Ancient snowfall likely carved Martian valleys

Mars from the Odyssey spacecraft

Water-carved valleys on Mars appear to have been caused by runoff from precipitation, likely meltwater from snow. Early Martian precipitation would have fallen on mountainsides and crater rims. Credit: Images from NASA

Valley networks branching across the Martian surface leave little doubt that water once flowed on the Red Planet. But where that ancient water came from — whether it bubbled up from underground or fell as rain or snow — is still debated by scientists. A new study by researchers at Brown University puts a new check mark in the precipitation column.