This time, it comes from the side effect of the Mars Rover getting the Martian equivalent of a flat tire...
NASA's Spirit Mars rover has been dealing with [a] right front tire [that] went bad nearly two years ago. It didn't go flat, but it's quit turning forcing NASA to move the rover around in reverse ever since, trailing the stuck wheel behind.
But nearly a year later, [it was noticed that [r]uts carved by the bad wheel last May churned up a bright spot in the rover's wake.
Rover guiders turned the craft back to the colorful streak for a closer look and discovered that the rock contains high levels of silica. Upon further investigation, however, another nearby rock cracked open that was jam-packed with silica.
Silica at this level of density, on Earth, tends to be associated with water, in one of a few differnt ways. Read all about it here, on The Buzz