Wednesday, July 8, 1998 Published at 15:25 GMT 16:25 UK
Life on Mars 'doubtful'
Fossilised micro-organisms or just mineral grains?
Yet another study has cast doubt on the claims that a rock from Mars contains evidence of past life. Our science editor Dr David Whitehouse examines the arguments.
Using an electron microscope, they found that the mineral crystals in the rock were intermingled with carbon compounds. This means that if the crystals were made at high temperatures then the carbon was as well.
The possibility that the carbon compounds formed as the result of bacterial life processes can be ruled out say the scientists.
The new research is published in the journal Meteoritics and Planetary Science.
It is the third scientific paper in a series that have all disputed claims of life in the meteorite.
'These three papers in combination basically invalidate much of the evidence' says Dr John Bradley of the Georgia Tech School of Minerals Science and Engineering.
The rock is believed to have been blasted from Mars during an asteroid impact hundreds of millions of years ago. After millions of years in space it fell onto Antarctica.
The JSC team claimed to have seen tiny structures, far smaller than earth bacteria, They called them microfossils or nanobacteria.
They also said that the rock contained carbon compounds that were the result of life processes.
Most scientists were unconvinced. Since the 1996 announcement, almost every investigation into the rock has concluded that it bears no evidence of past life.
Nevertheless, according to Dr Bradley 'Until the JSC team concedes, the debate will never die.'