An alternative explanation for how large carbon-containing molecules might be formed in interstellar space is presented in Nature Communications this week. These molecules, whose formation in space is still a puzzle, are proposed to be formed by breaking up the graphite surface of a stardust particle. This theory is tested by emulating interstellar conditions in an ultrahigh vacuum chamber.

With the help of big radiotelescopes, polycyclic aromatic hydrocarbons - large carbon-containing molecules - could be observed in abundance in interstellar space but why they exist and how they can form in interstellar conditions is still unclear. Many previous formation theories proposed a bottom-up chemical process where small molecules react to form larger molecules. But the bottom-up mechanisms cannot explain the abundance of polycyclic hydrocarbons in space. Pablo Merino, Jose Martin-Gago and colleagues now show that an alternative top-down approach might also play a role in polycyclic hydrocarbon formation in the interstellar medium. Emulating the conditions in space in an ultrahigh vacuum chamber, they show that stardust particles composed of silicon carbide with a graphite surface can be broken down to form polycyclic aromatic hydrocarbons when the dust is exposed to atomic hydrogen. This mechanism could explain the amount of polycyclic hydrocarbons in space.