If aliens existed on Mars 3.7 billion years ago, they would have needed umbrellas

A series of dried up river beds streak across the reddish surface of Mars as seen from low orbit.

Mars was a rainier, wetter place than planetary scientists previously thought, according to a new study of ancient, inverted river channels that span more than 9,000 miles (14,484 kilometers) in the Red Planet's southern Noachis Terra region.

"Our work is a new piece of evidence that suggests that Mars was once a much more complex and active planet than it is now, which is such an exciting thing to be involved in," study leader Adam Losekoot of the U.K.'s Open University said in a statement.