METEORITES FROM THE MOON AND MARS

When asteroids strike the surface of the Moon or Mars, portions of these planetary bodies are ejected into space in much the same manner as when a child dives onto a bed and dust is launched into the air.

As would be imagined, samples of the planet Mars possess a highly specific chemical signature. Such samples will possess water-bearing minerals—thereby eliminating the asteroid belt as a point of origin—and will show evidence of having crystallized fairly recently in a planetary-sized (but smaller than Earth's) gravitational field, with levels of cosmic radiation consistent with originating in the inner solar system.

There was a time when scientists knew that certain meteorites originated from either Mars or Venus but it could not proven. Such samples were believed to be Martian as it would be more difficult for an object to attain the escape velocity necessary to have been successfully "launched" off the Venusian surface as a result of the planet's stronger gravitational field and denser atmosphere. The proof came in 1995 when it was reported by The New York Times and Science magazine that minute volumes of gas trapped in tiny bubbles within a suspected Martian meteorite perfectly matched the atmospheric composition of Mars (as determined by the unmanned Viking lander in 1976). More recently, the abundances of argon, krypton, xenon and heavy nitrogen found in other Martian meteorites were also found to comport with the unique signature of the Martian atmosphere.

Mars is among the very rarest substances on Earth. The total amount of Mars on Earth weighs less than an adult male and a large fraction of this amount is forever locked away in the foremost museums and research institutions. A strange gouge-like blemish on the Martian surface was recently identified as where a large asteroid tangentially struck the Martian surface with a force that would readily "kick" portions of Mars into space.