Melas Chasma, part of Valles Marineris, the “Grand Canyon of Mars.” The site tucks into a small basin below the south rim of Valles Marineris. Researchers say the basin, at center, likely contains deposits left when it was once filled with a lake. Even now, bottom sediments could preserve evidence of microbial activity, if it existed.

by Robert Burnham

Spirit and Opportunity are still making new discoveries. NASA's two Mars rovers have been working for more than 1,300 days on the planet’s surface. Their original missions were designed to last for 90 days.

Earlier this summer, Spirit was working in the geologically complex Columbia Hills within Gusev Crater. The rover found a deposit of virtually pure silica. Mini-TES (Miniature Thermal Emission Spectrometer) made the discovery. The instrument was designed by Philip Christensen of ASU's School of Earth and Space Exploration.

On Earth, silica typically forms in hot springs and volcanic environments. It can be found in the geyser pools in Yellowstone National Park. The material commonly preserves traces of microbial life. No one knows if Mars ever had life—and neither rover is equipped to detect it anyway—but the silica discovery is intriguing and suggestive.

NASA is now planning where to send its next-generation rover. The Mars Science Laboratory is due for launch in 2009. In October 2007, scientists, including those at ASU's Mars Space Flight Facility, winnowed a big list of possible landing sites down to a handful.

One of the higher-ranked sites lies in western Melas Chasma, part of Valles Marineris, the “Grand Canyon of Mars.” The site tucks into a small basin below the south rim of Valles Marineris.

Researchers say the basin—seen dead center in the big image above—likely contains deposits left when it was once filled with a lake. Even long after the water dried up, bottom sediments could preserve evidence of microbial activity, if it existed.

The image is a false-color mosaic of daytime and nighttime photos. It was taken by ASU's Thermal Emission Imaging System (THEMIS), a multi-wavelength camera on NASA's Mars Odyssey orbiter. THEMIS circles Mars every two hours. It scans the Martian surface in five visible colors and 10 infrared colors.

The false colors hint at the nature of the ground surface. Rusty tones show where rocks and hard deposits abound. Greens and blues indicate areas where gravel, fine sand, and dust particles predominate.