Washington – Newly released images from the Mars Global Surveyor offer the strongest evidence to date that water still flows on the Martian surface, and NASA's twin Mars rovers are nearing the third anniversary of their landings, operating nearly 12 times as long as their original missions of 90 Martian days (a Martian day is approximately 39.5 minutes longer than an Earth day).

The images, taken in 2004 and 2005, suggest water carried sediment through two gullies sometime during the past seven years. The images heightened intrigue about the potential for microbial life on Mars.

Elsewhere on the planet, NASA's long-lived robotic rover Opportunity achieved the long-held goal of reaching the massive Victoria Crater, with the rover beginning to explore layered rocks in cliffs ringing the crater. (See related article.)

While Opportunity spent its first week at the crater, NASA's newest eye in the Martian sky, the Mars Reconnaissance Orbiter, photographed the rover and its surroundings. The new level of detail in the images from the orbiter will help guide the rover's exploration of the area. (See related article.)

WATER ON MARS

Liquid water, as opposed to the water ice and water vapor known to exist on Mars, generally is considered necessary for life.

The atmosphere of Mars is so thin and the temperature so cold that liquid water at the surface would evaporate or freeze rapidly. Researchers propose that water could remain liquid long enough, after breaking out from an underground source, to carry debris downhill before freezing.

Mars Global Surveyor has discovered tens of thousands of gullies on slopes inside craters and other depressions on Mars. Dr. Michael Malin of Malin Space Science Systems in San Diego and his team of researchers first reported the discovery of the gullies in 2000, according to a December 6 announcement from NASA’s Jet Propulsion Laboratories (JPL).

That is the first evidence of newly deposited material apparently carried by fluids after earlier imaging of the same gullies. The two sites are inside craters in the Terra Sirenum and the Centauri Montes regions of southern Mars.

"These fresh deposits suggest that at some places and times on present-day Mars, liquid water is emerging from beneath the ground and briefly flowing down the slopes," Malin said. "This possibility raises questions about how the water would stay melted below ground, how widespread it might be and whether there's a below-ground wet habitat conducive to life. Future missions may provide the answers."

Mars Global Surveyor began orbiting Mars in 1997. The spacecraft is responsible for many important discoveries. NASA has not heard from the spacecraft since early November, but attempts to contact it continue.

THE OTHER MARS EXPLORERS

The Mars rovers, initially slated for three-month missions, continue to provide scientists with valuable data. Spirit, will begin its fourth year on Mars January 3, 2007; Opportunity on January 24, 2007. This unexpected longevity gives NASA a chance to field-test new capabilities useful to these and future rovers.

Along with their continuing scientific observations, the rovers are testing four new skills, instructions for which were included in revised flight software recently uploaded to their onboard computers. One capability lets spacecraft examine images and recognize certain kinds of features, like dust storms or clouds.

Another feature, "visual target tracking," allows a rover keep recognizing a designated landscape feature as the rover moves.

Visual target tracking can be combined with a third new feature - autonomy in calculating where it is safe to reach out with the contact tools on the rover's robotic arm. The combination gives Spirit and Opportunity a capability called "go and touch" that is yet to be tested on Mars.

So far in the mission, when a rover drives to a new location, the crew on Earth has to evaluate images of the location to decide where the rover could put out its contact instruments on a subsequent day. After the new software is tested and validated, the crew will have the option of letting a rover choose an arm target for itself the same day it drives to a new location.

The new software also improves the autonomy of each rover for navigating away from hazards by building better maps of their surroundings. This is the most comprehensive of four revisions to the rovers' flight software since launch.

"This new software will be a baseline for development of flight software for Mars Science Laboratory," said John Callas, JPL project manager for the Mars Exploration Rovers, "but it's also helpful in operating Spirit and Opportunity." NASA's Mars Science Laboratory is a next-generation Mars rover in development for planned launch in 2009.

Over nearly three years, Spirit has driven 6.9 kilometers and Opportunity has driven 9.8 kilometers. Spirit has returned more than 88,500 images, Opportunity more than 80,700.

Images and additional information about the Mars rovers are available at the NASA Web site.

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