|Volume: 02, Issue: 04||02/25/2004|
Mars Exploration Rovers Continue to DazzleNASA’s Mars Exploration Rovers continue to excite the scientists monitoring their progress. Over the past two weeks, Opportunity and Spirit have made significant advances in both science and communications.
On January 16, Opportunity scooped a trench with one of its wheels to reveal what is below the surface of a selected patch of soil.
"We took a patient, gentle approach to digging," said Jeffrey Biesiadecki, a rover planner at NASA's Jet Propulsion Laboratory (JPL), Pasadena, California. The process lasted 22 minutes.
The resulting trench—the first dug by either Mars Exploration Rover—is about 50 centimeters (20 inches) long and 10 centimeters (4 inches) deep.
Two features that caught scientists' attention were the clotty texture of soil in the upper wall of the trench and the brightness of soil on the trench floor, said Dr. Rob Sullivan of Cornell University in Ithaca, New York, a science-team member who worked closely with engineers to plan the digging.
By inspecting the sides and floor of the trench, Opportunity is now finding some things it did not see beforehand, including round pebbles that are shiny and soil so fine-grained that the rover's microscope can't make out individual particles.
"What's underneath is different than what's at the immediate surface," said Dr. Albert Yen, rover science team member at JPL.
Opportunity has manipulated its robotic arm to use its microscope on five different locations within the trench the rover dug on February 16. It has also taken spectrometer readings of two sites.
"We've given the arm a very strenuous workout," said JPL's Dr. Eric Baumgartner, lead engineer for the arm.
The accuracy of the tool placements—within 5 millimeters, or less than a quarter inch—is remarkable for mobile robotics on Earth, much less on Mars.
Once data are analyzed from the alpha particle X-ray spectrometer and the Mössbauer spectrometer about what elements and what iron-bearing minerals are present, the differences between the subsurface and the surface will be easier to interpret, Yen said.
While Opportunity has been digging and examining its trench this week, it has also been catching up on transmission of pictures and information from its survey last week of a rock outcrop along the inner wall of the small crater in which the rover is working.
Based on the outcrop survey, scientists have chosen a feature they have dubbed "El Capitan" as the next target for intensive investigation by Opportunity.
"We've planned our assault on the outcrop," said Dr. Steve Squyres of Cornell University, Ithaca, New York, principal investigator for the rovers' science instruments. "The whole stack of rocks seems to be well exposed here."
Upper and lower portions appear to differ in layering and weathering characteristics. Planners anticipate that Opportunity's arm will be able to reach both the upper and lower parts from a single parking spot in front of "El Capitan."
Meanwhile, halfway around the planet, Spirit will use a front wheel to dig a trench during the Martian day, or "sol," ending at 12:36 p.m. PST on February 27. Spirit's trenching at the shallow depression dubbed "Laguna Hollow" could answer questions about whether traits on the soil surface resulted from repeated swelling and shrinking of an upper layer bearing concentrated brine, among other possibilities.
Some soil in "Laguna Hollow" appeared to stick to Spirit's wheels. Possible explanations include very fine-grained dust or concentrated salt making the soil sticky, said Dr. Dave Des Marais, a rover science team member from NASA Ames Research Center, Moffett Field, California. Pictures of the surface there also show pebbles arranged in clusters or lines around lighter patches Des Marais described as "miniature hollows." This resembles patterned ground on Earth that can result from alternating expansion and shrinkage of the soil. Possible explanations for repeated expanding and contracting include cycles of freezing and thawing or temperature swings in salty soil.
After trenching to seek clues about those possibilities, Spirit will continue on its trek toward the rim of a crater nicknamed "Bonneville," now estimated to be about 135 meters (443 feet) away from the rover. As of February 19, Spirit had already driven 128 meters since leaving its lander, surpassing the total distance driven by the Mars Pathfinder mission's Sojourner rover in 1997.
Spirit has also begun using a transmission rate of 256 kilobits per second, double its previous best, said JPL's Richard Cook. Cook became project manager for the Mars Exploration Rover Project today when the former manager, Peter Theisinger, switched to manage NASA's Mars Science Laboratory Project, in development for a 2009 launch.
Spirit's drive toward "Bonneville" is based on expectations that the impact that created the crater "would have overturned the stratigraphy and exposed it for our viewing pleasure," said Dr. Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rovers' science instruments. That stratigraphy, or arrangement of rock layers, could hold clues to the mission's overriding question—whether the past environment in the region of Mars where Spirit landed was ever persistently wet and possibly suitable for sustaining life.
The rover made another significant accomplishment recently: a successful pioneering demonstration of communications between Spirit and the European Space Agency’s Mars Express orbiter.
On February 6, while Mars Express was flying over the area Spirit was examining, the orbiter transferred commands from Earth to the rover and relayed data from the robotic explorer back to Earth.
"This is the first time we have had an in-orbit communication between European Space Agency and NASA spacecraft, and also the first working international communications network around another planet," said Rudolf Schmidt, the European Space Agency's project manager for Mars Express. "Both are significant achievements—two more 'firsts' for Mars Express and the Mars Exploration Rovers."
Jennifer Trosper, Spirit mission manager at NASA's Jet Propulsion Laboratory, Pasadena, California, said, "We have an international interplanetary communications network established at Mars."
The European Space Agency and NASA planned this demonstration as part of continuing efforts to cooperate in space and to enable plans to use joint communications assets to support future missions to the surface of Mars.
The commands for the rover were transferred from Spirit's operations team at JPL to the European Space Operations Centre in Darmstadt, Germany, where they were translated into commands for Mars Express. The translated commands were transmitted to Mars Express, which used them to successfully command Spirit. Spirit used its ultra-high frequency antenna to transmit telemetry information to Mars Express. The orbiter relayed the data back to JPL, via the European Space Operations Centre.
"This is excellent news," said JPL's Richard Horttor, project manager for NASA's role in Mars Express. "The communication sessions between Mars Express and Spirit were pristine. Not a single bit of data was missing or added, and there were no duplications."
This exercise demonstrated the increased flexibility and capabilities of interagency cooperation and highlighted the spirit of close support essential in undertaking international space exploration.
Spirit and Opportunity frequently use two NASA orbiters, Mars Odyssey and Mars Global Surveyor, for relaying communications. The rovers also can communicate directly with the Earth-based antennas of NASA's Deep Space Network in California, Spain and Australia, another layer of international cooperation.
The rovers' main task is to explore their landing sites for evidence in the rocks and soil about whether the sites' past environments were ever watery and possibly suitable for sustaining life.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project and NASA participation in Mars Express for NASA's Office of Space Science, Washington, D.C.
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