NASA scientists yesterday confirmed that the Mars Rover Opportunity has discovered a meteorite on the surface of the red planet. The rover spotted the rock in early January. When its thermal signature suggested it was metallic, researchers realised it could be alien to the planet.

Subsequent investigations with the Rover's spectrometer confirmed that the rock contained mainly iron and nickel, a composition characteristic of meteorites. Mission scientists told New Scientist that the discovery was a wonderful surprise.

Steve Squyres, the Rovers' lead scientist, based at Cornell University, New York, commented: "I didn't see this one coming."

He explained the further analysis would be difficult because mission designers had not expected to find any meteorites on Mars, so did not send the Rovers equipped to take samples from them.

Testing by the original equipment manufacturer revealed that, sadly, the rover's existing grinding tool was not up to the task of drilling into a meteorite. After an hour of grinding in a test lab, a quarter of the drill head had worn away.

It is possible that both Rovers have unknowingly passed meteorites on their travels across the Martian plains and mountains. The vast majority of meteorites on Earth are just rock. Assuming the same is true on Mars, (and why wouldn't it be?) they would not be visually distinctive from the rest of the rocks scattered on the surface.

Spirit and Opportunity have been on Mars for over a year, well beyond their expected life span. In September, NASA agreed to fund a further six months of study. ®

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