Spirit Rover Traces Mars' Explosive Past, Opportunity Slowly Digs Out

Explosionsand falling rock once peppered the Martian hills that NASA's Mars rover Spiritcurrently calls home, astronomers said Tuesday.

Spirit,currently scaling Husband Hill above its Gusev Crater landing site, has foundevidence of an explosive period in the region's history, in which volcanoes ora massive impact showered the land with debris and possibly unearthed magma.Whether they were volcanicor impact explosions, however, is not yet known.

"Earlier inits history, this part of Gusev Crater was a violent place," said StevenSquyres, lead scientist from CornellUniversity for the MarsExploration Rover (MER) mission. "There were explosions going and there wasstuff raining from the sky, and some of it was altered to a significant degree bya fairly modest size of water."

Squyres andhis fellow rover team members announced the find, which is based on a trio ofrock outcrops observed by Spirit's cameras, during a Tuesday press conferenceat an American Geophysical Union meeting in New Orleans, Louisiana.

"Really, forthe first time since the start of the Spirit mission, we've got the kind of geologywe can sink our teeth into," Squyres said. "The last six weeks, I'd say, haveprobably been the most productive of the whole Spirit mission."

Spirit'ssister rover Opportunity has also made progress, though not altogether scientific,at its Meridiani Planum. The rover is slowly but surely inching its way out ofa deepsand dune, though mission managers don't expect to free the robot foranother few weeks.

Thesecret's in the rocks

It took theSpirit rover months to clamber up Husband Hill's steep, slippery side, duringwhich time the robot found little to suggest the region differed from thevolcanic rock remains scattered across the rest of Gusev Crater.

But nowhalfway up Husband, after studying three rock outcrops, researchers are tellinga different story.

"All of asudden, we have geologic structure...everything changed," Squyres said. "It wasnothing more than you had to look at it from a different angle."

Analysis bySpirit of rock outcrops known as "Larry's Lookout," "Methuselah" and "Jibsheet"contained signs of the Gusev's tumultuous past, researchers said.

"Theirchemical composition is very distinct from what we found out on the plains,"said rover science team member Richard Morris, of NASA's Johnson Space Centerin Houston, adding that there are signs of the mineral ilmenite - which isoften formed in magma. "This is the first appearance of this mineral we'veseen."

While therocks around Spirit share some compositional traits, the amount of weatheringdue to water differs among the outcrops, as do their textures. At "Methuselah,"for example, astronomers found the finest rock layers seen by Spirit to date,while "Jibsheet" sported a bulbous, globular look.

"Gusev hascertainly turned out to be different than we expected it to be," Squyres said,adding that he still believes that the crater was once the watery lake suggestedby orbital photographs.

The rocksof the Columbia Hill chain, which includes Husband Hill, may completely predatethat Gusev lake, rising like an island above the plains, Squyres added.

Opportunityekes forward

WhileSpirit continues to explore Husband Hill, its robotic twin Opportunity isslowly but surely crawlingout of a sandy quagmire on the other side of Mars.

The roverhas moved about 10 inches (27 centimeters) - though its wheels turned enough totravel 157 feet (48 meters) - which mission controllers say isgood progress. [An animation of Opportunity's wheel-spinning is available byclicking here.]

"We're onlytraveling about half a percent of what we're commanding," explained JimErickson, rover project manager at NASA's Jet Propulsion Laboratory. "So it's avery low number, but very consistent."

At thecurrent rate, it may be two more weeks before Opportunity once again reachessafe ground, Erickson added.

Opportunityis currently stuck in the outskirts of a region known as the "etched terrain"which contains - scientists hope - exposed bedrock that could shed more lighton water's role in the history of Meridiani Planum. Astronomers know that the regionwas once awashwith the liquid stuff.

"We'relearning that's it's a tough place to do business," Squyres said of the area.

Now wellpast the one-yearmark, NASA's Spirit and Opportunity rovers are still going strong.

"We'restill trying to decide exactly how long they'll go by running them until theywear out," Erickson said. "We just don't know how long these things are goingto last."

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