What's carving active gullies on Mars? It's not water

Scientists were shocked when they received the first images of Martian gullies, which appeared to change over time. The gullies are similar to those on Earth but cannot be explained by water runoff, as Mars lacks liquid water. A new paper suggests the gullies are caused by CO2 frost turning into a fluid. The authors used data from Mars Express and Mars Reconnaissance Orbiter to prove this, focusing on the Sisyphi Cavi region. The gullies are not formed by geysers, as the timing does not match. The third theory, the Air Hockey Effect, suggests that CO2 frost fluidization causes the gullies without liquid water. The findings challenge the idea that Earth-like features require Earth-like physics. The study shows that the gullies are formed through a freeze-thaw cycle, not water. The paper concludes that the gullies are carved by the movement of CO2 ice, proving that liquid water is not necessary. The discovery highlights how planetary processes can create Earth-like features without liquid water.

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