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Cyanides signal complex chemistry: Biomolecule precursors found in disk around young star.

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

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 needed for life, appear in abundances similar to those found in local comets, report astrophysicist Karin Oberg of 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 Oberg. Now that we know planets are common around other stars, the next step "is to figure out how unique our chemistry is."

Oberg and colleagues used the Atacama Large Millimeter/submillimeter Array in Chile to detect radio waves emitted by the cyanide molecules. Oberg's team mapped cyanide abundances around MWC 480 at distances from the young star that are about 30 to 100 times farther than Earth is from the sun. The team figured this was a region where comets probably form.

"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 substances such as methyl cyanide shows that disks are breeding grounds for more complex organic molecules. That means that these ingredients can be present when comets, asteroids and planets are forming.

Cyanide might not be the first chemical that pops to mind when thinking about environments conducive to life. But the molecules needed to originate life are not necessarily the best ones to sustain it, Oberg notes. Lab experiments indicate that conditions producing methyl cyanide 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. Oberg's observations help put our own solar system in context.

Oberg plans to investigate other young stars to see how common the complex cyanides are.

Caption: Cyanides, precursors to more complex organic molecules', may be common in planet-forming disks swirling around young stars, like the one illustrated here.

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Title Annotation:ATOM & COSMOS; MWC 480
Author:Crockett, Christopher
Publication:Science News
Date:May 2, 2015
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