The first results are in from the organic analysis of the Tagish Lake Meteorite, a rare,
carbon-rich meteorite classified as a “carbonaceous chondrite” that fell on a frozen
Canadian lake in January 2000 and is the most pristine specimen ever studied of this
group of important space objects.
Carbonaceous chondrite meteorites contain vital clues to the evolution of carbon
compounds in our solar system preceding the origin of life.
The analysis, conducted by a team headed by chemist Sandra Pizzarello, a research
scientist at Arizona State University, on 4.5 grams taken from the sealed interior of the
meteorite, found organic compounds in the meteorite with some similarities to other
known carbonaceous chondrites, but also clear differences — most notably the
near-absence of the amino acids found in some meteorites studied before.
In an article scheduled to appear in the August 24 issue of the online journal Science
Express (with publication in Science to follow) http://www.sciencemag.org/cgi/content/abstract/1063734v1]the team notes that the chemistry of the
Tagish Lake Meteorite appears to preserve organics that accumulated or developed in
the early history of the Solar System – including molecular bubbles of carbon
(fullerenes or “buckyballs”) containing the noble gasses helium and argon in a ratio
similar to the gas and dust cloud that formed the planets — and thus perhaps reflects
an early stage in a process of evolution of complex carbon compounds in space.
“The chemistry here is different from that we have seen in any other meteorite,” said
Pizzarello. “It’s simple, when compared with Murchison (a famous carbon meteorite
found in Australia in 1969 that contained numerous amino acids and a variety of other
organic compounds) and probably represents a separate line of chemical evolution.
However, it still includes compounds that are identical to biomolecules.”
Other members of the research team include Yongsong Huang from the Department
of Geological Sciences at Brown University; Luann Becker from the Institute for Crustal
Studies at the University of California Santa Barbara; Robert J. Poreda from the
Department of Earth and Environmental Sciences, University of Rochester; George
Cooper from the NASA Ames Research Center; and Ronald A. Nieman and Michael
Williams, both also from ASU.
The Science paper notes that many of the organic compounds found in the Tagish
Lake sample have also been found in other meteorites, but that the distribution of
compounds is different, particularly for the amino acids and carboxylic acids.
“Some people have been disappointed that we found virtually no amino acids, but
scientifically this is very exciting,” Pizzarello said. “This meteorite shows the complexity
of the history of organic compounds in space — it seems to have had a distinct
evolution.
“We found some compounds identical to some in Murchison that show the same
‘interstellar connection’ in their abundance of deuterium (heavy hydrogen), while
some others differ from Murchison in amounts and variety,” said Pizzarello, meaning
that for some groups of organic molecules, only the simplest species were found in
Tagish Lake, as opposed to a broader distribution of species found in Murchison.
“Overall, Tagish Lake represents a simpler, more unaltered stage than we have seen
before.”
What emerges from the analyses is evidence for what Pizzarello calls “a different
outcome” of organic chemical evolution in space likely to have happened during the
formation and development of the solar system, “but one that still might have
contributed molecular precursors of biomolecules to the origins of life,” she noted.
###
Source: Sandra Pizzarello, 480-965-3370, pizar@asu.edu
Contact: James Hathaway
Hathaway@asu.edu
480-965-6375
Arizona State University
