Megaripples Reveal Ancient Global Flooding on Mars

Mars from Hubble: Astronomers took advantage of a rare close approach by Mars in 2001. When the Red Planet was just 43 million miles away, Hubble snapped this picture with the WFPC2. It has a surface resolution of just 10 miles. This is the best image we’ve gotten of Mars that didn’t involve sending a robot there.

New findings from the Curiosity rover point to megafloods in the planet's past. NASA couldn't see the evidence of this event from space, but Curiosity was able to make the determination by scanning Martian geology from the surface.