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Recognizing Extraterrestrial Life

From: UFO UpDates - Toronto <ufoupdates@virtuallystrange.net>
Date: Sat, 24 Nov 2001 03:51:38 -0500
Fwd Date: Sat, 24 Nov 2001 03:51:38 -0500
Subject: Recognizing Extraterrestrial Life

http://www.asu.edu/asunews/current_releases/extraterrestrial111501.htm


News Release

Office of Media Relations and Public Information

November 15, 2001

ASU researchers set criteria for recognizing extraterrestrial
life


For as long as people have gazed at the night sky, they have
wondered if neighboring planets could be populated by living
things. In fact, recent explorations of our solar system have
relayed several enticing hints that the life-supporting
conditions on Earth may not be so unique.

Evidence for water and organic compounds on Mars and Europa has
astrobiologists seriously pursuing the possibility that
primitive life once existed on other planets and moons. As they
gear up for the real acid test - collecting samples from these
distant bodies to examine them directly for evidence of life -
they are tackling nothing less profound than the origins of life
in the universe.

But this pursuit is nagged by an uncertainty: We have never seen
our extraterrestrial cousins before. How will we recognize them
if we meet face to face? Peter Buseck and Martha McCartney, new
members of ASU's arm of the NASA Astrobiology Institute, are
among many scientists who predict the best clues are to be found
in lowly bacteria.

Buseck, Regents Professor of geological sciences and professor
of chemistry and biochemistry at ASU, and McCartney, a research
scientist at ASU's Center for Solid State Science, were recently
funded by NASA to help develop reliable criteria for identifying
traces of life, or "biomarkers," for use during future
astrobiology missions.

Study of organisms from Earth, Buseck and McCartney argue, is
the most promising way to start. After all, Earthly life is the
only life we know, making it our one reference point in judging
whether extraterrestrial life exists. Therefore, Buseck reasons,
"if you find something in extraterrestrial samples that
resembles life on Earth then it's reasonable to think that you
have found traces of life" on other planets.

Because astrobiologists expect extraterrestrial life, if it
exists, to be simple, terrestrial bacteria are getting top
billing as model Martians. Bacteria are single-celled organisms,
among the most primitive life forms on Earth. But the hunt for
ancient bacteria presents some special challenges. Bacteria, all
soft parts and no bones, do not usually leave any traces in the
rock record, making their presence hard to prove. To
unequivocally demonstrate that bacteria were ever present,
Buseck stresses that "you need some sort of biomarker, some sort
of remainder." Preferably, that biomarker should be a durable
material, such as a mineral, that can survive for billions of
years.

Just such a long-lasting biomarker may have already been found -
in a NASA scientist team's 1996 claim of fossil bacteria in a
4.5 billion-year-old Martian meteorite, perhaps the most
stunning evidence to date of extraterrestrial life. Not
surprisingly, the claim continues to spark heated controversy.
Buseck and McCartney aim to moderate the debate by putting the
Martian life hypothesis to a very thorough test.

The group of scientists originally studying the now-renowned
meteorite - known as ALH84001 - presented a slew of findings,
including organic chemicals and "bacterium-shaped objects," that
collectively cried "life." Since then, intense scrutiny by other
researchers has shown that most of that evidence could have
resulted from non-biological processes or artifacts introduced
during study of the meteorite.

Only one of the original findings is still thought to be a
unique indicator of life: Crystals of an iron-based mineral
called magnetite. The crystals found in the meteorite are
striking because magnetite grains with similar size, purity, and
structural perfection previously have been seen only in bacteria
found on Earth. According to the NASA group's report, no
inorganic process could have produced the meteoritic crystals.
Only so-called "magnetotactic" bacteria, which form the
magnetite grains through a controlled process, can generate
these particular shapes.

Magnetotactic bacteria, common in aquatic and marine habitats,
produce and carry the magnetic crystals in a chain. The chain,
which looks like a faux backbone under a microscope, acts like a
compass as the bacterium swims along Earth's magnetic field
lines.

These crystals are at the center of Buseck and McCartney's
planned work. If bacterial synthesis is the single possible
explanation for the magnetite grains found in ALH84001, they
could be the one clear indication that life ever existed outside
Earth. But, Buseck worries, if no major holes have yet been
punched in this argument, that may be because it has not been
examined closely enough.

And when Buseck says "closely," he means it quite literally.
"These crystals are at the limit of what one can see, even with
powerful electron microscopes," he says.

At 40 to 100 billionths of a meter wide, magnetite nanocrystals
have evaded clear three-dimensional imaging. That's a problem
for the hypothesis of life on Mars, which now hinges on precise
matching of the complex shapes of the magnetite crystals from
ALH84001 and from magnetotactic bacteria.

"There are questions about how well we know the shapes of these
tiny crystals and how secure the identity is between those in
the meteorites and those in the bacteria," says Buseck.

To be able to match the crystals from the two sources with
confidence, Buseck says astrobiologists must first fulfill four
clear objectives. "What we need to do is determine the shapes in
the meteorites with high accuracy, determine the shapes of the
crystals in bacteria with comparable accuracy, demonstrate their
identity, and then somehow determine that there are no other
ways of forming such crystals. Then we'd have a tight case." Of
these four steps, Buseck and McCartney intend to test the first
three. They are studying the shapes, chemical composition, and
magnetic properties of both the meteoritic and bacterial
magnetite grains in unprecedented detail. New developments in
transmission electron microscopy, a technique in which samples
are viewed with a beam of electrons rather than a beam of light,
have only recently made such precise study of crystal shapes
possible.

Using the recently improved techniques, the team will generate
dozens of two-dimensional images taken from different angles as
well as three-dimensional holograms of each magnetite grain. The
resolution of their images will be in the range of hundreds of
trillionths of a meter.

In these efforts, Buseck and McCartney plan to continue ongoing
collaborations with fellow scientists Dennis Bazylinski (of Iowa
State University), Richard Frankel (of the California
Polytechnic State University), Rafal Dunin-Borkowski, (of
Cambridge University, England), and Mih=E1ly P=F3sfai (of the
University of Veszpr=E9m, Hungary).

Their work will provide improved data and criteria for use in
evaluating whether other magnetite grains, from meteorites or
from samples collected in outer space, have a biological origin.
Of course, ALH84001 will be the first Martian rock subjected to
Buseck and McCartney's uncompromising analysis.


    -ASU-






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