Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected the presence of complex carbon-based molecules – methyl cyanide (CH3CN), cyanoacetylene (HC3N) – and their simpler cousin, hydrogen cyanide (HCN), in a protoplanetary disc surrounding the young star MWC 480.
Artist impression of the protoplanetary disc around MWC 480. Image credit: B. Saxton / NRAO / AUI / NSF.
MWC 480 is about twice the mass of our Sun. It is located approximately 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.
Scientists 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 CH3CN, 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, however, 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.
But now a team of astronomers led by Dr Karin Öberg of the Harvard-Smithsonian Center for Astrophysics in Cambridge has detected these molecules in the cold outer reaches of the MWC 480’s newly formed disc, in a region that they believe is analogous to the Solar System’s Kuiper Belt – a band of comets similar in many ways to the main asteroid belt found in the inner Solar System.
“Studies of comets and asteroids show that the solar nebula that spawned the Sun and planets was rich in water and complex organic compounds. 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,” said Dr Öberg, the first author of the paper published in the journal Nature.
“This is particularly intriguing since the molecules found in MWC 480 are also found in similar concentrations in the Solar System’s comets.”
Importantly, the molecules the scientists detected are much more abundant than would be found in interstellar clouds.
This tells scientists that protoplanetary discs are very efficient at forming complex organic molecules and that they are able to form them on relatively short timescales.
As MWC 480 continues to evolve, Dr Öberg and co-authors 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. 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,” Dr Öberg said.
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Karin I. Öberg et al. 2015. The comet-like composition of a protoplanetary disk as revealed by complex cyanides. Nature 520, 198-201; doi: 10.1038/nature14276
