A review of possible optical absorption features of oxygen molecules in the icy surfaces of outer solar system bodies

In this review we provide the data needed to interpret remote spectroscopic studies of O2 molecules embedded in the icy surfaces of outer solar system bodies. O2 produced by radiolysis has been seen in the gas phase and as the so-called ‘solid O2’ trapped in the icy surfaces of Ganymede, Europa and Callisto. It may also have been indirectly observed on a number of objects by its radiolysis product, O3. These observations indicate the importance of O2 for understanding the chemical processes occurring on icy outer solar system surfaces. Therefore, the published absorption spectra of gaseous, liquid and solid O2 and of O2 embedded in H2O ice are reviewed in some detail. Particular emphasis has been placed on the presentation of transition probabilities for the various O2 spectral series so that their relative importances can be assessed when they are used for modelling the radiation chemistry occurring in such environments.