Second Opportunity

NASA’s Opportunity rover is about to embark on a second journey of exploration. Opportunity spent the past several days taking in the view from the rim of Endurance Crater. The first full-color panorama of the crater, released by NASA late last week, reveals large bedrock outcrops that mission scientists are anxious to study.

Initial Pancam images and spectral analysis performed by the rover’s Mini-TES instrument indicate that the Endurance Crater outcrops are not composed of the same sulfate-rich material found in Eagle Crater. Steve Squyres, principal investigator for the Mars Exploration Rover (MER) mission, said the new outcrop material “really looks different,” both to the rover’s panoramic camera (Pancam) and to its thermal emission spectrometer (Mini-TES), which provides information about mineral composition.

Squyres said the outcrops in Endurance Crater formed under different environmental conditions than the rocks in Eagle Crater. The Eagle Crater rocks contained high concentrations of sulfates. This, along with other physical and chemical evidence, led the MER science team to conclude that they were deposited in water, when a shallow sea evaporated.

Opportunity image gallery and slideshow

In its initial observations of the Endurance Crater outcrops, Opportunity has not seen evidence of sulfates. “This is fundamentally different than anything that we have seen before,” Squyres said. He speculated that the outcrops are “probably a sedimentary rock made up of particles that have accumulated on a fairly flat surface. Did they accumulate in air? Did they accumulate in water? That’s the kind of thing we’re going to try to settle.”

Squyres said that, from a distance, it looks like there are “massive crossbeds” in the outcrops. “That’s the kind of stuff that forms when you have dunes, so we may be looking at a dune environment. We’re going to be looking for evidence of a beach environment. Was there something like that going on? I don’t know what it’s going to be, but it ain’t what we saw back at Eagle. It’s something different.”

MER scientists believe the rocks exposed in Endurance Crater not only are different from those in Eagle Crater, but also are older. By examining this older material, they hope to learn about an earlier period in the history of the Meridiani Planum, a vast plain that encompasses both craters.

The rocks in Eagle Crater revealed a watery tale of one relatively brief period in the history of Meridiani. The rocks in Endurance Crater, “we believe, lie lower than the rocks that we saw at Eagle Crater. They preserve the record of what came before the events that took place at Eagle Crater,” Squyres said.

One particularly impressive section of outcrop, dubbed Burns Cliff, is a rock face several meters tall [see banner image]. Opportunity Ledge, by comparison, was only about one-third of a meter (about 10 inches) tall. Mission scientists would like to send the rover to investigate Burns Cliff in detail. But Opportunity is unlikely to be able to access it safely. The “cliff” designation isn’t frivolous: Its face is nearly vertical.

Fortunately, there is a second outcrop, Karatepe, not far from Burns Cliff, where the same rock layers are exposed. Karatepe lies at a modest 20-degree angle. In theory, Opportunity should be able to traverse an incline that steep. Mission planners have already begun studying images of the Karatepe region to determine whether there is a safe access path.

Opportunity won’t be heading into Endurance Crater any time soon. The rover will spend the next few weeks traversing the rim of the crater, collecting extensive sets of Pancam images and Mini-TES spectra from at least two additional vantage points, and perhaps examining a few interesting rocks it encounters along the way. Only after this survey is complete will mission planners decide whether – and when – to send the rover into the crater.

That decision is a complex one, which must weigh the potential scientific gain of entering the crater against the potential risk of doing so. Even if the rover driving team decides that it is safe to send Opportunity in to Endurance Crater, they may not be equally confident that they can get it back out. By studying the interior of the crater from different angles and different vantage points around the rim, MER mission planners will be able to weight the options.

There are also several interesting science targets on the plains, which Opportunity noted but did not study thoroughly while on its way from Eagle to Endurance Crater. The science team would like to return to these targets before the rover’s extended mission ends in September. If mission planners conclude that Opportunity can safely enter Endurance Crater, study the Karatepe outcrop and then safely exit, they may send the rover in as soon as its circuit around the rim is complete. If, on the other hand, they determine that Opportunity could probably make it in but not out, they will first send the rover to a series of science targets out on the plains, and then return to investigate the interior of the crater.

One such target, which sits only about 150 to 200 meters away, is the spacecraft’s heat shield. Opportunity hasn’t yet visited the site where it slammed into the martian surface, but images taken by the Mars Orbital Camera (MOC) aboard Mars Global Surveyor (MGS) pinpoint its location.

“I think we could take some pictures of the heat shield,” Squyres said, “that might help people design better heat shields for Mars at some point in the future.” He added that when the heat shield hit the ground, it “probably dug the deepest fresh hole that we’re going to find anywhere, certainly deeper than we can dig with our wheels.”

Other targets on the plains include the Anatolia fractures, a trench dug by one of the rover’s wheels and Fram Crater. The fractures are intriguing because it’s unclear how they formed. They are also “the one place that we can go and look at exposed bedrock that was exposed by a process other than impact [and] that has really not been significantly damaged,” said Squyres. The trench that Opportunity dug was in a region of sand ripples, but the rover didn’t take the time to examine the ripples closely. Scientists would like to learana more about how they formed and what they are made of. Finalaly, at Fram Crater, Mini-TES detected a rock that appeared to have a different mineral composition than the sulfate-bearing rocks the rover studied in Eagle Crater.

All that lies off in the future, however. For the next few weeks, while mission planners plot a course of action, Opportunity will continue to send back stunning panoramic vistas of Endurance Crater.