Ever since high-resolution images of Mars’ surface have become available, scientists have wondered about the cause of long gullies seen running down along the slopes of ridges and crater walls. Here on Earth such features are often created by water flowing downhill, carving channels as it goes — but on Earth similar features usually end in fans of deposited material, while on Mars the channels simply just… stop.
To search for an answer to this mystery, NASA researchers took a field trip to some southwestern sand dunes and saw what happened when they sent various materials sliding down the slopes. As it turns out, dry ice — that is, frozen carbon dioxide, which is plentiful on Mars — does a very nice impression of a sled, picking up considerable momentum on black diamond and bunny slopes alike. The reason? Sublimation creates a pocket of gas that the slab of solid CO2 sits on, cutting down friction and giving it a smooth air-ride downhill.
If these were larger blocks, one could easily imagine how they might create channels visible from orbit… and why the channels would simply peter out and stop at the end of their run once the ice loses forward momentum and eventually sublimates completely.
In fact, some HiRISE images have even shown bright objects inside the channels.
Check out the video above from NASA’s Jet Propulsion Laboratory… who knows, maybe future explorers will be shredding the Martian slopes with snowboards made of CO2!
UPDATE JULY 29, 2016: Researchers have announced that observed gullies on Mars are likely not formed by liquid water, based on spectrometer data acquired by NASA’s Mars Reconnaissance Orbiter, lending further credence to the carbon dioxide “sled” hypothesis. (This does not, however, counter the discovery of liquid water related to the development of recurring slope lineae, or RSLs.) Read more here.