Now free to roam after weeks of being stuck in a sand trap, NASA’s Mars rover Opportunity is inspecting the terrain at Meridiani Planum and cautiously getting ready to move on.

Rover operators are attempting to discern what caused Opportunity to run into trouble in an area now dubbed “Purgatory Dune.” Part of that assessment is using the rover’s robot arm to study the problem area and plot out an exit strategy for safely leaving the area.

“It’s been slow going at Meridiani lately,” said Steve Squyres, lead scientist for the Mars Exploration Rover missions at Cornell University in Ithaca, N.Y.

“We need to take a good hard look at Purgatory Dune with the instrument arm, but we’ve also got to show this dune a lot of respect… it got us once, and we don’t want it to get us again. So as we’re maneuvering into position on it, we’re using a great deal of caution,” Squyres explained in an update posted on Cornell’s Mars Web site.

“We’ve got most of our safeguards on as we approach Purgatory, and we’ve been setting the limits very conservatively, to make sure we keep the vehicle safe in this treacherous terrain,” Squyres said.

Opportunity has positioned itself a few meters away from the trouble-making dune.

“Just enough to turn around,” Squyres said. “Then we’re going back to Purgatory to see what we can learn.”

By using the extended robot arm, Squyres said researchers hope to learn more about grain sizes of the sand, its composition and whether or not there’s a cemented crust near the surface.

“Whatever we can learn to help us better understand Purgatory Dune,” he added.

Why wasn’t the robot arm used to disrupt the dune, to help extract the rover from its predicament? “The arm is a precision device for placing instruments … it’s not for digging or hauling,” Squyres explained. “We were always confident that the wheels would get us out if we used them properly … and they did.”

Squyres said that, with Opportunity in position, the plan now is to use the robot’s arm and investigate the area quickly, “and then be on our way.”

“It’ll feel very good finally to be moving again,” Squyres reported via his Web site update.

On the other side of Mars, Opportunity’s rover twin Spirit is on the move at Gusev Crater. The robot is being maneuvered through the Columbia Hills and now is at the south side of an area tagged as Husband Hill.

“We’ve been spiraling up and around the west side of the hill, heading generally south and gaining elevation as we go,” Squyres noted on the Cornell Web site. “I’ve been surprised, as I think the whole team has, at how well this part of the climb has gone so far.”

Spirit has knocked off several drives of over 20 meters lately, with one spurt adding nearly 3 meters of elevation to the rover’s climb. From its vantage point, the robot’s camera system recently caught another passing dust devil.

There are two big questions that face the Spirit team: Will they go for the summit? And if that is accomplished, what will be visible when the rover gets its first good view to the south?

“I really don’t know about the summit. We all want it, of course…who wouldn’t? We’re doing the first mountaineering on another planet, and it would be a little frustrating to get this close and not make it to the top,” Squyres said.

Both Squyres and one of the lead Spirit drivers, Chris Leger, are rock climbers when they are not ascending features on Mars. “So we both want this,” Squyres said.

On the other hand, driving Spirit to the summit must make sense scientifically.

“The summit is directly between us and the terrain to the south that we want to explore … so going over the top may be a pretty efficient route to the good stuff,” Squyres explained. “Also, the summit really is going to offer a pretty good view.

Geologists in the field routinely climb to the top of the highest hill to get a good look at their surroundings and plan what they’re going to do next, and we may want to do that here as well.”

What still needs to be evaluated is just how hard Spirit’s climb will be. Wasting a lot of time and eating up valuable Martian days, called sols, has to be weighed. But for now, the robot is pressing forward, Squyres said.

“So I simply don’t know what’s going to happen. But for now the going is good … and we’ll just take it sol by sol.”

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...