While NASA's Mars rover Opportunity toils away inside a crater, its robotic twin Spirit has rolled over its first rock outcrop on the other side of the planet.
NASA scientists were elated at Spirit's rocky find, which came as the rover rolled backwards along the foot of a region called the West Spur at the Columbia Hills.
"This is what we came to the Columbia Hills for," said an excited Matt Golombek, a rover science team member, during a press briefing today at NASA's Jet Propulsion Laboratory (JPL). "We've been seeking it, and we've finally found it."
An initial look at the outcrops under Spirit's wheels appears to show rocks with layers of materials stacked on top of each other. But researchers aren't sure if the layers depict the slow depositing of sediment or volcanic rock over time, or if the effect is the result of wind erosion. They may be some of the oldest rocks seen during Spirit's mission, dating back three or four billion years.
"Until we get a fresh look at it, we won't know," Golombek said, adding that Spirit will take a circuitous route up to the top of West Spur where images show a hefty dollop of exposed rock. "Up the on the hill, the rock outcrop looks pretty massive."
Spirit months trekked across 2 miles (3.2 kilometers) from the rover's Gusev Crater landing site to reach the Columbia Hills, where mission scientists hoped to find clues into the region's geologic and, if possible, watery past.
Rover engineers also said Spirit's quirky wheel problems are steadily being addressed.
The rover's right front wheel has been drawing more current than the other five, a sign of wear now that Spirit has driven about six times the distance it was designed to handle.
Efforts to warm wheel and free up lubrication yielded a 25 percent increase in performance, not as much as expected but still a good sign. Engineers decided to not use the finicky wheel except when all six wheels are needed, such as driving up challenging, sandy slopes.
Meanwhile, rover drivers are steering the rover in reverse, which handlers said resembles driving with an anchor along the side.
"The rover was designed to drive in reverse just as well as it does forward," said Joe Melko, a rover engineer at JPL, of Spirit during the briefing. "It's still capable of doing everything we ask it to do."
The direction change has forced some of Spirit's handlers to refresh their standard vision of the rover's Martian position.
"As scientists, we're always referring to the front of the rover," Golombek said. "Well now the front is the back."
Opportunity looks deeper
At Meridiani Planum, Opportunity's science instruments have picked up small, teeth-like rock formations and a puzzling amount of chlorine inside Endurance Crater.
The small formations, which jut in a line called "Razorback," may have been formed by fluid - possibly water - that flowed into cracks and deposited material that has weathered the effects of erosion, said Jack Farmer, a rover science team member from Arizona State University.
Opportunity's robot arm-mounted alpha particle X-ray spectrometer has detected a growing concentration of chlorine in Martian rocks as the rover has delved deeper into Endurance. Chlorine levels at the rover's current position are three times higher than a region closer to the crater's lip, but researchers aren't sure why.
"We don’t understand which mineral is the carrier for this chlorine," explained Jutta Zipfel, a rover science team member from Germany's Max Planck Institute of Chemistry. "What we need to do is go further down [into Endurance] and look at more layers."
Winter weather expected
In the meantime, Mars researchers and engineers are working to prepare both Spirit and Opportunity for the Martian winter.
The worst conditions of the season will be Sept. 20, when the least amount of sunlight will strike the rover's solar panels. Mars is also approaching solar conjunction -when it will be on the other side of the Sun from Earth - forcing a 13-day communication blackout with the rovers around mid-September.
"Both of these vehicles are very healthy right now," said Jim Erickson, project manager for the rover mission at JPL. "During the winter, we will gradually adjust the amount of activity to what we're doing."
Spirit and Opportunity will most likely spend winter on Mars alternating between benign remote sensing studies, uploading data to spacecraft in Mars orbit and resting in "deep sleep" modes, he added.