quite so permanent as we thought," Caplinger said in a telephone interview.
A second study of both poles finds that Red Planet snow is more dense and hard than the euphemistic "packed powder" advertised by Eastern ski resorts, and nothing like the soft flakes expected in Utah for the 2002 Olympics. Instead, it's hard as ice.
Though unrelated, the two studies were based on observations made by NASA's Mars Global Surveyor and both will be published in the Dec. 7 issue of the journal Science.
The combined observations represent an exciting new way to look at Mars' atmosphere and how it interacts over time with the polar caps and even soil at mid-latitudes, said David A. Paige, a researcher at the University of California, Los Angeles.
"The new data are showing what's going on on Mars seasonally as well as on interannual time scales in much more detail than we had with previous observations," Paige told SPACE.com.
Where the snow is
Both of Mars' polar regions are covered in permanent caps of ice. Scientists have known since the 1970s that some of the ice in the north is water ice. There may be water ice in the south, too, but there is no firm evidence. Both poles are covered in a veneer of carbon dioxide ice, popularly called "dry ice" here on Earth.
Each cap grows during its winter and recedes in summer.
The research into snow density, lead by David E. Smith of NASA's Goddard Space Flight Center, confirm that much of the Martian snow is in fact composed of carbon dioxide.
The study involved more than 400 million elevation measurements spanning more than one Martian year, from February 1999 through May of 2001.
The orbiting spacecraft bounced a beam of laser light to the surface and back, recording the round-trip time to determine elevations within 4 inches (10 centimeters). To determine snow density, this data was compared with measurements of tiny variations in the gravity field caused when there is more or less snow at given locations.
Smith and his colleagues also measured for the first time how the elevation of Mars' surface changes during the seasons, as ice builds up in winter and returns to the atmosphere in summer.
As expected, each polar ice cap is highest in the dead of its winter, when it is in total darkness. Also no surprise was the finding that the biggest changes in snow depth -- more than 6 feet (2 meters) occurred close to the poles.
But the overall bulk of snow accumulation seems to take place at in thinner but vast sheets at lower latitudes, the study found.
Strange snows
As with Earth, the
can be strange.Smith's study also found odd off-season snowfalls on Mars. Because carbon dioxide does not like to be a liquid, it freezes directly out of the atmosphere into surface dry ice. It's possible shadowed areas could accumulate this "snow" regardless of the season, said Maria T. Zuber, an MIT geophysicist who also worked on the study.
In one case, patches of snow disappeared during autumn in the northern hemisphere -- a time when cooler temperatures should have generated accumulations. A
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