From the shoreline of an ancient salty sea to the bottoms of deep, flood-carved channels, Mars is scarred with geological signs that indicate liquid water once flowed on the its surface. These findings, combined with the discovery of tiny, spherical "blueberries" and the detection of water ice in the planet's polar ice caps, have lead scientists to scour the planet for liquid water in recent years. The elusive quarry has remained hidden, possibly because it may not exist for more than a fleeting second. Due to Mars' low temperatures and extremely low atmospheric pressure – less than a hundredth that...