Rocks from the Moon and Mars

Several hundred meteorites are pieces of the Moon or Mars, thrown off by impacts. This lesson explains how they were identified and what they have revealed.

Proof of origin

In 1982 a meteorite found in Antarctica, Allan Hills A81005, was recognised as lunar because its minerals, chemistry and isotopes matched rocks brought back by the Apollo missions. Lunar meteorites sample the whole Moon, including the far side, which no Apollo crew visited.

Martian origin was proved by gas. Pockets of glass in the meteorite Elephant Moraine 79001 contain trapped gases whose composition and isotope ratios match the Martian atmosphere as measured by the Viking landers in 1976. Their oxygen isotopes also differ from those of Earth and the Moon.

Martian meteorite types

Most Martian meteorites are shergottites, basaltic rocks that are mostly a few hundred million years old. Nakhlites, such as Nakhla, which fell in Egypt in 1911, are about 1.3 billion years old and contain minerals altered by water. Chassignites are olivine-rich. The young ages of the shergottites were once a puzzle, because many Martian surfaces are ancient; they show that volcanism continued on Mars until relatively recently in geological terms. NWA 7034, nicknamed Black Beauty, is a breccia of soil and rock fragments, some over 4.4 billion years old.

ALH 84001

In 1996 a team argued that the Martian meteorite ALH 84001, about 4.1 billion years old, contained possible signs of ancient life: carbonate globules, magnetite crystals and microscopic structures resembling bacteria. Further research showed that each feature could form without life, and most scientists do not accept the claim. The debate was valuable: it drove research into how to recognise genuine signs of life and how to avoid contamination, lessons now built into sample-return missions.

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