Mars craters that could hold the key to meteorite ALH84001

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The Independent Online
A week after Nasa's announcement that life could have existed on Mars, a scientist has searched 42,283 craters on the planet - and narrowed the source of the fossil-containing meteorite down to two of them.

Dr Nadine Barlow, who carried out the search electronically on a computer database of Mars craters, says that the results could be used to direct future space missions to the planet to give them the best chance of finding fossil remains. "There are no plans to land spacecraft at these locations at present, but there is the possibility to focus on these areas," she said yesterday.

Both lie within a few hundred miles of each other in the eastern area of the heavily cratered southern highlands of Mars, where asteroids have repeatedly hit the planet during its life. Meteorites would be thrown into space from the surface by an asteroid's impact.

Dr Barlow, a physicist at the University of Florida, began checking possible sources almost immediately after last week's news from scientists at the United States space agency that meteorite ALH84001, which is thought to show signs that early life developed on Mars 4.5 billion years ago, was thrown from the planet 16 million years ago before drifting in space and landing in Antarctica about 13,000 years ago.

"Sixteen million years may sound like a long time ... but for geologic processes it is a very short period, particularly for a planet like Mars which has apparently experienced little geologic activity over the past billion years," she said.

She fed a set of search criteria into the computer which held a database of all the craters on Mars - a catalogue she had produced as a postgraduate in the Eighties. Then she told it to search for craters that were comparatively young, but in ancient terrain - since the rock itself was very old - and in sites where water had once been, as the rock contained carbonates.

A high-speed search cut the 42,283 candidates down to 23, which were in turn reduced to two by further refinement. "I'm fairly confident this is correct," Dr Barlow said yesterday. "I think that the criteria we used were conservative. But I have been working almost around the clock on this."

Dr Barlow hopes to publish her work later this year.