NASAのジュノー探査機、エウロパの酸素生成を測定(NASA’s Juno Mission Measures Oxygen Production at Europa)

2024-03-04 NASA

＜関連情報＞

• https://www.nasa.gov/missions/juno/nasas-juno-mission-measures-oxygen-production-at-europa/
• https://www.nature.com/articles/s41550-024-02206-x

エウロパの水氷表面の解離による酸素生成 Oxygen production from dissociation of Europa’s water-ice surface

J. R. Szalay,F. Allegrini,R. W. Ebert,F. Bagenal,S. J. Bolton,S. Fatemi,D. J. McComas,A. Pontoni,J. Saur,H. T. Smith,D. F. Strobel,S. D. Vance,A. Vorburger & R. J. Wilson
Nature Astronomy  Published:04 March 2024
DOI:https://doi.org/10.1038/s41550-024-02206-x

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 H₂ and O₂, 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 O₂ 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 H₂⁺ and O₂⁺ 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 H₂ neutral atmosphere is dominated by a non-thermal, escaping population. We find 12 ± 6 kg s⁻¹ (2.2 ± 1.2 × 10²⁶ s⁻¹) O₂ 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.