Comparative Planetary Auroras

Marina Galand

Space and Atmospheric Physics Group, Department of Physics, Imperial College London, UK

Different types of plasma interactions are taking place in the Solar System including electromagnetic, flow-object, radiation-plasma, and plasma-neutral. Auroral emissions are the result of the interaction of an energetic particle population; be it electrons, ions, or neutrals; of extra-atmospheric origin with atmospheric species of a Solar System body (planet, moon, or comet). Due to the large variety of settings (e.g., atmospheric composition, particle origin, magnetized environment and acceleration processes), auroral emissions have a wide range of characteristics in terms drivers, morphology, temporal and spatial timescales and spectral features, which are all signatures of these settings. The cross-body approach that we will use for comparing auroral emissions is therefore of great relevance. For planets with an intrinsic magnetosphere, aurora is the consequence of electromagnetic interactions resulting from the transfer of mass, momentum, and energy between the ionosphere and the magnetosphere. While similar emissions (e.g., H Lyman alpha) have been analyzed and similar techniques (e.g., color ratios) have been used at different Solar System bodies (Earth and Jupiter), we will show that the information retrieved from the analysis varies from one body to another. For instance, the type of aurora detected or the range of particle energies covered by the approach is body-dependent. Multispectral analyses of auroral emissions are critical to better constrain the energetic particles in terms of origin, type, and energy. Lessons learned from comparative planetary auroras will be critical for extending the analysis of atmospheric observations beyond the heliosphere.