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

NASAの木星探査ミッションであるJunoの科学者たちは、木星の衛星であるエウロパで酸素が生成される速度を計算しました。この研究は、Junoの宇宙船のJovian Auroral Distributions Experiment(JADE)機器で収集されたデータを使用して、ユーロパの氷の表面からの水素の放出を測定することで導かれました。研究では、エウロパの表面で毎秒約26ポンド(12キログラム)の酸素が生成されると推定されています。これは、従来の推定値よりもはるかに低いです。この酸素の一部は、地下の海に浸透し、代謝エネルギーの可能性のある源となると考えられています。


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

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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.