References of "Grodent, Denis"
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See detailIsolating auroral FUV emission lines using compact, broadband instrumentation
Molyneux, P.M.; Bannister, N.P.; Bunce, E.J. et al

in Planetary and Space Science (in press)

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region ... [more ▼]

Images of auroral emissions at far ultraviolet (FUV, 122–200 nm) wavelengths are useful tools with which to study magnetospheric-ionospheric coupling, as the scattered sunlight background in this region is low, allowing both dayside and nightside auroras to be imaged simultaneously. The ratio of intensities between certain FUV emission lines or regions can be used to characterise the precipitating particles responsible for auroral emissions, and hence is a useful diagnostic of magnetospheric dynamics. Here, we describe how the addition of simple transmission filters to a compact broadband imager design allows far ultraviolet emission ratios to be deduced while also providing large-scale instantaneous images of the aurora. The low mass and volume of such an instrument would make it well-suited for both small satellite Earth-orbiting missions and larger outer planet missions from which it could be used to characterise the tenuous atmospheres observed at several moons, as well as studying the auroral emissions of the gas giants. We present a study to investigate the accuracy of a technique to allow emission line ratio retrieval, as applied to the OI 130.4 nm and 135.6 nm emissions at Ganymede. The ratio of these emissions provides information about the atmospheric composition, specifically the relative abundances of O and O2. Using modelled FUV spectra representative of Ganymede's atmosphere, based on observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), we find that the accuracy of the retrieved ratios is a function of the magnitude of the ratio, with the best measurements corresponding to a ratio of ∼1.3 . [less ▲]

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See detailSaturn's aurorae
Stallard, Tom; Badman, Sarah; Dyudina, Ulyana et al

Scientific conference (2014, August 05)

The aurora at Saturn represents a direct manifestation of the interaction between the planet’s surrounding space environment and its upper atmosphere. Our understanding of this interaction has greatly ... [more ▼]

The aurora at Saturn represents a direct manifestation of the interaction between the planet’s surrounding space environment and its upper atmosphere. Our understanding of this interaction has greatly improved over the past decade, as a result of both in-situ and remote sensing of the aurora by Cassini, as well as through Earth-based observations. On Earth, the interaction is dominated by the connection between the magnetosphere and the Solar Wind, with opening and closing of magnetic field lines leading to sporadic aurora that are strongly controlled by changes in the solar wind. On Jupiter, internal plasma sources combine with a rotationally-dominated magnetosphere to produce intense currents associated with the breakdown in co-rotation in the magnetosphere, producing powerful and continuous aurora. Investigations into Saturn’s aurora have shown that the overall morphology changes dramatically with the arrival of compressions in the solar wind, suggesting a strong interaction with the solar wind at Earth. However, the varying rotation rate of Saturn’s magnetosphere, first identified by measurements of Saturn’s radio emission, can also be measured in many aspects of the auroral emission. This in turn suggests a degree of rotational control within the aurora. As such, the better we understanding the relative strength of these influences on the aurora of Saturn, the more we can understand how the magnetosphere interacts the planet and how, in turn, the planet drives changes in the magnetosphere. Here, we will present observations of the auroral emission directly produced by particles precipitating into Saturn’s atmosphere (radio emission), the resultant atmospheric auroral excitation this produces within of atomic hydrogen (UV and visible emission) and molecular hydrogen (UV emission), as well as thermal emission from both ions produced through auroral ionization and neutral species heated within the auroral region (IR emission). These observations show a wide variety of different auroral features ranging from the rotational pole, though the main auroral emission and down to latitudes where Saturn’s atmosphere interacts with Enceladus. Observations at these different wavelength, when compared and contrasted, reveal details about the particle precipitation process that drive them, as well as the affect these currents have on the surrounding neutral atmosphere. In-situ measurements by Cassini of the particles and magnetic field above the polar region allow us to measure and understand the field-aligned currents that produce the aurora. In comparing these currents with the auroral emission at the foot of these field lines, it is possible to understand the magnetospheric origin for Saturn’s auroral emission, as well as understanding the two-way interaction between the atmosphere and magnetosphere that is driven though the currents that produce this aurora. [less ▲]

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See detailCassini Ultraviolet Images of Saturn's Aurorae
Pryor, Wayne; Jouchoux, Alain; Esposito, Larry et al

Scientific conference (2014, August 04)

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies ... [more ▼]

Cassini has been obtaining auroral images and spectra of Saturn with the Ultraviolet Imaging Spectrograph (UVIS). We will present highlights of the auroral images, showing a variety of morphologies, including multiple arcs, spiral forms, polar cusp activity, and rotating emission features, some of them pulsating with a roughly 1-hour period. A satellite footprint of Enceladus is occasionally visible. [less ▲]

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See detailA Brief Review of Ultraviolet Auroral Emissions on Giant Planets
Grodent, Denis ULg

in Space Science Reviews (2014)

The morphologies of the ultraviolet auroral emissions on the giant gas planets, Jupiter and Saturn, have conveniently been described with combinations of a restricted number of basic components. Although ... [more ▼]

The morphologies of the ultraviolet auroral emissions on the giant gas planets, Jupiter and Saturn, have conveniently been described with combinations of a restricted number of basic components. Although this simplified view is very handy for a gross depiction of the giant planets’ aurorae, it fails to scrutinize the diversity and the dynamics of the actual features that are regularly observed with the available ultraviolet imagers and spectrographs. In the present review, the typical morphologies of Jupiter and Saturn’s aurorae are represented with an updated and more accurate set of components. The use of sketches, rather than images, makes it possible to compile all these components in a single view and to put aside ultraviolet imaging technical issues that are blurring the emission sources, thus preventing one from disentangling the different auroral signatures. The ionospheric and magnetospheric processes to which these auroral features allude can then be more easily accounted. In addition, the use of components of the same kind for both planets may help to put forward similarities and differences between Jupiter and Saturn. The case of the ice giants Uranus and Neptune is much less compelling since their weak auroral emissions are very poorly documented and one can only speculate about their origin. This review presents a current perspective that will inevitably evolve in the future, especially with upcoming observing campaigns and forthcoming missions like Juno. [less ▲]

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See detailQuasi-periodic flares in Jupiter's aurora : new results
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, April 29)

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode ... [more ▼]

Two recent Hubble Space Telescope observation campaigns have been dedicated to the Jovian Far-UV aurora (GO 12883 – PI: D. Grodent and GO 13035 – PI: S. Badman). Both of them made use of the Time-Tag mode of the Space Telescope Imaging Spectrograph (STIS), a high time resolution mode which allows to observe temporal variations on timescales of tens of seconds. In the present study, we focus on sudden and spectacular bursts of auroral emissions taking place in the active region located poleward of the main emissions and called “flares”. A previous study, based on only two image sequences acquired with rather unfavorable viewing angles, showed that these flares could reappear quasi-periodically on time scales of 2-3 minutes. Phenomena with similar timescales have been identified by in-situ spacecraft in relativistic electron and radio data as well as in reconnection signatures, for example. But the physical mechanism behind these ubiquitous signatures remains to be unveiled. Here we make use of the most recent and much larger data set to study in further details the occurrence rate, the period, the location, the extent and the motion of these quasi-periodic flares and to compare their behavior in both hemispheres. Quantifying these parameters allows us to narrow down the possibilities among likely explanations and provide a tentative scenario for these short timescale quasi-periodic features. [less ▲]

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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 science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets
Arridge, C. S.; Achilleos, N.; Agarwal, J. et al

in Planetary and Space Science (2014), (0), -

Abstract Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice ... [more ▼]

Abstract Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus’ atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013. [less ▲]

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See detailCusp observation at Saturn’s high-latitude magnetosphere by the Cassini spacecraft
Jasinski; Arridge; Lamy et al

in Geophysical Research Letters (2014)

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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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