[meteorite-list] Study May Cast Doubt on Some 1996 Evidence of Past Life on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed May 5 13:35:42 2004
Message-ID: <200405051734.KAA10599_at_zagami.jpl.nasa.gov>

http://www.jsc.nasa.gov/news/releases/2004/J04-025.html

William Jeffs
Johnson Space Center, Houston
281-483-5111

Release: #J04-025
May 5, 2004

STUDY MAY CAST DOUBT ON SOME 1996 EVIDENCE OF PAST LIFE ON MARS

The scientific debate over whether a meteorite contains
evidence of past life on Mars continues to intensify, with
colleagues of the team that announced the possibility in 1996
revealing new findings that may cast doubt on some of that
earlier work.

"These new findings illustrate the excellent scientific
process that was ignited by the announcement in 1996 of
possible meteorite evidence of past life on Mars," said Dr.
Steven Hawley, Associate Director, Office of Astromaterials
Research and Exploration Science at the Johnson Space Center.
"As work on this fundamental question continues, it is quite
likely the final answer may not be known until Mars samples
can be retrieved for study by scientists there or back on
Earth."

In the recent study, a team of scientists based largely at JSC
found that a mineral in Mars meteorite ALH84001 that had been
asserted to be most likely caused by an ancient microscopic
organism may have been caused by a non-biological process. The
team, led by D.C. Golden of Hernandez Engineering Inc. in
Houston and including many NASA scientists from the Office of
Astromaterials Research and Exploration Science, will have its
work published in the May/June issue of American Mineralogist.
The same office includes Dave McKay, Everett Gibson and
several other scientists who contributed to the 1996 findings.

The new paper reports that magnetite, an iron-bearing mineral
found in Martian meteorite ALH84001, was likely caused by
inorganic processes, and that those same processes can be
recreated in the laboratory, forming magnetite identical to
that found in the Mars meteorite.

Magnetite crystals in ALH84001 have been a focus of debate
about the possibility of life on Mars. The 1996 study led by
McKay suggested that some magnetite crystals associated with
carbonate globules in ALH84001 are biogenic because they share
many characteristics with those found in bacteria on Earth. A
study led by Kathie Thomas-Keprta in 2000 showed that some of
the magnetite crystals in ALH84001 carbonate globules are
characterized by elongation, a "unique habit" identical to
magnetite grains produced by bacteria on Earth.

Golden and his team first investigated whether an inorganic
process can produce magnetite crystals identical to those in
ALH84001 claimed by Thomas-Keprta's team to be biogenic. Then,
they sought to replicate the tenet of McKay's 1996 hypothesis
that the purported biogenic magnetite grains in ALH84001 are
identical to those produced by a bacterium called MV-1.

Golden's team concluded that the shapes of the MV-1 and
ALH84001 elongated crystals differ. Their study concluded that
inorganic processes can make the magnetite crystals in
ALH84001, so any claim to a biological source is uncertain.
Golden's team found that decomposition of iron-bearing
carbonate under high heat produced magnetite crystals
identical to those found in ALH84001.

"The strength of the inorganic process provided here is that
not only does it produce elongated magnetite crystals
identical to those of the ALH84001 meteorite, but also it
produces a whole range of features found in the meteorite,"
said Golden, a mineralogist at JSC.

McKay, chief scientist for astrobiology at JSC, stands by his
1996 findings. "We originally proposed a suite of four lines
of evidence which, taken together, were consistent as a
package with a possible biological origin," McKay said. "The
Golden group has singled out one very specific feature, the
shape of the magnetite crystals, to try to discredit the whole
biogenic hypothesis. Their alternative inorganic hypothesis,
thermal decomposition of carbonate, will not explain many of
the features described by us in ALH84001. A plausible
inorganic model must explain simultaneously all of the
properties that we and others have suggested as possible
biogenic properties of this meteorite."

ALH84001 was discovered in 1984 in the Allan Hills region of
Antarctica by an annual expedition of the National Science
Foundation's Antarctic Meteorite Program. Its Martian origin
was not recognized until 1993. One of about 30 meteorites
discovered on Earth thought to be from Mars, it is a
softball-sized igneous rock weighing 1.9 kilograms (4.2
pounds). With the exception of ALH84001, all are less than 1.3
billion years old. ALH84001 is 4.5 billion years old.

To view the study on the Internet, visit:

http://www.minsocam.org/MSA/AmMin/AmMineral.html For
information about space research on the Internet, visit:
http://spaceresearch.nasa.gov/ Video to accompany this release
will air on the NASA Television Video File at 11 a.m. CDT May
5. NASA TV is on AMC-9, transponder 9C, C-Band, at 85 degrees
west longitude, frequency 3880.0 MHz, polarization vertical,
audio monaural at 6.80 MHz.

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Received on Wed 05 May 2004 01:34:33 PM PDT