Oxygen production from dissociation of Europa’s water-ice surface
J. R. Szalay, F. Allegrini, R. W. Ebert, F. Bagenal, S. J. Bolton, Shahab Fatemi, D. J. McComas, Angèle Pontoni, Joachim Saur, H. T. Smith, D. F. Strobel, S. Vance, Audrey Vorburger, R. J. Wilson
Abstract
Abstract Jupiter’s moon Europa has a predominantly water-ice surface that is modified by exposure to its space environment. Charged particles break molecular bonds in surface ice, thus dissociating the water to ultimately produce H 2 and O 2 , which provides a potential oxygenation mechanism for Europa’s subsurface ocean. These species are understood to form Europa’s primary atmospheric constituents. Although remote observations provide important global constraints on Europa’s atmosphere, the molecular O 2 abundance has been inferred from atomic O emissions. Europa’s atmospheric composition had never been directly sampled and model-derived oxygen production estimates ranged over several orders of magnitude. Here, we report direct observations of H 2 + and O 2 + pickup ions from the dissociation of Europa’s water-ice surface and confirm these species are primary atmospheric constituents. In contrast to expectations, we find the H 2 neutral atmosphere is dominated by a non-thermal, escaping population. We find 12 ± 6 kg s −1 (2.2 ± 1.2 × 10 26 s −1 ) O 2 are produced within Europa’s surface, less than previously thought, with a narrower range to support habitability in Europa’s ocean. This process is found to be Europa’s dominant exogenic surface erosion mechanism over meteoroid bombardment.