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Scientists can tell when meteorites are from Mars because they know what the Martian atmosphere is made of, thanks to numerous probes sent there. The chemical signature of the rocks and the Martian air match, Irving said. Another clue is that because planets like Mars are more geologically active, its rocks tend to be much younger _ millions of years old instead of hundreds of millions or more _ than those from the moon or asteroids.

Most of the Martian rocks on Earth have been around for centuries or longer and have been found in Antarctica or the desert. They look so similar to dark Earth rocks that if they fell in other places, such as Maryland, they would blend right in and never be discovered, Irving said.

Jeff Grossman, a NASA scientist who is the Meteoritical Society’s database editor, said there is a higher probability of finding “something interesting” from Mars on these rocks because they fell so recently. However, six months is a long time for Earthly contamination to take root, he said.

Herd said the first thing he would do with the rocks would be to rinse them with solvents to try to get rid of earthly contamination and see what carbon-based compounds are left.

A Martian meteorite that was buried in Antarctica made news in 1996. NASA scientists theorized that the rock, found in 1984, showed signs of traces of life from Mars, fossils of what seemed to be lifelong forms. Even the White House made an announcement about it as the first sign of life outside of Earth. Years of study since then have led much of the astronomy world to conclude that there was not enough evidence to support the claim.

Because known Martian meteorite falls happen only once every 50 years or so _ 1815 in France, 1865 in India, 1911 in Egypt and 1962 in Nigeria _ this is a once-in-a-career or even one-in-a-lifetime event.

“It’s incredibly fresh. It’s highly valuable for that reason,” said Carl Agee, director of the Institute of Meteoritics and curator at the University of New Mexico. “For someone who knows their Martian, this is a beauty. It’s gorgeous.”

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Online:

The Meteoritical Society: http://bit.ly/xDh6zz

Tony Irving’s list of Martian meteorites: http://bit.ly/yl7jBD