Martian gullies may have been carved by dry ice

BBC : From images captured by NASA’s Mars Reconnaissance Orbiter, researchers have observed long, closely packed grooves on Mars’s surface. Unlike anything seen on Earth, the linear gullies were probably formed by the movement of dry ice rather than by liquid water flow, according to Serina Diniega, a planetary scientist at NASA’s Jet Propulsion Laboratory and lead author of a paper published in the journal Icarus. Diniega and her colleagues base their theory on evidence of pits at the bottom of the gullies. In debris flows, water carries sediment downhill and deposits it in a fan shape; in linear gullies, material is not transported but pushed to the sides. To test their theory, the researchers slid blocks of dry ice down sand dunes in the western US. Despite differences in temperature and pressure from those on Mars, they found that as the melting blocks of ice slid down the dunes, they divided the sand into sections, similar to the features seen on Mars.