CH4 emission variability on the Jupiter southern aurora as observed by the Juno/JIRAM spectrometer

JIRAM (InfraRed Auroral Mapper) is the imaging spectrometer on board the NASA Juno mission. Data collected since August 2016 on both Jupiter Northern and Southern aurora have an unprecedented spatial resolution [1,2,3]. The analyses of the acquired images and spectra confirmed the presence of methane (CH4) on both auroras through its emission at 3.31 ?m that overlap an H3 + signature [4]. Here we compare CH4 emissions from the first and fourth Juno Perijove (PJ) passage on the southern aurora (period JM0003 and JM0041 respectively). Methane column densities have been retrieved for the first time. In the inner part of the main oval we observe column densities varying between 1 × 1012 cm-2 and 4 × 1012 cm-2 for JM0003, while during PJ4 the intensity is significantly lower with column densities <= 1 × 1012 cm-2. For PJ4 the more uniform coverage in time has allowed to derive the CH4 column density behavior as a function of Jovian local time. We have found that the mean of the CH4 column density in the dayside is 60% higher than the mean value in the night side.