Models of Jupiter's Polar Aurora

Abstract

Auroral emissions from Jupiter have been observed across the photon spectrum including ultraviolet and x-ray wavelengths. UV observations suggest an input flux power of 1013 - 1014 W for the aurora in each hemisphere. X-ray emissions with a total power of about 1 GW were observed by the Einstein Observatory, the Roentgen satellite, Chandra x-ray Observatory (CXO), and XMM-Newton. Previous theoretical studies have shown that precipitating energetic sulfur and oxygen ions can produce the observed x-rays. This study focuses on the ion precipitation of the polar region and its effects in the ionosphere. We present the results of a hybrid Monte Carlo model for sulfur and oxygen ion precipitation at high latitudes, look at differences with the continuous slowdown model, and compare the results to synthetic spectra fitted to observations. We concentrate on the effects of altitude on the observed spectrum and find that the opacity of the atmosphere to the outgoing x-ray photons is important for incident ion energies greater than about 1.2 MeV per nucleon for both sulfur and oxygen. Quenching of longer-lived excited states of the oxygen ions is also found to be important. Opacity considerably diminishes the outgoing x-ray intensity calculated, particularly when the viewing geometry is not favorable. We estimate an emission efficiency for the x-ray aurora of &epsilon ~ 7 x 10-5. Secondary electrons from the ion precipitation as well as photoelectrons and auroral electrons also affect the polar cap atmosphere. We calculated the secondary electron production due to the oxygen ion precipitation for the first time. We analyze the secondary electron fluxes due to the ion aurora and estimate their effects on the ionosphere and field aligned electrical currents. We find that the secondary electrons affect the ionosphere similarly to auroral electrons responsible for the diffuse UV aurora and are therefore important for the magnetospheric dynamics and our better understanding of the ionosphere-magnetosphere coupling.