For a desert, there’s a bunch of cool science news coming out of the Atacama — no dry spell here. We just heard about a pterosaur fossil, found in the Atacama in a place that was once ocean, that provides evidence the flying reptiles were distributed throughout Gondwana. Now astrophysicists have used the ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) interferometer to find and analyze dense swathes of important organic molecules within active protoplanetary disks orbiting several young, nearby sunlike stars. Earth, it seems, isn’t the only place to find the ingredients for primordial soup.
The research team was looking for three molecules – “cyanoacetylene (HC3N), acetonitrile (CH3CN), and cyclopropenylidene (c-C3H2)” – in the protoplanetary disks around five young stars, between 300 and 500 light-years from Earth. All of the disks show signatures of ongoing planet formation. They’re also at a distance from their parent star of about 50-100 AU, so they’re way out beyond the “snow line” into the comet-forming region, where gases freeze into ice.
The image above shows four of the protoplanetary discs. The top row shows emission from large dust in the disks, while the bottom row shows a three-color composite image of emission from the large organic molecules HC3N (red), CH3CN (green) and c-C3H2 (blue) in each disk. Dashed circles with a radius of 50 AU indicate the scale of the comet-forming region in our own Solar System. (Image: Dr J.D.Ilee/University of Leeds)
The scientists picked those three molecules for a few reasons. The first and simplest is the difficulty of identifying complex molecules in space, to begin with. The study notes that “it has only been very recently that organic molecules with more than four atoms have been successfully detected in protoplanetary disks,” so it’s a win to confidently identify their chosen three at all. Science is also always trying to learn more about the chemistry of planet formation, including which parts of Earth’s primordial soup came from where: comets, lightning strikes, deep-sea vents, and other extreme conditions. So it’s an even bigger win that the comet-forming clouds bearing these organic molecules were right where we thought they should be.
Despite how cold, and therefore dim, the clouds are, the team was able to find them by using ALMA, which was specifically designed to look at cold stuff. In the ESO’s words, “ALMA is the most powerful telescope for observing the cool Universe — molecular gas and dust.” It even has variable resolution, which means that it can zoom: important when trying to determine exactly where one of these cold clouds might be. But the clouds of gas and dust that ALMA studies emit light with millimeter-scale wavelengths. A lot of millimeter-scale radiation is absorbed by water, so to look at cold things, ALMA needs to be somewhere very dry.
A picture of the ALMA antennas on the Chajnantor Plateau, 5,000 meters above sea level. Nineteen antennas are on the plateau. (Photo: ALMA (ESO/NAOJ/NRAO)/W. Garnier (ALMA))
Finally, finding these molecules elsewhere in space may expand our understanding of the origins of life on Earth. The molecules in this study have been identified as precursors to three of the four major classes of biomolecules: sugars, proteins, and even nucleic acids. Cyanoacetylene is one of the molecules produced during the Miller-Urey primordial soup experiment. Recent work has raised the possibility that cyanoacetylene could be an important precursor to the formation of the double-ring purine nucleobases: the “A” and “G” of DNA’s four-letter code. Acetonitrile, in where it is with lots of other nitrogen-containing molecules, may also signal the presence of aminoacetonitrile (which is the same CH3CN molecule but with an amino group tacked onto one side), a precursor to glycine, the smallest amino acid.
Dr. Catherine Walsh, one of the five co-principal investigators leading the study, said, “The key result of this work shows that the same ingredients needed for seeding life on our planet are also found around other stars. It is possible that the molecules that are needed to kick-start life on planets are readily available in all planet-forming environments.”
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