JGustin2015_ICARUS14359_revised.pdf (4.35 MB)
Download file

Characteristics of north jovian aurora from STIS FUV spectral images

Download (4.35 MB)
journal contribution
posted on 07.11.2016, 16:36 by J. Gustin, D. Grodent, L. C. Ray, B. Bonfond, E. J. Bunce, J. D. Nichols, N. Ozak
We analyzed two observations obtained in Jan. 2013, consisting of spatial scans of the jovian 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 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. The 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 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 H2 emission profiles, resulting from secondary electrons produced by precipitation of heavy ions in the 1–2 MeV/u range, have been applied to our model. The low CR obtained from this emission suggests that heavy ions, presumably the main source of the X-ray aurora, do not significantly contribute to typical UV high latitude emission.


J.G. was supported by the PRODEX program managed by ESA in collaboration with the Belgian Federal Science Policy Office. B.B. acknowledges support from the Belgian Fund for Scientific Research (FNRS). L.C.R. was supported by STFC’s UCL Astrophysics Consolidated grant ST/J001511/1. This research is based on observations with the Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA.



Icarus, 2016, 268, pp. 215-241 (27)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


AM (Accepted Manuscript)

Published in



Elsevier for Academic Press



Acceptance date


Available date


Publisher version