Using Multi-Spacecraft Measurements to Shed Light on Jupiter’s Auroral and Disk X-ray Emissions

Abstract: 
The shimmering, dancing curtains of light from our planet’s aurorae have mesmerised people for generations. However, it wasn’t until 1979 that the first extra-terrestrial aurora was detected during Voyager 1’s visit to Jupiter. The gas giant planet’s auroral emissions span several wavebands that includes X-rays. Studies show that Jupiter’s powerful magnetic field accelerates ions primarily from the local environment into the planet’s atmosphere above the polar regions. The ions undergo charge stripping before they charge exchange with atmospheric neutrals and produce soft X-rays (photon energy < 2 keV). These emissions also often pulse with periods of tens of minutes. A ring of hard auroral X-rays (photon energy > 2 keV) arising from electron bremsstrahlung usually surrounds the soft X-ray emissions. Jupiter’s X-ray aurorae are fixed on the planet’s frame so that as Jupiter spins on its axis, the aurorae rotate in and out of view, rather like how a pulsar’s beam of radiation sweeps across the sky. X-rays are also emitted by Jupiter’s disk and is predominantly due to Thomson scattering of solar X-ray photons off the Jovian atmosphere. I will give an overview of how measurements taken by XMM-Newton, in conjunction with those by the Hubble Space Telescope, Hisaki, and Juno, have helped to better our understanding of how a planet can produce such bright X-ray emissions.