Dry-Ice Sled Tracks Identified on Mars [VIDEO]

NASA researchers identified what appear to be hunks of frozen carbon dioxide, also known as dry ice, gliding down Martian sand dunes on cushions of gas similar to miniature hovercraft, leaving furrows as they go.

The phenomenon may explain one enigmatic class of gullies seen on Martian sand dunes, the scientists deduced by examining images from NASA’s Mars Reconnaissance Orbiter (MRO) and by performing experiments on sand dunes in Utah and California.

Serina Diniega is a planetary scientist at NASA’s Jet Propulsion Laboratory and the lead author of the study published in the journal Icarus.

“I have always dreamed of going to Mars,” she said in a press release. “Now I dream of snowboarding down a Martian sand dune on a block of dry ice.”

The hillside grooves, called linear gullies, show a relatively constant width of a few yards, or meters, with raised banks or levees along the sides. Unlike gullies caused by water flows on Earth, and possible Mars as well, they do not have aprons of debris at the base but rather tend to feature pits.

“In debris flow, 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,” Diniega said. “In the linear gullies, you’re not transporting material. You’re carving out a groove, pushing material to the sides.”

Images from MRO’s High Resolution Imaging Science Experiment (HiRISE) camera portray sand dunes with linear gullies covered by carbon-dioxide frost during the Martian winter in a location that spends the season covered in it. By comparing before-and-after images from different seasons, researchers determined that the grooves are formed during early spring, with some images even catching bright objects in the gullies scientists theorize are pieces of dry ice that broke off from higher points on the slope.

Based on this new hypothesis, the pits should result from blocks of dry ice completely sublimating away into carbon-dioxide gas after they come to a stop.

“Linear gullies don’t look like gullies on Earth and other gullies on Mars, and the process wouldn’t happen on Earth,” Diniega explained. “You don’t get blocks of dry ice on Earth unless you go buy them.”

Co-author Candice Hansen of the Planetary science Institute in Tucson, Ariz. did just that and slid them down a dune in an effort to test her theory that Mars’ gullies were formed by similar a process.

As she did this, she observed how gaseous carbon dioxide from the thawing ice maintained a lubricating layer under the slab and pushed sand aside into small levees as it glided down even at low-angle slopes.

While the tests did not simulate Martian temperature and pressure, calculations indicate the dry ice would act similarly in early Martian spring where the gullies form.

Furthermore, while water ice is also capable of sublimating directly to gas under some Martian conditions, it would stay frozen at the temperatures at which these gullies form, the scientists determined.

“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.”

Hansen further noted that the process could be unique to the linear gullies seen on Martian sand dunes.

“There are a variety of different types of features on Mars that sometimes get lumped together as ‘gullies,’ but they are formed by different processes,” she said. “Just because this dry-ice hypothesis looks like a good explanation for one type doesn’t mean it applies to others.”