Microbes on Earth-bound asteroid. Artwork of an Earthward-bound asteroid with conceptual microbial colonies shown on its surface. It is thought that bacteria in the core of asteroids could survive to reach other worlds, such as Earth. The bacteria could originate from other worlds, such as in the case of asteroid ALH84001. This asteroid, found in Antarctica in 1984, is believed to have originated from Mars, where it may have been ejected by an asteroid impact. ALH84001 is thought to contain micro-fossils due to bacteria. The theories of panspermia hold that microbes from Mars, other planets or outer space, may have led to the origin of life on Earth.