The Western Sahara, a fertile hunting ground for enthusiasts seeking meteorites, offered up two rare Martian rocks in the past few months. The discoveries bring the total of all known Martian meteorites to twenty-six. (Meteorites are smallish rocks from space that fall to Earth. If they don’t impact, they are meteors.) Of the two, one is a rock that is unique to Mars, called nakhlite. Nakhlite is composed of pyroxine, a mineral common to Earth rocks, but a nakhlite’s ratio of calcium, magnesium and iron in its pyroxine is what makes it unique.