|Volume: 02, Issue: 08||04/21/2004|
Mars Rocks Resemble Meteorites Found on EarthNASA's Opportunity rover has found an odd volcanic rock on the plains of Mars' Meridiani Planum region with a composition unlike anything previously seen on Mars. Scientists have, however, found similarities between the rock and meteorites that have fallen to Earth.
Bounce Rock, the name given to the football-sized rock Opportunity struck while bouncing to a stop inside protective airbags on landing day, bears strong resemblance to meteors found on Earth. Mars Exploration Rover scientists described two such meteorites in particular. One rock, named Shergotty, was found in India in 1865 and gave its name to a class of meteorites called shergottites. A shergottite named EETA79001 was found in Antarctica in 1979 and has an elemental composition even closer to Bounce Rock's. Those two and nearly 30 other meteorites found on Earth are believed to have been ejected from Mars by the impacts of large asteroids or comets hitting Mars.
According to science-team collaborator Deanne Rogers of Arizona State University, Tempe, Opportunity's miniature thermal emission spectrometer indicates that the main ingredient in Bounce Rock is a volcanic mineral called pyroxene, which was also detected by the Moessbauer spectrometer. The high proportion of pyroxene makes it unlike any other rock studied by Opportunity or Spirit and the volcanic deposits mapped extensively around Mars by a similar spectrometer on NASA's Mars Global Surveyor orbiter, Rogers said.
Thermal infrared imaging by another orbiter, Mars Odyssey, suggests a possible origin for Bounce Rock. An impact crater about 25 kilometers wide (16 miles wide) lies about 50 kilometers (31 miles) southwest of Opportunity. The images show that some rocks thrown outward by the impact that formed that crater flew as far as the distance to the rover.
"Some of us think Bounce Rock could have been ejected from this crater," Rogers said.
The resemblance also helps resolve a paradox about the meteorites. Bubbles of gas trapped in them match the recipe of Martian atmosphere so closely that scientists have been confident for years that these rocks originated from Mars. But examination of rocks on Mars with orbiters and surface missions had never found anything like them, until now.
"There is a striking similarity in spectra," said Christian Schroeder, a rover science-team collaborator from the University of Mainz, Germany, which supplied both Mars rovers' Moessbauer spectrometer instruments for identifying iron-bearing minerals.
Opportunity is driving eastward, toward a crater dubbed "Endurance" that might offer access to thicker exposures of bedrock than the rover has been able to examine so far. With new software to improve mobility performance, the rover may reach Endurance within two weeks, said Jan Chodas, flight software manager for both Mars Exploration Rovers at NASAís Jet Propulsion Laboratory, Pasadena, California.
Mission controllers at JPL successfully sent new versions of flight software to both rovers. Spirit switched to the new version successfully on Monday, and Opportunity did late Tuesday.
A parting look at the small crater in which Opportunity landed is part of a full 360-degree color panorama released at the news conference. The view combines about 600 individual frames from the rover's panoramic camera, said science-team collaborator Jason Soderblom of Cornell University, Ithaca, N.Y. It is called the Lion King panorama because it was taken from a high-ground viewpoint at the edge of the crater, like the high-ground viewpoint used by animal characters in the Lion King story. The panorama gives a good sense of how wind has uncovered the outcrop at the upwind side of the crater and deposited sand in the downwind side of the crater and bright Martian dust in the wind shadow of the crater, Soderblom said. On the wide plain outside the crater lies Bounce Rock.
Earlier in the week, NASA approved an extended mission for both Opportunity and its twin Mars Exploration Rover, Spirit, handing them up to five months of overtime assignments as they finish their three-month prime mission.The first of the two rovers, Spirit, met the success criteria set for its prime mission. Spirit gained check marks in the final two boxes on April 3 and 5, when it exceeded 600 meters (1,969 feet) of total drive distance and completed 90 Martian operational days after landing.
Opportunity landed three weeks after Spirit. It will complete the two-rover checklist of required feats when it finishes a 90th Martian day of operations April 26. Each Martian day, or "sol," lasts about 40 minutes longer than an Earth day.
"Given the rovers' tremendous success, the project submitted a proposal for extending the mission, and we have approved it," said Orlando Figueroa, Mars Exploration Program director at NASA Headquarters, Washington, D.C.
The mission extension provides $15 million for operating the rovers through September. The extension more than doubles exploration for less than a two percent additional investment, if the rovers remain in working condition. The extended mission has seven new goals for extending the science and engineering accomplishments of the prime mission.
"Once Opportunity finishes its 91st sol, everything we get from the rovers after that is a bonus," said Dr. Firouz Naderi, manager of Mars exploration at JPL. "We look forward to continued discoveries by both rovers in the months ahead."
Beyond the quantifiable criteria, such as using all research tools at both landing sites and investigating at least eight locations, the rovers have returned remarkable science results. The most dramatic have been Opportunity's findings of evidence of a shallow body of salty water in the past at Meridiani Planum.
"We're going to continue exploring and try to understand the water story at Gusev," said JPL's Dr. Mark Adler, deputy mission manager for Spirit. Spirit is in pursuit of geological evidence for an ancient lake thought to have once filled Gusev Crater.
Reaching the "Columbia Hills" region, which could hold geological clues to that water story, is one of seven objectives for Spiritís extended mission. Opportunity has a parallel one: to seek geologic context for the outcrop in the "Eagle" crater by reaching other outcrops in the "Endurance" crater and perhaps elsewhere. Other science objectives are to continue atmospheric studies at both sites to encompass more of Mars' seasonal cycle, and to calibrate and validate data from Mars orbiters for additional types of rocks and soils examined on the ground.
Three new engineering objectives are to traverse more than a kilometer (0.62 mile) to demonstrate mobility technologies; to characterize solar-array performance over long durations of dust deposition at both landing sites; and to demonstrate long-term operation of two mobile science robots on a distant planet. During the past two weeks, rover teams at JPL have switched from Mars-clock schedules to Earth-clock schedules designed to be less stressful and more sustainable over a longer period.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University at http://athena.cornell.edu.
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