New findings on amino-acids in meteorites show the potential of Rosetta for astrobiology
1 March 2001An object that fell to Earth more than 136 years ago has revealed new clues about the origin of meteorites in space and new information about how life may have risen on the early Earth. The new study by astrobiologist Pascale Ehrenfreund and collaborators shows that the Orgueil meteorite, which fell in France in 1864, may be the first meteorite traced to a comet, rather than to an asteroid, the source widely believed to produce meteorites. The contents within Orgueil, the study says, may have been just the type of fundamental ingredients necessary to help generate life on Earth. Scientists have generally believed that a wide variety of amino acids were required for the origin of life on Earth. "Recent research suggests, however, that only a few types of simple amino acids may have been required, and that is exactly what was found to be present in Orgueil" .
These new findings illustrate the enormous potential of ESA's ROSETTA mission to be launched to comet Wirtanen in January 2003.
The study appeared in the Feb. 27 issue of the Proceedings of the National Academy of Sciences and is led by Pascale Ehrenfreund from Leiden Observatory in The Netherlands and coauthored by Daniel Glavin, Oliver Botta and Jeffrey Bada of Scripps Institution of Oceanography and George Cooper of the NASA Ames Research Center.
Although the Orgueil meteorite had been analysed decades ago, Ehrenfreund and her colleagues conducted a new study using sophisticated techniques and instruments aimed at detecting trace levels of amino acids. Amino acids are the fundamental components of proteins and are synthesized in living cells.
After obtaining a pristine piece of the interior portion of Orgueil from Paris Natural History Museum, the researchers found that it contained a relatively simple mixture of amino acids, consisting primarily of glycine and beta-alanine. They also analysed the sample's carbon isotope concentration and found that the aminoacids were not derived from earthly contamination, but are indeed extraterrestrial. The research team then compared their results with three meteorites: Murchison and Murray, which have been studied extensively, and Ivuna, a meteorite that fell in Tanzania in 1938.
Murchison and Murray contain a complex mix of amino acids made up of more than 70 different types of amino acids. Orgueil and Ivuna, however, have a much simpler composition made up primarily of just two amino acids. Based on the unique amino acid composition within Orgueil, the researchers were able to deduce information about the meteorite's past. Murchison and Murray are widely believed to be products of asteroids, as are virtually all meteorites scientists have studied. However Orgueil and Ivuna, the paper indicates, show evidence that the parent body of CI carbonaceous chondrites may have been an extinct comet. Thus, the paper suggests, the amino acids that helped generate life on Earth may have been delivered by meteorites that were derived from the remnants of comets.
The amino acid signatures within Orgueil and Ivuna were likely synthesised from components, such as hydrogen cyanide, which have been recently observed in two exceptionally bright comets, Hyakutake and Hale-Bopp. "Optical, radio and ISO infrared observations of those two exciting comets have strongly improved our knowledge on cometary outgassing, but there's really a lot we still have to learn about the chemistry of a comet nucleus, which we can do especially with ESA's ROSETTA mission to comet Wirtanen", concludes Ehrenfreund. "Space measurements with ROSETTA orbiter and lander will give key information on the structure of cometary nucleus, but also its composition, including the prebiotic organic compounds we detected in the meteorites."
Prof. Pascale Ehrenfreund
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2300 RA Leiden