In situ measurement of O2 in the coma of comet 67P/Churyumov–Gerasimenko shows local abundances ranging from one per cent to ten per cent relative to H2O; the spatial and temporal uniformity of the O2/H2O ratio suggests that primordial O2 was incorporated into the nucleus during the comet’s formation.
- A. Bieler
- K. Altwegg
- P. Wurz