Fragments of a chemically primitive meteorite that landed near Murchison, Australia, in 1969 have long been known to harbor a variety of interesting compounds, including dozens of amino acids. But as analytic techniques become more sophisticated, the Murchison meteorite continues to reveal even more diversity and complexity in the early solar system, and new work by a team of European researchers is no exception.
In the study, set to be published in Proceedings of the National Academy of Sciences, analytical chemist Philippe Schmitt-Kopplin of the Helmholtz German Research Center for Environmental Health in Munich and his colleagues used high-resolution mass spectrometry to look at the organic (carbon-based) content of three Murchison samples. The group found more than 14,000 unique molecular compositions, or collections of atoms, in the samples; there may be 50,000 or more such compositions, if the limited scope of the mass spectrometry analysis is taken into account. And because each collection of atoms can be arranged in numerous ways, the authors estimate that there may be millions of distinct organic compounds in the meteorite.
Many researchers have analyzed the chondritic meteorite for amino acids and other possible precursors to life, because some theories hold that life on Earth began with the delivery of prebiotic organic compounds from space via asteroids or comets. Schmitt-Kopplin says that he and his colleagues took a less targeted approach to try to unlock the meteorite's full chemical complexity and, by extension, the chemical complexity of the early solar system. "What we've seen out of this is that we had such a multitude of signals as we never saw in any other sample before," he says. "Even in petroleum, you have really complex materials, but not necessarily as complex as this."
Daniel Glavin, an astrobiologist at the NASA Goddard Space Flight Center in Greenbelt, Md., who did not contribute to the latest study, has worked on Murchison and other meteorites to look for possible precursors to life that may have arrived on Earth from space. "I think that the issue of diversity and complexity in chemistry is something that has been known for a while with meteorites," Glavin says. "I don't think we knew it was this complex, as what they're showing."
Murchison is a popular meteorite for study partly because roughly 100 kilograms of its stony fragments were quickly collected in 1969 and so did not suffer from much terrestrial contamination. It carries the signature of the solar system from around the time of the sun's formation, roughly 4.6 billion years ago. "It really is some of the first condensates of the early solar system," Glavin says. "This stuff basically freezes a record of some of the earliest chemistry taking place in the solar system that we have access to."
Glavin and his colleagues have had similar success in applying modern analytic approaches to the Murchison meteorite in a targeted search for compounds more relevant to life, finding evidence for hundreds of amino acids. "It really shows the benefits of having these samples and keeping them around until new, more advanced techniques come about to analyze them," Glavin says.
He notes that it will take time to match specific compounds to the potentially millions of chemical species in the Murchison meteorites. "It's exciting, but it also scares me at the same time," Glavin says. "We have a lot of work to do to even pretend to understand what this stuff is."