References of "Grodent, Denis"
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See detailThe Ultraviolet Spectrograph on NASA’s Juno Mission
Gladstone, G Randal; Persyn, Steven C.; Eterno, John S. et al

in Space Science Reviews (2014)

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These ... [more ▼]

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS. [less ▲]

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See detailDynamics of the aurora at Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, February 19)

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See detailThe 2-3 minutes periodicity in the polar aurora and the magnetosphere of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Poster (2013, December 10)

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer ... [more ▼]

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer magnetosphere or correspond to field lines open to the interplanetary medium and most of the auroral emissions from this region are still poorly understood. Among these polar auroral emissions are the flares, dramatic brightenings of several million square kilometers over a couple of minutes. Two previously reported observations of the southern hemisphere showed that these flares can be quasi-periodic with a re-occurrence time of 2-3 minutes. Here we report results from the Hubble Space Telescope campaign carried out in 2012-2013 with the STIS FUV instrument in time-tag mode (PI: D. Grodent). This campaign consisted in alternating observations of the two hemispheres. Based on the analysis of this dataset, we confirm that these quasi-periodic flares are ubiquitous and occur in both hemispheres. Moreover, in at least one case, these flares appear to occur in phase in both hemispheres. We compare the characteristics of these flares with those of the relativistic electron bursts observed by the Ulysses spacecraft with the HET instrument. We find that 2-3 minutes quasi-periodic burst are much more frequent than previously reported and that they magnetically map to the same auroral area as the flares. We conclude that these two phenomena are most probably related and arise from a common origin. [less ▲]

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See detailSaturn’s UV aurora: the (high latitude) point of view of Cassini
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gustin, Jacques ULg et al

Conference (2013, December 09)

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of ... [more ▼]

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of the associated particles and magnetic field. Cassini’s T83 flyby of Titan significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined phase 1 which will last until March 16, 2015. We will give an overview of the auroral emissions observed so far with the UVIS camera on board Cassini. In particular we will link the morphology of the aurora with specific magnetospheric processes, such as dayside reconnection and auroral bifurcations, nightside reconnection, hot plasma injections. We will also take advantage of the view from nearly above the poles to describe the overall shape and size of the aurora, which are expected to respond to the solar wind conditions. Moreover, this presentation will focus on small-scale features, which can only be observed by an instrument close enough to the planet. We will also present movies of these observations, allowing us to explore the auroral dynamics at various timescales. This information will be used to identify the various mechanisms at play in Saturn’s magnetosphere. [less ▲]

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See detailEvolution of the Io Footprint Brightness II: Modeling
Hess, Sébastien; Bonfond, Bertrand ULg; Chantry, Virginie ULg et al

in Planetary and Space Science (2013), 88

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons ... [more ▼]

The interaction of Io with the Jovian magnetosphere creates the best known and brightest satellite-controlled aurorae in our solar system. These aurorae are generated by the precipitation of electrons, which are accelerated by the Alfvén waves carrying the current between the satellite and the planet. A recent study computed the energy deposited on top of Jupiter's ionosphere due to the electron precipitation and retrieved the correct mean brightness of Io-related aurorae. The model developed in this study takes into account the acceleration mechanism and the Alfvén wave propagation effects. We use the same method to investigate the brightness variation of the different components of the Io footprint as a function of longitude. These observations are discussed in a companion paper. We identify several effects that act together to modulate the footprint brightness such as Alfvén wave reflections, magnetic mirroring of the electrons, the local interaction at Io and kinetic effects close to Jupiter. We identify the effects contributing the most to the modulation of the brightnesses of the three brightest components of the Io footprints: the main and reflected Alfvén wing spots and the transhemispheric electron spot. We show in particular that the modulation of the efficiency of the electron acceleration can be of greater importance than the modulation of the power generated at Io. We reproduce the average modulation of the spot brightnesses and present an extensive discussion of possible explanations for the observed features not reproduced by our model. [less ▲]

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See detailEvolution of the Io footprint brightness I: Far-UV observations
Bonfond, Bertrand ULg; Hess, Sébastien; Gérard, Jean-Claude ULg et al

in Planetary and Space Science (2013), 88

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the ... [more ▼]

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude of Io. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2 W/m² are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots' brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface. [less ▲]

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See detailIo plasma torus science through UV remote sensing
Grodent, Denis ULg

Scientific conference (2013, November)

In this presentation, I am providing a short review of the scientific information on the Io plasma torus that may be inferred from UV remote sensing. This includes past observations with the Hubble Space ... [more ▼]

In this presentation, I am providing a short review of the scientific information on the Io plasma torus that may be inferred from UV remote sensing. This includes past observations with the Hubble Space Telescope and the Cassini-UVIS spectrograph during the 2000-Jupiter flyby and future observations with the EXCEED (Sprint-A) telescope. [less ▲]

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See detailThe multiple spots of the Ganymede auroral footprint
Bonfond, Bertrand ULg; Hess, Sébastien; Bagenal, Fran et al

in Geophysical Research Letters (2013), 40

The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have ... [more ▼]

The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have been detected for Io, Europa, Ganymede, and Enceladus. These footprints are usually seen as single spots. However, the Io footprint, the brightest one, displays a much more complex morphology made of at least three different spots and an extended tail. Here we present Hubble Space Telescope FUV images showing evidence for a second spot in the Ganymede footprint. The spots separation distance changes as Ganymede moves latitudinally in the plasma sheet, as is seen for the Io footprint. This indicates that the processes identified at Io are universal. Moreover, for similar Ganymede System III longitudes, the distance may also vary significantly with time, indicating changes in the plasma sheet density. We identified a rapid evolution of this distance 8 days after the detection of a volcanic outburst at Io, suggesting that such auroral observations could be used to estimate the plasma density variations at Ganymede. [less ▲]

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See detailCassini UVIS Saturn Auroral Images from the 2013 HST/Cassini Campaign
Pryor, Wayne; Jouchoux, Alain; Esposito, Larry et al

Conference (2013, October)

In 2013 coordinated observations of Saturn by the Cassini spacecraft and Hubble Space Telescope (HST) were obtained. During these observations the Cassini spacecraft provided a high-latitude view of ... [more ▼]

In 2013 coordinated observations of Saturn by the Cassini spacecraft and Hubble Space Telescope (HST) were obtained. During these observations the Cassini spacecraft provided a high-latitude view of Saturn's auroras. Intense auroras were observed by the Ultraviolet Imaging Spectrograph (UVIS) from close range (about 5 Saturn radii away). A 6-frame UVIS movie has been constructed from some of the observations from May 20- 21, 2013 showing the evolution of two bright auroral features. We report on the UVIS images, the corresponding spectra, and compare the UVIS data to HST images and data from other Cassini instruments. [less ▲]

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See detailHubble observations of Jupiter’s north–south conjugate ultraviolet aurora
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

in Icarus (2013), 226

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a ... [more ▼]

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines. [less ▲]

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See detailThe Ganymede auroral footprint: implications of the spots’ multiplicity
Bonfond, Bertrand ULg; Hess, Sébastien; Bagenal, Fran et al

Conference (2013, September 10)

We report here the finding of a secondary spot for the Ganymede auroral footprint on Jupiter. Moreover, we characterize the evolution of the Ganymede footprint morphology with longitude and time. Finally ... [more ▼]

We report here the finding of a secondary spot for the Ganymede auroral footprint on Jupiter. Moreover, we characterize the evolution of the Ganymede footprint morphology with longitude and time. Finally, we discuss the implications of these results with respect to the morphology of the other satellite footprints. [less ▲]

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See detailCassini’s recent high inclination views of Saturn’s UV aurorae
Grodent, Denis ULg; Gustin, Jacques ULg; Radioti, Aikaterini ULg et al

Conference (2013, September)

On 22 May 2012, Cassini flew by Titan at a closest approach distance of 955 km. This T83 flyby significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined ... [more ▼]

On 22 May 2012, Cassini flew by Titan at a closest approach distance of 955 km. This T83 flyby significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined phase 1 which will last until March 16, 2015. During this 3-year period, the inclination of Cassini’s orbit reaches very high values, up to 62° in April 2013. This makes it possible to obtain exceptionally good views of Saturn’s poles to observe the auroral emissions in different wavelength ranges. In this presentation, we will summarize the auroral observations taken in the UV with the UVIS camera. We will focus on the morphology of the emission and pinpoint signatures that are attributed to various magnetospheric processes, such as dayside reconnection and auroral bifurcations, nightside reconnection, hot plasma injections. We will also take advantage of the view from nearly above the poles to describe the overall shape and size of the aurora, which are expected to respond to the solar wind conditions. This set of data is to be compared with the contemporaneous observations obtained from the different remote and in situ instruments onboard Cassini. It will also be completed by quasi- simultaneous UV observations of the northern aurorae caught by HST in April 2013 and may allow inter hemispheric comparisons. This information will be used to constrain the various processes at play in Saturn’s magnetosphere. [less ▲]

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See detailThe Ganymede aurora …
Gérard, Jean-Claude ULg; Shematovich, Valery; Bisikalo, Dmitry et al

Poster (2013, September)

In this Report we present the Monte Carlo model for calculation of oxygen UV and IR emissions due to the electron precipitation in the Ganymede polar regions. These techniques will provide column ... [more ▼]

In this Report we present the Monte Carlo model for calculation of oxygen UV and IR emissions due to the electron precipitation in the Ganymede polar regions. These techniques will provide column densities of atmospheric species at better than or equal to 1 km spatial resolution, and will constrain the amount of some specific compounds from limb scans and during stellar occultation. This investigation also needs characterization of the vertical temperature profile from ground up to about 400 km altitude with ~5 km vertical resolution as well as mapping of water vapour concentration. This can be performed by multiple water line observations in the 200-600 μm wavelength range. It shall be complemented by ion and neutral mass spectrometry of plasma particles, radio occultations to measure structures of the neutral atmosphere and ionosphere, and plasma wave measurements to constrain plasma density and temperature of the ionosphere. [less ▲]

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See detailIsolated transient UV auroral structures at Jupiter: possible signatures of magnetospheric injections 
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2013, July 11)

We investigate transient ultraviolet auroral features located equatorward of the main emission (130 features) based on Hubble Space Telescope (HST) observations of the northern and southern Jovian ... [more ▼]

We investigate transient ultraviolet auroral features located equatorward of the main emission (130 features) based on Hubble Space Telescope (HST) observations of the northern and southern Jovian hemispheres (2000-2007). Several properties of the auroral emissions are analyzed, such as their position in auroral region, power and brightness. Additionally, we magnetically map the auroral structures to the equatorial plane using VIPAL model and we compare their observed properties with those of magnetospheric injections observed by Galileo. We suggest that these transient auroral structures could be related to magnetospheric injections. The mapped radial position and system III longitude of the observed auroral features are in good agreement with those of the injections observed in the equatorial plane by Galileo. Based on power and brightness of the auroral features, we discuss the mechanisms involved in the ionosphere-magnetosphere coupling injections. This comparative study demonstrates that the structures under study are related to magnetospheric injections and sheds light to the mechanism involved in the magnetosphere-ionosphere dynamics. [less ▲]

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See detailVariability of the Jovian aurorae: focus on a selection of recent results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2013, July 11)

The aurorae at Jupiter can be separated into four main components: the satellite footprints, the outer emissions, the main emissions and the polar emissions. Each of these components displays some form of ... [more ▼]

The aurorae at Jupiter can be separated into four main components: the satellite footprints, the outer emissions, the main emissions and the polar emissions. Each of these components displays some form of variability in location, brightness and/or shape. The nature and the timescale of these changes is particularly revealing of the processes at play. The footprints of Io and Ganymede are often made of several spots. The distance between these spots and their brightness essentially varies as the planetary magnetic dipole rotates relative to the moons and as the plasma torus or plasma sheet wobble across the satellite orbital plane. However, the spots brightness can also considerably vary on a timescale of minutes as well as from one year to another. The outer emissions are made of diffuse, patchy or arc-shaped emissions. Two different sources have been proposed to explain these features: injections of hot plasma from the outer magnetosphere and the pitch angle scattering boundary. These features usually last for a few Jovian rotations, but their occurrence rate appears to be related to the global dynamics of the inner magnetosphere on timescales of months. The main emissions sometimes appear as a complete oval, but they usually have a more chaotic appearance, with broken arcs, gaps and forks. Their brightness and morphology respond to changes in the solar wind characteristics. Nevertheless, the dawn portion of the main emissions sometimes displays spectacular brightening apparently unrelated to the solar wind: the dawn storms. Moreover, on timescales of several months, the statistical location of the main emissions also evolves as the material input from Io increases or decreases. Globally speaking, the polar emissions also respond to the solar wind input. However, the term “polar emissions” encompasses many different auroral features obviously driven from different mechanisms. Spots and arcs, located just inside the main emissions on the dawn and night side and lasting for a few tens of minutes, have been seen to re-occur every 2 to 3 days. They have thus been associated with night-side reconnection related to the Vasyliũnas cycle. On the other hand, the dusk-side of the polar region is the locus of quasi-periodic UV flares on timescales of 2 to 3 minutes, while periodicities of 20 to 45 minutes have been identified for their X-ray counterpart. The central part of the polar region is very dynamic, with patches of emissions constantly appearing, moving and disappearing within minutes. However, along with these patches, elongated auroral arcs dubbed “polar auroral filaments” may remain present for several consecutive days. As we will see in this review talk, the current data set of UV images from the Hubble Space Telescope, including the brand new time-tag sequences from the latest 2012-2013 campaign, gives access to a wide range of auroral phenomena that only begin to reveal their secrets. [less ▲]

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See detailJupiter’s elusive bald patch
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gustin, Jacques ULg et al

Conference (2013, July)

The detailed morphology of Jupiter’s UV auroral emissions is definitely very complex. To some extent, this complexity depicts the zoo of processes taking place inside, and sometimes, outside Jupiter’s ... [more ▼]

The detailed morphology of Jupiter’s UV auroral emissions is definitely very complex. To some extent, this complexity depicts the zoo of processes taking place inside, and sometimes, outside Jupiter’s enormous magnetosphere. One is naturally more inclined to focus on the bright emissions, but recent progresses in cosmology teach us that there is also important information in the darkness. In this present, preliminary study, we are exploring a dark region of Jupiter’s polar aurora -“Jupiter’s bald patch”- located poleward of the main emission (oval). It appears to be bordered by patchy features belonging to auroral regions often referred to as the swirl and flare regions. These regions contain the poleward most auroral features. Therefore, it is legitimate to ask whether this dark region, even closer to the pole, is actually the polar cap, implying some level of reconnection of Jupiter’s strong magnetic field with the interplanetary magnetic field. An ongoing HST campaign is providing stunning high temporal and spatial (and spectral) resolution time tagged images of Jupiter’s northern and southern aurora. They show that the bald patch is conspicuous on some images but much less obvious in others. They also suggest that it is not always completely devoid of emission, possibly alluding to a weak, intermittent, Dungey-like cycle. [less ▲]

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See detailJupiter's conjugate ultraviolet aurora
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2013, July)

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See detailDynamics of the auroral bifurcations at Saturn and their role in magnetopause reconnection
Gérard, Jean-Claude ULg; Radioti, Aikaterini ULg; Grodent, Denis ULg

Conference (2013, June)

We summarize recent results obtained with the UVIS instrument on board Cassini. They demonstrate that auroral signatures of magnetic field reconnection events in the flanks of the magnetopause are ... [more ▼]

We summarize recent results obtained with the UVIS instrument on board Cassini. They demonstrate that auroral signatures of magnetic field reconnection events in the flanks of the magnetopause are observed in the UV images collected by UVIS. [less ▲]

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See detailStatistical analysis of Saturn's UV auroral outer emission
Grodent, Denis ULg; Radioti, Aikaterini ULg; Schippers, Patricia et al

Conference (2013, March 15)

Recent observations of Saturn’s aurora with the UVIS spectrograph on-board Cassini not only confirm the presence of a quasi-permanent partial ring of emission equatorward of the main auroral oval, but ... [more ▼]

Recent observations of Saturn’s aurora with the UVIS spectrograph on-board Cassini not only confirm the presence of a quasi-permanent partial ring of emission equatorward of the main auroral oval, but they also increase the number of positive cases and allow for a statistical analysis of the characteristics of this outer emission. This faint but distinct auroral feature appears at both hemispheres in the nightside sector. It magnetically maps to relatively large distances in the nightside magnetosphere, on the order of 9 RS. It was initially thought that pitch angle scattering of electrons into the loss cone by whistler waves would be responsible for the outer auroral emission. Rough estimates suggested that a suprathermal electron population observed with Cassini in the nightside sector between 7 and 10 RS might power this process. However, a new analysis of 7 years of Cassini electron plasma data indicates the presence of layers of upward and downward field aligned currents. They appear to be part of a large-scale current system involving dayside-nightside asymmetries as well as trans- hemispheric variations. This system comprises a net upward current layer, carried by warm electrons, limited to the nightside sector which may as well generate the outer UV auroral emission. The growing dataset of UVIS spectro- images is used to find any such asymmetries in the outer auroral emission. [less ▲]

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