In some of the coldest regions on Mars, water appears to have recently gushed from just beneath the surface, running down crater walls and steep valleys. Those startling findings, based on an analysis of images taken by a high-resolution camera aboard NASA’s Mars Global Surveyor spacecraft, could radically revise the way scientists think about Mars and profoundly affect where and how they will search for life on the Red Planet.

Icy rivers thunder through steep canyons. Floodwaters spill out of lakebeds. Rushing streams drag house-size boulders and carve long, sinuous channels. To these images of what Mars may have looked like some 2 billion years ago, when it was warmer and wetter than today, scientists can now add a seascape.