Signs of ancient stream discovered on Mars by Curiosity

The NASA rover Curiosity has beamed back pictures of bedrock that suggest a fast-moving stream, possibly waist-deep, once flowed on Mars -- a find that the mission's chief scientist called exciting.

There have been previous signs that water existed on the red planet long ago, but the images showing pebbles rounded off, probably by water, offered the most convincing evidence so far of an ancient stream-bed.