M A I N   N E W S

Bedrock ‘Halos’
New evidence of water on Mars

Washington, February 16
An orbiting spacecraft has sent back new evidence for the presence of water on Mars. Scientists have long debated whether water flowed on the Red planet, with evidence increasing in recent years. The presence of water will raise the possibility of at least primitive life forms existing there.

Images from a camera aboard NASA's Mars Reconnaissance Orbiter show alternating layers of dark-and-light-toned rock in a giant rift valley.

Within those deposits are a series of linear fractures, called joints, that are surrounded by "halos" of light-toned bedrock, according to researchers from the University of Arizona.

Their findings, published in yesterday's edition of the journal Science, were presented at the annual meeting of the American Association for the Advancement of Science in San Francisco.

Lead author Chris H. Okubo said the "halos" indicate areas where fluids, probably water, passed through the bedrock. Minerals in the fluid strengthen and bleach the rock, he said, making it more resistant to erosion than other areas.

"On the Earth, bleaching of rock surrounding a fracture is a clear indication of chemical interactions between fluids circulating within the fracture and the host rock," Okubo and co-author Alfred S. McEwen reported in the paper.

They said that layered outcrops can indicate cycles with materials deposited by regular episodes of water, wind or volcanic activity. — AP