Light-toned layered rock in Mars' Becquerel Crater. Layers show cyclic changes in thickness. The areas coloured blue are sand dunes. (Image: Science)
Shots of the deep valley Candor Chasma show light coloured areas of rock where water could have flowed.
These "haloes" surround fractures in the Martian bedrock which provide a promising target in the search for evidence of past life on the planet.
The images, published in Science journal, were taken by a camera aboard Nasa's Mars Reconnaissance Orbiter.
"It lends support to the idea that a substantial body of groundwater existed on Mars in the past and may still persist to the present day," said Professor Stephen Clifford of the Lunar and Planetary Institute in Houston, Texas.
"The fact that there is such persuasive evidence of joints and fractures in the crust also suggests that this groundwater had the ability to flow enormous distances."
