for National Geographic News
Martian sand grains can make giant leaps compared to those on Earth, even though the red planet rarely experiences wind powerful enough to move them.
That's the key finding in a controversial new study led by Murilo Almeida, a physicist at Federal University of Ceara in Brazil.
The researchers found that a Martian dust storm only needs a short gust of wind to create a dramatic chain reaction. (Related: "Mars Warming Due to Dust Storms, Study Finds" [April 4, 2007].)
Even a small amount of sand can trigger a process called saltation, in which windblown dust grains crash into the surface in low ballistic trajectories and kick up other grains.
Almeida and his colleagues used computer simulations to mimic environmental conditions on Earth and Mars over a range of wind speeds. They found that sand grains on Mars can travel a hundred times higher and longer, and reach speeds five to ten times faster than sand on Earth.
"Because of the giant grain trajectories, sand on Mars can be effectively transported at surprisingly low wind velocities," said study co-author Jose Andrade, of the Federal University of Ceara and the Swiss Federal Institute of Technology in Zurich.
The results may help explain how dust storms can arise on a planet with virtually no atmosphere—and why scientists have recently observed sand dunes migrating on Mars without the lasting wind speeds previously believed to be necessary. (Related photo: windblown Mars dunes.)
The study appears in this week's issue of the Proceedings of the National Academy of Sciences.
Ever since Mariner 9 sent back the first images of Mars dunes in the 1970s, scientists have wondered whether the features could form under present-day conditions.
Confirmation came only recently, with noticeable changes on the surface of a few Martian dunes being reported in the past several years. (Related: "New Hi-Res Color Images of Mars Released" [October 11, 2007].)
Almeida and colleagues set out to explain the shifting Martian dunes by conducting simulations in a virtual wind tunnel. Their experiments compared sand saltation on Earth and Mars under environmental conditions on both planets over a range of wind speeds.
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