NASA released on Tuesday images taken by a Mars orbiter that reveal changes in the surface of Mars such as new gullies, impact craters and tracks of rolling boulders, suggesting a more active Red Planet than expected.

"To see new gullies and other changes in Mars surface features on a time span of a few years presents us with a more active, dynamic planet than many suspected before Mars Global Surveyor got there," said Michael Meyer, Mars Exploration Program chief scientist at NASA Headquarters, Washington.

NASA's Jet Propulsion Laboratory, which manages the orbiter project, said two gullies appear in an April 2005 image of a sand-dune slope where they did not exist in July 2002. The Mars Orbiter Camera also found tracks left by more than a dozen boulders when they rolled down a hill because of strong wind or a quake.

The discoveries also include new impact craters that formed since the 1970s, suggesting a slow forming process at a pace one-fifth of the previous estimate. Images also find that deposits of frozen carbon dioxide near Mars' south pole had been shrinking in a row of three Martian summers, suggesting a climate change in progress.

Mars Global Surveyor was launched in 1996 and began orbiting Mars in 1997. It is healthy and may be expected to work for five to 10 more years.

(Xinhua News Agency September 21, 2005)