[1] Auroral X-ray emissions from Jupiter with a total power of about 1 GW have been observed by the Einstein Observatory, Roentgen satellite, Chandra X-ray Observatory, and XMM-Newton. Previous theoretical studies have shown that precipitating energetic sulfur and oxygen ions can produce the observed X-rays. This study presents the results of a hybrid Monte Carlo (MC) model for sulfur and oxygen ion precipitation at high latitudes, looks at differences with the continuous slow-down model, and compares the results to synthetic spectra fitted to observations. We concentrate on the effects of altitude on the observed spectrum. The opacity of the atmosphere to the outgoing X-ray photons is found to be important for incident ion energies greater than about 1.2 MeV per nucleon for both sulfur and oxygen. Model spectra are calculated for intensities with and without any opacity effects. These synthetic spectra were compared with the results shown by Hui et al. (2010) which fit Chandra X-ray Observatory observations for the north and south Jovian auroral emissions. Quenching of long-lived excited states of the oxygen ions is found to be important. Opacity considerably diminishes the outgoing X-ray intensity calculated, particularly when the viewing geometry is not favorable.

We analyzed two observations obtained in Jan. 2013, consisting of spatial scans of the Jovian 30 north ultraviolet aurora with the HST Space Telescope Imaging Spectrograph (STIS) in the spectroscopic mode. The color ratio (CR) method, which relates the wavelength-dependent absorption of the FUV spectra to the mean energy of the precipitating electrons, allowed us to determine important characteristics of the entire auroral region. The results show that the spatial distribution of the precipitating electron energy is far from uniform. The morning main emission arc is associated with 35 mean energies of around 265 keV, the afternoon main emission (kink region) has energies near 105 keV, while the 'flare' emissions poleward of the main oval are characterized by electrons in the 50-85 keV range. A small scale structure observed in the discontinuity region is related to electrons of 232 keV and the Ganymede footprint shows energies of 157 keV. Interestingly, each specific region shows very similar behavior for the two separate observations. 40The Io footprint shows a weak but undeniable hydrocarbon absorption, which is not consistent with altitudes of the Io emission profiles (~900 km relative to the 1 bar level) determined from HST-ACS observations. An upward shift of the hydrocarbon homopause of at least 100 km is required to reconcile the high altitude of the emission and hydrocarbon absorption.The relationship between the energy fluxes and the electron energies has been compared to 45 curves obtained from Knight's theory of field-aligned currents. Assuming a fixed electron temperature of 2.5 keV, an electron source population density of ~800 m -3 and ~2400 m -3 is obtained for the morning main emission and kink regions, respectively. Magnetospheric electron densities are lowered for the morning main emission (~600 m -3 ) if the relativistic version of Knight's theory is applied.Lyman and Werner H 2 emission profiles resulting from secondary electrons, produced by 50 precipitation of heavy ions in the 1-2 MeV/u range, have been applied to our model. The low CR 3 obtained from this emission suggests that heavy ions, presumably the main source of the X-ray aurora, do not significantly contribute to typical UV polar emission. 4 1.Introduction 55 BackgroundThe ultraviolet Jovian aurora is mainly produced by the interaction between the H 2 atmosphere and precipitating magnetospheric electrons. In the far ultraviolet (FUV, between 1200 and 1700 Å), the emission is dominated by the Lyman-α line from atomic hydrogen resulting from H 2 dissociation and H 2 vibronic lines from the Lyman ( 1 ∑ + → 1 ∑ + ) and Werner ( 1 ∏ + → 1 ∑ + ) system bands. The 60 auroral emission is known to interact with the atmosphere through absorption by the main hydrocarbons. Methane (CH 4 ) attenuates the emission at wavelengths below 1400 Å, ethane (C 2 H 6 ), which has a continuous absorption cross-section shortward of 1550 Å, has a typical signature between 1400 and 1480 Å in the case of strongly attenuated spectra, and acetylene (C...

[1] The spatially localized and highly variable polar cap emissions at Jupiter are part of a poorly understood current system linking the ionosphere and the magnetopause region. Strong X-ray emission has been observed from the polar caps and has been explained by the precipitation of oxygen and sulfur ions of several MeV energy. The present paper presents results of an extended model of the ion precipitation process at Jupiter. Specifically, we add to a previous model a more complete treatment of ionization of the atmosphere, generation of secondary electron fluxes and their escape from the atmosphere, and generation of downward field-aligned currents. Predictions relevant to observations by the upcoming NASA Juno mission are made, namely the existence of escaping electrons with energies from a few eV up to 10 keV, auroral H 2 band emission rates of 80 kR, and downward field-aligned currents of at least 2 MA.

[1] The inner magnetosphere of Saturn contains both neutral gas and plasma whose composition is dominated by water group ion species. This gas is distributed in a torus-shaped region located near the orbit of Enceladus. The source of this gas is the predominately water vapor plume located in the south polar region of Saturn's icy satellite Enceladus. The electron distribution in the torus comprises two populations: a relatively cold (<3 eV) thermal population with a less dense, hot (>10 eV) suprathermal tail. This paper describes model calculations of the electron energy distribution and energetics in the torus in order to explore how the observed electron distributions can be explained. A thermal electron energy equation is numerically solved, and electron temperatures are calculated. A separate electron energy deposition model determines suprathermal electron fluxes as functions of energy. The main suprathermal electron population is due to photoelectron production from the absorption of solar radiation by water and other neutral species, and this is demonstrated by a comparison of the model results with recently published Cassini data. The model includes heating of thermalized electrons by fresh photoelectrons and by hot pickup ions and also includes cooling by collisions with water and other neutral species. Calculated electron temperatures for the thermal population are about 10 4 − 2 × 10 4 K (i.e., 1-2 eV), values which are somewhat lower than recently published Cassini Langmuir probe electron temperature values of 2-3 eV.