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See detailAuroral evidence of a localized magnetic anomaly in Jupiter's northern hemisphere
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research (2008), 113(A9),

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede ... [more ▼]

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede form individual footpaths, which are fitted with three reference contours. The satellite footprints provide a convenient mapping between the northern Jovian ionosphere and the equatorial plane in the middle magnetosphere, independent of any magnetic field model. The VIP4 magnetic field model is in relatively good agreement with the observed footprint of Io. However, in the auroral kink sector, between the 80 degrees and 150 degrees System III meridians, the model significantly departs from the observation. One possible way to improve the agreement between the VIP4 model and the observed footprints is to include a magnetic anomaly. We suggest that this anomaly is characterized by a weakening of the surface magnetic field in the kink sector and by an added localized tilted dipole field. This dipole rotates with the planet at a depth of 0.245 R-J below the surface, and its magnitude is set to similar to 1% of Jupiter's dipole moment. The anomaly has a very limited influence on the magnetic field intensity in the equatorial plane between the orbits of Io and Ganymede. However, it is sufficient to bend the field lines near the high-latitude atmosphere and to reproduce the observed satellite ultraviolet footpaths. JUNO's in situ measurements will determine the structure of Jupiter's magnetic field in detail to expand on these results. [less ▲]

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See detailAuroral evidence of Io's control over the magnetosphere of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2012), 39

Contrary to the case of the Earth, the main auroral oval on Jupiter is related to the breakdown of plasma corotation in the middle magnetosphere. Even if the root causes for the main auroral emissions are ... [more ▼]

Contrary to the case of the Earth, the main auroral oval on Jupiter is related to the breakdown of plasma corotation in the middle magnetosphere. Even if the root causes for the main auroral emissions are Io's volcanism and Jupiter's fast rotation, changes in the aurora could be attributed either to these internal factors or to fluctuations of the solar wind. Here we show multiple lines of evidence from the aurora for a major internally-controlled magnetospheric reconfiguration that took place in Spring 2007. Hubble Space Telescope far-UV images show that the main oval continuously expanded over a few months, engulfing the Ganymede footprint on its way. Simultaneously, there was an increased occurrence rate of large equatorward isolated auroral features attributed to injection of depleted flux tubes. Furthermore, the unique disappearance of the Io footprint on 6 June appears to be related to the exceptional equatorward migration of such a feature. The contemporary observation of the spectacular Tvashtar volcanic plume by the New-Horizons probe as well as direct measurement of increased Io plasma torus emissions suggest that these dramatic changes were triggered by Io's volcanic activity. [less ▲]

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See detailAuroral excitation and time variations
Gérard, Jean-Claude ULg; Harang, O.

in Annales de Géophysique (1974)

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See detailThe auroral footprint of Enceladus on Saturn
Pryor, Wayne R; Rymer, Abigail M; Mitchell, Donald G et al

in Nature (2011), 472

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between ... [more ▼]

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. [less ▲]

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See detailThe auroral footprint of Ganymede
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

in Journal of Geophysical Research. Space Physics (2009), 114(A07212),

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede ... [more ▼]

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede footprint. Based on an analysis of ultraviolet images obtained with the Hubble Space Telescope we demonstrate that the auroral footprint surface matches a circular region in Ganymede's orbital plane having a diameter of 8 to 20 RG. Temporal analysis of the auroral power of Ganymede's footprint reveals variations of different timescales: 1) a 5 hours timescale associated with the periodic flapping of Jupiter's plasma sheet over Ganymede, 2) a 10 to 40 minutes timescale possibly associated with energetic magnetospheric events, such as plasma injections, and 3) a 100 s timescale corresponding to quasi-periodic fluctuations which might relate to bursty reconnections on Ganymede's magnetopause and/or to the recurrent presence of acceleration structures above Jupiter's atmosphere. These three temporal components produce an auroral power emitted at Ganymede's footprint of the order of ~0.2 GW to ~1.5 GW. [less ▲]

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See detailThe auroral footprint signatures of satellites on Jupiter
Gérard; Bonfond, Bertrand ULg; Grodent, Denis ULg

Conference (2007, June 25)

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See detailAuroral footprints of tail reconnection at Jupiter and Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010, May 03)

Tail reconnection at Jupiter’s magnetosphere, has recently been shown to leave its signature in the aurora. The Hubble Space Telescope observed transient polar dawn spots on the Jovian aurora, with a ... [more ▼]

Tail reconnection at Jupiter’s magnetosphere, has recently been shown to leave its signature in the aurora. The Hubble Space Telescope observed transient polar dawn spots on the Jovian aurora, with a characteristic recurrence period of 2-3 days. Because of their periodic occurrence cycle and observed location, it is suggested that the transient auroral features are related to the precipitated, heated plasma during reconnection processes taking place in the Jovian magnetotail. Particularly, it is proposed that the transient auroral spots are triggered by the planetward moving flow bursts released during the process. A comparison of their properties with those of the <br />auroral spots strengthen the conclusion that they are signatures of tail reconnection. <br />Cassini recently revealed magnetotail reconnection events at Saturn similar to those observed at Jupiter. Based on the UVIS dataset we present transient features at Saturn’s polar auroral region, which are possible signatures of tail reconnection. We study their size, power, duration and duty cycle and we suggest possible triggering mechanisms associated with magnetotail dynamics. We compare these auroral emissions with those at Jupiter and we discuss how energy is transferred to the ionosphere during tail reconnection. [less ▲]

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See detailAuroral footprints; everywhere
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2010, May 06)

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and ... [more ▼]

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and the Jovian magnetosphere causes strong Alfvénic perturbations which propagate along the magnetic field lines. On their way towards Jupiter’s polar regions, these perturbations accelerate charged particles which then interact with Jupiter’s ionosphere where they loose a fraction of their energy in the form of auroral emissions. Each of the three moons leaves an auroral footprint around the poles of Jupiter which departs from the bulk of the auroral emission. Their location is mainly controlled by the topology of the field lines and thus analysis of the auroral footprints provides information on the magnetic field itself. In that regard, the satellites auroral footpaths were used to highlight the presence of a strong magnetic anomaly in the northern hemisphere of Jupiter. Detailed inspection of the footprints’ brightness and morphology as a function of time reveals fundamental information on the interaction mechanisms near the moons, on the particles acceleration mechanisms as well as on the Jovian ionosphere. For example, it was suggested that the Io footprint actually consists of several spots resulting from successive steps in the perturbation propagation process. Another example is the finding of three different timescales in the variations of Ganymede’s footprint; each of them is pointing to a different part of the electromagnetic interaction between the moon’s mini-magnetosphere and the Jovian plasma. Several recent images of Saturn’s auroral regions obtained with Cassini/UVIS at high latitude show an obvious auroral spot at the predicted location of Enceladus’ footprint. This major finding demonstrates that the electromagnetic interaction between a moon and its parent planet is not unique to Jupiter but appears to be a common feature in planetary systems. [less ▲]

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See detailThe auroral ionosphere - Comparison of a time-dependent model with composition measurements
Gérard, Jean-Claude ULg; Rusch, D. W.

in Journal of Geophysical Research (1979), 84

A time-dependent model of the auroral ionosphere including the odd nitrogen species, NO, N(D-2), and N(S-4), is used for comparison with data from a coordinated rocket-satellite measurement of an auroral ... [more ▼]

A time-dependent model of the auroral ionosphere including the odd nitrogen species, NO, N(D-2), and N(S-4), is used for comparison with data from a coordinated rocket-satellite measurement of an auroral event. The chemical scheme and the adopted rate coefficients have been shown to be compatible with daytime mid-latitude ionospheric chemistry. The electron flux and neutral atmospheric parameters measured on the satellite are used to compute the appropriate ionization and dissociation rates. The calculated NO(plus), O2(plus), O(plus), Ne, and NO densities agree well with the rocket measurements. The calculated N2(plus) densities are larger than the measured densities by a factor of 3 at most altitudes. The calculations show that the nitric oxide content of the aurora (about 1.2 times 10 to the 9th NO molecules/cu cm at 105 km) is below the saturation value. [less ▲]

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See detailAuroral Lyman alpha and H2 bands from the giant planets. 2: Effect of the anisotropy of the precipitating particles on the interpretation of the 'color ratio'
Prange, Renee; Rego, Daniel; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1995), 100

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals ... [more ▼]

Previous spectral analyses have given evidence of collisionally excited Jovian and (at times) Saturnian H2 Werner bands being absorbed by hydrocarbons at the shortest wavelengths along the auroral ovals, and of a longitudinal dependence of this absorption in the Jovian aurorae. This 'color ratio' has been used to estimate the energy of the primary particles. In such estimates, particles are generally assumed to penetrate vertically into the atmosphere. However, the precipitating particle angular distribution is unknown, and a model developed for a diffuse aurora by Prange and Elkhamsi (1991), for instance, predicts quite different possible distributions. We consider here the influence of the angular distribution used in the model, and show that distributions peaking far from vertical may increase the energy derived from a given color ratio by as much as a factor of 3. We discuss previous interpretations of the color ratio longitudinal modulation (variation of the auroral atmosphere structure, or of the incident particle energy) in view of the subsequent increase in energy input. We argue that an interpretation in terms of energy variations only is not consistent with the energy available in the magnetosphere if the aurorae are diffuse, and we discuss this finding in the context of recent Hubble Space Telescope (HST) images. [less ▲]

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See detailAuroral Lyman alpha and H2 bands from the giant planets: 1. Excitation by proton precipitation in the Jovian atmosphere
Rego, Daniel; Prange, Renee; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident ... [more ▼]

This paper is part of a work aimed at modeling the ratio of the observed Jovian auroral intensity at H Lyman-alpha and in the H2 Lyman and Werner bands and interpreting them as diagnostic of the incident magnetospheric particle species and energy. The work is planned in three steps: (1) modeling of the volume excitation rate, (2) modeling of the radiative transfer at Lyman-alpha, (3) application to existing observational data and new data obtained from the Hubble Space Telescope. The present paper deals with the first step. Models of the volume excitation rate have previously been developed for low energy electrons and oxygen ions. However, the energy range of the study has to be extended towards higher energy in view of recent results on the penetration depth of the primary particles. Protons have not been modeled so far. We have used an existing electron code of degradation of energy (Gerard and Singh, 1982) which has been improved, updated and adapted to the case of precipitating protons. The issues of nonequilibrium beam H/H(+) fractions and of getting reliable cross sections over a wide energy range have been considered with particular care. The altitude distribution of the volume excitation rate is compared for electrons and protons, for various initial energies in the range 10-50 keV and 50 keV to 1 MeV, respectively. [less ▲]

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See detailAuroral Movies and Spectroscopy from Cassini UVIS
Pryor, W. R.; West, R.; Stewart, I. et al

Conference (2007, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting us to create images, spectra, and at times movies. We will present an auroral movie from 2007-145 that has been processed to remove flat-fielding artifacts and deconvolved to remove scattering along the slit. The movie shows near co- rotation of N polar auroral features with the planet's rotation. An auroral oval is present. The oval appears doubled on the midnight side. Other images from this year show emissions inside the auroral oval. We will discuss these images and their spectra. Additional images and movies are planned in coming months. [less ▲]

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See detailAuroral oval equatorward boundary during strong magnetic storms
Bojanowska, M.; Hubert, Benoît ULg; Nowakowski, R.

in 36th COSPAR Scientific Assembly (2006)

Data has been collected for selected strong magnetic storms during which auroras were seen from ground at middle- and low-latitudes as reported by amateur observers all over the world Auroral reports from ... [more ▼]

Data has been collected for selected strong magnetic storms during which auroras were seen from ground at middle- and low-latitudes as reported by amateur observers all over the world Auroral reports from ground were compared with auroral images from space Timed Image Polar and in situ measurements of plasma and magnetic electric fields in the disturbed inner magnetosphere A new version of the Weimer2005 electric potential model gives the boundary that defines the low-latitude edge of both the convection electric field and the magnetic perturbation due to the field-aligned currents We tried to find out whether it is possible to predict auroral oval position during strong magnetic storms using this improved ionospheric electrodynamic model A quite good compatibility between FAC pattern and oval position has been found This suggests that during strong magnetic storm Weimer2005 FAC model may be used to predict equatorward boundary of the auroral oval We also compared the observed low-latitude oval boundaries with projections of Alfven layer for plasma sheet electrons Particle trajectories were traced using T04 s magnetic field model and Weimer 2005 electric field model for given solar wind conditions Results will be discussed [less ▲]

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See detailAuroral polar dawn spots: Signatures of internally driven reconnection processes at Jupiter's magnetotail
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2008), 35(3), 03104

We report the presence of polar spots located in the dawn auroral region, based on the HST ACS 2007 campaign. We study the location of these features in the equatorial plane as well as their time scales ... [more ▼]

We report the presence of polar spots located in the dawn auroral region, based on the HST ACS 2007 campaign. We study the location of these features in the equatorial plane as well as their time scales and periodicities, based on a comprehensive series of images taken between February 21 and June 11, 2007. It is shown that the majority of polar dawn spots magnetically map to the dawn sector. Additionally, they occur quasi-periodically every 2-3 days, a periodicity observed for the first time in auroral features. Because of their mapped location and their periodic cycle, we interpret the polar dawn spots as signatures of internally driven magnetic reconnection in the Jovian magnetotail. [less ▲]

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See detailAuroral Precipitation during the Bastille Day Storm Recovery
Immel, T. J.; Mende, S. B.; Frey, H. U. et al

Conference (2001, December 01)

The recovery period following the geomagnetic storm of July 15-16, 2000 is marked by rapid changes in auroral morphology and brightness in the sunlit hemisphere. These observations are made by the FUV and ... [more ▼]

The recovery period following the geomagnetic storm of July 15-16, 2000 is marked by rapid changes in auroral morphology and brightness in the sunlit hemisphere. These observations are made by the FUV and EUV imagers aboard the IMAGE satelite. Clear signatures of magnetospheric convection are observed in the motion of the auroral forms, indicating sunward convection of plasma in the polar cap under the strong northward component of the IMF. Precipitation is also observed equatorward of the auroral oval on the dayside in large diffuse arcs. Unlike previously observed detached proton arcs, this precipitation appears to have a significant electron component. Determination of the characteristic energies and fluxes of electrons and protons requires the proper removal of FUV airglow emissions, which in this case have been strongly affected by the recent magnetic activity. EUV images provide a very clear signature of these events, with practically no airglow contamination. With proper modeling, these EUV images could provide improvements to the characterization of the magnetospheric energy input to the thermosphere and ionosphere from space-based imaging. [less ▲]

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See detailAuroral Processes
Kurth, W. S.; Bunce, E. J.; Clarke, J. T. et al

in Dougherty, M. K.; Esposito, L. W.; Krimigis, S. M. (Eds.) Saturn from Cassini-Huygens (2009)

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number ... [more ▼]

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number of campaigns were coordinated with the Hubble Space Telescope such that Cassini could provide either ground truth on the impinging solar wind or in situ measurements of magnetospheric conditions leading to qualitative and sometimes quantitative relationships between the solar wind influence on the intensity, the morphology and evolution of the auroras, and magnetospheric dynamics. The Hubble UV images are enhanced by Cassini’s own remote sensing of the auroras. Cassini’s in situ studies of the structure and dynamics of the magnetosphere discussed in other chapters of this book provide the context for understanding the primary drivers of Saturn’s auroras and the role of magnetospheric dynamics in their variations. Finally, Cassini’s three dimensional prime mission survey of the magnetosphere culminates in high inclination orbits placing it at relatively small radial distances while on auroral field lines, providing the first such in situ observations of auroral particles and fields at a planet other than Earth. The new observations have spawned a number of efforts to model the interaction of the solar wind with the magnetosphere and how such dynamics influence the auroras. [less ▲]

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See detailAuroral Processes at Earth, Jupiter and Saturn.
Grodent, Denis ULg

Conference (2004, May 17)

We review the main characteristics of the auroral ultraviolet emissions at Earth, Jupiter and Saturn. Based on auroral morphology considerations, we discuss and compare the different solar wind ... [more ▼]

We review the main characteristics of the auroral ultraviolet emissions at Earth, Jupiter and Saturn. Based on auroral morphology considerations, we discuss and compare the different solar wind - magnetosphere - ionosphere coupling processes giving rise to these emissions. Earth's magnetosphere is usually described as 'open', meaning that its field reconnects with the interplanetary magnetic field (IMF) frozen in the solar wind. This reconnection process allows solar-wind plasma and energy to be transferred to the magnetosphere and to provide the main driving force for the auroral emissions. Different cases of solar-wind plasma conditions have been recognized to give rise to different types of auroral features. Jupiter is opposed to Earth, with a 'closed' magnetosphere. Its larger distance to the Sun and its enormous magnetic field make it difficult for the reconnection process with the IMF to occur efficiently. Io's volcanism is considered to be the prime (internal) plasma source for the magnetosphere, and corotation enforcement of this outward moving plasma is the likely process generating field aligned currents, responsible for the main auroral emissions. Saturn's aurora has not been as extensively studied as Earth's and Jupiter's. Owing to fainter magnetic field and internal plasma source than Jupiter, it has been expected to be intermediate between the cases of Earth and Jupiter. Recent detailed analysis of the Terrestrial, Jovian and Saturnian auroral morphology and dynamics suggests that the simple open/closed/open-closed magnetosphere picture is somewhat oversimplified. They show a much more complex situation with, for example, auroral activity without solar-wind reconnection at Earth, Earth-like reconnection signatures at Jupiter, or extreme auroral variability at Saturn. [less ▲]

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See detailAuroral processes at the outer planets
Gérard, Jean-Claude ULg

Conference (2010, January 04)

The mean electron energy may be significantly different in different auroral zones. The Io tail CR is remarkably low in comparison with the high-latitude aurora and independent of its brightness (<E> ~ 50 ... [more ▼]

The mean electron energy may be significantly different in different auroral zones. The Io tail CR is remarkably low in comparison with the high-latitude aurora and independent of its brightness (<E> ~ 50 keV or less). This is consistent with a model where the tail corresponds to an upward field aligned current closing the magnetospheric circuit in Jupiter’s ionosphere. The CR in the main oval is associated with electron energies from ~50 to several 100 keV. It is statistically positively correlated with the intensity. Brightness increase in the main oval is accompanied by hardening of the electron energy spectrum. This result is consistent with acceleration by potential drops accompanying upward field-aligned currents which carry a nearly constant particle number flux. The electron mean energy is also variable in the polar spots but it is not correlated with the main oval brightness nor its own intensity, suggesting different, uncorrelated mechanisms. Polar brightenings (duration ~ 50-100 sec, rise time ~30 sec) have been observed. They are not necessarily associated with an increase of the mean electron energy. The mean electron energy can even decrease during the intensification. No correlation is observed between changes in main oval and high latitude (polar cap) features. [less ▲]

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See detailAuroral Signature of the Interaction of Comet Shoemaker-Levy 9 with the Jovian Magnetosphere
Prangé; Emerich, C.; Rego, D. et al

in Bulletin of the American Astronomical Society (1994, June 01)

Not Available

Detailed reference viewed: 5 (1 ULg)