A powerful camera on NASA's Mars Reconnaissance Orbiter (MRO) may have solved one of the mysteries of the Martian surface. Scientists now speculate that chunks of dry ice -- frozen carbon dioxide -- may glide down the Red Planet's famous dunes, leaving behind deep furrows on the surface. These "linear gullies" were captured by the MRO's High Resolution Imaging Science Experiment (HiRISE) camera. NASA's theory is that the dry ice rides down the dunes on cushions of gas, essentially mimicking a miniature hovercraft:
The hillside grooves on Mars show relatively constant width -- up to a few yards, or meters, across -- with raised banks or levees along the sides. Unlike gullies caused by water flows on Earth and possibly on Mars, they do not have aprons of debris at the downhill end of the gully. Instead, many have pits at the downhill end."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," said Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory and lead author of a report published online by the journal Icarus. "In the linear gullies, you're not transporting material. You're carving out a groove, pushing material to the sides."
Report co-author Candice Hansen, of the Planetary Science Institute in Tucson, Ariz., purchased some dry ice from a supermarket and slid them down sand dunes in California and Utah. According to NASA, "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." There are some great images of the linear gullies here. Now read this: