Did water carve canyon on Mars?

This view of the Nanedi Vallis canyon on Mars offers what may be the best evidence yet that water once flowed on the Red Planet. Taken Jan. 8 by the Mars Global Surveyor spacecraft, the image is the first to show a channel (arrow) at the bottom of the canyon.

The dried-up, 200-meter-wide channel suggests that a continual flow of water helped carve Nanedi Vallis, says Michael C. Malin of the Surveyor camera team and Malin Space Science Systems in San Diego. In contrast to the rounded boulders near the Mars Pathfinder landing site, which suggest that a catastrophic flood coursed through that area, the channel points to a steady stream of water that may have lasted millions of years.

"A lot of people have been talking about water on Mars, but this is getting down to the next level of detail," says Malin. Both water and volcanic activity may be responsible for sculpting the canyon, he adds. Vice President Al Gore unveiled the image Feb. 2 at a federal budget briefing.