Mars meteorite providing clues about
Red Planet’s environmental past

August 17, 2009 — A meteorite larger than any other known meteorite on Mars is yielding clues about the planet’s past. NASA’s Mars rover Opportunity is investigating the rock, which is about the size of a large watermelon. Scientists calculate it is too massive to have hit the ground without disintegrating unless Mars had a much thicker atmosphere when it fell than now. Additional studies also may provide clues about how weathering has affected the rock since it fell. Two weeks ago, Opportunity had driven approximately 600 feet past the rock in a Mars region called Meridiani Planum. An image the rover had taken a few days earlier and stored was then transmitted back to Earth. The image showed the rock is approximately 2 feet in length, half that in height, and has a bluish tint that distinguishes it from other rocks in the area. The rover team decided to have Opportunity backtrack for a closer look, eventually touching the meteorite with its robotic arm. "There's no question that it is an iron-nickel meteorite," said Ralf Gellert of the University of Guelph in Ontario, Canada. Gellert is the lead scientist for the rover's alpha particle X-ray spectrometer, an instrument on the arm used for identifying key elements in an object. "We already investigated several spots that showed elemental variations on the surface. This might tell us if and how the metal was altered since it landed on Mars." The microscopic imager on the arm revealed a distinctive triangular pattern in the surface texture of the meteorite, dubbed Block Island. It matches a pattern common in iron-nickel meteorites found on Earth. Opportunity found a smaller iron-nickel meteorite, called "Heat Shield Rock," in late 2004. At about a half-ton or more, Block Island is roughly 10 times as massive as Heat Shield Rock and several times too big to have landed intact without more breaking than today's Martian atmosphere could provide. When the investigation of Block Island concludes, the team plans to resume driving Opportunity on a route from Victoria Crater, which the rover explored for two years, toward the much larger Endeavour Crater. Opportunity has covered about one-fifth of the 12-mile route plotted for safe travel to Endeavour since the rover left Victoria nearly a year ago.

This is a false-color, red-green-blue composite view of Block Island generated from images taken through the Opportunity’s camera filters. The exaggeraged color is used for enhancing the visibility of differences among the types of rock and soil materials. Image Credit: NASA/JPL-Caltech/Cornell University NASA's Mars Exploration Rover Opportunity used its microscopic imager to get this view of the surface of a rock called "Block Island" on Aug. 1, 2009. The triangular pattern of small ridges seen at the upper right and elsewhere on the rock is characteristic of iron-nickel meteorites found on Earth, especially after they have been cut, polished and etched. Image Credit: NASA/JPL-Caltech/Cornell University/USGS

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