There is never a dull moment for a robot on Mars.
A fleeting dust devil comes into view -- just right for picture taking. An outcrop of rock is found that yields insight into the planet's past. And then there's need to trudge over and around ever-larger sand fields to reach primetime science.
Those spunky, full of life rovers -- Spirit and Opportunity -- continue to hit the dusty exploration trail on Mars.
From its vantage point up in the Columbia Hills at Gusev Crater, Spirit is hard at work and highly productive explained Steve Squyres, the lead scientist for the Mars Exploration Rover (MER) project at Cornell University in Ithaca, New York.
Spirit has been eyeing an outcrop named Methuselah, and last weekend took several hundred megabits of Panoramic Camera images of the geology, Squyres said. Those images have helped ground controllers to pick a spot on the outcrop to move in for work with the robot's instrument arm, he said.
Spirit has also produced "blow by blow" movies of passing dust devils -
whirlwinds that hoist dust from the martian surface high
into the air.
"The dust devil movies are just spectacular," Squyres told SPACE.com. "We've known these things were out there, of course, and we've seen them at low resolution on several occasions. But to see them up close and moving like this was a real treat. And they're big!"
The largest dust devil recorded in the movies is more than 328 feet (100 meters) in diameter, Squyres said.
Slipping and digging in
Spirit's present position offers both a new view and new science, said MER science team member, Larry Crumpler, a research curator in volcanology and space sciences at the New Mexico Museum of Natural History and Science in Albuquerque.
Spirit's climb to that setting wasn't easy.
"We stumbled on this outcrop while driving away from Larry's Lookout a couple of weeks ago. We were trying to drive up the slope towards the summit, and kept slipping and digging in like trying to drive up a road covered with deep snow. We were digging in...to the hubs. So we started to back down," Crumpler explained.
"This is one of the more exciting places yet," Crumpler added. "We are about to do some real field geology here on the side of the Columbia Hills. We are likely to be here for a while."
Given Spirit's solar panel cleaning, apparently thanks to a passing dust devil, the rover has lots of power. That being the case, the urgency to get to the summit of the hills is somewhat less than it was before, Crumpler advised.
"So we will have time to carefully examine this new site the way you would if you stumbled upon it in the field here on Earth," Crumpler said. "In fact, it is just this sort of low, small outcrop with visible evidence of tilting that one usually gets excited about -- and learns a lot about the geology from - right here on Earth. This is real field geology on another planet."
Story to tell
"It's another new mission," said Ray Arvidson, Chair of Earth and Planetary Sciences at Washington University in St. Louis, Missouri and the deputy principal investigator for the Mars Exploration Rovers.
Arvidson said that for months it was clear that the rocks Spirit had in sight had a story to tell in terms of the origin and modification of the Columbia Hills. They were different than those seen in the plains of Gusev Crater, across which the robot had driven from its original landing spot.
The geometry of the rocks, their layering, how they conform to the landscape - all are clues that scientists are using to develop multiple hypotheses about their origin and the past history of the area.
One view, Arvidson suggested, is that Spirit is perhaps wheeling about a set of coalesced volcanic cinder cones.
"You need all the observations...pieces of information to put the overall story together," Arvidson said. Spirit will be hard at work within the area for about a month. The Mars machinery then has to wrap up its survey tasks and start heading southward to follow the Sun, he explained.
Larger and larger ripples
Then there's Opportunity on the other side of Mars, tooling about at Meridiani Planum.
The rover has started to rumble through what scientists called etched terrain, said Squyres. "When you look at the etched terrain carefully, you see that there's a lot of variability to it. Some of it has a distinct 'mottled' appearance, and seems likely to have a lot of exposed rock. We haven't gotten to any of that yet...though we will soon," he said.
Squyres said that other parts of the etched terrain have a distinctive north-south "grain" to the surface texture, but are more uniform in brightness.
"That's what we're in now. The 'grain', it turns out, is caused by these big parallel ripples that we've been driving through. That wasn't obvious in the orbital images, but it's real obvious when you're down on the ground," Squyres noted.
And those ripples have been getting larger and larger as Opportunity has driven farther to the south. "We're handling them fine for now, but the larger they get, the more of a challenge to driving they will pose," Squyres said.
The next big goal for Opportunity is reaching Erebus crater, nestled inside an even larger crater now named Terra Nova. "So we're going to pull up to the north side of Erebus, take a good look around, and then decide what to do next," Squyres said.
Beyond Erebus, but far off in the distance, sits another hoped for Opportunity science target: Victoria Crater.
Take home message
Thanks to the work of Spirit and Opportunity, there's an important take home message - this time for those blueprinting future expeditions of humans to the red planet.
"There's a clear message," Arvidson said. "What we're doing is reconnaissance...understanding the geological evolution and the role of water...helping to hone in on the sites where you want to do detailed work," he said.
At some point in the future, there will be humans on the surface of Mars, Arvidson said.
What's apparent to Arvidson is that the optimal way to do exploration is with humans and robots acting together. "You can have a dozen of these rovers moving off in various directions. Astronauts can be directing the robots, with humans then field-checking key areas. I look at it as an integrated system," he concluded.