(Xinhua)
Updated: 2008-03-04 06:56

WASHINGTON, March 3 -- A NASA spacecraft in orbit around Mars has taken the first ever image of active avalanches near Mars' north pole, the space agency of the United States announced on Monday.

This handout shows a false color image, capturing a Martian avalanche or debris fall, in action on Mars North Polar region, which was taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter February 19, 2008 and released by NASA March 3, 2008. [Agencies]

The image posted on NASA's official website shows tan clouds billowing away from the foot of a towering slope, where ice and dust have just cascaded down.

The High Resolution Imaging Experiment (HiRISE) camera on NASA' s Mars Reconnaissance Orbiter took the photograph February 19. It is one of approximately 2,400 HiRISE images being released on Monday.

Ingrid Daubar Spitale of the University of Arizona, who works on targeting the camera and has studied hundreds of HiRISE images, was the first person to notice the avalanches. "It really surprised me," she said. "It's great to see something so dynamic on Mars. A lot of what we see there hasn't changed for millions of years."

The camera is looking repeatedly at selected places on Mars to track seasonal changes. However, the main target of the February 19 image was not the steep slope.

"We were checking for springtime changes in the carbon-dioxide frost covering a dune field, and finding the avalanches was completely serendipitous," said Candice Hansen, deputy principal investigator for HiRISE, at NASA's Jet Propulsion Laboratory.

The full image reveals features as small as a desk in a strip of terrain 3.7 miles (about 6 km) wide and more than 10 times that long, at 84 degrees north latitude. Reddish layers known to be rich in water ice make up the face of a steep slope more than 2, 300 feet (700 meters) tall, running the length of the image.

"We don't know what set off these landslides," said Patrick Russell of the University of Berne, Switzerland, a HiRISE team collaborator. "We plan to take more images of the site through the changing Martian seasons to see if this kind of avalanche happens all year or is restricted to early spring."

More ice than dust probably makes up the material that fell from the upper portion of the scarp. Imaging of the site during coming months will track any changes in the new deposit at the base of the slope. That will help researchers estimate what proportion is ice.

Mars Reconnaissance Orbiter reached Mars in March 2006 and has returned more data than all other current and past missions to Mars combined, according to NASA.