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11. Lunar Meteorite ALHA 81005

11. Lunar Meteorite ALHA 81005

The idea that rocks could fall from the sky was generally accepted by the early nineteenth century; at first, people thought these rocks formed in the atmosphere, hence the name meteorites (derived from the same word as meteorology, the study of the atmosphere). By the beginning of the twentieth century, scientists were sure that meteorites came from space and fairly sure they came from our solar system. Evidence mounted that meteorites came from the asteroid belt (between Mars and Jupiter) and, until the early 1980s, most scientists thought that all meteorites came from the asteroid belt. This meteorite, found in Antarctica in 1981, was the first exception. It is almost identical to rocks that the Apollo astronauts brought back from the Moon, and detailed study showed that it was from the Moon. The white fragments are rich in anorthite, a calcium-rich silicate mineral that makes up most of the lunar highlands. Lunar meteorites have a distinctive greenish tinge to their fusion crusts. Twelve lunar meteorites had been identified by late 1996, and include rocks from the lunar highlands and the maria (the dark areas of the Moon). All the lunar meteorites, like the Apollo rocks, are ancient; they formed more than 3 billion years ago.

A rock from the lunar highlands, collected in the Allan Hills area of Antarctica in 1981. The cube at the lower left is 1 centimeter on a side. S82-35865, NASA/JSC.

Click here to view a high-resolution version of the image (8.20 MB)



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