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Meteorites from Mars

Thirty-four meteorites, almost certainly from Mars, have been discovered as of May 2006. They are known as SNCs1 (named for the towns where the original 12 meteorites were found: Shergotty, India, in 1865; Nakhla, Egypt, in 1911; and Chassigny, France, in 1815). This hypothesis is based largely on the composition of noble gases (particularly argon and xenon) trapped in the meteorites, and the shergottites in particular, which resemble measurements of the Martian atmosphere made by the Viking spacecraft. Major element compositions of the SNCs are also similar to Martian soil analyses made by Viking.

The relatively young isotopic ages of the SNC meteorites (1.3 billion years or less) suggest that Mars has been volcanically active during its recent past.

A 40-pound meteorite that crashed to Earth in Nigeria in 1962 has been classified as coming from Mars. It was named Zagami for the region in which it was found. It is the largest single Martian meteorite ever found.

A 4-pound, 7-ounce (1.9-kilogram) meteorite, ALH 84001, found in the Allen Hills of Antarctica in 1984, was reclassified in 1993 as coming from the Red Planet, making it the tenth meteorite known to have originated from Mars. In 1996, NASA announced that meteorite ALH 84001 contained fossils of ancient Martian microbial life-forms.

A 0.38-ounce (12-gram) meteorite (QUE 94201) found in Antarctica in 1995 became the 12th meteorite identified as having a Martian origin.

In 1997, the thirteenth known Martian meteorite, Dar al Gani 476, a 4.8-pound (2.2-kilogram) meteorite, was found in the Sahara Desert.

Two rock specimens weighing 8.6 oz (245.4 g) and 16 oz (452.6 g) that were found in the Mojave Desert about 20 years ago were classified in Feb. 2000 as the fourteenth Mars meteorite. The rocks are known as the Los Angeles meteorites.

The most recent finds from 2001–2004 were discovered in Antarctica and the deserts of northern Africa, which have become the favored hunting grounds for meteorite collectors, since there is little or no ground cover to hide the rocks.

In April 2004, the Mars Exploration Rover Opportunity analyzed “Bounce Rock,” a rock it hit during its January landing. Bounce Rock's composition resembled the original Shergotty meteorite and matched even more closely a meteorite found in 1979 in Antarctica.

1. Pronounced “snick.”

Information Please® Database, © 2007 Pearson Education, Inc. All rights reserved.

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