Mémoire

Abstract

The aurora on Jupiter is a remarkable phenomenon in our solar system. After having been observed for the first time by the Voyager 1 spacecraft in 1979, many spectral observations of these polar lights have been conducted on a continuous basis. Since 2016, the Juno spacecraft, in polar orbit around Jupiter, is gathering images and spectroscopic data that allow us to unravel the complex interplay between Jupiter’s magnetosphere and atmosphere. In this work, we use data from the UVS spectrograph onboard Juno to construct northern and southern spectral cubes for perijoves 1 to 48. From these spectral cubes, we derive H2 brightness maps, emission angle maps and color ratio maps. We then use use a relation between color ratio, emission angle of the photons and energy of the precipitating electrons to compute energy maps for each of Juno’s orbits, considering both monoenergetic and kappa energy flux distribution of electrons. These maps give an interesting overview of the evolution of several characteristics of the auroral regions over time. We then perform a statistical analysis of the energy of the precipitating electrons as a function of time. We divide each auroral region into three sub regions: the polar, main and outer emission regions. We compare the energy of the electrons falling into these three sub regions and the energy of the electrons falling into their counterpart in the other hemisphere. We also study the correlation between the H2 auroral brightness and the energy of the precipitating electrons for the whole auroral emission region and for each sub re- gion. We find that the H2 auroral brightness is not correlated with the energy of the impinging photons by studying correlation plots as well as correlation coefficients for each perijove. In the last part, we identify zones of the auroral emission where the color ratio seems to call into question the validity of the atmospheric model that we used. We then use TransPlanet to model synthetic spectra produced by populations of electrons falling into the atmospheric model that we use. We attempt to fit the modeled spectra to the observed ones by adjusting the energy of the impinging electrons that we computed as well as the amount of hydrocarbons in the model atmosphere. We find that the observed spectra for some of the selected zones can be fit by tuning the energy of the electrons while for others, changing the atmospheric composition is necessary. This raises the question of the consistency of the atmospheric composition across the entire auroral emission region.