Nasa has found what it calls “strong evidence” that life once existed on Mars after re-examining a meteorite.
A research team at Johnson Space Centre in Houston has been re-examining a meteorite that hit Antarctica 13,000 years ago, and found the most compelling evidence yet that the planet once harboured bacterial life.
The team says that microscopic crystals found in the rock are almost certainly fossilised bacteria that have many characteristics in common with bacteria found on Earth.
“The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade,” said David McKay, Nasa chief scientist for exploration and astrobiology.
“This evidence includes signs of past surface water including remains of rivers, lakes and possibly oceans and signs of current water near or at the surface.”
The debate centres on magnetite crystals found in the meteorite. A study carried out in 1996 suggested that they were biogenic - produced by living organisms.
Critics, however, suggested that the magnetite was formed by a chemical process called thermal decomposition.
The new paper uses more advanced instruments to refute the critics’ theory, arguing that ancient life remains the most plausible explanation.
“We believe that the biogenic hypothesis is stronger now than when we first proposed it 13 years ago,” said Everett Gibson, a Nasa scientist.
2009-12-03 17:05 编辑：kuaileyingyu
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