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Smithsonian Institution photograph by Terry McCrea.
|There is strong evidence that this rock came from
Mars. It is one of the SNC meteorites, which are named after three locations
where this rare type of meteorite was first found: "S"hergotty (India),
"N"akhla (Egypt), and "C"hassigny (France). This particular specimen is
from a meteorite (designated EETA79001) discovered in Antarctica in 1979.
Meteorite on display in Exploring The Planets - Loaned to the National Air and Space Museum by Division of Meteorites, National Museum of Natural History
Radioactive dating techniques reveal that almost all meteorites solidified from molten rock about 4.5 billion years ago, when the solar system was formed. The SNC meteorites, however, are only about 1.3 billion years old. Their relatively young age suggests that SNCs cannot have come, like other meteorites, from the small asteroids. They must have solidified on a planet--a body large enough to retain heat and produce molten rock even billions of years after it formed.
Why from Mars?
The SNC meteorite exhibited here was found to contain some gas trapped
in its interior. Analysis showed that the composition of this gas was
nearly identical to that of the atmosphere on Mars, as measured by the
Landers in 1976.
|Collecting Antarctic Meteorites|
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Photo courtesy of Ursula B. Marvin, Smithsonian Astrophysical Observatory
|Meteorites fall on all parts of the Earth. Resembling ordinary rocks, they are often difficult to recognize. In Antarctica, however, meteorites stand out on the windswept, ice-covered landscape and are easy to locate. The slowly flowing glacial ice also acts like a conveyor belt. It concentrates the meteorites in regions where the flow is obstructed by hills, and where wind and evaporation rapidly remove the ice and snow.|
Mars Impact Ejecta
Most of the debris produced by crater-forming collisions on Mars falls back to the surface of the planet. Some of the rocks strewn about the Martian surface may have been ejected long ago by such impacts elsewhere on Mars. But such cratering events may also eject some rocks with such great speed that they escape from the planet. Some of these escaped Mars rocks, orbiting in interplanetary space, may in turn eventually collide with Earth, resulting in SNC meteorites, such as the sample exhibited here. A few meteorites appear to be lunar rocks that escaped from the Moon in the same way.
Similar collisions of asteroids or comets with Earth could have blasted
terrestrial rocks into escaping orbits that eventually carried them
to Mars. Some of these rocks could have been large enough to shield
any dormant spores or microbes inside them for millions of years against
the sterilizing efects of solar and cosmic radiation. Some of the rocks
could have broken apart when they landed on Mars.
More Mars Meteorite Information