Billions of years ago, it rained on Mars. The water collected in valleys and rivers, filled and spilled over the rims of craters, and was funneled into canyons, perhaps even making its way to a large ...

Long before Mars turned into the frozen desert you see today, water shaped its surface in dramatic ways. Rivers cut through highlands, lakes pooled inside craters, and floods tore open canyon walls.

For the first time, scientists have mapped vast, continent-scale river drainage systems on Mars — ancient networks that may also be among the most promising places to search for signs of past life.

Billions of years ago, it rained on Mars. The water collected in valleys and rivers, filled and spilled over the rims of craters, and was funneled into canyons, perhaps even making its way to a large ...

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