Almost by accident, NASA's Mars rover Opportunity has found a rock that may point to a second water event in the red planet's past.
The rover was backing away from potentially treacherous, sandy terrain at the bottom of Endurance Crater when its cameras came across "Escher," an oddly cracked rock that researchers said may have fractured after being soaked during some sort of water event.
But more evidence is needed to be sure.
"There may have been some frost, some water present, but it's not a definite result," said Steve Squyres, the rover mission's principal investigator, adding that some follow up observations at a rock called "Wopmay" may shed more light. "Our hope is that it will reveal more to us about the possibility of a secondary water episode."
If verified, it would point to a secondary water episode that occurred after Endurance Crater formed on the plains of Meridiani Planum, Opportunity's landing site.
The robust rover has already found evidence indicating the region was initially soaked in the distant past, prior to the crater's formation, Squyres said.
Squyres and other mission scientists discussed the current progress of Opportunity and its robotic twin Spirit during an Oct. 7 teleconference that connected researchers from Cornell University, Massachusetts Institute of Technology (MIT) and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
The tantalizing prospect popped up when Opportunity found "Escher" cracked and fractured into polygonal shapes. On Earth, such polygonal rock patterns have been known to be associated with water, but they could just as well have formed when an impact smacked into the surface elsewhere on Meridiani Planum, researchers said.
"As the [Earth] rock dries out, it reduces its volume and contracts in all directions," explained John Grotzinger, a rover science team member from the MIT. "This is not to say these [Mars formations] aren't tectonic, but we have to consider this water option as well."
Opportunity drilled into "Escher's" surface with its arm-mounted rock abrasion tool (RAT), finding the chemistry of its innards substantially different from its surface. While that hints at a possible past interaction with water, "Escher" is the first Martian rock in which the polygonal patterns have been found and its flat orientation on the floor of Endurance Crater poses a limited view into the rock's history.
Wopmay, which researchers said shows some similarities with Escher, stands upright on the Martian surface and could answer questions its predecessor leaves outstanding.
"If you're going to reach a conclusion for water, you're going to need all the data," Squyres said.
Spirit pushes forward
Opportunity is not alone in making new discoveries.
Sitting atop the West Spur of the Columbia Hills in its Gusev Crater landing site, Spirit overcame a recent steering problem to study the nearby rock "Ebenezer," which appears to reinforce views that water once soaked the hilly region, researchers said.
"We're beginning to suspect that almost all of the rocks in Columbia Hills look like this," Squyres said, adding that while "Ebenezer" differs in outward appearance from other nearby rocks, their chemical signatures all indicate past interactions with water.
Meanwhile, Spirit's panoramic camera snapped a new vista dubbed Cahokia from its West Spur perch, which includes a clear, 50-mile (80-kilometer) view to the very edge of Gusev Crater.
"It's a spectacular view," said Jim Bill, rover lead scientist for panoramic cameras at Cornell University, adding that the image was taken over 10 Martian days - or sols - and relayed to Earth over a period of weeks.
Rover engineers are still trying to understand the exact nature of Spirit's steering glitch, which apparently cleared up on its own. While Spirit is again mobile, engineers hope to prepare a plan to handle the problem should it occur again.
"We don't have a root cause for this event yet but as they age we'll see more aches and pains," said Jim Erickson, rover project manager at JPL. "We'll just have to deal with the problems as they go."
Next up for Spirit is the summit of nearby Husband Hill, while Opportunity will complete its Wopmay studies and finally head to the rock outcrop of Burns Cliff on the rim of Endurance Crater.
"We've got a lot of good stuff ahead of us," Squyres said.
- Rover Special Report