NASA unveiled a dramatic image from the Opportunity Mars rover today, a color panorama looking into a 30-foot-deep, football field-wide crater showing cliffs of exposed bedrock that may help unlock the geologic history of the region.

This approximate true-color panorama from Opportunity shows the impact crater known as "Endurance." Credit: NASA/JPL/Cornell Download a larger version here | Download super high-res version here

"It has been a great week on Mars," said principal investigator Steve Squyres. "Opportunity has arrived now at the lip of Endurance Crater and has returned to Earth what is surely the most spectacular image yet from this mission. It's spectacular both from just the sheer scenic grandeur of it, but it's spectacular also for the scientific potential that it offers."

But it will take engineers several weeks to guide Opportunity safely around the rim of the crater to collect the images and other data they will need to determine if the robot can safely traverse relatively steep slopes without bogging down in fine, sandy soil.

Aside from obvious cliff-like outcrops with vertical drops of several feet or more, the crater wall revealed in the Endurance panorama shows sandy, 20-degree slopes that may give the rover access to exposed outcrops. In theory, the rover can handle slopes as steep as 35 degrees, but on-board software has tighter limits and engineers want to make sure the six-wheeled robot can handle the terrain before making a potentially life-or-death decision.

"This is a big hole in the ground," Squyres said. "What that means, it's good news and bad news. It's good news in the sense that it exposes a lot of rock, this is meters of rock, and that means lots of history. But it's bad news in the sense that this is a dangerous place.

At the much smaller Eagle Crater where Opportunity landed, "we could rove with impunity over whatever there was," Squyres said. "Here, there are cliffs that the rover could fall off and die if we're not careful. So we are going to proceed cautiously, we are going to proceed slowly, we are going to proceed very, very methodically."

To visualize the scale of the rover and crater wall, an illustration of Opportunity is placed over the panorama imagery. Credit: NASA/JPL/Cornell Download a larger version here

Proceeding around the rim of the crater, Opportunity's Panoramic Camera and other instruments will make repeated observations to fully characterize the terrain, to make 3-D maps and to identify possible entry and exit points that are within the rover's capabilities.

"Then when the time comes, when all of that safety assessment has been done, we're going to have to make some decisions about what we're going to do with this vehicle," Squyres said. "If we go in and try to sample that rock, it's going to have enormous scientific potential, but it may have some risk as well. if the decision ... is to go in, despite what might be small but non-zero risk, then we're going to have some other things to do first. ... We're not done with science out on the plains yet. So if we decide to try dipping our toes into the upper reaches of Endurance Crater with the rover, we will almost certainly do some more science out on the plains. There's a lot of stuff out there."

One high-priority target: the Opportunity lander's discarded heat shield, which is resting on the frigid soil 500 to 650 feet from the rover's current position. The heat shield was jettisoned a minute and a half before the rover's airbag-cushioned landing and it hit the martian surface at several hundred miles per hour.

Along with digging a small but fresh crater that might have scientific value, photographs showing how much of the shield's ablative surface burned away during descent could help engineers develop improved designs for future spacecraft.

But the top priority is Endurance Crater, where scientists believe they see exposed, layered rocks that were deposited before the water-influenced rocks observed at Eagle Crater.

"There's a lot for us to figure out here," Squyres said. "But the most appealing the most attractive, the most scientifically important part of all is what you're seeing right here, and it's this lovely exposure of bedrock, which is going to tell us much about what happened in Meridiani Planum before the rocks that were deposited at Eagle Crater were laid down."

Any decision to actually send Opportunity into Endurance Crater will require multiple levels of review and approval. No one wants to take any undue risks, Squyres said. The goal is simply to learn as much as possible before moving inside and then to climb out and continue the rover's exploration.

But if the potential science payoff is high enough, NASA might elect to send Opportunity into Endurance Crater even if engineers said it might not be possible to climb back out. Even so, with Opportunity and its twin, Spirit, operating in near flawless fashion, no one is in any hurry.

"This is not something we're going to go about in a hasty fashion, Squyres said. "It took four sols (martian days) just to do the remote sensing that we've done from this first spot on the rim. We're going to go to two more spots on the rim and do very similar things. So it's going to take a period of weeks to do the initial survey. That will give the rover drivers enough time to figure out how they feel about going down into this thing or not."

The design requirement for the rovers was to operate on the surface for 90 days. Spirit and Opportunity are both beyond that point. But based on temperature data, telemetry from the spacecraft and the amount of dust slowly building up on the rovers' solar arrays, engineers believe the hardy robots will survive well into the summer months, if not longer.

"I'm not worried about whether or not we're going to have enough gas in the tank when it comes time to go into (Endurance Crater) or not," he said. "I think the real issue is going to be the safety, not how much time we have left."

Asked what the rock outcrops in Endurance might have to say about the history of water on mars, Squyres said it's too soon to tell, adding "we're a long way from understanding this."

"This is like the mission has started over again," he said. "Think back to when we were at Eagle Crater, we were looking off into the distance, there's something cool, we don't know what it is, let's go there. Well, here we are again. Give us a few weeks!"