EARTH INVADES MARS
with Simon Mansfield
........


Mars Meteorite Contaiminated By Antarctic Life
Los Alamos - Jan 16, 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.

  • Scripps Institution of Oceanography


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