Buckyballs in space

Infrared measurements from a space telescope have identified fullerene molecules in a planetary nebula.

Credit: © 2010 NASA

The story of the discovery of fullerenes is well known: researchers trying to understand the chemistry of carbon molecules in space generated large and surprisingly stable clusters. These turned out to be the cage-like molecules — spherical in the case of C₆₀ — we all know today. So far, however, the largest molecules actually observed in space have been more simple species, such as benzene and smaller polyynes up to 13 atoms in size.

Now, Jan Cami from the University of Western Ontario and colleagues have discovered¹ C₆₀ and C₇₀ in the planetary nebula Tc 1 using an infrared spectrograph on board the Spitzer space telescope. Most planetary nebulae contain molecules with hydrogen, often polyaromatic hydrocarbons, but no hydrogen was observed in Tc 1. The infrared spectrum is instead dominated by C₆₀ bands, with smaller C₇₀ bands also present.

No charged species were observed, indicating both C₆₀ and C₇₀ are present as neutral molecules. The results also suggest that the molecules are anchored on carbonaceous dust particles. The environment of Tc 1 is strikingly similar to that used in laboratories to synthesize C₆₀, where graphite is vaporized in a hydrogen-poor, helium-rich atmosphere. Of course, the scale of the 'synthesis' is much greater: Cami and colleagues estimate that the amount of fullerenes present in Tc 1 is equivalent to the mass of three Moons. This amounts to around 1.5% of the carbon present in the planetary nebula.