The organism is a common terrestrial microbe that has lived deep inside the cracks of a Martian meteorite which fell to earth 13,000 years ago, landing on an ice sheet at the South Pole.
Scientists believe the microbe has lived off the meteorite's organic carbon molecules, which originated when Mars had liquid water, and possibly life, of its own.
"Under the principle 'you are what you eat', it could be described as a Martian," said Andrew Steele, a British scientist who made the find while working at the Johnson Space Center in Houston, Texas.
Dr Steele left Britain two years ago to work with scientists at the US National Aeronautics and Space Administration (Nasa) who announced in 1996 that they had found signs of life on the Martian meteorite known as ALH84001. But, instead of finding a Martian microbe, Dr Steele came across a type of terrestrial bacteria belonging to a group called the actinomycetes, a common microbe found almost everywhere on the planet.
"It must have lived deep inside the rock and could only have got its food source of carbon from the meteorite itself. It is the only known organism on earth which has been eating Martian food," Dr Steele said.
The results of the two-year investigation into the ALH84001 meteorite will be released next week at the Lunar and Planetary Science Conference in Houston, where Nasa scientists will continue to argue that the meteorite shows genuine signs of extraterrestrial life.
Dr Steele said that the microbe was overlooked in the past because scientists had been using inappropriate detection methods.
"In the particular case of ALH84001, a terrestrial organism went undetected by all the techniques that claim to be able to detect life."
Meteorites from Antarctica were once thought to be free from earthly contamination because of the pristine state of the frozen continent, but this is no longer the case.Reuse content