July 27, 2009
There is good circumstantial evidence that abundant underground ice and, possibly, liquid water exist on Mars.
These pictures introduce the basic features of a martian gully. The figure on the left is an example from Mars, the figure on the right is a gully on Earth. In the Earth picture, rain water flowing under and seeping along the base of a recently-deposited volcanic ash layer has created the gully. For Mars, water is not actually seen but is inferred from the landforms and their similarity to examples on Earth.
Photo by JPL/NASA/Malin Space Science Systems
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