Water on Mars

Exquisite colour images of the Martian surface give a tantalising glimpse into the Red Planet's watery past.

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."

The High Resolution Imaging Science Experiment (HiRise) camera started its surveys in November 2006, eight months after Mars Reconnaissance Orbiter (MRO) entered orbit around the Red Planet.

It is best known for capturing stunning images of Nasa's robot explorers Spirit and Opportunity as they surveyed the planet from the ground.