Ancient Mars may have resembled Antarctica (but without penguins). The frozen Red Planet probably had liquid water on its surface for only relatively short times, according to a new analysis of craters on the surface. The finding that the Martian atmosphere was not dense enough to keep flowing water for more than a few hundred thousand years at a time adds to a growing pile of evidence that Mars probably remained cold and dry throughout most of its history, punctuated by brief periods of relative warmth.
Mars today has a very tenuous atmosphere, not nearly dense enough to keep water from instantly boiling away. But deep canyons and ancient river deposits point to a time when water flowed across the Red Planet. Researchers, however, disagree on whether those features indicate long-lasting temperate climates or brief bursts of warming interspersed throughout a long, dry winter.