Study of the Jupiter system with the Line Emission Mapper probe: Exploring Fundamental Atomic and Plasma Physics in a Natural Laboratory
Résumé
The Jupiter system produces a cornucopia of X-ray emissions, providing a diverse range of invaluable local analogues for bodies and plasmas across the cosmos. These include thermal and non-thermal bremsstrahlung from the aurorae and magnetosphere, charge exchange emissions from the aurorae, Inverse Compton scattering from the radiation belts, X-ray fluorescence (ion-induced and thick-target bremsstrahlung) from the moons and rings, and elastic scattering of solar photons by hydrogen in the atmosphere. Here, we explore how the Line Emission Mapper (LEM) will revolutionise our understanding of these emissions in the 0.2-2.0 keV energy range. In particular, the 1 eV spectral energy resolution provided by the instrument will enable unprecedented access to the charge exchange emissions from Jupiter and the solar emission lines scattered from the jovian atmosphere. We will showcase how LEM's exploration of this natural laboratory will offer access to fundamental atomic physics (e.g. constraining cross-sections for a range of ion species). For the first time, LEM will unambiguously distinguish between the emissions from Iogenic plasma and those from solar wind ions, revealing under what circumstances such systems are open to the solar wind. The extent of this has been debated for decades and has fundamental implications for the nature of rapidly rotating magnetospheres more generally. Through line broadening and Doppler shifts, LEM will also measure the thermal and collisional velocities of the ions at the point of impact with the atmosphere. This will provide valuable new measurements to inform studies of energy transfer in the system and the processes governing Jupiter's aurorae. Alongside planetary science, solar system objects offer the unique opportunity in High Energy Astrophysics of enabling direct comparison between the remotely detected X-ray emissions and in-situ measurements of the precise plasma conditions and processes that generate them. Future missions, such as ESA's JUICE and NASA's Europa Clipper, will make detailed observations across the wider Jupiter system. Using a catalogue of in situ and remote sensing instruments, this next generation fleet of spacecraft will conduct measurements that will offer irreplaceable ground-truths for comparison with LEM's observations of X-ray emissions.