Volume: 03, Issue: 05 03/09/2005 
Opportunity used its navigation camera to take the images combined into this view of the rover's surroundings, including a small crater dubbed "Naturaliste," seen in the right foreground. Image courtesy NASA/JPL.
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Spirit used its navigation camera to take the images combined into this 360-degree view of the rover's surroundings on "Cumberland Ridge" for looking into "Tennessee Valley" to the east. Image courtesy NASA/JPL.
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Other Articles in This Issue:
Virgin Atlantic Global Flyer Lands in Record Books
Lunar Reflectors Help Test Einstein Theory
Discovery Solid Rocket Boosters Mate with External Tank
Chat about Cassini-Huygens Mission to Saturn and its Moons

Mars Exploration Rovers Shatter Expectations

NASA's Mars Exploration Rover Opportunity accomplished unprecedented feats of Martian motion, covering more total ground in three days than either Opportunity or its twin, Spirit, did in their first 70 days on Mars. Meanwhile, Spirit found salt-laden soil that further advances the notion of past water on Mars.

Opportunity set a one-day distance record for Martian driving at 582 feet on Feb. 19, 2005. That was the first day of a three-day plan transmitted to the rover as a combined set of weekend instructions. The new record exceeded a former best by 13 percent.

As on all previous long drives by either rover, the traverse began with "blind" driving, in which the rover followed a route determined in advance by rover planners at JPL using stereo images. That portion lasted an hour and covered most of the day's distance. Then Opportunity switched to autonomous driving for two and a half hours, pausing every 2 meters to look ahead for obstacles as it chose its own route ahead. It continued autonomous driving the next day.

"This is the first time either rover has picked up on a second day with continued autonomous driving," said Dr. Mark Maimone, rover mobility software engineer at JPL. "It's good to sit back and let the rover do the driving for us."

Not only did Opportunity avoid obstacles for four hours of driving, it covered more ground than a football field. Opportunity has a favorable power situation, due to relatively clean solar panels and increasing minutes of daylight each day as spring approaches in Mars' southern hemisphere. This allows several hours of operations daily.

On the third day of the three-day plan, the robotic geologist continued navigating itself and drove even farther, 109 meters, pushing the three-day total to 390 meters (nearly a quarter mile). In one long weekend, Opportunity covered a distance equivalent to more than half of the 600 meters that had been part of each rover's original mission-success criteria during their first three months on Mars.Opportunity has now driven 3,014 meters (1.87 miles) since landing. The rover is heading south toward a rugged landscape called "etched terrain," where it might find exposures of deeper layers of bedrock than it has seen so far.

Spirit, meanwhile, has uncovered soil that is more than half salt, adding to the evidence for Mars' wet past. The rover has driven 4,157 meters (2.58 miles) since landing on Mars and is climbing "Husband Hill."

Spirit paused on a ridge overlooking a valley north of the summit to see whether any potential targets below warrant a side trip. As the rover struggled up the slope, its wheels churned up soil that grabbed scientists' attention.

"This was an absolutely serendipitous discovery," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments. "We said, 'My gosh, that soil looks very bright. Before we go away, we should at least take a taste."

The bright patch of disturbed soil, dubbed "Paso Robles," has the highest salt concentration of any rock or soil ever examined on Mars. Combined information gained from inspecting it with Spirit's three spectrometers and panoramic camera suggests its main ingredient is an iron sulfate salt with water molecules bound into the mineral. The soil patch is also rich in phosphorus, but not otherwise like a high-phosphorus rock, called "Wishstone," that Spirit examined in December.

"We're still trying to work out what this means, but clearly, with this much salt around, water had a hand here," Squyres said.

The robots successfully completed their three-month primary missions in April 2004 and are continuing extended mission operations. JPL, a division of the California Institute of Technology, has managed NASA's Mars Exploration Rover project since it began in 2000.

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