Evidence for Mars floods all dried up?
来源：未知 作者：仪轳 时间：2019-02-27 14:06:05
By David Shiga (Image: ESA/DLR/FU Berlin/G Neukum) Lava, not water, may have carved the biggest channels on Mars. Ever since NASA’s Mariner 9 spacecraft beamed back the first images of the channels in the 1970s, most people have assumed they were created by massive floods. But David Leverington of Texas Tech University in Lubbock says flowing water would have left behind much more sediment than is seen. There are also few minerals that form in liquid water present. Lava, however, is known to have carved big channels on the moon. And Leverington points out that some of the channels on Mars start on the flanks of volcanoes and end in large deposits of solidified lava (Geomorphology, DOI: 10.1016/j.geomorph.2011.05.022). Kelin Whipple of Arizona State University (ASU) in Tempe agrees that lava probably carved the huge channels, such as Kasei Valles (shown). He says the study calls into question the case for huge volumes of water – and possibly an ocean – on ancient Mars. But Phil Christensen, also at ASU, says clays and fans of sediment still point to the existence of smaller Martian lakes and rivers. These would be better places to search for life, he says, because they would have held water for longer periods than the giant channels, where floods – if there ever were any – would have been fleeting. “Lakes and deltas are probably the places people are going to look for life,” he says. More on these topics: