One of the largest of the recently carved channel systems on Mars, once sculpted by massive floods but now smothered under ancient lavas, is more than twice as deep as previously thought. Using radar data gathered by the Mars Reconnaissance Orbiter, researchers were able to see several dozens of meters below ground level in an area (dotted box, above) including the presumed source of Marte Vallis, a chaotic system of channels (depicted in white) created less than 500 million years ago—a geologically recent era in the Red Planet's history. Previous studies, which considered only the exposed portions of Marte Vallis, suggested that the deepest valleys hidden by lavas that erupted about 10 million years ago were only around 40 meters deep. The new findings reveal that the deepest channels in the 1000-kilometer-long, 100-km-wide system are more than twice that depth, the researchers report online today in Science. Radar data also reveal that the upstream portions of the channels lie near a lengthy system of fissures called Cerberus Fossae, the presumed source of the massive outflow of ground water thought to have carved Marte Vallis. Scientists aren't clear about the total volume of water that flowed from the fissures or the duration of those ancient floods, but the team notes that the depth of the channels in Marte Vallis rivals those sculpted by Earth's largest known megaflood—the so-called Missoula floods that carved the Channeled Scablands of Washington state near the end of the last ice age.'