Article Posted on : - Oct 30, 2010

The gullies on a Martian sand dune in this trio of images from NASA's Mars Reconnaissance Orbiter deceptively resemble features on Earth that are carved by streams of water. Photo by NASA/JPL-Caltech/University of Arizona

PASADENA, CALIFORNIA (BNS): Researchers have tracked changes in gullies on faces of sand dunes in seven locations on southern Mars, according to NASA.

The timing of new activity in one type of the enigmatic gullies on Mars implicates carbon-dioxide frost, rather than water, as the agent causing fresh flows of sand.

"Gullies that look like this on Earth are caused by flowing water, but Mars is a different planet with its own mysteries," said Serina Diniega, lead author of the study published in the journal Geology.

"The timing we see points to carbon dioxide, and if the mechanism is linked to carbon-dioxide frost at these dune gullies, the same could be true for other gullies on Mars, she said.

Scientists have suggested various explanations for modern gullies on Mars since fresh-looking gullies were discovered in images from NASA's Mars Global Surveyor in 2000.

The 18 dune gullies in which the researchers observed new activity range in size from about 50 meters or yards long to more than 3 kilometers (2 miles) long.

Because new flows in these gullies apparently occur in winter, rather than at a time when any frozen water might be most likely to melt, the new report calls for studies of how carbon dioxide, rather than water, could be involved in the flows.

Some carbon dioxide from the Martian atmosphere freezes on the ground during winter and sublimates back to gaseous form as spring approaches. The dunes studied are poleward of 40 degrees south latitude.

"One possibility is that a pile of carbon-dioxide frost accumulating on a dune gets thick enough to avalanche down and drag other material with it," Diniega said.

Other suggested mechanisms are that gas from sublimating frost could lubricate a flow of dry sand or erupt in puffs energetic enough to trigger slides.

The new report uses images from NASA's Mars Reconnaissance Orbiter Camera on Mars Global Surveyor and from the High Resolution Science Imaging Experiment (HiRISE) camera and Context Camera.