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 would 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.