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Another clue is that because Mars is 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 known 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.

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 a once-in-a-lifetime event.

Jeff Grossman, a NASA scientist who is the meteorite 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 occur, he said.

University of Alberta meteorite expert Chris Herd, who heads the committee that certified the discovery, 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.

But Cornell University astronomer Steve Squyres, who is the principal investigator for NASA’s Mars Exploration Rover Program and the space agency’s go-to guy on Mars, said unfortunately this type of rock isn’t the kind scientists are most hoping for. This find is igneous, or volcanic, rock.

A softer kind of rock that could hold water or life would be better, but that type is unlikely to survive a fiery re-entry through Earth’s atmosphere, he said.

Scientists are hoping NASA and the European Space Agency team up in 2018 to send robotic spaceships to Mars that can bring back samples of rock and dirt. Just this past weekend, a Russian probe that was going to try to bring samples back from a Martian moon came plummeting back to Earth in failure.

A Martian meteorite that was buried in Antarctica made news in 1996. NASA scientists theorized the rock showed traces of life from Mars. Even the White House declared it the first sign of life outside of Earth. Years of study since then have led much of the astronomy world to conclude there was insufficient evidence to support the claim.