A system of gigantic ancient valleys — some as much as 125 miles (200 kilometers) wide — has been spotted partly buried under eons of volcanic lava, ash and wind-blown dust on Mars. Observations made using a laser altimeter on the Mars Global Surveyor spacecraft reveal what may be large flood channels near a volcano called Arsia Mons. The features are in Mars’ western hemisphere, south of Amazonis Planitia, an area thought to have once been a vast ocean. The study adds to plenty of evidence collected in recent years, most of it by the Mars Global Surveyor, that the Red Planet was once warm and wet.
