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Two meteorites thought to have come from the planet Mars have been found in the Sahara, announced Dr Anthony Irving from Washington University earlier this week. This brings the total number of known martian meteorites to 26. The meteorites, named NWA (Northwest Africa) 1195 and NWA 998 consist of two different kinds of rock from the martian surface, shergotite and nahklite respectively, and despite their extraterrestrial origins are superficially similar to igneous rocks from Earth. Martian meteorites provide us with our only samples of the red planet and are important since they allow us to study the evolution of Mars and its interior in the laboratory. The 26 martian meteorites are collectively known as the SNC meteorites after their three main types. The SNC's are thought to be from Mars since many of them have ages, determined from the decay of radioactive elements, that are as little as 165 million years, much younger than the 4.5 billion year ages of meteorites from asteroids. The young ages of the martian meteorites mean they must come from a large body such as a planet which could retain its heat and generate molten rocks. Gases trapped within glass in martian meteorites also have almost identical compositions to that of the martian atmosphere. Martian meteorites were thrown from the surface of Mars millions of years ago during the collision of asteroids and comets and many of them have been affected by the intense pressures generated during such impacts.
More info: NASA Martian Meteorite Page
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