Image: Opportunity track
NASA / JPL
As shown in this backward-looking image, NASA's Opportunity rover is staying between the lines — or in this case, dune crests — as it makes its way south toward Erebus crater.
By Senior space writer
updated 7/19/2005 8:56:28 PM ET 2005-07-20T00:56:28

Those plucky robots — Spirit and Opportunity — are continuing their respective missions on Mars, each wheeling toward new science objectives.

Images from Opportunity show an expanse of dunes at Meridiani Planum. Rover operators are taking precautions that the golf cart-sized robot won’t get bogged down in any sand trap — to avoid a repeat performance that halted movement of the machine last April.

It took nearly five weeks for engineers to extricate Opportunity’s wheels that became buried in soft sand of a small Martian dune — later dubbed “Purgatory Dune” by the Mars Exploration Rover team.

On the other side of Mars at Gusev Crater, Spirit continues to climb Husband Hill within the Columbia Hills. Using its science-instrumented robot arm, the rover has made observations that are causing a stir within the circle of Mars rover scientists on the project.

In a maze
Opportunity is pressing onward to Erebus crater, said Steve Squyres, lead science team member for the Mars Exploration Rover effort at Cornell University in Ithaca, N.Y.

In a rover update, Squyres noted that driving the rover across the sandy landscape is a challenge.

“We are literally in a maze. The easiest going is to stay within the troughs between the ripple crests, which run roughly north-south. So the best way to make southward progress is to follow a trough until it peters out, make a ‘lane change’ to a nearby trough, and continue onward,” Squyres explained.

Using imagery taken from Mars orbit, scientists and engineers see what they term the “Erebus Highway.” It is a stretch of light-toned terrain, perhaps consisting of exposed bedrock. If so, that’ll make easier going for Opportunity.

“We also like the idea of getting to bedrock from a science perspective,” Squyres added. “It’s been a long time since we’ve looked at any rock with Opportunity.”

Cross-country driving
But there’s a catch, Squyres warned.

“The entrance to the Erebus Highway is not straight south of us, along the troughs. It is a bit off to the east, on a heading closer to 160 degrees or so,” Squyres explained. To get there, the rover has to go “cross-country, going up and over quite a few ripple crests.”

“That’s doable,” said Squyres, “but it’s also a lot slower than just bombing straight south down a nice trough.”

A driving decision is forthcoming. Heading for the highway means making slow progress for a while, but perhaps a better route to Erebus Crater. If the rover wheels down the troughs instead, it’s a speedier path to Erebus Crater.

“So it should work either way,” Squyres said. “Whether or not we’re actually going to ‘hit the Highway’ is an open question at this point, but Erebus isn’t too far off either way you cut it.”

There’s some other good news about what Opportunity is driving through. The terrain appears to be changing as it moves south of Purgatory Dune. Rover images show fewer tall dunes, more pebbles in the troughs and what might be tiny outcrops of bedrock.

“I don’t want to jump to conclusions,” said Squyres, “but the driving definitely looks a little nicer here than it did a hundred meters back.”

Chugging through the data
The Spirit robot at Gusev Crater is also on the move.

During its ascent of Husband Hill within the Columbia Hills, the robot came across a “very cool outcrop” of layered bedrock that has been tagged as Independence Rock, Squyres said.

NASA / JPL
NASA's Spirit rover continues its climb to higher ground up Husband Hill.
“We’ve thoroughly worked it over with all of the arm instruments now, and it’s very strange stuff,” Squyres reported. He said it was one of the oddest things seen at Gusev.

“I’m not ready to go into much detail here about the chemistry and mineralogy yet, since we’re still chugging through the data,” Squyres noted. The rock is clearly highly altered, sporting an unusually low iron content, he said, “which isn’t something we’ve seen much of before.”

Science work at the Independence Rock has been completed. Spirit has resumed its ascent. “The ground is real solid here, and the climbing is good. I still don’t know if we’ll reach the summit or not, but the recent progress has been excellent,” Squyres concluded.

According to rover operator Jake Matijevic of NASA’s Jet Propulsion Laboratory, both Spirit and Opportunity have benefited from clearing skies at the two landing sites.

Furthermore, the rovers have improved energy levels. That is due to dust-clearing events that have been seen on both vehicles, Matijevic reported.

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