A high resolution camera mounted on a spaceship orbiting Mars has found evidence that water once ran under the planet's surface. The geological features could be probed for fossil evidence for past life or used to point to other regions of the planet where running water - and maybe life - can be found today.
The pictures were taken by Nasa's Mars Reconnaissance Orbiter which was launched in August 2005 and began sending data back from the planet in November last year. They show discoloured rocky ridges in the Candor Chasma, part of a massive canyoned region at the equator called the Valles Marineris, the largest geological rift in the solar system. The ridges are evidence of chemical changes caused by a fluid (almost certainly water) as it flowed down a fissure in the rock.
The changes cemented the rock together making it stronger, so erosion left strengthened ridges. Chris Okubo, a geologist at the University of Arizona's Lunar and Planetary Laboratory, studies similar geological evidence for ancient flowing water on Earth. "When I started to look at some of the HiRISE images of Mars we started to see the exact same features along the fractures. HiRISE [the High Resolution Science Experiment] is a camera on the orbiter with a resolution of about 30cm (12in).
"It is hard to say how long ago the fluids were there - hundreds of millions or perhaps a billion years ago," said Dr Okubo. "But the fact that we see evidence for chemical reactions between the fluids and the rock means that the fluids were sitting there for quite a long time ... that's perhaps good if you want to look for any habitable areas that might support any biological activity." He presented his data, which also appears in the journal Science, at the American Association for the Advancement of Science's annual meeting in San Francisco yesterday.
He suggested that the regions of altered rock would be a good place to look for fossilised simple organisms and that landers might find water flowing underground. In December Nasa scientists, using images from another orbiter, Mars Global Surveyor, found evidence for water flowing fleetingly on the surface in the last five years. They compared images of the side of a crater taken in 2001 and 2005. The second showed gullies apparently caused by water bursting out of the crater wall.
"The Nasa campaign since 1997 has been 'follow the water'," said Colin Pillinger at the Open University, who led the ill-fated Beagle II mission to land on Mars in 2003. Experiments to look for life should be performed where water is thought to be or to have been. "That's what Beagle II attempted to do and that would be my strategy if I was doing it again." Examining water-changed rocks would be an obvious place to look for evidence of past life on Mars, he added.
"On Earth sedimentary rocks are where you look for the relict of organic matter ... this is the logical progression of the search for life on Mars."
The location of the ridges could be difficult for a spacecraft to land in. The canyoned Valles Marineris is 4,500km long, 200km wide and up to 8km deep.
Tectonic fractures within the Candor Chasma region of Valles Marineris, Mars, retain ridge-like shapes as the surrounding bedrock erodes away. This points to past episodes of fluid alteration along the fractures and reveals clues into past fluid flow and geochemical conditions below the surface. NASA's Mars Reconnaissance Orbiter has discovered more evidence on the Planet Mars that water may have flowed beneath the surface and that "cracks" that lead below the surface may have, at one time, been "habitable" for "microbial life," according to the head investigater for the orbiter's camera, Dr. Alfred McEwen. The location of the find is near the Candor Chasma canyon and images of the cracks were taken in September of 2006.

"This result shows how orbital observations can identify features of particular interest for future exploration on the surface or in the subsurface or by sample return. The alteration along fractures, concentrated by the underground fluids, marks locations where we can expect to find key information about chemical and perhaps biologic processes in a subsurface environment that may have been habitable," said McEwen.

According to NASA scientists, "mineralization" was found on the surface of the cracks and the crack's fractures. Scientists say the minerals became visible after layers of sand and dirt eroded away from the cracks. The minerals were likely placed on the rocks after dissolving in water and then evaporating onto the rocks, causing the minerals to become rock. Another possibility on how the minerals were placed there is that the "fluid" circulating on the rock was a gas, which might or might not have contained water.

"What caught my eye was the bleaching or lack of dark material along the fracture. That is a sign of mineral alteration by fluids that moved through those joints. It reminded me of something I had seen during field studies in Utah, that is light-tone zones, or 'haloes,' on either side of cracks through darker sandstone," said University of Arizona, Tucson geologist, Dr. Chris Okubo.

"The haloes visible along fractures seen in the Candor Chasma image appear to be slightly raised relative to surrounding, darker rock. This is evidence that the circulating fluids hardened the lining of the fractures, as well as bleaching it. The harder material would not erode away as quickly as softer material farther from the fractures," said a statement on NASA's website.

It is not clear how long the minerals might have been present or how long it took them to get on the rocks.

"It is hard to say how long ago the fluids were there - hundreds of millions or perhaps a billion years ago. But the fact that we see evidence for chemical reactions between the fluids and the rock means that the fluids were sitting there for quite a long time ... that's perhaps good if you want to look for any habitable areas that might support any biological activity," added Okubo.

"This publication is just the first of many, many to come. The analysis is based on test observations taken even before the start of our main science phase. Since then, Mars Reconnaissance Orbiter has returned several terabits of science data, sustaining a pace greater than any other deep space mission. This flood of data will require years of study to exploit their full value, forever increasing our understanding of Mars and its history of climate change," added Okubo.