Spectral morphology of the X-ray emission from Jupiter's aurorae

in Journal of Geophysical Research (2008), 113(A2),

Simultaneous Chandra X-ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re-examined to investigate the spatial morphology of the X-ray events in ... [more ▼]

Simultaneous Chandra X-ray and Hubble Space Telescope FUV observations of Jupiter's aurorae carried out in February 2003 have been re-examined to investigate the spatial morphology of the X-ray events in different energy bands. The data clearly show that in the Northern auroral region (in the main auroral oval and the polar cap) events with energy > 2 keV are located at the periphery of those with energy < 2 keV and coincide with FUV bright features. In addition, X-ray spectra extracted from the areas where the two event distributions are concentrated possess different shapes. We associate the > 2 keV events (similar to 45 MW emitted power) with the electron bremsstrahlung component recently revealed by XMM-Newton in the spectra of Jupiter's aurorae, and the < 2 keV emission (similar to 230 MW) with the product of ion charge exchange, now established as the likely mechanism responsible for the soft X-ray Jovian aurora. We suggest that the same population of energetic electrons may be responsible for both, the X-ray bremsstrahlung and the FUV emission of Jupiter's aurorae. Comparison of the > 2 keV X-ray and FUV (340 GW) powers measured during the observations shows that they are broadly consistent with the predicted emissions from a population of energetic electrons precipitating in the planet's atmosphere, thus supporting our interpretation. [less ▲]

High color ratio and high temperature in Jupiter's auroral atmosphere

Poster (2001, October 27)

A high FUV color ratio usually implies that most of the energy of the impinging auroral particles is deposited below the methane homopause. In this region, the resulting auroral heating is efficiently ... [more ▼]

A high FUV color ratio usually implies that most of the energy of the impinging auroral particles is deposited below the methane homopause. In this region, the resulting auroral heating is efficiently balanced by the strong hydrocarbon cooling. Therefore, this auroral process cannot sustain the high temperature observed in the Jovian auroral atmosphere. This work is an attempt to remove the ambiguity between the high color ratios and high temperatures deduced from the HST data. In order to study this apparent contradiction, the two-stream energy deposition model described by Grodent et al. (2001) has been upgraded with a Joule heating module and an adiabatic cooling approximation. The most recent hydrocarbon auroral density profiles have been included. A new EUV-FUV spectral generator has been developed and allows one to consider new observational constrains, such as the very high H2 scale heights deduced from the Cassini-Jupiter flyby HST observations. [less ▲]

HST/STIS images of UV auroral footprints from Io, Europa, and Ganymede.

in Bulletin of the American Astronomical Society (1999)

Ultraviolet images of Jupiter's aurora have been obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) since September 1997 with much higher sensitivity than ... [more ▼]

Ultraviolet images of Jupiter's aurora have been obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) since September 1997 with much higher sensitivity than earlier cameras. Higher sensitivity permits shorter exposures, freezing Jupiter's rotation and providing the highest angular resolution obtained to date. This combination of sensitivity and resolution has revealed new emissions from the magnetic footprints of Io, Europa, and Ganymede, which will be reported and discussed. Io's auroral footprint, while well studied with earlier cameras, appears highly extended at a low brightness in the wake or plasma flow direction. Ganymede's auroral footprint emission is now well established from the repeated appearance of this feature under the magnetic field trace of Ganymede, and there is initial evidence for auroral emission at Europa's magnetic footprint. Ganymede's auroral footprint appears consistently equatorward of the main auroral oval, which clearly constrains the main oval auroral currents to originate from beyond about 20 R_J. The observation that the main oval emissions are observed to corotate with Jupiter's magnetic field further constrains the origin of these currents to be within about 30 R_J, so that the source region for the main oval auroral is now fairly well constrained to a region in Jupiter's middle magnetosphere and within the current sheet. This work was supported by NASA under grant GO-7308.01-96A to the University of Michigan. [less ▲]

HST Observations of Jupiter's Aurora Simultaneous with GALILEO Measurements

in Bulletin of the American Astronomical Society (1997, July 01)

An HST observing program is underway to obtain images and spectra of Jupiter's ultraviolet aurora during key events in the GALILEO orbiter mission, including remote observations of the nightside aurora ... [more ▼]

An HST observing program is underway to obtain images and spectra of Jupiter's ultraviolet aurora during key events in the GALILEO orbiter mission, including remote observations of the nightside aurora and measurements of the magnetic field and charged particle environments. We have obtained WFPC 2 images and GHRS spectra of Jupiter's aurora overlapping with GALILEO measurements during GALILEO orbits G1 (June 1996), G2 (Sept. 1996), G7 (April 1997), and G8 (May 1997), and at the time of writing we are scheduling STIS spectra for summer 1997. The WFPC 2 images appear similar to earlier reported auroral images, with the main oval at the same location observed over the last 2 years, rapidly variable emission poleward of the main oval, and the Io footprint with a similar longitudinal offset from the local magnetic field. Spectra were obtained of auroral emission features including the northern and southern main ovals, the diffuse emission poleward of the main oval, and the northern and southern Io footprints. These spectra will be presented with estimates of the overlying hydrocarbon columns, the energy of the exciting electrons, the rotational temperature of the emitting hydrogen, and the overlying column of atomic hydrogen. This work was supported by NASA under contract JPL 959122 and grants GO-5828.01-94A and GO-6743.01-95A to the University of Michigan. [less ▲]