The Jovian aurora: Electron or ion precipitation?

Abstract

High signal‐to‐noise spectra of the Jovian aurora at UV wavelengths obtained using the International Ultraviolet Explorer Observatory (including the brightest Jovian aurora observed to date) are used to study the existence of sulfur and oxygen emissions which would be associated with the precipitation of energetic heavy ions in the upper Jovian atmosphere. Model calculations of heavy ion precipitation and corresponding estimates of the associated sulfur and oxygen UV emissions carried out in the preceding companion paper of Horanyi et al. suggest emission values for 1304‐Å O I emission that are at least 50 times larger than the upper limit values set by the IUE observations reported here. On the other hand a possible emission feature of S II at 1256 Å is comparable to the theoretically predicted emission intensity. Earlier X ray observations and in situ plasma observations have indicated the existence of energetic heavy ion precipitation in the Jovian auroral zone. Based on the IUE observations reported here, we suggest a scenario where heavy ion auroral energy deposition is concentrated at altitudes below the homopause (i.e., >300 keV/nucleon) and electrons with energies of 10 to 30 keV are responsible for the bulk of the observable UV and EUV emissions since they deposit their energy above the methane‐absorbing layer defined by the homopause.

Spatially Resolved Far Ultraviolet Spectroscopy of the Jovian Aurora

“…The 1295-1330-Å region shows significant discrepancies that can partly be ascribed to the residual presence of the terrestrial OI triplet at 1302.17, 1304.86, and 1306.03Å in the observed spectrum following subtraction of the sky background contribution. The presence of the 1304Å triplet in the jovian auroral spectrum has been a matter of controversy since Waite et al (1998) observed a weak feature in jovian auroral spectra obtained with the spectrograph on board the International Ultraviolet Explorer (IUE) satellite. Trafton et al (1998) analyzed a spectrum obtained between 1282 and 1318Å at 0.5-Å resolution with the Goddard High Resolution Spectrometer (GHRS).…”

Spectroscopic Evidence for High-Altitude Aurora at Jupiter from Galileo Extreme Ultraviolet Spectrometer and Hopkins Ultraviolet Telescope Observations

“…We choose to use the same approach to model the EUV spectra as Grodent et al (2000) have prescribed for the analysis of HST FUV spectra. Our model is a synthesis of (1) the spectral line H 2 Rydberg code for electron impact described by Shemansky (1985) and Ajello et al (1984Ajello et al ( , 1988Ajello et al ( , 1998, (2) the two-stream electron energy degradation transport code derived by Waite et al (1983Waite et al ( , 1988, and (3) the one-dimensional heat conduction, which includes the heating of the atmosphere by the auroral electron precipitation . Grodent et al (2000) recognized that the thermal constraints placed on the upper atmosphere by the H + 3 rovibrational temperatures required soft electron impact with an E o of ∼1 keV to achieve the exospheric temperatures of 700-1300 K. We will show that an even softer electron flux of E o of about 0.1 keV is needed to explain the EUV spectrum.…”

Long‐term study of longitudinal dependence in primary particle precipitation in the north Jovian aurora

“…Auroral activity near Jupiter's north pole has been observed in the FUV by means of rocket experiments, the Voyager ultraviolet spectrometer, and Earth-orbiting telescopes such as the International Ultraviolet Explorer (IUE) satellite [Broadfoot et al, 1981;Durrance et al, 1982;Giles et al, 1976;Rottman et al, 1973;Skinner, 1984;Skinner et al, 1984;Waite et al, 1988]. The IUE is particularly valuable, as its stable orbital position allows consecutive observations sequenced over several hours in order to resolve short time scale variability, while its extraordinary durability has permitted the construction of a data collection spanning more than a decade.…”