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P. Drossart, Th. Encrenaz (DESPA, Obs. Paris-Meudon), R.W. Carlson, L.W. Kamp (JPL), NIMS Team
Observations of the auroral regions of Jupiter with the Galileo Near Infrared Mapping Spectrometer have provided spectral images of Northern and Southern aurorae during several orbits. A detection of H3+ emission has been obtained in orbits C3, G7, C9, C10 and E11 of the nominal Galileo mission. Some real time observations are also available for several orbits in the GEM mission. Recent improvements in the NIMS spectral/radiance calibration have allowed a comparison of the observations to synthetic spectra, with a measurement of the rotational temperature of H3+ and its column density. Compared to ground based observations, Galileo/NIMS observations provide the following additional information: (1) a record of the \nu2 band of H3+ over an extended spectral range from 3.2 to 4.5~\mum, including all the strong H3+ lines of the domain, (2) night side observations of the morphology of the auroral emissions, (3) an estimate of the contribution of the \nu3 band of CH4 in emission at 3.3~\mum.\\
During the E11 orbit a spectral map of the Northern auroral regions has been recorded on the night side. The spatial resolution is of the order of 600 km only, a factor of 2 better than the best ground based observations. System III longitudes vary from145 to 215 dg. A comparison is made with the predicted position of the auroral ovals from the model of magnetic field VIP4 by Connerney et al. (JGR, 1998). It shows that H3+ emissions generally follow the auroral ovals, with an extension in latitude, and high spatial variability at small scale. The observed location seems shifted to the North, compared with Galileo/SSI observations in the visible during the G7 orbit (Ingersoll et al., Icarus, 1998). Some emission is also observed inside the auroral oval. In average, temperature retrieval is consistent with a rotational temperature of the order of 1000 K, as has been found from ground based observations over the last ten years. Variability in the zones is examined, with both temperature and intensity variations being present.