Vast Ocean Once Covered Half of Mars

A single huge ocean fed by rivers once covered much of the northern half of Mars, according to a new analysis of the planet's network of valleys. The researchers say their computer analysis—which replaces maps hand-drawn from satellite images in the '90s—shows that Mars was once much rainier and more humid than initially believed, making the existence of life much likelier.

"All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars," the lead researcher tells the Telegraph. "It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet's surface." (More Mars stories.)