Water on Mars. Life on Mars. Wow.

Human beings reached a milestone in our understanding of the universe today, thanks in part to a hard-working robot. The NASA Mars rover Opportunity found evidence that an abundance of water once covered an area of the planet's surface. Where there was once water, it is presumed that there was once life — and that living things may in fact still exist on the red planet.

[A] rock outcrop at the site, a shallow impact crater in Meridiani Planum, was once "drenched" in water, Ed Weiler, the National Aeronautics and Space Administration's deputy associate administrator for space science, said at the agency's headquarters in Washington. "The rocks here were once soaked in liquid water," Steve Squyres, the mission's principal scientist, said in elaborating on the discovery. The concentration of salts in the rock suggests the formation may have emerged in a briny sea, he said.