Samples of a colony of Martians have been put on display in the Natural History Museum, in London. A scanning electron microscope (SEM) image of a series of partly filled pits on the surface of a mineral grain from the Nakhla meteorite Photo: NASA/David McKay The microscopic aliens are on a slice of a meteorite in the museum. Nasa scientists, who used a scanning electron microscope to take snaps, say the bumpy surface resembles a fossilised colony of microbacteria – a simple form of life.