Assigned ID: 566 ----- Submission 1 (Fri Jan 21 23:54:58 GMT 2005) ----- Europa's tenuous atmosphere was discovered by HST/GHRS in OI 1304 A and OI] 1356 A emissions that were inferred to be produced by Jovian plasma electrons dissociatively exciting molecular oxygen (the dominant end product of a water-derived atmosphere). The properties and spatial distribution of Europa's FUV emissions are diagnostic for the specific characteristics of Europa's magnetospheric interactions and atmosphere. Although Europa's plasma interaction was expected to resemble Io's, later HST/STIS FUV imaging studies have yielded unexpected, puzzling results. Therefore, many fundamental questions regarding the nature of Europa's thin, water-derived atmosphere, and of its plasma interactions, induced magnetic field, and emission excitation processes still remain. The proposed Archival program will address these questions by analyzing the existing set of STIS FUV images of Europa concentrating on the temporal variations that have not been reported in the literature. The derived distribution of the emissions and variations with magnetic System III longitude and plasma conditions will be compared with expectations based on the various published models of the Europa's magnetospheric interaction.

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