Grooves on Mars 'formed by dry ice surfing' The location of the linear gullies is on dunes that spend the Martian winter covered by carbon-dioxide frost, according to the study published in the journal Icarus. This frost can be several feet thick at the poles and as the Martian spring approaches and temperatures rise chunks break off, leaving trails as they slide down the dunes. The conditions in the experiments carried out on earth could not replicate those on Mars, but by using dry ice the team claim that their results support their hypothesis. "Linear gullies don't look like gullies on Earth or other gullies on Mars, and this process wouldn't happen on Earth," said Dr Diniega. You don't get blocks of dry ice on Earth unless you go buy them. Dr Candice Hansen, co-author of the study, added: ""MRO is showing that Mars is a very active planet. Some of the processes we see on Mars are like processes on Earth, but this one is in the category of uniquely Martian.