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Organic Material In Martian Meteorite Found To Be From Earth

Scripps Institution of Oceanography
University of California-San Diego

MEDIA CONTACTS:

Scripps Institution of Oceanography
Cindy Clark or Janet Howard, (619) 534-3624
Email: cclark@ucsd.edu; jehoward@ucsd.edu

University of Arizona
Lori Stiles, (520) 621-1877
lstiles@u.arizona.edu

ORGANIC MATERIAL IN MARTIAN METEORITE FOUND TO BE FROM EARTH
January 15, 1998

Organic material contained in a meteorite heralded as bearing signs of
previous life on Mars is actually from Earth. Scientists at UCSD's Scripps
Institution of Oceanography and the University of Arizona in Tucson report
in two separate papers in the Jan. 16 issue of Science that the potato-
sized rock was contaminated by the surrounding Antarctic ice in which it
was found. The scientists are the first to publish results of tests of
organic material contained in the meteorite, named Allan Hills 84001
(ALH84001), since research teams at NASA's Johnson Space Center and
Stanford University announced their results in August, 1996.

"This is bad news with respect to using these meteorites to assess whether
there ever was or is life on Mars," said Jeff Bada, a professor of marine
chemistry who headed the Scripps team. "It shows that the meteorites
aren't going to give us a definitive answer."

Bada's team analyzed amino acids contained within a sample from the
meteorite while Timothy Jull's team at the University of Arizona examined
the radiocarbon activity of the bulk organics. 

"What we found was that, yes, there are amino acids in the meteorite at
very low levels, but they are clearly terrestrial and they look similar to
amino acids we see in the surrounding Antarctic ice," Bada said. "How
they got in there is still an open issue."

Likewise, Jull's team used 14C and 13C tracers to determine the origin
of the carbonate minerals and organic carbon in the meteorite. Their
results indicated that the bulk of organic material in ALH84001 is
contaminated material it acquired after falling to Earth.

"It looks like regular terrestrial organic material," Jull said. "The 14C
content of it suggests that there were several episodes of contamination."

Scientists at Johnson Space Center and Stanford reported in Aug. 1996
that they had found the first organic molecules thought to be Martian in
origin. Called polycyclic aromatic hydrocarbons (PAHs), these organic
molecules were found in easily detectable amounts in tiny globs of
carbonate within the meteorite. They also noted finding several mineral
features characteristic of biological activity and possible microscopic
fossils of primitive, bacteria-like organisms inside the meteorite. Their
findings were published in the Aug. 16, 1996, issue of Science.

The scientists proposed that very primitive microorganisms may have
assisted in the formation of the carbonate, and some of the microscopic
organisms may have become fossilized, in a fashion similar to the
formation of fossils in limestone on Earth.

Jull's analysis of isotopes contained in organic material and carbonate
from the meteorite, however, indicates the two are of a completely different
origin, making a relationship between the two impossible.

"The organic material contains 14C and the carbonate doesn't because
the carbonate came from somewhere in space, presumably Mars, and the
organic material is a recent addition which took place while the meteorite
was sitting on the ice," Jull said. "So, there is no connection between the
two things." 

Bada said he chose to focus his analysis on amino acids within the
meteorite because, unlike PAHs, they play an essential role in
biochemistry.

An expert in the analysis of amino acids, Bada used high-performance
liquid chromatography to analyze amino acids in the meteorite to
determine their "handedness." He found that the bulk of the amino acids
consisted of the left-handed forms similar to that seen in the Allan Hills ice
in Antarctica where the meteorite was found. Bada said he could not rule
out the possibility that minute amounts of some extra-terrestrial amino
acids such as right-handed forms of alanine were preserved in the
meteorite.

"What we and Tim Jull's team have shown is that there is no evidence in
our hands that the meteorite contains any compounds that we could
definitely trace to Mars except maybe some tiny mysterious component
that we don't understand at this point," he said.

Bada said scientists will have to wait until a Mars mission scheduled for
2005 to bring back samples from the Martian surface to determine whether
life ever graced the planet.

"In the meantime, we can throw any kind of analyses that we want to at
these meteorites and we are not going to provide an answer one way or
another about whether life existed on Mars," he said.

Co-authors of the Scripps paper are Daniel Glavin, a Scripps graduate
student; Gene McDonald, of NASA's Jet Propulsion Laboratory; and
Luann Becker, of the University of Hawaii. Co-authors of the University of
Arizona paper are Christopher Courtney, Daniel Jeffrey and Warren Beck,
all of the University of Arizona.

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http://sio.ucsd.edu
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