Cyanides around young star signal complex organic chemistry

Precursors to molecules needed for life may be common in planetary nurseries

A planet-forming disk around a star

CSI SPACE  The planet-forming disk swirling around a young star (illustrated) contains cyanides, which might be precursors to more complex organic molecules.

JPL-Caltech/NASA

Cyanide shows up in apple seeds, toxicology reports and now a planetary nursery encircling a young star. Cyanide compounds found in a planet-forming disk suggest that the rich brew of organic compounds in asteroids and comets around our sun might be common in other solar systems as well.

A vapor of hydrogen cyanide, methyl cyanide and cyanoacetylene swirls around the star MWC 480, about 460 light-years away in the constellation Auriga. The molecules, possible precursors to substances essential for life, appear in abundances similar to those found in local comets, report Karin Öberg, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and colleagues in the April 9 Nature.

“One of the existential questions is how unique our solar system is,” says Öberg. Now that we know planets are common around other stars, she says, the next step “is to figure out how unique our chemistry is.”

Öberg and colleagues used the Atacama Large Millimeter/submillimeter Array in Chile to detect radio waves emitted by the cyanide molecules. Öberg’s team then mapped the cyanide abundances at distances from MWC 480 ranging from 30 to 100 times as far as Earth is from the sun. The researchers figured this was a region where comets probably form around the young star.

“People used to say that disks inherited their chemical composition from the interstellar medium and … that’s the end of the story,” says Joan Najita, an astrophysicist at the National Optical Astronomy Observatory in Tucson. “These data show that the story is more complex and interesting than people used to think.”

To date, researchers have been able to see only relatively small molecules in young disks. The presence of a substance such as methyl cyanide shows that disks are breeding grounds for more complex organic molecules. That finding means that these ingredients are present when comets, asteroids and planets are forming.

Cyanide might not be the first chemical that pops to mind when thinking about environments that are conducive to life. But the molecules needed to originate life are not necessarily the best ones to sustain it, Öberg notes. Laboratory experiments indicate that the conditions that produce methyl cyanide, for example, also lead to simple sugars. And cyanide is a chemical precursor to amino acids,the building blocks of proteins,which are also found in meteorites.

Meteorite data show that amino acids were floating around the sun as asteroids and planets were taking shape. But those data provide just a glimpse of the early solar system’s inventory of complex organics. “How abundant would those have been? Where were they synthesized?” Najita asks. Öberg’s observations are a first step to putting our own solar system in context.

Öberg plans to investigate other young stars to see how common the complex cyanides are. She also wants to pursue laboratory experiments to see what molecules can form in these environments. If MWC 480 is typical, then cyanides and perhaps other organics form quickly around stars throughout galaxies. When icy asteroids then pummel rocky planets with special deliveries of water from the outer reaches of their solar systems, the

incoming boulders might also seed the planets with ingredients that are essential for the more complex chemistry — and life — that’s yet to come.

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