NASA's Mars rover Spirit was expected to roll off its lander early today, and if all goes well, scientists hoped to begin their search for evidence of water on Mars almost immediately.
In a series of experiments involving Spirit and three Mars-orbiting satellites, investigators hope to improve their understanding of the Martian atmosphere and the accuracy of their search for minerals on the surface that formed in the presence of water.
The idea for the unusual effort was born in a Paris cafe last summer, scientists said, and came together in recent weeks when it became clear that the satellites would fly over the rover's landing site.
"It's really an historic opportunity," said Ray Arvidson, a professor at Washington University in St. Louis and a member of the rover science team.
Spirit, after being repositioned yesterday, was poised at the top of its ramp, and mission controllers were expected to order it to roll off its ramp about 3 or 4 a.m. EST.
It's only about a 5-inch drop to the surface. "That's well within our capability," said engineer Kevin Burke. The rover has been tested and managed ramps up to 22 inches high.
Spirit's first job on the surface would be to stop three feet away, look backward and take pictures of the lander, which it is leaving forever. Then it was to deploy its little robot arm for some close-up looks at the soil with its microscopic imager.
When that's done, Spirit was expected to head for a closer look at a small meteorite crater about 250 yards away.
NASA engineers said yesterday that their spacecraft remained in good condition, and that it has already uploaded more than 3,900 photographs.
Scientists were also beginning their coordinated observations with Mars-orbiting satellites.
Shortly after the rover was to leave its lander, NASA's Mars Odyssey spacecraft was expected to fly almost directly over the Gusev Crater landing site, as it will do every 30 days.
Tomorrow, the European orbiter, Mars Express, is expected to make a similar pass 186 miles overhead. NASA's Mars Global Surveyor is also expected to participate in the studies.
With each pass, instruments on the orbiters will look down, while Spirit's instruments look up. Together, they can provide detail on the dust, carbon dioxide, water vapor and water ice content of both the upper and lower layers of the atmosphere.
Spectrometers on the orbiters will also take measurements that can reveal the distribution of mineral types on the surface, particularly those that may either contain water or that likely formed in the presence of water.
By accounting for the atmospheric water they are looking through, scientists will be able to more accurately interpret the orbital data they receive on the amount of water-bearing minerals on the ground. Mineral mapping from orbit will also help planners decide where to send the rover.