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See detailHow large is the Io UV footprint?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010)

Located close to the feet of the magnetic field lines connecting Io to each Jovian hemisphere, the Io footprint is the auroral signature of the electromagnetic interaction between Io and Jupiter's ... [more ▼]

Located close to the feet of the magnetic field lines connecting Io to each Jovian hemisphere, the Io footprint is the auroral signature of the electromagnetic interaction between Io and Jupiter's magnetosphere. It consists of several spots followed downstream by an extended tail. The size of the main spot is expected to scale to the size of the interaction region close to Io. Consequently, this quantity is crucial to understand the processes involved. However, the main spot size is a controversial issue as previously published values range from ~400 km to ~10000 km, leading to contradictory conclusions. Based on observations carried on with the Hubble Space Telescope STIS and ACS FUV instruments from 1997 to 2009, we estimate the size of the main footprint spot on a much larger image sample than previously. Additionally, we carefully selected the images in order to avoid viewing geometry ambiguities when measuring the spatial extent of the different features. The main spot length along the footpath is ~900 km while its width perpendicular to the footpath is <200 km. The spot length is larger than the projected diameter of Io along unperturbed magnetic field lines, which appears to be consistent with recent simulations. The vertical extent and the peak altitude of the main spot are similar to those measured in the tail. Nevertheless, the secondary spot attributed to trans-hemispheric electron beams has been measured to peak at ∼200 km below the main spot and the tail, which confirms their different origins. [less ▲]

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See detailHow bright is the Io UV footprint?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010)

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint ... [more ▼]

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint emissions in both hemispheres. Recent results showed that this footprint is formed of several spots and an extended tail. Each feature is suggested to correspond to a different step in the propagation of the perturbation and in the electron energization processes. The present study focuses on the variations of the spots' brightness at different timescales from minutes to years through the rotation period of Jupiter. It relies on FUV images acquired with the STIS and ACS instruments onboard the Hubble Space Telescope. Since the footprint is composed of several localized features, a good understanding of the emission region geometry is critical to derive the actual vertical brightness and thus the precipitated energy flux. We developed a 3D emission model in order to assess as precisely as possible the respective contribution of each individual feature and to correctly estimate the precipitating energy flux. As far as the brightness variations on timescales of minutes are concerned, we will present results from the high time resolution campaign executed during summer 2009. On timescale of several hours, we will show that the variation of the emitted power as a function of the location of Io in the plasma torus suggests that the Jovian surface magnetic field strength is an important controlling parameter. Finally, the measured precipitated power and particle fluxes will be discussed in comparison with recent simulations considering both Alfvén waves filamentation and electron acceleration when the Alfvén waves become inertial. [less ▲]

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See detailModeling of the longitudinal modulation of the Io interaction
Hess, S.; Bonfond, Bertrand ULg; Delamere, P. A. et al

Poster (2010)

The Io interaction with the Jovian magnetosphere is the best known case of moon-magnetosphere interaction. It leads to bright emissions from radio to UV, which are mostly due to the acceleration of ... [more ▼]

The Io interaction with the Jovian magnetosphere is the best known case of moon-magnetosphere interaction. It leads to bright emissions from radio to UV, which are mostly due to the acceleration of electrons by Alfvén waves along the magnetic field lines passing Io. We previously presented a model of the electron acceleration by the Iogenic Alfvén waves, which explains the average brightness of the emissions. We now present a study of the modulation of the Io-magnetosphere interaction with longitude, and compare our results with the observed brightness modulation of the auroral emissions. This study highlights how the satellite-magnetosphere interactions depend on the variation of the magnetic field, the equatorial plasma density,... A new model of the Jovian internal magnetic field, giving an accurate description of the longitudinal modulations of the Jovian magnetic field has been computed for this study, and is also presented. [less ▲]

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See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2010)

Not Available

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See detail"Giant Planets Aurorae" - Europlanet RI Science Case in the Working Packages
Rucker, M Scherf H O; Blanc, M.; André, N. et al

Conference (2010)

Not Available

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See detailVariation of Saturn's UV aurora with SKR phase
Nichols, J. D.; Cecconi, B.; Clarke, J. T. et al

in Geophysical Research Letters (2010), 37

It is well known that a wide range of kronian magnetospheric phenomena, including the Saturn kilometric radiation (SKR), exhibit oscillations near the planetary rotation period. However, although the SKR ... [more ▼]

It is well known that a wide range of kronian magnetospheric phenomena, including the Saturn kilometric radiation (SKR), exhibit oscillations near the planetary rotation period. However, although the SKR is believed to be generated by unstable auroral electrons, no connection has been established to date between diurnal SKR modulations and UV auroral power. We use an empirical SKR phase determined from Cassini observations to order the 'quiet time' total emitted UV auroral power as observed by the Hubble Space Telescope in programs during the interval 2005-2009. Our results indicate that both the northern and southern UV powers are dependent on SKR phase, varying diurnally by factors of similar to 3. We also show that the UV variation originates principally from the morning half of the oval, consistent with previous observations of the SKR sources. Citation: Nichols, J. D., B. Cecconi, J. T. Clarke, S. W. H. Cowley, J.-C. Gerard, A. Grocott, D. Grodent, L. Lamy, and P. Zarka (2010), Variation of Saturn's UV aurora with SKR phase, Geophys. Res. Lett., 37, L15102, doi: 10.1029/2010GL044057. [less ▲]

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See detailLocation and spatial shape of electron beams in Io's wake
Jacobsen, S.; Saur, J.; Neubauer, F. M. et al

in Journal of Geophysical Research. Solid Earth (2010), 115

The Galileo spacecraft observed energetic field-aligned electron beams very close to Io during several flybys. We apply a three-dimensional magnetohydrodynamic (MHD) model of the far-field Io-Jupiter ... [more ▼]

The Galileo spacecraft observed energetic field-aligned electron beams very close to Io during several flybys. We apply a three-dimensional magnetohydrodynamic (MHD) model of the far-field Io-Jupiter interaction to simulate for the first time the location and spatial shape of field-aligned electron beams. Io continuously generates MHD waves by disturbing the Jovian magnetoplasm. Currents carried by Alfven waves propagate predominantly along the magnetic field lines. As the number of charge carriers decreases along the travel path, electrons are accelerated toward Jupiter. These energetic electrons precipitate into the Jovian ionosphere, visible as prominent Io footprint emission. Electrons are also accelerated toward Io and form the equatorial beams observed by the Galileo spacecraft. Unlike the beam formation, the position and spatial structure of these beams have not been addressed in detail before. We use a 3-D MHD model with initial conditions corresponding to the individual Galileo flyby and determine the spatial morphology of the beams in Io's orbital plane. Our results for the beam locations are in good agreement with the Galileo Energetic Particle Detector observations. We find that the ratio of the one-way travel time of the Alfven wave from Io to Jupiter and the convection time of the plasma past the obstacle controls the location of the beam. This leads to the conclusion that at other satellites with other plasma environments, the electrons might not be close to the satellite but can be shifted significantly downstream along its plasma wake. Thus, the future search for electron beams near a satellite should be further extended to the wake region. [less ▲]

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See detailThe Spatial Morphology of Equatorial Electron Beams Near Io
Jacobsen, S.; Saur, J. S.; Neubauer, F. M. et al

Conference (2009, December 14)

The Galileo spacecraft observed energetic field-aligned electron beams very close to Io during several flybys. We apply a three-dimensional magnetohydrodynamic (MHD) model of the far-field Io-Jupiter ... [more ▼]

The Galileo spacecraft observed energetic field-aligned electron beams very close to Io during several flybys. We apply a three-dimensional magnetohydrodynamic (MHD) model of the far-field Io-Jupiter interaction to simulate for the first time the location and spatial shape of field-aligned electron beams. Io continuously generates MHD waves by disturbing the Jovian magnetoplasma. Currents carried by Alfvén waves propagate predominantly along the magnetic field lines. As the number of charge carriers decreases along the travelpath, electrons are accelerated towards Jupiter. These energetic electrons precipitate into the Jovian ionosphere, visible as prominent Io footprint (IFP) emission. Electrons are also accelerated towards Io and form the equatorial beams observed by the Galileo spacecraft. Unlike the beam formation, the position and spatial structure of these beams has not been addressed in detail before. We use a 3D MHD model with initial conditions corresponding to the individual Galileo flyby and determine the spatial morphology of the beams in Io's orbital plane. Our results are in good agreement with the Galileo observations. We find that the ratio of the one-way traveltime of the Alfvén wave from Io to Jupiter and the convection time of the plasma past the obstacle controls the location of the beams. This leads to the conclusion that at other satellites with other plasma environments, e.g. Ganymede, Callisto, Europa and Enceladus, the electron beams might not be close to the satellite, but can be shifted significantly downstream along its plasma wake. Thus, the future search for field-aligned electron populations near a satellite should be further extended to the wake region. [less ▲]

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See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. W. et al

in American Geophysical Union, Fall Meeting 2009 (2009, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. 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 ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. 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 2007-2009 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. Selected movies will be presented with geometric overlays and in polar projections. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. Other movies show similar cusp-related structures that resemble the letter "Q" where a dynamical feature at right angles to the oval moves away from the cusp region. The 2008 day 201 movie also shows one bright "polar flare" inside the oval with a spectrally distinct signature indicating the presence of higher energy electrons. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. Several frames show emissions associated with the footprint of the Enceladus field line. We will discuss these features, their locations, and possible interpretations. [less ▲]

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See detailRecurrent energization of plasma in the midnight-to-dawn quadrant of Saturn's magnetosphere, and its relationship to auroral UV and radio emissions
Mitchell, D. G.; Krimigis, S. M.; Paranicas, C. et al

in Planetary and Space Science (2009), 57

We demonstrate that under some magnetospheric conditions protons and oxygen ions are accelerated once per Saturn magnetosphere rotation, at a preferred local time between midnight and dawn. Although ... [more ▼]

We demonstrate that under some magnetospheric conditions protons and oxygen ions are accelerated once per Saturn magnetosphere rotation, at a preferred local time between midnight and dawn. Although enhancements in energetic neutral atom (ENA) emission may in general occur at any local time and at any time in a Saturn rotation, those enhancements that exhibit a recurrence at a period very close to Saturn's rotation period usually recur in the same magnetospheric location. We suggest that these events result from current sheet acceleration in the 15-20 Rs range, probably associated with reconnection and plasmoid formation in Saturn's magnetotail. Simultaneous auroral observations by the Hubble Space Telescope (HST) and the Cassini Ultraviolet Imaging Spectrometer (UVIS) suggest a close correlation between these dynamical magnetospheric events and dawn-side transient auroral brightenings. Likewise, many of the recurrent ENA enhancements coincide closely with bursts of Saturn kilometric radiation, again pointing to possible linkage with high latitude auroral processes. We argue that the rotating azimuthal asymmetry of the ring current pressure revealed in the ENA images creates an associated rotating field aligned current system linking to the ionosphere and driving the correlated auroral processes. [less ▲]

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

Conference (2009, September 13)

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See detailJupiter's ultraviolet polar auroral emissions
Coumans, Valérie ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2009, September)

Not Available

Detailed reference viewed: 13 (6 ULg)
See detailRecurrent Energization of Plasma in the Midnight-to-Dawn Quadrant of Saturn's Magnetosphere, and its Relationship to Auroral UV and Radio Emissions
Mitchell, D.; Krimigis, S.; Paranicas, C. et al

Poster (2009, August 11)

Detailed reference viewed: 4 (1 ULg)
See detailHST observations of Europa's atmospheric UV emission
Saur, J.; Feldman, P. D.; Strobel, D. F. et al

Conference (2009, July 27)

Detailed reference viewed: 8 (2 ULg)
See detailDoes Saturn's UV aurora vary with SKR phase?
Nichols, J. D.; Cowley, S. W. H.; Clarke, J. T. et al

Conference (2009, July 27)

Detailed reference viewed: 3 (1 ULg)
See detailSaturn's equinoctial auroras
Nichols, J. D.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2009, July 27)

Detailed reference viewed: 7 (2 ULg)