![Gullies on the steep north wall of a Martian impact crater on the floor of Newton Crater, in a …[Credits : NASA/JPL/Malin Science Space Systems]](http://media-2.web.britannica.com/eb-media/66/73466-004-0E5A16B5.jpg)
Gullies on the steep north wall of a Martian impact crater on the floor of Newton Crater, in a high-resolution composite image obtained by Mars Global Surveyor in early 2000. The many narrow, fresh-appearing channels appear to have been cut by fluid flow in perhaps hundreds of separate events; the rocks and soil entrained in the flows were deposited in lobes and fingers at the base of the crater wall. Some scientists have interpreted the fluid to be subsurface water that seeped from below the top of the crater wall, although other fluids such as liquid carbon dioxide also have been proposed.
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