These blocks seem to have flowed down Martian sand dunes on cushions of carbon dioxide gas. Researchers liken these icy sleds to small hovercraft "ploughing furrows as they go". The findings, published in the journal Icarus, were discovered on images from Nasa's Mars Reconnaissance Orbiter. The grooves - or linear gullies, were on Martian sand dunes and varied in length from only a few hundred metres to 2.5km. They were found on dunes which are covered by frost during the Martian winter. Every winter Mars' southern polar region is blanketed by a layer of dry ice, up to one metre deep. In the springtime, this seasonal polar cap sublimes - turns directly from solid into gas. "Linear gullies don't look like gullies on Earth or other gullies on Mars, and this process wouldn't happen on Earth," said Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory and lead author of the paper. Read more http://www.bbc.co.uk/news/science-environment-22869184
