Image: Martian craters
This annotated photo from the THEMIS thermal imager on NASA's Mars Odyssey orbiter shows Endurance and Victoria craters, which already have been explored by the Opportunity rover, as well as the much larger Endeavour Crater. Click on the image for a larger version.
updated 9/22/2008 2:34:01 PM ET 2008-09-22T18:34:01

NASA's Opportunity rover has studied several craters during its four years on Mars, but now it's going after the biggest crater yet.

The science team behind the twin Mars rover missions announced Monday that Opportunity would head out for a 13.7-mile-wide (22-kilometer-wide) crater dubbed Endeavour. The feature is more than 20 times larger than Victoria Crater, which is where Opportunity has spent the last two years. The rover climbed back onto level ground just this month.

To reach Endeavour, Opportunity will need to drive about 7 miles (11 kilometers) to the southeast, matching the total distance it has traveled since landing on the Red Planet in January 2004.

"We may not get there, but it is scientifically the right direction to go anyway," Cornell University's Steve Squyres, principal investigator for the rover science mission, said in Monday's announcement. "This crater is staggeringly large compared to anything we've seen before."

Scientists expect to see a much deeper stack of rock layers than those examined in Victoria Crater.

"I would love to see that view from the rim," Squyres said. "But even if we never get there, as we move southward we expect to be getting to younger and younger layers of rock on the surface. Also, there are large craters to the south that we think are sources of cobbles that we want to examine out on the plain. Some of the cobbles are samples of layers deeper than Opportunity will ever see, and we expect to find more cobbles as we head toward the south."

A two-year journey?
The rover team estimates Opportunity may be able to travel about 110 yards (meters) during each day it is driven toward the Endeavour crater. Even at that pace, the journey could take two years.

"This is a bolder, more aggressive objective than we have had before," said John Callas, the project manager for the rover mission at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's tremendously exciting. It's new science. It's the next great challenge for these robotic explorers."

Opportunity, like its twin rover Spirit, is well past its expected lifetime on Mars, and might not keep working long enough to reach the crater. However, NASA said two new resources not available during Opportunity's 4-mile (6.4-kilometer) drive toward Victoria Crater in 2005 and 2006 are expected to aid in this new trek.

One is imaging from orbit of details smaller than the rover itself, using the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter. The MRO probe and its HiRISE cameras arrived at the Red Planet in 2006.

"HiRISE allows us to identify drive paths and potential hazards on the scale of the rover along the route," Callas said.

Other advantages come from a new version of software uplinked to Opportunity and Spirit in 2006, boosting their ability to choose routes autonomously and avoid hazards such as sand dunes.

Over the past four years, Opportunity has explored 65-foot-wide (20-meter-wide) Eagle Crater — the crater it rolled into after its landing — as well as 430-foot-wide (130-meter-wide) Endurance Crater, the half-mile-wide (800-meter-wide) Victoria Crater and smaller impact sites.

Early on, Opportunity found geological evidence that the area around Eagle Crater had surface and underground water in the distant past. The rover's explorations since then have added information about how that environment changed over time. Finding rock layers above or below the layers already examined adds windows into later or earlier periods of time.

This report was based on information from NASA.

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