An 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 started on early Earth. The new study by researchers at Scripps Institution of Oceanography at the University of California, San Diego, and their colleagues shows that the Orgueil meteorite, which fell in France in 1864, may be the first meteorite traced to a comet, rather than from 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 we have found to be present in Orgueil," said Jeffrey Bada, a professor of marine chemistry at Scripps.
The study appears in the Feb. 27 issue of the Proceedings of the National Academy of Sciences and is authored by Bada, Daniel Glavin, and Oliver Botta of Scripps; Pascale Ehrenfreund of the Leiden Observatory in the Netherlands; and George Cooper of the NASA Ames Research Center.
Although the Orgueil meteorite, named after the French town near where it fell in 1864, had been analyzed decades ago, Bada and his 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, the researchers found that it contained a relatively simple mixture of amino acids, consisting primarily of glycine and beta-alanine. They also analyzed the sample’s carbon isotope concentration and found that the amino acids were not derived from earthly contamination.
"We found that the amino acids in Orgueil are abiotic. They were formed without the help of biology, only chemical reactions," said co-author Botta. "We think these amino acids were synthesized in space."
The research team then compared their results with three other meteorites: Murchison and Murray, which have been studied extensively, and Ivuna, a meteorite that fell in Tanzania, Africa, in 1938 that had not been analyzed for amino acids.
The research team broke the meteorites down into two classes. The Murchison and Murray meteorites were placed in a category containing a complex mix of amino acids made up of more than 70 different types of amino acids. Orgueil and Ivuna, however, were categorized with 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 pieces of an asteroid, as are virtually all meteorites scientists have studied. However the paper suggests Orgueil and Ivuna show evidence that they are likely derived from a comet. The amino acid signatures within Orgueil and Ivuna suggest that these compounds were likely synthesized from components such as hydrogen cyanide, which have been recently observed in the comets Hale-Bopp and Hyakutake.
"This suggested to us that what we may be seeing in Orgueil and Ivuna are the products of reactions that once took place in the nucleus of a comet," said Bada.
"If it’s true, this would be the first time that a meteorite from the nucleus of a comet has been identified," said co-author Glavin. "There is really a lot we don’t understand about the chemistry of a comet nucleus and this would be our first insight."
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 study was funded by the National Aeronautics and Space Administration Specialized Center of Research and Training in Exobiology at Scripps, the Austrian Academy of Sciences, and the Netherlands Research School for Astronomy.