Exospheric O₂ densities at Europa during different orbital phases

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• 作者：C. Plainaki ; A. Milillo ; A. Mura ; J. Saur ; S. Orsini ; S. Massetti
• 关键词：Europa ; Exospheres ; Jupiter's satellites ; Monte Carlo simulations ; Radiolysis
• 刊名：Planetary and Space Science
• 出版年：November, 2013
• 年：2013
• 卷：88
• 期：Complete
• 页码：42-52
• 全文大小：1422 K

文摘

Europa's exosphere is a mixture of different species among which sputtered H₂O and H₂ dominate in the highest altitudes and O₂, formed mainly by radiolysis of ice and subsequent release of the produced molecules, prevails at lower altitudes. Europa's O₂ exosphere has been demonstrated through both observation and simulation-based techniques to be spatially non-uniform. In the present study we investigate Europa's exospheric O₂ characteristics under the external conditions that are likely in the Jupiter's magnetospheric environment, applying the Europa Global model of Exospheric Outgoing Neutrals (EGEON, ) for different configurations between the positions of Europa, Jupiter and the Sun. We demonstrate for the first time that the spatial distribution of Europa's exosphere is explicitly time-variable due to the time-varying relative orientations of solar illumination and the incident plasma direction. We show that the O₂ release efficiency depends both on solar illumination and plasma impact direction. The modeled densities at different orbital phases of Europa are compared, a posteriori, with the analysis results from two observations in order to validate the model. Using the outputs of EGEON we also calculate the supply of neutral oxygen atoms of exospheric origin to Europa's neutral cloud.