Water on Mars
These high-resolution images taken by a camera on the Mars Global Surveyor hint at the presence of sub-surface water on Mars. (a) Extensively layered deposits in the Arabia Terra region; the smallest resolved layers are about 50 m thick in this view.
(b) Gullies emanating from the inner wall of a small southern-hemisphere crater. The smallest features visible in this image are only 5-10 m across.
(Picture credit:NASA)