New HST observations of Io’s time-variable UV aurora: Probing Io's magma ocean and neutral and plasma environment

Monday, 15 December 2014: 2:25 PM
Lorenz Roth1,2, Joachim Saur3, Kurt D Retherford1, Darrell F Strobel4, Paul D Feldman4, Aljona Bloecker3, Nickolay Ivchenko2 and Anita Kullen2, (1)Southwest Research Institute San Antonio, San Antonio, TX, United States, (2)EES KTH Stockholm, Stockholm, Sweden, (3)University of Cologne, Cologne, Germany, (4)Johns Hopkins University, Baltimore, MD, United States
We report on new Space Telescope Imaging Spectrograph (STIS) observations of Io's oxygen and sulfur UV aurora obtained during two visits with the Hubble Space Telescope (HST) in December 2013 and January 2014. Io's aurora was monitored over a full variation cycle of the Jovian magnetic field to map the temporal behavior of the bright auroral spots. The aurora oscillates around the equator roughly in correlation with the time-variable orientation of the local magnetic field of Jupiter. Magnetic field perturbations near Io measured by the Galileo spacecraft were proposed to originate from induction in an electrically conductive global magma ocean. If magnetic induction modifies Io's local magnetic field environment, it will also alter the time-variable morphology of the aurora. We analyze the observed aurora variability and compare it to theoretically predicted spot morphologies for different magma ocean properties. Additionally, we compare the global O and S aurora morphology and brightness in the new observations to a large set of previous STIS images taken over a decade ago between 1997 and 2001 and investigate long-term changes of Io's neutral and plasma environment.