Images from NASA’s Mars Reconnaissance Orbiter have revealed that mysterious gullies are forming on Mars as a result of frozen carbon dioxide that’s piling up on Martian dunes.

The piles may trigger avalanches that carve out the mysterious gullies.

"Gullies that look like this on Earth are caused by flowing water, but Mars is a different planet with its own mysteries,” said lead author Serina Diniega.

"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,” Diniega said.

Some fresh gullies are on sand dunes, commonly starting at a crest.

Others are on rockier slopes, such as the inner walls of craters and sometimes starting partway down the slope.

"The alcove is a cutout at the top. Material being removed from there ends up in a fan-shaped apron below,” Diniega said. Because new flows in these gullies apparently occur in winter, the new report calls for studies of how carbon dioxide, rather than water, could be involved in the flows.

"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 Mars Reconnaissance Orbiter is enabling valuable studies of seasonal changes in surface features on Mars,” said Sue Smrekar of orbiter.