On Mars: lines that add to evidence of water
Water once flowed through underground cracks beneath the surface of Mars, according to research to be published today.
Spectacular high resolution images reveal lines running through dark and light layers in canyon walls consistent with the passage of a fluid thought to be water along fractures in bedrock.
The pictures add to evidence that early Mars had an active hydrological cycle of streams, lakes, precipitation and ground water flows, and a potentially life-sustaining climate similar to that of Earth.
A series of past and future missions to Mars have adopted a "follow the water" strategy because the presence of water is seen as an essential precursor of life.
Since September, Nasa's Mars Reconnaissance Orbiter has been taking images from its orbit 155 to 196 miles above the planet's surface that show surface features measuring one foot across — the best quality pictures taken of the Red Planet.
Those presented at the American Association for the Advancement of Science conference show sections of Candor Chasma, one of the larger canyons that make up Valles Marineris — a Martian rift valley six times deeper than the Grand Canyon.
The regions shown in the images would have been several miles underground millions of years ago — when, the researchers believe, water flowed through faults in the sedimentary bedrock.
Dr Chris Okubo, at the University of Arizona's Lunar and Planetary Laboratory, said light and dark rings in the images represent fine- and course-grained layers that have eroded at different rates. In close-up sections of the images, straight lines measuring from several hundred yards to several miles provide evidence of rock having been bleached and strengthened by chemical reactions with minerals carried by fluid running through cracks.
Dr Okubo, whose analysis of the images is published today in the journal Science, said: "On Earth, bleaching of rock surrounding a fracture is a clear indication of chemical interactions between fluids circulating within the fracture and the host rock. What we are seeing today are windows into areas that used to be several miles underground. These images show us there was fluid, probably water, flowing along these fractures. We are seeing similar fluid flow features elsewhere on Mars, so we can start to piece together the global distribution of these features. That will help to define interesting areas that we might want to send a future rover to investigate."
Alfred McEwen, a professor of planetary science at the University of Arizona, is the lead scientist on the HiRISE (the High Resolution Imaging Science Experiment), the camera that took the images.
Prof McEwen said they strongly suggest that fluid that once flowed in the underground fault was water, possibly liquid carbon dioxide or maybe a combination of both.
In December Nasa published images from Mars Global Surveyor suggesting that water may have flowed briefly in two Martian gullies within the past few years.
By Nic Fleming, Science Correspondent, in San Francisco
Last Updated: 2:04am GMT 16/02/2007
Telegraph, UK