NASA today announced the discovery of what appear to be signs of water recently flowing on the surface of Mars. In new photos of large Martian gullies taken by the Mars Global Surveyor not long before it expired, scientists noticed several instances of light-colored streaks that had not appeared in past photos of the same regions taken as recently as 2001. The light coloring is especially exciting considering that meteor impacts and Mars rovers tend to leave dark trails in the soil.

"We have revealed this canyon like no one before us." So proclaims Olivier de Goursac, a French spatial imaging specialist who, along with colleague Adrian Lark, produced the spectacular image (left) of Mars' Valles Marineris, or Mariner Valley. Named for the Mariner 9 satellite that first revealed it some three decades ago, the chasm is often called the Martian Grand Canyon, though at 2,500 miles long, it is actually five times longer (about the span of the continental United States) and as much as four times deeper than Earth's.