Astronomers have detected the presence of complex organic molecules, the building blocks of life, in a protoplanetary disc surrounding a young star named MWC 480. That means the conditions that spawned the Earth and Sun are not unique in the Universe.
MWC 480, which is about twice the mass of the Sun, is located 455 light-years away in the Taurus star-forming region. Its surrounding disc is in the very early stages of development — having recently coalesced out of a cold, dark nebula of dust and gas. Studies with ALMA and other telescopes have yet to detect any obvious signs of planet formation in it, although higher resolution observations may reveal structures similar to HL Tauri, which is of a similar age. MWC 480 is only about one million years old and by comparison the Sun is more than four billion years old. The name MWC 480 refers to the Mount Wilson Catalog of B and A stars with bright hydrogen lines in their spectra.
Artistic impression of the protoplanetary disc surrounding the young star MWC 480. Credit: B. Saxton (NRAO/AUI/NSF)
Observations using the Atacama Large Millimeter/submillimeter Array (ALMA reveal that the protoplanetary disc surrounding MWC 480 contains large amounts of methyl cyanide (CH3CN), a complex carbon-based molecule. There is enough methyl cyanide around MWC 480 to fill all of Earth’s oceans. Both this molecule and its simpler cousin hydrogen cyanide (HCN) were found in the cold outer reaches of the star’s newly formed disc, in a region that astronomers believe is analogous to the Kuiper Belt , the realm of icy planetesimals and comets in our own Solar System beyond Neptune.
“We now have even better evidence that this same chemistry exists elsewhere in the Universe, in regions that could form solar systems not unlike our own.” This is particularly intriguing, notes Karin Öberg, an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, and lead author of the new paper, since the molecules found in MWC 480 are also found in similar concentrations in the Solar System’s comets.
Astronomers have known for some time that cold, dark interstellar clouds are very efficient factories for complex organic molecules — including a group of molecules known as cyanides. Cyanides, and most especially methyl cyanide, are important because they contain carbon–nitrogen bonds, which are essential for the formation of amino acids, the foundation of proteins and the building blocks of life. Until now, it has remained unclear if these same complex organic molecules commonly form and survive in the energetic environment of a newly forming solar system, where shocks and radiation can easily break chemical bonds.
The molecules ALMA detected are much more abundant than would be found in interstellar clouds. This tells astronomers that protoplanetary discs are very efficient at forming complex organic molecules and that they are able to form them on relatively short timescales. This rapid formation is essential to outpace the forces that would otherwise break the molecules apart. Also, these molecules were detected in a relatively serene part of the disc, roughly 4.5 to 15 billion kilometers from the central star. Though very distant by Solar System standards, in MWC 480’s scaled-up dimensions, this would be squarely in the comet-forming zone.
As this system continues to evolve, astronomers speculate that it’s likely that the organic molecules safely locked away in comets and other icy bodies will be ferried to environments more nurturing to life.
“From the study of exoplanets, we know the Solar System isn’t unique in its number of planets or abundance of water,” concluded Öberg. “Now we know we’re not unique in organic chemistry. Once more, we have learnt that we’re not special. From a life in the Universe point of view, this is great news.”
Citation: K.I. Öberg et al., “The Cometary Composition of a Protoplanetary Disk as Revealed by Complex Cyanides” Nature 9 April 2015. The team is composed of Karin I. Öberg (Harvard-Smithsonian Centre for Astrophysics, Cambridge, Massachusetts, USA), Viviana V. Guzmán (Harvard-Smithsonian Centre for Astrophysics), Kenji Furuya (Leiden Observatory, Leiden University, Leiden, the Netherlands), Chunhua Qi (Harvard-Smithsonian Centre for Astrophysics), Yuri Aikawa (Kobe University, Kobe, Japan), Sean M. Andrews (Harvard-Smithsonian Centre for Astrophysics), Ryan Loomis (Harvard-Smithsonian Centre for Astrophysics) and David J. Wilner (Harvard-Smithsonian Centre for Astrophysics).
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