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Analysis: 'Bounce' rock's cosmic portent

By PHIL BERARDELLI, United Press International   |   April 17, 2004 at 12:02 AM
WASHINGTON, April 16 (UPI) -- Opportunity's phenomenal luck continues.

Not only did NASA's rover land smack-dab in the middle of a neatly excavated and navigable crater on Mars, where it promptly uncovered persuasive evidence that water once flowed across the red planet, and not only has it been performing nearly flawlessly since it touched down on Jan. 24. Now, it also, essentially, has stubbed its toe on a rock whose discovery portends cosmic implications.

A few days ago, on its slow roll across the Martian terrain at its landing site at Meridiani Planum, an iron-oxide-rich area near the planet's equator, Opportunity's controllers noticed an odd-looking, football-shaped rock lying in the red dust. They named the rock "Bounce," because the lander most likely hit it as it bounced along the surface, cushioned by its airbags, before coming to rest inside the little crater called Eagle.

Controllers considered Bounce an odd find because it did not resemble any of the other rocks in the crater's vicinity -- nor did it resemble anything seen before on Mars, they said.

So they ordered Opportunity to train its formidable instruments on the rock, including the tool NASA engineers affectionately called the "RAT," for rock abrasion tool, which grinds away surface impurities to expose the undisturbed, primordial composition below.

The results stunned the NASA team.

The main ingredient in Bounce is a volcanic mineral called pyroxene, said rover science team member Deanne Rogers, of Arizona State University in Tempe. The high proportion of pyroxene means Bounce not only is unlike any other rock studied by Opportunity or Spirit, but also is unlike the volcanic deposits mapped extensively around Mars by NASA's Mars Global Surveyor orbiter, Rogers said.

Bounce is a unique rock, and it has been sitting at Opportunity's feet.

"We think we have a rock similar to something found on Earth," said Benton Clark of Lockheed Martin Space Systems in Denver, a science-team member for the missions of both Opportunity and its twin, Spirit.

Rather more than that. Bounce's chemical composition exactly matches that of a meteorite that hit the ground in Shergotty, India, on Aug. 25, 1865.

Called the Shergotty meteorite -- and the source name for a class of meteorites called shergottites -- its chemical composition is a "matching fingerprint" to Bounce, said David Grinspoon, professor of planetary science at the University of Colorado in Boulder.

The resemblance helps confirm something meteorite specialists and planetary scientists have suspected for more than two decades but until now have been unable to prove: Micro-bubbles of gas trapped in dozens of meteorites found on Earth -- including Shergotty -- match the recipe of Martian atmosphere so closely that they must have originated on Mars.

"There is a striking similarity in spectra," said Christian Schroeder, a rover science-team collaborator from the University of Mainz in Germany, which supplied both Mars rovers with Moessbauer spectrometers -- exceedingly sensitive instruments for identifying chemical compositions.

A less-distinctively named shergottite, EETA79001, found in Antarctica in 1979, has a composition even closer to Bounce's.

As a result, NASA scientists are convinced Shergotty, EETA79001 and Bounce -- and maybe a couple dozen other Martian rocks that found their way to Earth -- were ejected from Mars by the impact of a large asteroid or comet.

The instruments aboard another orbiter, Mars Odyssey, suggest Bounce may have originated at an impact crater about 16 miles wide that lies about 31 miles southwest of Opportunity. The orbiter's images show some of the rocks thrown outward by the impact that formed the crater flew as far as the distance to the rover.

"Some of us think (Bounce) could have been ejected from this crater," Rogers said.

So far, no one has broached the bigger implication: Bounce provides conclusive evidence not only of Martian meteorites on Earth, but also of the possibility of cross-seeding.

During the early eons of the solar system, planetary impacts were downright common. Given the relative proximity of Earth and Mars, it is easy to accept the possibility that materials propelled upward from one planet eventually could make their way to the other.

The first organisms on Earth originated around 3.5 billion years ago and maybe earlier. Back then, impacts from asteroids and comets still were common. It is conceivable that material ejected from Earth by those impacts could have landed on Mars carrying some of those organisms -- or their raw ingredients. The converse also is possible -- early organisms from Mars could have landed on Earth.

The discovery of Bounce raises the distinct possibility that life arising from a common source could have existed for a time on both worlds.

The way Opportunity's luck has been going, it would not be surprising to learn the rover has detected Martian microbes.

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Phil Berardelli is UPI's Science & Technology Editor. E-mail sciencemail@upi.com

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Editors: UPI photos WAX2004041601 and WAX2004041602 are available

© 2004 United Press International, Inc. All Rights Reserved. Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.
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