Synergistic observations of the giant planets with HST and JWST: Jupiter's auroral emissions

The James Webb Space Telescope is perfectly suited to observe most Solar System objects, including the extended giant planets. Its high sensitivity, high spatial resolution, field of view, very high spectral resolution and wide spectral coverage all combine to make JWST a fantastic instrument that will result in significant advances and progress in most fields of Solar System exploration.
Here, we focus on the case of Jupiter’s aurora for several reasons. 1) The auroral emissions on Jupiter are very intense, both in ultraviolet and in infrared. Each of these bandpasses is bringing complementary information on how Jupiter is interacting with its near and distant environment. 2) Even though Jupiter’s aurora appears to be responding to the conditions prevailing in the solar wind, contrary to the Earth it is a permanent emission that can also be observed on the sunlit side of the planet. 3) The NASA Juno mission is currently exploring the magnetosphere and the atmosphere of this planet with a suite of in situ and remote instruments, including an ultraviolet spectrograph (UVS) and an infrared imaging spectrograph (JIRAM). The Juno mission is gathering a broad scientific community that will foster the study of Jupiter’s system for several years. 4) A large HST program was allocated in support of the NASA Juno prime mission (GO-14634) and is currently providing us with regular movies of Jupiter’s ultraviolet aurora. They provide a global magnetospheric context for the different Juno instruments, as well as for the numerous ground based (infrared) and space based observatories participating to the Juno mission. 5) It is currently very difficult to plan truly simultaneous UV and IR observations, mainly because of the inherent limitations of Earth based infrared telescopes. As a result, comparisons of Jupiter’s auroral emissions rest on a very limited dataset. Nevertheless, they are suggesting similarities and discrepancies between IR and UV aurorae, the study of which would greatly benefit from synergistic observations with HST and JWST. 6) The case of Saturn’s aurora is as important, especially in view of the upcoming ‘Grand Finale’ of the Cassini mission, and all above arguments apply to Saturn as well. The case of Uranus and Neptune’s aurorae still belongs to the area of discovery and will take full advantage of JWST’s advanced capabilities.