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  sci-tech > space > story pagecorner  

Mars a dynamic world of shifting sands

 Martian storm
The four images above show the evolution of a storm system that developed over the martian north polar region on June 30, 1999. Each picture was taken approximately 2 hours later than the previous.  

August 10, 1999
Web posted at: 7:46 p.m. EDT (2346 GMT)

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) -- Mars is covered with Earth-sized sand dunes that remain active to this day, scientists said Tuesday. The dunes resemble those in California's Mojave Desert and could be dusted with snow.

Images taken in the past year by NASA's Mars Global Surveyor orbiter show the red planet's surface as a dynamic, still-evolving topography with dark sand streaming in the past month over new white frost in the planet's northern polar regions.

"This is proof positive that in fact the sand is moving at present," said Peter Thomas, a Cornell University researcher with the orbiter's camera team.

Although previous missions revealed large dunes on Mars, the newly discovered dunes in the south that form as a result of wind and frost are the same size as those geologists study on Earth, said Jim Zimbelman, a planetary geologist with the Smithsonian Institution.

Frost that clings to shifting dunes at the planet's poles may fall as snow to the ground, said Michael Malin of Malin Space Science Systems, which oversees the orbiter's camera.

"We don't know whether (the frost) forms on the ground, and grows up out of the ground, or falls out of the atmosphere as snow," he said.

The leading theory is that the polar frost is made of frozen water and frozen carbon dioxide that accretes around dust particles, which may snow down or evaporate off dunes at different times, he said.

Malin and his colleagues made their comments at a briefing at NASA headquarters in Washington, D.C.

The $150 million Mars Global Surveyor mission was launched in 1996 and arrived at Mars the following year. It has orbited the red planet for a full martian year, or 26 months. It started collecting extensive data earlier this year.

Sand poking through south pole ice

With spring arriving at the planet's south pole, the ice cap there is defrosting in a strangely uniform way, Malin said.

Swiss-cheese holes are opening up at the tips of the dunes beneath the ice cap. The exposed sand then is whipped up by strong gusts of wind and dropped on the frost. The sand then heats up more than the white ice, absorbing more sunlight than the lighter frost around it and further melting and darkening the sandy spots.

"Over the course of the season we'll see these spots merge and all of the frost will dissipate," Malin said.

Thomas said the Surveyor data shows a planet shaped by ancient and contemporary wind, dust and water forces -- a fact that scientists hadn't fully grasped before.

"It really for me has become a full-fledged respectable planet for the variety of features all over the planet," he said.

Three missions to be at Mars by year's end

frosty dunes
Dark features are found in pictures taken of sand dunes in the polar regions as they are beginning to defrost after a long, cold winter  

The Surveyor data will be used to help engineers select a landing site for the Mars Polar Lander, set to land on the red planet on December 3. Mission planners will announce the site on August 25.

Mars Climate Orbiter, its partner mission, is set to arrive at Mars on September 23.

"By the end of this year, we're going to have three Mars missions active all at the same time," Malin said. "That should give us a very good picture of what's going on today."

There still are many structures on Mars that scientists cannot explain, Malin said. For example, how thick is the polar frost -- a few centimeters (an inch or so) or up to tens of centimeters thick (up to a yard)?

The Surveyor images reveal nothing new about the prospects for past life on Mars, Malin said.

"Mars was very cold and dry," Malin said. "All the features we are seeing reinforce that view, that's it's cold and dry today."



RELATED STORIES:
Martian spring reveals frozen water at south pole
August 3, 1999
Scientists debate implications of Mars pictures
July 20, 1999
Mars photos: The devil is in the details
July 5, 1999

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