Altitude and temperature of Saturn’s aurora from VIMS observations

We present an estimate of the average temperature and altitude of the north polar aurora on Saturn using H3+ infrared (IR) observations from the image spectrometer VIMS onboard Cassini. Our analysis is based on the observations realized during S42 session in July 2008. On Saturn, as on other hydrogen-rich giant planets, a percentage of the ionized particles accelerated through the magnetic field impinge on the neutral hydrogen atmosphere, yielding H3+ molecules. H3+ has a multitude of emission bands in the IR between 1 and 5 microns. We take advantage of the band between 3 and 4 microns, where atmospheric absorption by methane is strong and thus atmospheric contamination is minimized. The average temperature of the main oval was estimated by comparing H3+ IR emission intensities measured by VIMS with a simulation of the H3+ emission as a function vibrational temperature. The altitude of the main structure has been derived by a collection of procedures, based on the SPICE observation geometries, and implemented at IFSI-INAF of Rome, Italy. Preliminary results indicate the auroral plane at approximately 800 km, while peaks in the H3+ infrared emissions seem to agree with simulations at 500 K vibrational temperature.