References of "Gérard, Jean-Claude"
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See detailTerrestrial OH nightglow measurements during the Rosetta flyby
Migliorini, A.; Gérard, Jean-Claude ULg; Soret, Lauriane ULg et al

in Geophysical Research Letters (2015), 42

We present a study of the terrestrial hydroxyl nightglow emissions observed with the Visible and Infrared Thermal Imaging Spectrometer on board the Rosetta mission. During these observations, the OH Δv  ... [more ▼]

We present a study of the terrestrial hydroxyl nightglow emissions observed with the Visible and Infrared Thermal Imaging Spectrometer on board the Rosetta mission. During these observations, the OH Δv = 1 and 2 sequences were measured simultaneously. This allowed investigating the relative population of the v = 1 to 9 vibrational levels by using both sequences. In particular, the relative population of the vibrational level v = 1 is determined for the first time from observations. The vibrational population decreases with increasing vibrational quantum number. A good agreement is found with a recent model calculation assuming multiquantum relaxation for OH(v) quenching by O2 and single-quantum relaxation for OH(v) by N2. [less ▲]

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See detailThe Mars discrete aurora: Mars Express observations and modeling.
Gérard, Jean-Claude ULg

Scientific conference (2015, June)

Summary of earlier work Detection of additional ultraviolet auroral events (nadir and limb) Concurrent SPICAM-­‐ASPERA 3 observations Model results Perspectives

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See detailVenus nightglow intensity and solar activity: any correlation?
Soret, Lauriane ULg; Gérard, Jean-Claude ULg

Conference (2015, May 26)

We examine if any correlation is observed between the brightness of the O2 nightside airglow and the EUV solar irradiance using the full database of VIRTIS IR images. We conclude that, as was the case for ... [more ▼]

We examine if any correlation is observed between the brightness of the O2 nightside airglow and the EUV solar irradiance using the full database of VIRTIS IR images. We conclude that, as was the case for the NO airglow observed during the Pioneer Venus mission, no response to solar activity is observed. [less ▲]

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See detailJupiter’s aurora, ultraviolet, visible and infrared views: what can we learn?
Gérard, Jean-Claude ULg

Scientific conference (2015, May 15)

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See detailJupiter's equatorward auroral features
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2015, May 13)

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See detailThe crucial role of HST during the NASA Juno mission: a “Juno initiative”
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg et al

E-print/Working paper (2015)

In 2016, the NASA Juno spacecraft will initiate its one-year mission around Jupiter and become the first probe to explore the polar regions of Jupiter. The HST UV instruments (STIS and ACS) can greatly ... [more ▼]

In 2016, the NASA Juno spacecraft will initiate its one-year mission around Jupiter and become the first probe to explore the polar regions of Jupiter. The HST UV instruments (STIS and ACS) can greatly contribute to the success of the Juno mission by providing key complementary views of Jupiter’s UV aurora from Earth orbit. Juno carries an ultraviolet Spectrograph (UVS) and an infrared spectral mapper (JIRAM) that will obtain high-resolution spectral images providing the auroral counterpart to Juno’s in situ particles and fields measurements with the plasma JADE and JEDI particle detectors. The Juno mission will be the first opportunity to measure simultaneously the energetic particles at high latitude and the auroral emissions they produce. Following programmatic and technical limitations, the amount of UVS data transmitted to Earth will be severely restricted. Therefore, it is of extreme importance that HST captures as much additional information as possible on Jupiter’s UV aurora during the one-year life of the Juno mission. This white paper is a plea for a “Juno initiative” that will ensure that a sufficient number of orbits is allocated to this unique solar system mission. [less ▲]

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See detailTen years of Martian nitric oxide nightglow observations
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Gagné, Marie-Eve et al

in Geophysical Research Letters (2015)

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See detailMonte Carlo Simulation of Metastable Oxygen Photochemistry in Cometary Atmospheres
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Astrophysical Journal (2015), 798

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical ... [more ▼]

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O([SUP]1[/SUP]D) and O([SUP]1[/SUP]S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but in disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O([SUP]1[/SUP]D) level, which has a longer lifetime. [less ▲]

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See detailThe EChO science case
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2015), 1502

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general ... [more ▼]

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets. [less ▲]

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See detailAuroral spirals at Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2015)

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See detailConcurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Libert, Ludivine ULg et al

in Journal of Geophysical Research. Space Physics (2015)

The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures ... [more ▼]

The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures of CO Cameron and CO<inf>2</inf>+ doublet ultraviolet auroral emissions. This study has almost doubled the number of auroral detections based on SPICAM spectra. Auroral emissions are located in the vicinity of the statistical boundary between open and closed field lines. From a total of 113 nightside orbits with SPICAM pointing to the nadir in the region of residual magnetic field, only nine nightside orbits show confirmed auroral signatures, some with multiple detections along the orbital track, leading to a total of 16 detections. The mean energy of the electron energy spectra measured during concurrent Analyzer of Space Plasma and Energetic Atoms/Electron Spectrometer observations ranges from 150 to 280eV. The ultraviolet aurora may be displaced poleward or equatorward of the region of enhanced downward electron energy flux by several tens of seconds and shows no proportionality with the electron flux at the spacecraft altitude. The absence of further UV auroral detection in regions located along crustal magnetic field structures where occasional aurora has been observed indicates that the Mars aurora is a time-dependent feature. These results are consistent with the scenario of acceleration of electrons by transient parallel electric field along semiopen magnetic field lines. © 2015. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailAuroral spirals at Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2015)

We report Cassini/UVIS observations of auroral vortices at Saturn propagating from midnight to noon via dawn. The emission in the dawn auroral sector is observed to consist of several detached features ... [more ▼]

We report Cassini/UVIS observations of auroral vortices at Saturn propagating from midnight to noon via dawn. The emission in the dawn auroral sector is observed to consist of several detached features that swirl with time. They have a diameter of 6000 km in the ionosphere, which would correspond to plasma vortices in the magnetosphere of 12 to 15 Rs. ENA enhancements are observed simultaneously. However, they do not show any clear vortices. We estimate the velocity of the UV auroral feature to decrease from 85% of rigid corotation (28o/h) in the most equatorward part of the aurora to 68% of rigid corotation (22o/h) in the poleward part and we demonstrate that such velocity gradient could result in swirling auroral features. Particle velocities derived from magnetospheric data in previous studies, confirm large variations of the corotation fraction as a function of radial distance. We suggest that the auroral vortices could be the ionospheric footprints of hot dynamic populations containing strong velocity gradients. Alternatively, we consider another scenario that could generate auroral vortices based on field line deformation from the magnetosphere to the ionosphere, like it is proposed for the Earth. In that case the auroral spiral is the result of some processes that occurred in the transition region between the centers of vortices where strong shear flows existed. Finally, a third possibility is considered, according to which the auroral vortices reported here are the direct optical signatures of the plasma vortical flows in the magnetopause related to Kelvin-Helmholtz instabilities. However, this might be less possible due to the very different spatial scales of the auroral features (12-15 Rs) and the observed plasma vortices in the magnetopause (1 Rs). [less ▲]

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See detailA multi-scale magnetotail reconnection event at Saturn and associated flows: Cassini/UVIS auroral observations
Radioti, Aikaterini ULg; Grodent, Denis ULg; Jia, X. et al

Conference (2015)

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the ... [more ▼]

We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the midnight-dawn quadrant in an extended local time sector (~02 to 05 LT), which rotates with an average velocity of ~ 45% of rigid corotation. The auroral dawn enhancement reported here, given its observed location and brightness, is most probably due to hot tenuous plasma carried inward in fast moving flux tubes returning from a tail reconnection site to the dayside. These flux tubes could generate intense field-aligned currents that would cause aurora to brighten. However, the origin of tail reconnection (solar wind or internally driven) is uncertain. Based mainly on the flux variations, which do not demonstrate flux closure, we suggest that the most plausible scenario is that of internally driven tail reconnection which operates on closed field lines. The observations also reveal multiple intensifications within the enhanced region suggesting an x-line in the tail, which extends from 02 to 05 LT. The localised enhancements evolve in arc and spot-like small scale features, which resemble vortices mainly in the beginning of the sequence. These auroral features could be related to plasma flows enhanced from reconnection which diverge into multiple narrow channels then spread azimuthally and radially. We suggest that the evolution of tail reconnection at Saturn may be pictured by an ensemble of numerous narrow current wedges or that inward transport initiated in the reconnection region could be explained by multiple localised flow burst events. The formation of vortical-like structures could then be related to field-aligned currents, building up in vortical flows in the tail. An alternative, but less plausible, scenario could be that the small scale auroral structures are related to viscous interactions involving small-scale reconnection. [less ▲]

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See detailSolar Wind Interaction with the Magnetosphere of Jupiter : Impact on the Magnetopause and the Aurorae
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, November 20)

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in ... [more ▼]

The outcome of the interaction between the solar wind and the Jovian magnetic field bears many differences compared to the Earth's case. At Earth, the solar wind is the major particle and energy source in the magnetosphere. At Jupiter, the tremendous volcanism on the moon Io is the main plasma source and Jupiter's rapid rotation (relative to its size) is the main energy source for the particles populating its magnetosphere. Combined with a weaker solar wind pressure and a larger Alfvén Mach number as the distance from the Sun increases, all these parameters modify the relative importance of large scale Dungey reconnection and viscous interaction at the magnetopause. In order to study these differences, here we present a statistical analysis of magnetopause waves and flux tube event on the Jovian magnetopause, based on in-situ measurement from the spacecraft that flew-by or orbited around Jupiter. Moreover, variations of the solar wind have significant impact on the Jovian magnetospheric current systems and such changes reflect on the aurora. In this presentation, we will also review the recent findings concerning the aurora at Jupiter and their relationship with the solar wind. [less ▲]

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See detailSpace Weather at Saturn - Auroral observations
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, November)

Unlike to Earth, Saturn is a fast rotator and its magnetosphere is dominated by fast planetary rotation and internally driven processes. However, the interaction of the solar wind with Saturn’s ... [more ▼]

Unlike to Earth, Saturn is a fast rotator and its magnetosphere is dominated by fast planetary rotation and internally driven processes. However, the interaction of the solar wind with Saturn’s magnetosphere is not negligible and it is manifested among others in the auroral region. The interplanetary magnetic field reconnects with the dayside magnetopause at Saturn and results in enhancements in the auroral emission accompanied by entry of significant amount of open flux in the magnetosphere. The solar wind affects also the nightside magnetosphere. Dramatic enhancements of the nightside-dawn auroral emissions have been attributed to solar wind-induced auroral storms. Additionally, recent auroral observations revealed the presence of a transpolar arc at Saturn, one of the most spectacular auroral features at Earth, which could be possibly related to solar wind driven tail reconnection. Finally, there is evidence of viscous interaction of the solar wind with Saturn’s magnetosphere, which involves magnetic reconnection on a small scale. [less ▲]

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See detailMapping the electron energy in Jupiter’s aurora: Hubble spectral observations
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2014), 119

Far ultraviolet spectral observations have been made with the Hubble Space Telescope in the time-tag mode using the Space Telescope Imaging Spectrograph (STIS) long slit. The telescope was slewed in such ... [more ▼]

Far ultraviolet spectral observations have been made with the Hubble Space Telescope in the time-tag mode using the Space Telescope Imaging Spectrograph (STIS) long slit. The telescope was slewed in such a way that the slit projection scanned from above the polar limb down to midlatitudes, allowing us to build up the first spectral maps of the FUV Jovian aurora. The shorter wavelengths are partly absorbed by the methane layer overlying part of the auroral emission layer. The long-wavelength intensity directly reflects the precipitated energy flux carried by the auroral electrons. Maps of the intensity ratio of the two spectral regions have been obtained by combining spectral emissions in two wavelength ranges. They show that the amount of absorption by methane varies significantly between the different components of the aurora and inside the main emission region. Some of the polar emissions are associated with the hardest precipitation, although the auroral regions of strong electron precipitation do not necessarily coincide with the highest electron energies. Outputs from an electron transport model are used to create maps of the distribution of the characteristic electron energies. Using model atmospheres adapted to auroral conditions, we conclude that electron energies range between a few tens to several hundred keV. Comparisons of derived energies are in general agreement with those calculated from magnetosphere-ionosphere coupling models, with values locally exceeding the standard model predictions. These results will provide useful input for three-dimensional modeling of the distribution of particle heat sources into the high-latitude Jovian upper atmosphere. [less ▲]

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See detailVenus III book: aeronomy of the upper atmosphere
Gérard, Jean-Claude ULg; Bougher, Stephen; Drossart, Pierre et al

Conference (2014, September 12)

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