Buckyballs in space

Buckminsterfullerene, the hollow ball of 60 carbon atoms, turned up in space 25 years after chemists first made it on Earth.

The search for buckyballs began with space. In the 1970s Harold Kroto worked with radio astronomers who found long chains of carbon atoms ending in a nitrile group, such as HC₇N, in clouds between the stars and round carbon-rich red giants. He wanted to see how such chains form, so in 1985 he joined Robert Curl and Richard Smalley at Rice University, whose laser could turn graphite into a hot vapour of carbon, much like the gas streaming from those stars. The chains formed, and so did C₆₀.

Seen by an infrared telescope

In 2010 Jan Cami and his colleagues studied Tc 1, a planetary nebula: the glowing gas round a dying star that has blown its outer layers away. NASA's Spitzer Space Telescope had recorded its infrared light. Among the glow were four bands at the wavenumbers of C₆₀, and more bands from C₇₀, a longer ball of 70 carbon atoms, stretched out like a rugby ball. With 60 and 70 atoms, they are the largest molecules yet found in space.

C₆₀'s 60 atoms can vibrate in 174 ways, which share 46 different frequencies. The ball is so even that almost all of these vibrations keep its charge evenly spread, and only four of the frequencies move charge in a way that absorbs infrared. Four clear lines make C₆₀ easy to pick out, even among the glow of other molecules.

A buckyball with a charge

Starlight that has crossed the clouds between the stars arrives with more than 500 narrow dips in its spectrum, called diffuse interstellar bands. Astronomers first recorded them in 1922, and what made them stayed a puzzle for nearly a century. In 2015 a team led by John Maier at the University of Basel, in Switzerland, cooled C₆₀⁺ ions, buckyballs with one electron missing, to a few degrees above absolute zero, and measured the light they absorb. Two of their lines, near 963 nm and 958 nm, just beyond red light in the infrared, matched two of the bands exactly. C₆₀⁺ was the first molecule shown to make any of them.