New images show Martian dust devils

LOS ANGELES (AP) - Swirling dust devils were caught in the act of changing the surface of Mars by NASA's Mars Global Surveyor, scientists said Monday.

Dark streaks and lines on the planet's surface had been puzzling researchers since the spacecraft started orbiting the Red Planet in 1997. Then, in December, the probe finally snapped a picture of the culprit - a dust devil.

''We've captured them in the midst of sweeping up dust and leaving behind a dark streak,'' said Ken Edgett, a staff scientist at Malin Space Science Systems. ''This is the smoking gun that explains the wild ... dark streaks and trails we have been seeing.''

Dust devils, which look like small tornadoes and are common in desert areas, are caused on Earth and Mars by the spinning motion of rising air as it is heated. The spinning column then picks up dust as moves across the landscape.

The phenomena only last a few minutes on Earth, and that's probably the case on Mars as well, Edgett said.

Scientists believe the miniature tornadoes are removing some of the bright dust on the planet's surface, causing the dark streak to appear. In recent weeks, Global Surveyor has caught as many as five to 10 at a time on the arid planet.

Malin Space Science Systems operates the spacecraft's camera.

The dust devil report is the latest finding from Global Surveyor, which is the only spacecraft operating from the Red Planet after last year's loss of NASA's Mars Climate Orbiter and Mars Polar Lander.

Other findings in recent days include:

- A better of idea of what lurks beneath the surface. In last week's issue of the journal Science, researchers using elevation and gravity measurements found evidence of a rapid cooling period early in the planet's history as well large buried channels where water once might have flowed.

- Major differences in the planet's ice caps. High resolution images show the northern cap looks like cottage cheese, while the southern cap resembles Swiss cheese, according to research published in the journal Nature.

''The unusual shapes of the landforms on the north and south polar caps suggest that these regions have had different climates and histories for thousands or perhaps millions of years,'' said Peter Thomas of Cornell University.

Global Surveyor is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif.

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On the Net: Jet Propulsion Laboratory, http://www.jpl.nasa.gov

JPL's collection of spacecraft images: http://photojournal.jpl.nasa.gov/new

Malin Space Science Systems: http://www.msss.com