Abstract
Since the discovery of a cloud of neutral sodium atoms accompanying the jovian satellite, Io, in its orbit1, asymmetries of part of the cloud (region B)2 have often been noted3–6. Brightness variations with orbital longitude3,4 and asymmetries found by comparing images taken at orbital longitudes differing by 180° (ref. 5) have been explained as effects of solar radiation pressure7. Given that the vast majority of neutrals precede Io in its orbit, and that sputtering of Io is the principal source mechanism, Matson et al.8 postulated a hemispherical source centred 60° towards the sub-Jupiter point from the centre of the leading hemisphere to explain the general cloud shape. However, soft collisions with plasma ions may be important and call for a reassessment9. I show here that, given reasonable assumptions, the east–west brightness asymmetry can be explained by temporal changes in the number of emitting atoms in the cloud caused by atmospheric shielding of the surface.
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Thomas, N. An explanation of the east–west asymmetry of Io's sodium cloud. Nature 322, 343–345 (1986). https://doi.org/10.1038/322343a0
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DOI: https://doi.org/10.1038/322343a0
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