[meteorite-list] Nakhla Meteorite Re-Opens Life on Mars Debate

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Feb 8 12:23:52 2006
Message-ID: <200602081722.k18HMBf13640_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/2/hi/science/nature/4688938.stm

Space rock re-opens Mars debate
By Paul Rincon
BBC News
February 8, 2006

A carbon-rich substance found filling tiny cracks within a Martian
meteorite could boost the idea that life once existed on the Red Planet.

The material resembles that found in fractures, or "veins", apparently
etched by microbes in volcanic glass from the Earth's ocean floor.

Details will be presented at the Lunar and Planetary Science Conference
in Houston, Texas, next month.

All the processes of life on Earth are based on the element carbon.

Proving carbon in Martian meteorites is indigenous - and not
contamination from Earth - is crucial to the question of whether life
once arose on the Red Planet.

Initial measurements support the idea that the "carbonaceous material"
is not contamination, the scientists say.

The research team includes scientists who brought evidence for microbial
life in another Martian meteorite, ALH84001, to the world's attention in
1998.

The Martian meteorites are an extremely rare class of rocks. They are
all believed to have been blasted off the surface of the Red Planet by
huge impacts; the material would have drifted through space for millions
of years before falling to Earth.

Fresh samples

The latest data comes from examination of a piece of the famous Nakhla
meteorite which came down in Egypt, in 1911, breaking up into many
fragments.

London's Natural History Museum, which holds several intact chunks of
the meteorite, agreed for Nasa researchers to break one open, providing
fresh samples.

"It gives people a degree of confidence this had never been exposed to
the museum environment," said co-author Colin Pillinger of the UK's Open
University.

"I think it's too early to say how [the carbonaceous material] got
there... the important thing is that people are always arguing with
fallen meteorites that this is something that got in there after it fell
to Earth.

"I think we can dismiss that. There's no way a solid piece of carbon got
inside a meteorite."

Analysis of the interior revealed channels and pores filled with a
complex mixture of carbon compounds. Some of this forms a dark,
branching - or dendritic - material when seen under the microscope.

"It's really interesting material. We don't exactly know what it means
yet, but it's all over the thin sections of the Nakhla material," said
co-author Kathie Thomas Keprta, of Lockheed Martin Corporation and
Nasa's Johnson Space Center in Houston, Texas.

Indigenous component

Previous studies of the forms - or isotopes - of carbon in the Nakhla
meteorite found a component of which more than 75% is lacking any
carbon-14.

Since all terrestrial life forms contain some carbon-14, this component
was thought to be either indigenous carbon from Mars or ancient
meteoritic carbon.

Professor Pillinger and colleagues are carrying out direct isotopic
analysis of the carbonaceous material, but he admits terrestrial
contamination is occurring when thin slices of the meteorite are made
for analysis.

However, the ratio of carbon to nitrogen in the epoxy used to prepare
the thin sections is very different from that of the carbonaceous
material in the meteorite's veins.

If it is indigenous to Mars, the authors say the "carbonaceous material"
came either from another space rock that smashed into Mars hundreds of
thousands of years ago, or is a relic of microbial activity.

A resemblance between the material in the meteorite and features of
microbial activity in volcanic glass from our planet's ocean floor
further support the idea they are biological in origin, says the paper.

If this is the case, the remains of these organisms and their slimy
coatings might provide the the carbon-rich material found in Nakhla, the
researchers argue.

Peter Buseck, regent's professor of geological sciences at Arizona State
University told the BBC News website that he found no strong evidence of
a biological origin for the carbon in the meteorite.

He added that it was difficult to determine the origin of carbon in
rocks based on microscopy.

The 37th Lunar and Planetary Science Conference runs from 13-17 March in
Houston, Texas.
Received on Wed 08 Feb 2006 12:22:10 PM PST