Was Mars a friendly planet for water, even life, in its ancient past? Huge channel networks run across its surface. Rocks show signs of water immersion. Yet pictures sent back from NASA's Curiosity and Perseverance rover missions continue to show their tracks in the endless desert. Where did the water come from, how much of it was there, and why did it leave?
While the question of water is massively complex, a recent study in the Journal of Geophysical Research: Planets adds to the debate about how ancient water flowed – from the Red Planet's still icy poles, or in a water cycle that included precipitation, or in some combination.
