Abstract
We have analyzed 33 ultraviolet spectra of Jupiter's satellite Europa that we obtained with the International Ultraviolet Explorer (IUE) satellite from 1978 to 1982. The observations span orbital phase angles (longitudes) 21° to 343°. We confirm that the previously reported absorption feature ( A.L. Lane, R.M. Nelson, and D.L. Matson, 1981, Nature 292, 38–39) is centered at 280 nm, and is most apparent when spectra from orbital phase angles 223° to 333° (trailing side) are ratioed to those at or near 90° (leading side). We have found that the strength of this feature is unchanged over the 5-year period of this study, to at least 20%. This suggesting that no large endogenic- or exogenic-induced changes in the surface sulfur dioxide concentration have occured in this time period. The feature is strongest at 277° ± 3° long. We have compared this feature to laboratory spectra and we confirm similarities with sulfur dioxide gas. These results support the hypothesis of Lane et al. (1981) that the feature is created by the presence of sulfur ions from Io's plasma torus implanting into Europa's water-ice surface on the trailing side.
Published Version
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