Mysterious gullies seen on Martian sand dunes have been recreated in the desert by NASA researchers, and they found that chunks of frozen carbon dioxide -- dry ice -- may glide down the dunes on cushions of gas similar to miniature hovercraft.
"I have always dreamed of going to Mars," said Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory, 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."
Earlier this year, NASA's Mars Reconnaissance Orbiter (MRO), spotted the linear gullies on dunes that spend the Martian winter covered by carbon-dioxide frost. There were consistently up to a few meters wide with raised banks, or levees on either side.
By comparing before-and-after images from different seasons, researchers determined that the grooves are formed during early spring.
Unlike gullies caused by water flows on Earth and possibly Mars, they do not have aprons of debris and sediment at the downhill end, instead showing pits. "In the linear gullies, you're not transporting material. You're carving out a groove, pushing material to the sides," said Diniega.
Scientists theorize the blocks of dry ice that break away from the top of the slope and travel down the hillside leave a pit behind when they return to a gaseous state.
Researchers conducted experiments on sand dunes in Utah and California to recreate the gullies. Study co-author Candice Hansen, of the Planetary Science Institute in Tucson, Arizona bought several slabs of dry ice at the supermarket and slid them down the dunes.
Though the experiment did not simulate Martian pressure or temperature, they were able to form even, linear grooves similar to the Martian gullies.
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.