[BRIEF NOTE] Life on Mars, after all?

[rfmcdonald]

The controversy over whether or not microscopic structures embedded in the Mars-originating meteorite ALH 84001 were left by living things or not seems to be tipping in the direction of the life forces. Or so the Times reports.

Nasa scientists have produced the most compelling evidence yet that bacterial life exists on Mars.

It showed that microscopic worm-like structures found in a Martian meteorite that hit the Earth 13,000 years ago are almost certainly fossilised bacteria. The so-called bio-morphs are embedded beneath the surface layers of the rock, suggesting that they were already present when the meteorite arrived, rather than being the result of subsequent contamination by Earthly bacteria.

“This is very strong evidence of life on Mars,” said David Mackay, a senior scientist at the Nasa Johnson Space Centre , who was part of the team of scientists that originally investigated the meteorite when it was discovered in 1984.

In a 1996 study of the sample, Dr Mackay and others argued that the microfossils were evidence of life, but sceptics dismissed the claims, saying that similar-shaped structures might not be biological. The new analyses, the product of high resolution electron microscopy, make a strong case for the Allan Hills 84001 Meteorite having carried Martian life to Earth. The microscopes were focused on tiny magnetite crystals present in the surface layers of the meteorite, which have the form of simple bacteria. Some argued that these could be the result of a carbonate breaking down in the heat of the impact.

The new analyses show that this is very unlikely to have resulted in the kinds of structures seen in the rock. Close examination suggested that about 25 per cent of the crystal structures were chemically consistent with being formed from bacteria.

“We feel vindicated. We’ve shown the alternate explanation is absolutely incorrect, leading us back to our original position that these structures are formed by bacteria on Mars,” Dr Mackay said.

Dennis Bazylinski, an astrobiologist from the University of Nevada who peer-reviewed the findings, said: “Until now I was on the fence but this paper has really thrown out the non-biological explanation.” However, he added that the study was not a “smoking gun” for life on Mars. “One meteorite is never going to answer such a complex question,” he said.

Craig Couvault at Spaceflight Now writes that the balance was tipped by a combination of improved microscope technology that allowed for closer study of the remnants (magnetic crystals and carbonate clusters) and the discovery of Earthly bacteria which left the very same sorts of remains.

The new work centers on so-called magnetic bacteria that on Earth, and apparently Mars as well, leave distinctively-shaped remnants in the rock. In addition the features test with a high chemical purity more like a biological feature than geological.

These are just like the magnetite-related life forms found in the meteorite believed to represent Martian life forms, says Dr. Dennis Bazylinski, who peer reviewed the new findings. He also studies such Earth life forms in his laboratory at the University of Nevada at Las Vegas.

"I think the paper is really excellent. I have no trouble with the paper," Bazylinski told Spaceflight Now.

"I work on magnetic bacteria, and one indication there was life on ancient Mars are these particular magnetite crystals in the meteorite that look like they came out of magnetic bacteria. At first [when the data was reported in 1996], I thought there might have been an error. I have no doubt about that now. I know there is no error," Bazylinski stressed.