The surface composition of Amalthea |
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| Authors: | J Gradie P Thomas J Veverka |
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| Institution: | Laboratory for Planetary Studies, Cornell University, Ithaca, New York 14853, USA |
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| Abstract: | Voyager images have revealed that most of Amalthea's surface is very dark and very red, with a few isolated bright spots having a distinct greenish spectrum. These unique color characteristics probably result from the unusual environment of the satellite. It is proposed that charged particles from the Jovian magnetosphere, contaminants such as sulfur from Io, and high-velocity micrometeoritic matter combine to darken, redden, and alter Amalthea's surface. The effects of sulfur and sulfur allotrope contamination are shown to redden a variety of bulk compositions: (a) carbonaceous material, (b) refractory minerals, (c) iron and iron sulfides, and (d) moderate temperature silicates. Carbonaceous-sulfur systems provide good, but not unique, spectral matches to the dark areas. The bright, greenish spots probably identify locations in which atypical alteration processes occur. These may include variations in the amount of contaminant sulfur in micrometeoritic glasses or in the relative abundances of certain sulfur allotropes. A major conclusion of this work is that available spectral-reflectance data contain little information about the bulk composition of the satellite. Spectrophotometry over an extended spectral range may be useful in specifying the composition of the surface more uniquely, but a determination of the satellite's mean density may be the only way of discriminating among possible bulk compositions. |
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