Miércoles 22 de Febrero de 2006, Ip nº 141

Martian meteorite may have held life
Por Kimm Groshong

A mix of carbon compounds filling the miniscule veins in a Martian meteorite has refuelled the debate on the possibility of life on Mars. Similarities between the carbon-rich filler and that found in fractured volcanic samples from the Earth's ocean floor dangle the possibility that life produced the Martian material, say scientists.

A team of researchers led by David McKay and Everett Gibson of the Johnson Space Center in Houston, US, raise the scenario as just one possibility after extensively analysing new samples of the Nakhla meteorite.

The UK’s Natural History Museum recently provided the team with fresh samples from the interior of the meteorite, which broke into many pieces upon landing in Egypt in 1911.

Near the tube-like veins in the rock, researchers found iddingsite – a mineral also formed on Earth, mainly through alteration of an iron-based mineral called olivine by water. And within the cracks, they found carbon-rich material that appears dark brown or black.

"Indigenous stuff"
Astrobiologists look for carbon and water in their search for extraterrestrial life. Carbon is the building block of terrestrial life, forming the basis for organic chemistry, and water is necessary to support all forms of life on Earth.

Sceptics have cast doubt on previous claims of organic material in Nakhla, saying the carbonaceous matter was simply contamination from Earth. But Colin Pillinger, a team member from the Open University in Milton Keynes, UK, says results from the new samples from the carefully protected interior of the meteorite lay those concerns to rest. "We're pretty confident this is indigenous stuff,” he says. “We don't think it's contamination.”

Biogenic activity
In two abstracts submitted to the Lunar and Planetary Science Conference in Houston, US, happening in March, the team outlines possible sources of the carbon-containing components. Either a carbon-bearing impactor introduced them to Mars between 600,000 and 700,000 years ago or they are "products of biogenic activity and introduced by groundwater into the fracture features in Nakhla," the team writes.

The team cites an upcoming study by oceanographer Martin Fisk, of Oregon State University in Corvalis, US, who compared Earth features to Martian meteorites. The authors note "the close resemblance" of Nakhla's carbon-rich material to carbon Fisk noted in veins within basaltic glass from the ocean floor.

In this forthcoming paper in Astrobiology, Fisk reports that DNA is associated with the fractures, or tunnels, in rock samples from Earth's ocean floor, a mountain top in Oregon and a rainforest on the California-Oregon border. "There's not DNA distributed throughout the rock, it's very specific to the tunnels," Fisk says.

Nothing's certain
Furthermore, the size and shape of the tunnels in the Earth samples closely resemble those seen in Nakhla. And he says researchers have yet to see a non-biological explanation for the tunnels, although that does not rule out the possibility.

"We're saying here's a phenomena on Earth that we're pretty darn sure are caused by bacteria", and rocks from Mars sport similar features, Fisk says. "I'm letting people draw their own conclusions.”

Pillinger is careful to point out that the new findings do not mean the community has definitive evidence for life on Mars. "We're finding these very strange features, but we can't say anything more than that," he says. "They could have come from several processes and one of them is biological."

  10/02/2006. New Scientist Magazine.