[meteorite-list] No Knockouts in Martian Meteorite Showdown

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:31 2004
Message-ID: <200203201628.IAA15025_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/current/article_534_1.asp

No Knockouts in Martian Meteorite Showdown
By David L. Chandler
Sky & Telescopel
March 17, 2002

All last week, attendees at the 33rd annual Lunar and Planetary Science
Conference in Houston, Texas, looked forward to one of the meeting's final
sessions, whose main attraction was the controversial 4½-billion-year-old
Martian meteorite known as ALH 84001. For years David S. McKay (NASA/Johnson
Space Center) and his coauthors have maintained that this celebrated stone
contains strong evidence - but not proof - of fossilized microbial life.

Friday's debate focused on tiny, uniform, and chemically pure crystals of
magnetite embedded in carbonate globules within the meteorite, crystals that
look remarkably similar to those produced by certain strains of terrestrial
bacteria. Dadigamuwa C. Golden (Hernandez Engineering) and Douglas W. Ming
(NASA/Johnson Space Center) reported that the perfectly formed, chemically
pure magnetite crystals they've created in their laboratory also share the
distinctive size and shape of those in ALH 84001.

But members of the McKay team countered that 3-D views shown by Ming did not
unambiguously reveal the "truncated hexa-octahedrals," or THOs, that would
signify a unique biological signature. Kathie Thomas-Keprta (Lockheed Space
Systems) argued that while the synthesized crystals might be THOs, they were
more likely cubo-octahedrons - the most common shape of magnetite formed by
artificial means. Golden, in return, conceded that the images he presented
might not provide proof but claimed he had other images that would. To
complicate matters further, all parties agree that most of the meteorite's
magnetite grains were formed by some inorganic process.

And so the debate remains about where it has been for the last few years: a
standoff. But some tantalizing new research hints that the issue might
indeed be resolved after additional work. A second team, Andrea M. Koziol
(University of Dayton, Ohio) and Adrian J. Brearley (University of New
Mexico), has also synthesized meteorite-mimicking crystals, and it may be
only a matter of time before a few convincing images clinch the case for
nonbiological origin. However, as McKay stressed during Friday's
presentations, the laboratory conditions used to synthesize the crystals
differ significantly from those encountered by the meteorite itself.

Meanwhile, a team led by Joseph L. Kirschvink (Caltech) introduced some
brand-new techniques for studying these contentious crystals, which are less
than 100 nanometers (2 millionths of an inch) long. The results presented
are ambiguous, because so far only bulk material from ALH 84001 has been
tested. But Kirschvink's group has used three different methods to analyze
magnetite from a wide variety of sources. One of these outcomes did indeed
show the Martian magnetites to be much closer to those produced by certain
terrestrial bacteria than to the synthesized versions. However, results from
the other two methods, though only preliminary and less clear, suggest that
the Martian crystals share characteristics with both the synthesized
versions and those from fossilized bacteria (but not those produced by
living bacteria).

These techniques hold great promise to help resolve the question, McKay said
after the session. His group is also pursuing various lines of further
research, including close scrutiny of some additional formations in the
meteorite that may turn out to be microscopic fossils. But, clearly stung by
the intense and often bitter controversy that has surrounded their work
since the initial publication, he said the group will not attempt to publish
such findings until they have conducted sufficient tests to make the results
"bulletproof."
Received on Wed 20 Mar 2002 11:28:15 AM PST