Only two days away from the end of its primary mission, NASA's Mars rover Spirit has found more evidence that water once affected rocks strewn across its Gusev Crater landing site.
Spirit's studies of a target called Mazatzal found it covered with multiple coats of dust and flush with fractures containing material that apparently settled when water flowed through the rock in the past.
Scientists do not have evidence that there was an ocean or lake at the Spirit site, as existed at the Opportunity rover site on the other side of Mars.
Opportunity, meanwhile, has spent the last week poring over the only large rock it can see in the plains of Meridiani Planum. It is a rock the robot happened to crash into during its bouncy landing on the Red Planet back in January.
The two rovers are approaching the end of their nominal 91-day mission, Opportunity now in its 67th Martian day and Spirit into its 89th, and planners for the Mars Exploration Rover project are gearing up for an extended mission.
"Both spacecraft are going to last well into their long lifetime," Chris Lewicki, rover flight director, said during a press briefing held at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Tale of two rocks
Unlike its twin Opportunity, Spirit has had a tough time piecing together a history of water at Gusev Crater. But its Mazatzal studies support previous hints of water seen in a previous rock target called Humphrey.
"The rock is a basalt and clearly has been altered with fluids," said Hap McSween, a rover science team member from the University of Tennessee at Knoxville. "It the most enticing hint yet about water here."
Basaltic rock is born of volcanism and is one of the most common rock types on Earth.
Spirit used its mast and robot arm-mounted instruments to study Mazatzal, including a number of rock abrasion tool sessions to uncover upper portions of the rock that were then studied by the rover's microscopic imager.
Rover researchers said cracks in the rock's surface were still present after drilling through multiple layers of Mazatzal, and they would be good entry points for past water.
"They seem to be an area that water flowed through, potentially with minerals that precipitated through and lined the crack walls," said rover science team member Jeff Johnson.
A lucky Bounce
At Meridiani Planum, Opportunity has spent the week obsessed with a target called Bounce Mark Rock, aptly named because it lies in a bounce mark left by the rover's airbags when the spacecraft landed.
"It looks like there was one rock out there in the plains, and we managed to hit it," said Jim Bell, lead scientist for the rover's panoramic camera.
Covered in dust and standing about 4 inches (10 centimeters) high, the rock appears to be the first candidate for a truly basaltic rock seen by Opportunity, rover scientists said. They added that parts of the rock appear to contain the volcanic types of material more commonly detected at Gusev Crater.
Bounce Mark's encounter with Opportunity may have also left a scar.
"The whole rock may have been moved by the impact," Bell said, adding that signs of the impact appear in the cracked and crusty soil around the rock's base. "That rock had a very interesting day on Jan. 24 when we came flying to it."
The impact with Bounce Mark may have even pitched Opportunity into Eagle Crater, where it eventually rolled to a stop and began a most fortuitous few weeks of exploration, scientists said.
Possible sign of age
Earlier this week, Opportunity had problems with some command sequences written to a portion of its non-volatile EEPROM memory, and took that area offline.
"It didn't impact our science operations at all and we were able to recover the memory," Lewicki said, adding that the glitch was different than the flash memory malfunction that afflicted the Spirit rover earlier in its mission. "We understand the problem completely now, and safeguards are in place."
It is possible, Bell added, that the malfunction was the first sign of age by Opportunity.
But the rover was able recently to send the largest amount of data ever relayed home by a Mars robot in a single day, and is currently in the process of sending scientists the largest panoramic image taken of Mars. Dubbed the Lion King, the panorama of Meridiani Planum seen from the edge of Eagle Crater is a patchwork of 558 images taken in eight parts over two days, and sucks up much of the rover's onboard flash memory.
In the next two weeks, ground controllers plan to unleash Opportunity on long-haul drives across the flat expanse of Meridiani Planum to a crater dubbed Endurance.
Spirit, however, is being prepared for a 2-kilometer (1.2-mile) run to Columbia Hills, where scientists hope it will find more evidence of water in the rock face.