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See detailSimilarity of the Jovian satellite footprints: spots multiplicity and dynamics
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, S. V. et al

in Icarus (2017)

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the ... [more ▼]

In the magnetospheres of Jupiter and Saturn, the intense interaction of the satellites Io, Europa, Ganymede and Enceladus with their surrounding plasma environment leaves a signature in the aurora of the planet. Called satellite footprints, these auroral features appear either as a single spot (Europa and Enceladus) or as multiple spots (Io and Ganymede). Moreover, they can be followed by extended trailing tails in the case of Io and Europa, while no tail has been reported for Ganymede and Enceladus, yet. Here we show that all Jovian footprints can be made of several spots. Furthermore, the footprints all experience brightness variations on timescale of 2-3 minutes. We also demonstrate that the satellite location relative to the plasma sheet is not the only driver for the footprint brightness, but that the plasma environment and the magnetic field strength also play a role. These new findings demonstrate that the Europa and Ganymede footprints are very similar to the Io footprint. As a consequence, the processes expected to take place at Io, such as the bi-directional electron acceleration by Alfvén waves or the partial reflection of these waves on plasma density gradients, can most likely be extended to the other footprints, suggesting that they are indeed universal processes. [less ▲]

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See detailThe complex behavior of the satellite footprints at Jupiter: the result of universal processes?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah V. et al

Poster (2016, December 14)

At Jupiter, some auroral emissions are directly related to the electromagnetic interaction between the moons Io, Europa and Ganymede on one hand and the rapidly rotating magnetospheric plasma on the other ... [more ▼]

At Jupiter, some auroral emissions are directly related to the electromagnetic interaction between the moons Io, Europa and Ganymede on one hand and the rapidly rotating magnetospheric plasma on the other hand. Out of the three, the Io footprint is the brightest and the most studied. Present in each hemisphere, it is made of at least three different spots and an extended trailing tail. The variability of the brightness of the spots as well as their relative location has been tentatively explained with a combination of Alfvén waves’ partial reflections on density gradients and bi-directional electron acceleration at high latitude. Should this scenario be correct, then the other footprints should also show the same behavior. Here we show that all footprints are, at least occasionally, made of several spots and they all display a tail. We also show that these spots share many characteristics with those of the Io footprint (i.e. some significant variability on timescales of 2-3 minutes). Additionally, we present some Monte-Carlo simulations indicating that the tails are also due to Alfvén waves electron acceleration rather than quasi-static electron acceleration. Even if some details still need clarification, these observations strengthen the scenario proposed for the Io footprint and thus indicate that these processes are universal. In addition, we will present some early results from Juno-UVS concerning the location and morphology of the footprints during the first low-altitude observations of the polar aurorae. These observations, carried out in previously unexplored longitude ranges, should either confirm or contradict our understanding of the footprints. [less ▲]

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See detailJupiter’s auroras during the Juno approach phase as observed by the Hubble Space Telescope
Nichols, Jonathan D; Clarke, John T; Orton, Glennn S et al

Conference (2016, December 13)

We present movies of the Hubble Space Telescope (HST) observations of Jupiter’s FUV auroras observed during the Juno approach phase and first capture orbit, and compare with Juno observations of the ... [more ▼]

We present movies of the Hubble Space Telescope (HST) observations of Jupiter’s FUV auroras observed during the Juno approach phase and first capture orbit, and compare with Juno observations of the interplanetary medium near Jupiter and inside the magnetosphere. Jupiter’s FUV auroras indicate the nature of the dynamic processes occurring in Jupiter’s magnetosphere, and the approach phase provided a unique opportunity to obtain a full set of interplanetary data near to Jupiter at the time of a program of HST observations, along with the first simultaneous with Juno observations inside the magnetosphere. The overall goal was to determine the nature of the solar wind effect on Jupiter’s magnetosphere. HST observations were obtained with typically 1 orbit per day over three intervals: 16 May – 7 June, 22-30 June and 11-18 July, i.e. while Juno was in the solar wind, around the bow shock and magnetosphere crossings, and in the mid-latitude middle-outer magnetospheres. We show that these intervals are characterised by particularly dynamic polar auroras, and significant variations in the auroral power output caused by e.g. dawn storms, intense main emission and poleward forms. We compare the variation of these features with Juno observations of interplanetary compression regions and the magnetospheric environment during the intervals of these observations. [less ▲]

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See detailInitial observations of Jupiter’s aurora from Juno’s Ultraviolet Spectrograph (Juno-UVS)
Gladstone, Randy; Versteeg; Greathouse, Thomas et al

Conference (2016, December 13)

Juno-UVS is an imaging spectrograph with a bandpass of 70<λ<205 nm. This wavelength range includes important far-ultraviolet (FUV) emissions from the H2 bands and the H Lyman series which are produced in ... [more ▼]

Juno-UVS is an imaging spectrograph with a bandpass of 70<λ<205 nm. This wavelength range includes important far-ultraviolet (FUV) emissions from the H2 bands and the H Lyman series which are produced in Jupiter’s auroras, and also the absorption signatures of aurorally-produced hydrocarbons. The Juno-UVS instrument telescope has a 4x4 cm2 input aperture and uses an off-axis parabolic primary mirror. A flat scan mirror situated near the entrance of the telescope is used to observe at up to ±30° perpendicular to the Juno spin plane. The light is focused onto the spectrograph entrance slit, which has a “dog-bone” shape, with three sections of 2.55°x0.2°, 2.0°x0.025°, and 2.55°x0.2° (as projected onto the sky). Light entering the slit is dispersed by a toroidal grating which focuses FUV light onto a curved microchannel plate (MCP) cross delay line (XDL) detector with a solar blind UV-sensitive CsI photocathode. The two mirrors and the grating are coated with MgF2 to improve FUV reflectivity. Tantalum surrounds the spectrograph assembly to shield the detector and its electronics from high-energy electrons. All other electronics are located in Juno’s spacecraft vault, including redundant low-voltage and high-voltage power supplies, command and data handling electronics, heater/actuator electronics, scan mirror electronics, and event processing electronics. The purpose of Juno-UVS is to remotely sense Jupiter’s auroral morphology and brightness to provide context for in situ measurements by Juno’s particle instruments. Here we present the first near-Jupiter results from the UVS instrument following measurements made during PJ1, Juno’s first perijove pass with its instruments powered on and taking data. [less ▲]

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See detailSearch for low-latitude atmospheric hydrocarbon variations on Jupiter from Juno-UVS measurements
Hue, Vincent; Gladstone, Randy; Greathouse, Thomas et al

Conference (2016, December 13)

The Juno mission offers the opportunity to study Jupiter, from its inner structure, up to its magnetospheric environment. Juno was launched on August 2011 and its Jupiter orbit insertion (JOI) occurred on ... [more ▼]

The Juno mission offers the opportunity to study Jupiter, from its inner structure, up to its magnetospheric environment. Juno was launched on August 2011 and its Jupiter orbit insertion (JOI) occurred on July 4th 2016. The nominal Juno mission involves 35 science polar-orbits of 14-days period, with perijove and apojove distances located at 0.06 Rj and 45 Rj, respectively. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, designed to characterize Jupiter UV emissions. One of the main additions of UVS compared to its predecessors (New Horizons- and Rosetta- Alice, LRO-LAMP) is a 2.54 mm tantalum shielding, to protect it from the harsh radiation environment at Jupiter, and a scan mirror, to allow for targeting specific auroral and atmospheric features at +/- 30˚ perpendicular to the Juno spin plane. It will provide new constraints on Jupiter’s auroral morphology, spectral features, and vertical structure, while providing remote-sensing constraints for the onboard waves and particle instruments. It will also be used to probe upper-atmospheric composition through absorption features found in the UV spectra using reflected solar UV radiation. For example, stratospheric hydrocarbons such as C2H2 and C2H6 are known to absorb significantly in the 150-180 nm regions, and these absorption features can be used to determine their abundances. We will present our search for the spectroscopic features seen in Jupiter’s reflected sunlight during the first perijove. [less ▲]

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See detailDynamics of the flares in the active polar region of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, S. V. et al

in Geophysical Research Letters (2016)

The dusk-side of the polar region of Jupiter's UV aurorae, called the active region, sometimes exhibits quasi-periodic (QP) flares on time-scales of 2-3 minutes. Based on Hubble Space Telescope Far-UV ... [more ▼]

The dusk-side of the polar region of Jupiter's UV aurorae, called the active region, sometimes exhibits quasi-periodic (QP) flares on time-scales of 2-3 minutes. Based on Hubble Space Telescope Far-UV time-tag images, we show for the first time that the northern hemisphere also displays QP-flares. The area covered by these flares can reach up to 2.4 × 108 km2 (i.e. the whole active region), but often only involves an area an order of magnitude smaller. Using a magnetic field mapping model, we deduced that these areas correspond to the dayside outer magnetosphere. In our dataset, quasi-periodic features are only seen on half of the cases and even on a given observation, a region can be quiet for one half and blinking on the other half. Consecutive observations in the two hemispheres show that the brightening can occur in phase. Combined with the size and location of the flares, this behaviour suggests that the QP-flares most likely take place on closed magnetic field lines. [less ▲]

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See detailAnalysis of the Jovian aurorae
Bonfond, Bertrand ULg

Conference (2016, September)

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See detailJupiter’s magnetopause: A search for reconnection and wave signatures
Bonfond, Bertrand ULg; Kivelson, Margaret; Khurana, Krishan et al

Conference (2016, April 26)

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See detailThe many aurorae of Jupiter: proxis of the magentospheric dynamics
Bonfond, Bertrand ULg

Conference (2016, April 25)

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See detailThe many aurorae on Jupiter: an overview of recent results
Bonfond, Bertrand ULg

Scientific conference (2016, March 21)

The Hubble Space Telescope's high resolution observations of the Jovian aurorae in the UV domain have provided us with a wealth of new information in the recent years. Not only do we have now access to ... [more ▼]

The Hubble Space Telescope's high resolution observations of the Jovian aurorae in the UV domain have provided us with a wealth of new information in the recent years. Not only do we have now access to details down to a couple hundreds kilometers, but we can also analyze changes on timescales of tens of seconds. These images and spectra have taught us that the aurorae are made of many different features, each of them associated with a different process in the Jovian magnetosphere. This magnetosphere significantly differs from the Earth's one, being dominated by the rapid rotation of Jupiter and the plasma originating from Io's volcanism. The satellite footprints are the auroral signature of the electro-magnetic interaction between the Galilean moons and the magnetospheric plasma rotating around Jupiter. In the case of Io, Europa and Ganymede, this signature takes the form of a chain of spots followed by an elongated tail of emission. The tentative identification of a Callisto footprint will also be discussed. Poleward of Io's footprint, patches of emission of various sizes have been associated with injections of hot coming from the outer magnetosphere into the middle magnetosphere. These spots ares thus important markers of the plasma circulation in the Jovian magetnosphere. In the same auroral region, more diffuse emissions are associated with pitch angle scattering in the magnetospheric area where dipolar magnetic field lines become elongated. The most striking feature of the Jovian aurorae is the main emission. This structure sometimes appears as a continuous auroral oval, but it can also display much more complex patterns, especially on the dusk side. Moreover, the brightness strongly changes with local time, as a response to the variability of the corotation enforcement currents and the partial ring currents in the middle magnetosphere. Directly poleward of the main emission, patches regularly appear on the night and dawn sides, in a region generally devoid of any emissions (the polar dark region). Such patches are thought to be a signature of the reconnection process that allows the release of the plasma coming from Io into the magnetotail. The dusk side of the area enclosed in the main emission, called the active region, is the locus of intense and transient (sometimes, even quasi-periodic) flares as well as more stable arcs and diffuse patches. Poleward of this area, stable filaments can sometimes be seen along the noon to midnight axis. Finally, the polar-most region, tentatively associated with open field lines, display rapidly fluctuating patches of emissions. All these polar emissions are very poorly understood and will thus be the subject of fascinating investigations from the Juno spacecraft, arriving around Jupiter on July 4th. [less ▲]

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See detailThe Many AUrorae of Jupiter : Auroral Ffilaments, Flares, Transient features of the main oval, Swirls, Polar dawn spots, Injection signatures and Satellite footprints
Bonfond, Bertrand ULg

Conference (2016, March 07)

The presentation is a review of the many features of the Jovian aurorae in the frame of the imminent arrival of the Juno spacecraft around Jupiter, with a special focus on the most recent results.

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See detailCharacteristics of north jovian aurora from STIS FUV spectral images
Gustin, Jacques ULg; Grodent, Denis ULg; Ray, Licia et al

in Icarus (2016)

We analyzed two observations obtained in Jan. 2013, consisting of spatial scans of the jovian north ultraviolet aurora with the HST Space Telescope Imaging Spectrograph (STIS) in the spectroscopic mode ... [more ▼]

We analyzed two observations obtained in Jan. 2013, consisting of spatial scans of the jovian north ultraviolet aurora with the HST Space Telescope Imaging Spectrograph (STIS) in the spectroscopic mode. The color ratio (CR) method, which relates the wavelength-dependent absorption of the FUV spectra to the mean energy of the precipitating electrons, allowed us to determine important characteristics of the entire auroral region. The results show that the spatial distribution of the precipitating electron energy is far from uniform. The morning main emission arc is associated with mean energies of around 265 keV, the afternoon main emission (kink region) has energies near 105 keV, while the ‘flare’ emissions poleward of the main oval are characterized by electrons in the 50–85 keV range. A small scale structure observed in the discontinuity region is related to electrons of 232 keV and the Ganymede footprint shows energies of 157 keV. Interestingly, each specific region shows very similar behavior for the two separate observations. The Io footprint shows a weak but undeniable hydrocarbon absorption, which is not consistent with altitudes of the Io emission profiles (∼900 km relative to the 1 bar level) determined from HST-ACS observations. An upward shift of the hydrocarbon homopause of at least 100 km is required to reconcile the high altitude of the emission and hydrocarbon absorption. The relationship between the energy fluxes and the electron energies has been compared to curves obtained from Knight’s theory of field-aligned currents. Assuming a fixed electron temperature of 2.5 keV, an electron source population density of ∼800 m−3 and ∼2400 m−3 is obtained for the morning main emission and kink regions, respectively. Magnetospheric electron densities are lowered for the morning main emission (∼600 m−3) if the relativistic version of Knight’s theory is applied. Lyman and Werner H2 emission profiles, resulting from secondary electrons produced by precipitation of heavy ions in the 1–2 MeV/u range, have been applied to our model. The low CR obtained from this emission suggests that heavy ions, presumably the main source of the X-ray aurora, do not significantly contribute to typical UV high latitude emission. [less ▲]

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See detailAuroral evidence of radial transport at Jupiter during January 2014
Gray, R. L.; Badman, S. V.; Bonfond, Bertrand ULg et al

in Journal of Geophysical Research. Space Physics (2016)

We present Jovian auroral observations from the 2014 January Hubble Space Telescope (HST) campaign and investigate the auroral signatures of radial transport in the magnetosphere alongside contemporaneous ... [more ▼]

We present Jovian auroral observations from the 2014 January Hubble Space Telescope (HST) campaign and investigate the auroral signatures of radial transport in the magnetosphere alongside contemporaneous radio and Hisaki EUV data. HST FUV auroral observations on day 11 show, for the first time, a significantly superrotating polar spot poleward of the main emission on the dawnside. The spot transitions from the polar to main emission region in the presence of a locally broad, bright dawnside main emission feature and two large equatorward emission features. Such a configuration of the main emission region is also unreported to date. We interpret the signatures as part of a sequence of inward radial transport processes. Hot plasma inflows from tail reconnection are thought to flow planetward and could generate the superrotating spot. The main emission feature could be the result of flow shears from prior hot inflows. Equatorward emissions are observed. These are evidence of hot plasma injections in the inner magnetosphere. The images are thought to be part of a prolonged period of reconnection. Radio emissions measured by Wind suggest that hectometric (HOM) and non-Io decametric (DAM) signatures are associated with the sequence of auroral signatures, which implies a global magnetospheric disturbance. The reconnection and injection interval can continue for several hours. [less ▲]

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See detailThe color ratio-intensity relation in the Jovian aurora: Hubble observations of auroral components
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

in Planetary and Space Science (2016), 131

Spectral observations made with the long slit of the Space Telescope Imaging Spectrograph (STIS) on board Hubble have been used to construct spectral maps of the FUV Jovian aurora. They reveal that the ... [more ▼]

Spectral observations made with the long slit of the Space Telescope Imaging Spectrograph (STIS) on board Hubble have been used to construct spectral maps of the FUV Jovian aurora. They reveal that the amount of absorption by overlying methane shows significant spatial variations. In this report, we examine the relationship between the auroral brightness of the unabsorbed H2 emission that is proportional to the precipitated electron energy flux, and the ultraviolet color ratio, a proxy of the mean electron energy. We find that it varies significantly between the different components of the aurora and in the polar region. Although no global dependence can be found, we show that the two quantities are better organized in some auroral components such as regions of the main aurororal emission. By contrast, the dependence of the electron characteristic energy in high-latitude and diffuse aurora regions on the auroral energy input is generally more scattered. We conclude that the various auroral components are associated with different electron acceleration processes, some of which are not governed by a simple relation linking the value of a field-aligned acceleration potential with the parallel currents flowing from the ionosphere. [less ▲]

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See detailHST-Juno synergistic approach of Jupiter's magnetosphere and ultraviolet auroras
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg et al

E-print/Working paper (2016)

Jupiter's system is not only fundamental to our understanding of the solar system but also of planetary systems around other stars as well as more distant astrophysical bodies, not accessible to a ... [more ▼]

Jupiter's system is not only fundamental to our understanding of the solar system but also of planetary systems around other stars as well as more distant astrophysical bodies, not accessible to a detailed investigation. Fully exploiting any rare opportunity to explore the Jovian system through synergistic observations is thus critical, as it will impact significantly across wider astronomical studies. Such an exceptional opportunity will occur in Cycle 24, when the NASA Juno spacecraft will achieve its prime mission around Jupiter. Since Juno will literally fly through the auroral acceleration regions, the combination of HST auroral observations with Juno in situ measurements will allow us to finally unravel the origins and consequences of Jupiter's powerful and highly variable ultraviolet auroras. This occasion has never occurred before and is unlikely to ever repeat. Juno will address key scientific issues related to unexplored regions of the Jovian magnetosphere. The auroral signatures associated with these magnetospheric processes will be precisely observed with STIS and COS. This program responds to the UV initiative and is only possible during Cycle 24. Indeed, HST is the only observatory capable of making these high spatial and temporal resolution FUV observations during the Juno mission. This ambitious campaign will yield high-impact results and significantly augment the science return of the NASA Juno mission. [less ▲]

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See detailWeakening of Jupiter's main auroral emission during January 2014
Badman, S. V.; Bonfond, Bertrand ULg; Fujimoto, M. et al

in Geophysical Research Letters (2016), 43(3), 988-997

In January 2014 Jupiter's FUV main auroral oval decreased its emitted power by 70% and shifted equatorward by ∼1°. Intense, low-latitude features were also detected. The decrease in emitted power is ... [more ▼]

In January 2014 Jupiter's FUV main auroral oval decreased its emitted power by 70% and shifted equatorward by ∼1°. Intense, low-latitude features were also detected. The decrease in emitted power is attributed to a decrease in auroral current density rather than electron energy. This could be caused by a decrease in the source electron density, an order of magnitude increase in the source electron thermal energy, or a combination of these. Both can be explained either by expansion of the magnetosphere or by an increase in the inward transport of hot plasma through the middle magnetosphere and its interchange with cold flux tubes moving outward. In the latter case the hot plasma could have increased the electron temperature in the source region and produced the intense, low-latitude features, while the increased cold plasma transport rate produced the shift of the main oval. © 2016. The Authors. [less ▲]

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See detailUltraviolet auroral emissions on giant planets
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2015, November 25)

The aurorae on Jupiter and Saturn are the most powerful proper ultraviolet emissions in our solar system, after the Sun’s. They can only be observed outside the absorbing atmosphere of the Earth with ... [more ▼]

The aurorae on Jupiter and Saturn are the most powerful proper ultraviolet emissions in our solar system, after the Sun’s. They can only be observed outside the absorbing atmosphere of the Earth with space telescopes such as the Hubble Space Telescope or the Hisaki Telescope, or from Spacecraft orbiting these planets, like Cassini for Saturn and Juno for Jupiter. We will review the types of observation that can be obtained with these different instruments and how this information can be used to interpret the auroral emissions. [less ▲]

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See detailThe far-ultraviolet main auroral emission at Jupiter – Part 1: Dawn–dusk brightness asymmetries
Bonfond, Bertrand ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Annales Geophysicae (2015), 33

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted ... [more ▼]

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1.1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere. [less ▲]

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See detailThe far-ultraviolet main auroral emission at Jupiter – Part 2: Vertical emission profile
Bonfond, Bertrand ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Annales Geophysicae (2015), 33

The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as ... [more ▼]

The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as it accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range. The energy of the precipitating electrons is a crucial parameter to characterize the processes at play which give rise to these auroral emissions, and the altitude of the emissions directly depends on this energy. Here we make use of far-UV (FUV) images acquired with the Advanced Camera for Surveys on board the Hubble Space Telescope and spectra acquired with the Space Telescope Imaging Spectrograph to measure the vertical profile of the main emissions. The altitude of the brightness peak as seen above the limb is ~ 400 km, which is significantly higher than the 250 km measured in the post-dusk sector by Galileo in the visible domain. However, a detailed analysis of the effect of hydrocarbon absorption, including both simulations and FUV spectral observations, indicates that FUV apparent vertical profiles should be considered with caution, as these observations are not incompatible with an emission peak located at 250 km. The analysis also calls for spectral observations to be carried out with an optimized geometry in order to remove observational ambiguities. [less ▲]

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