资源环境科技发展态势分析平台

Studies of the global intensities of the oxygen emissions at 1356 Å and 1304 Å revealed in Europa’s atmosphere. Here we investigate the relative changes of the two oxygen emissions when Europa emerges from eclipse as well as the radial profiles of the relative emissions across the sunlit disk in Hubble Space Telescope observations taken in 1999, 2012, 2014 and 2015 while the moon was at various orbital positions. The eclipse observation constrains the O column density to or lower. We then find that the OI1356-Å/OI1304-Å ratio systematically decreases towards the disk center on the trailing hemisphere. The observed emission ratio pattern and the persistence of it from 1999 to 2015 imply a stable O abundance in the central sunlit trailing hemisphere with an O/ ratio of 12-22. On the leading hemisphere, the emissions are consistent with a pure atmosphere everywhere across the moon disk.