A unique meteorite that fell on a Soviet military base in Yemen in 1980 may have come from one of the moons of Mars. Several meteorites from the Red Planet have been found on Earth, but this could be the only piece of Martian moon rock. Andrei Ivanov, who is based at the Vernadsky Institute of Geochemistry and Analytical Chemistry in Moscow, Russia, spent two decades puzzling over the fist-sized Kaidun meteorite before he decided that it must be a chip off Phobos, the larger of the two Martian moons.