Where in the Solar System?

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Rocks from the Moon and Mars are easily distinguished from Earth rocks and other meteorites by their chemical compositions and age.

Lunar meteorites have the same chemical make-up as the rocks brought back from the Moon by the Apollo astronauts and gasses trapped inside the Martian meteorites are the same – and in the same proportion as gasses in Mars’ atmosphere that the Viking landers of the 1970s recorded.

Furthermore, Martian meteorites are all igneous, which means they must have crystallised from a melt. They are also quite young, which means they must have come from a body that has been geologically active. Even melted asteroids had cooled off by about four billion years ago because they were too small to retain their heat – the youngest Mars meteorite is about 165 million years old, which implies it must have come from a planet- sized body. The internal textures can yield a lot of information too.

Planetary meteorites and achondrites have no chrondrules, so must have come from fully differentiated bodies, while those with chondrules were formed in the nascent solar nebula. Asteroidal meteorites can be matched up to specific asteroids by looking at the way they reflect sunlight, using telescopes on Earth. Their reflectance characteristics are dependent on composition, which has enabled astronomers to divide asteroids up into different groups such as rocky, metallic, rock and metal, and carbonaceous. By using this technique, an incredible 920 meteorites have been paired up with asteroid (4) Vesta.

Next Chapter: Origins