Origin of Molecular Oxygen in Comets: Current Knowledge and Perspectives.

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard the Rosetta spacecraft has measured molecular oxygen (O) in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) in surprisingly high abundances. These measurements mark the first unequivocal detection of O in a cometary environment. The large relative abundance of O in 67P/C-G despite its high reactivity and low interstellar abundance poses a puzzle for its origin in comet 67P/C-G, and potentially other comets.

Protonated ions as systemic trapping agents for noble gases: From electronic structure to radiative association.

The deficiencies of argon, krypton, and xenon observed in the atmosphere of Titan as well as anticipated in some comets might be related to a scenario of sequestration by H in the gas phase at the early evolution of the solar nebula. The chemical process implied is a radiative association, evaluated as rather efficient in the case of H, especially for krypton and xenon. This mechanism of chemical trapping might not be limited to H only, considering that the protonated ions produced in the destruction of H by its main competitors present in the primitive nebula, i.