12. Martian Meteorite EETA 79001

This meteorite, which originally weighed nearly 8 kilograms, provided the first strong proof that meteorites could come from Mars. EETA 79001 is an achondrite meteorite, a basalt lava rock nearly indistinguishable from many Earth rocks. This picture shows a sawn face of this fine-grained gray rock (the vertical stripes are saw marks). The black patches in the rock are melted rock — glass — formed when a large meteorite hit Mars near the rock. This meteorite impact probably threw EETA 79001 off Mars and on its way to Antarctica on Earth. The black glass contains traces of martian atmosphere gases.

Most meteorites are approximately as old as the solar system: 4.5 billion years. A few achondrite (stony) meteorites were a great puzzle because they were much younger; they solidified from molten lava at about 1.3 billion years ago or less (as given by radioactive-element dating methods). These meteorites were called the SNCs, for the three subclasses of these strange “young” meteorites: Shergotty, Nakhla, and Chassigny. Like all meteorites, these three are named for the places where they fell, towns in India, Egypt, and France.

Rocks as young as the SNC meteorites had to have formed on a geologically active planet, and the most likely planet was Mars. The Mariner 9 and Viking Orbiter images had shown that Mars has enormous volcanos, up to 3 times as tall as Mauna Kea in Hawaii, and most of them could be as young as 1.3 billion years old. In 1979, a number of scientists seriously suggested that the young meteorites might be from Mars, but their ideas were met with great skepticism.

The discovery of a lunar meteorite in 1981 (slide #11) strengthened the idea that rocks from Mars might come to land on Earth. Then, in 1983, a scientist studying the EETA 79001 meteorite (this slide) examined its black patches of shock-melted glass. The glass was unexpectedly rich in atmosphere gases, especially nitrogen and argon. These and other gases have the same abundances and proportions as do those in the martian atmosphere, which was analyzed on Mars by the Viking lander in 1976. With this evidence of martian atmosphere gases, the martian origin of the SNC meteorites was generally accepted by the late 1980s.

Martian (SNC) basalt meteorite, collected in 1979 in the Elephant Moraine area of Antarctica. The cube at the lower left is 1 centimeter on a side. S80-37631, NASA/JSC.

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