There is strong evidence that this rock came from Mars. Its relatively young age indicates that it formed on a large body — a planet. And the composition of gases trapped inside it point toward a particular planet: Mars. It may have been thrown into space by an asteroid or comet impact, and eventually it fell to Earth.
This rock is one of the SNC meteorites, which are named after three locations where these rare meteorites were first found: Shergotty, India; Nakhla, Egypt; and Chassigny, France. This specimen is from a meteorite found in Antarctica in 1979.
Lent by the Division of Meteorites, Smithsonian National Museum of Natural History
A Planetary Origin
Almost all meteorites solidified from molten rock when the solar system formed about 4.5 billion year ago. SNC meteorites, however, are less than 1.5 billion years old, which means they are not pieces of small asteroids like other meteorites. They must have formed on a body large enough to retain heat and produce molten rock long after it formed—in other words, on a planet.
Scientists found in the meteorite trapped gas whose composition was nearly identical to the Martian atmosphere as measured by the Viking Landers. This graph compares the concentration of gases in the Martian atmosphere (vertical axis) with their concentration in the meteorite (horizontal axis). If they matched perfectly, the points would fall on the diagonal line. The close match strongly suggests that this meteorite came from Mars.
Meteorites resemble ordinary Earth rocks and are often hard to recognize. But they stand out on the ice-covered landscape of Antarctica. Slow moving glacial ice concentrates the meteorites where hills obstruct the ice flow, and where wind and evaporation remove the ice and snow covering them.
Photo courtesy of Ursula B. Marvin, Smithsonian Astrophysical Observatory