Most achondrites come from the crust of differentiated asteroids. However, three types of achondrites stand out from the others. They are called SNC meteorites, for the initials of three very special meteorites that fell in Shergotty, India, in Nakhla, Egypt, and in Chassigny, France. These meteorites are from Mars.

How can scientists be sure that these meteorites come from Mars? An unusual age of 1.3 billion years has been calculated for SNC achondrites, while meteorites from the asteroid belt are all 4.5 billion years old. The late-stage crystallization of the SNCs proves that they come from a body much bigger than an asteroid, and which cooled slowly. As it happens, volcanic activity continued on Mars for a long time after its formation. SNC meteorites contain other proof of their origin: the gases trapped in these meteorites very closely resemble the gases recorded in the Martian atmosphere by the Viking probe.

The SNCs are shocked achondrites-they were altered by the collision that ejected them from their planet. One serious candidate for the location they may come from is the oval-shaped impact crater at the base of the volcano Ceraunius Tholus. These meteorites roamed through the emptiness of space before coming to visit the neighbouring planet!