"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.