Extraterrestrial helium trapped in fullerenes in the Sudbury impact structure.
Fullerenes (C60 and C70) in the Sudbury impact structure contain trapped helium with a 3He/4He ratio of 5.5 × 10−4 to 5.9 × 10−4. The 3He/4He ratio exceeds the accepted solar wind value by 20 to 30 percent and is higher by an order of magnitude than the maximum reported mantle value. Terrestrial nuclear reactions or cosmic-ray bombardment are not sufficient to generate such a high ratio. The 3He/4He ratios in the Sudbury fullerenes are similar to those found in meteorites and in some interplanetary dust particles. The implication is that the helium within the C60 molecules at Sudbury is of extraterrestrial origin.