On the origin of molecular oxygen in cometary comae
Résumé
We have used generous assumptions in terms of production rates and ion fluxes to assess the production of O2- through ER reactions as a mechanism to explain Rosetta observations. Even with these assumptions, the amount of O2 produced is insignificant (by several orders of magnitude) with respect to what was detected by ROSINA–DFMS. There are not enough ions in the coma and the series of events required to trigger these processes are individually too rare. Furthermore, cometary ion fluxes are anti-correlated to the O2 densities observed by ROSINA. Finally, in terms of the instrument itself, there is little evidence of the production and detection of products O2- and energetic O2 by ROSINA–DFMS. While ER reactions may occur, they cannot explain the amounts of O2 detected. Primordial O21,3 remains compatible with the quantities and trends of molecular oxygen measured by ROSINA–DFMS, while other theories17 discuss other plausible sources.
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