Latest Mission Could Be Rover's Last

NASA scientists eyeing a crater they call "the candy store" have sent the Mars rover Opportunity to the very edge -- literally. The rover's front wheels Wednesday rolled over the lip of a crater called Endurance, onto a 25-percent grade. It's the kind of slope that could trip up Opportunity and send it crashing to the bottom of the abyss. Even if it makes it safely down that steep incline, there are questions about whether Opportunity can make it back out again.

But the risk might just be worth it. The "candy store" contains an outcropping of rock older than anything the rovers have seen to date. At the bottom of the crater, up to 23 feet below the edge, there's an outcropping that could allow scientists at the Jet Propulsion Lab in Pasadena (CA) see millions of years in the face of the exposed rock.

"If you want to learn about history, there are worse places to get stuck than in a library," said Firouz Naderi, Mars Exploration Rover Program Manager.

Opportunity was lured into the pit after finding deposits of salt -- perhaps sea salt -- on the rim of the Endurance crater. The rock at the bottom could show evidence of a warmer, wetter climate on Mars. You know, the kind of climate conducive to life.

"But we don't even know yet what that rock is like down there," said Chief Mission Scientist Steve Squyres. "We hope it will tell us a story of a planet that's mostly made of basalt, but we don't know whether the bedrock in the crater is volcanic or sedimentary -- and if it's sedimentary, then it could be evidence that old, old water was there, too."

On the other side of Mars, Opportunity's twin, Spirit, is also on the hunt for important clues about the presence of water. In a recently dug trench, Spirit made a rather amazing discovery. Chemical analysis of the material it scooped up showed enriched deposits of magnesium sulfate.

Epsom salt. "It's not the story that we expected. It's not the one that we initially went hunting for," said Squyres.

Spirit's Alpha Particle X-ray Spectrometer (APXS) detected concentrations of magnesium sulfate as high as 15 percent of the total sample. That's high.

"If you went and you tasted it, you would taste the salt," Squyres said.

Spirit is now just about 100 yards from the Columbia Hills, where Squyres expects to find even more evidence that water once covered at least parts of a planet now more barren than the harshest desert on Earth.

As for Opportunity's trip into the Endurance crater, experts give it a 50-50 chance of ever coming out again. But some at JPL are a lot more confident.

"In addition to being robots, the Mars rovers are interplanetary all-terrain vehicles. And this week, we're going to prove it one more time on Mars at Meridiani," said rover mobility engineer Randy Lindemann.

FMI: http://marsrovers.jpl.nasa.gov/home