关于这张图
This image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter shows gullies near the edge of Hale crater on southern Mars. The view covers an area about 1 kilometer (0.6 mile) across and was taken on Aug. 3, 2009. Martian gullies carved into hill slopes and the walls of impact craters were discovered several years ago. Scientists are excited to study these features because, on Earth, they usually form through the action of liquid water -- long thought to be absent on the Martian surface. Whether liquid water carves gullies under today's c…
