Abstract
DURING the favourable passage of the Earth through the plane of Jupiter's equator in 1973 many observations of the mutual phenomena of the Galilean satellites were obtained. Since then there have been numerous preliminary analyses1,2 arguing for the presence of a bright polar cap on Europa (J2), based essentially on photoelectric observations of a series of occultations of J2 by J1 (Io) in which increasingly larger fractions of the north polar region of the former were covered at mid-event with each successive occultation. These events—and especially the near-grazing, or polar ones—were substantially deeper than predicted. An inevitable explanation, in view of the finding of ice3 on J2 and J3, was the suggestion of a bright north polar cap for J2.
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AKSNES, K., FRANKLIN, F. de Sitter's theory ‘melts’ Europa's polar cap. Nature 258, 503–505 (1975). https://doi.org/10.1038/258503a0
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DOI: https://doi.org/10.1038/258503a0
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