Mapping of the sodium emission associated with Io and Jupiter

The sodium D-lines are observed in emission in a disklike distribution surrounding Io and extending outward in the orbital plane of the Galilean satellites to at least 23 R_J from Jupiter. A scale length for the sodium emission cloud in the orbital plane and the thickness of the sodium disk perpendicular to the orbital plane are determined. Weak D-line emission is also detected over the poles of Jupiter. Estimates of the apparent emission rates are derived from microdensitometer scans of the spectrograms as a function of position in the satellite orbital plane and perpendicular to the orbital plane. No other emission lines were detected down to a limit of ～50 R over the spectral range from 3500 Å to 9000 Å.