Do we have any Mars rocks on Earth? Perhaps. No spacecraft has brought back rock samples from Mars like the ones astronauts brought back from the Moon. But some Mars rocks might have made their way to Earth on their own. Scientists have found about a dozen rocks on Earth that might be meteorites from Mars. These are pieces of the planet that were chipped off by a collision with a space rock long ago. The rocks match samples of Martian soil analyzed by the Viking landers. Some scientists think that one such meteorite, found in Antarctica, might even contain fossils of tiny organisms called bacteria — but, as often happens, other scientists disagree.