Grooves on sand dunes reveal 'sledding' on Mars

Images from NASA’s Mars Reconnaissance Orbiter (MRO) reveal grooves in Martian sand dunes, the remnants of giant pieces of frozen carbon dioxide sledding their way across the planet.

The frozen carbon dioxide, more commonly referred to as dry ice, appears to glide along the dunes on cushions of gas similar to a miniature hovercraft, plowing furrows as they go.

"I've always dreamed of going to Mars," said Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author of a report published online by the journal Icarus. "Now I dream of snowboarding down a Martian sand dune on a block of dry ice."

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Images from the MRO show grooves, called linear gullies, up to a few yards wide with raised levees along the sides which are covered by carbon dioxide frost during the planet’s winter season. The Martian gullies are unlike those on Earth that are formed due to waterfalls.

Diniega explains, "In debris flows, you have water carrying sediment downhill, and the material eroded from the top is carried to the bottom and deposited as a fan-shaped apron. In the linear gullies, you're not transporting material. You're carving out a groove, pushing material to the sides."

Bright objects have also been caught on camera in the gullies. Scientists believe these vivid objects may be pieces of the dry ice that have broken away on the slope. According to this new hypothesis, the pits could actually be the result of blocks of dry ice turning into pure carbon-dioxide after they stop traveling.

In order to further understand this strange phenomenon, researchers have been conducting similar experiments on sand dunes in Utah and California.

Report co-author Candice Hansen, of the Planetary Science Institute in Tucson, Ariz., went out and bought hunks of dry ice at a supermarket and slid them down sand dunes. "Linear gullies don't look like gullies on Earth or other gullies on Mars, and this process wouldn't happen on Earth," explained Diniega. "You don't get blocks of dry ice on Earth unless you go buy them."

Although not conducted under the same temperature and weather conditions as on Mars, Hansen’s experiments indicate that gaseous carbon dioxide from the thawing ice maintained a lubricating layer under the slab and also pushed sand aside into small levees as the slabs glided down even low-angle slopes.

"MRO is showing that Mars is a very active planet," Hansen said. "Some of the processes we see on Mars are like processes on Earth, but this one is in the category of uniquely Martian."