References of "Gustin, Jacques"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailSmall-scale structures in Saturn's ultraviolet aurora
Grodent, Denis ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2011), 116

On 26 August 2008, the Ultraviolet Imaging Spectrograph Subsystem (UVIS) instrument onboard the Cassini spacecraft recorded a series of spatially resolved spectra of the northern auroral region of Saturn ... [more ▼]

On 26 August 2008, the Ultraviolet Imaging Spectrograph Subsystem (UVIS) instrument onboard the Cassini spacecraft recorded a series of spatially resolved spectra of the northern auroral region of Saturn. Near periapsis, the spacecraft was only five Saturn radii (R[SUB]S[/SUB]) from the surface and spatially resolved auroral structures as small as 500 km across (0.5° of latitude). We report the observation of two types of UV auroral substructures at the location of the main ring of emission, bunches of spots and narrow arcs. They are found in the noon and dusk sectors, respectively, at latitudes ranging from 73 to 80° corresponding to equatorial regions located beyond 16 R[SUB]S[/SUB]. Their brightness ranges from 1 to 30 kR and their characteristic size varies from 500 km to several thousands of km. These small-scale substructures are likely associated with patterns of upward field aligned currents resulting from nonuniform plasma flow in the equatorial plane. It is suggested that magnetopause Kelvin-Helmholtz waves trigger localized perturbations in the flow, like vortices, able to give rise to the observed UV auroral substructures. [less ▲]

Detailed reference viewed: 26 (8 ULg)
Full Text
Peer Reviewed
See detailBifurcations of the main auroral ring at Saturn: ionospheric signatures of consecutive reconnection events at the magnetopause
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2011), 116

This work reports for the first time on bifurcations of the main auroral ring at Saturn observed with the UVIS instrument onboard Cassini. The observation sequence starts with an intensification on the ... [more ▼]

This work reports for the first time on bifurcations of the main auroral ring at Saturn observed with the UVIS instrument onboard Cassini. The observation sequence starts with an intensification on the main oval, close to noon, which is possibly associated with dayside reconnection. Consecutive bifurcations appear with the onset of dayside reconnection, between 11 and 18 magnetic local time, while the area poleward of the main emission expands to lower latitudes. The bifurcations depart with time from the main ring of emission, which is related to the open-closed field line boundary. The augmentation of the area poleward of the main emission following its expansion is balanced by the area occupied by the bifurcations, suggesting that these auroral features represent the amount of newly open flux and could be related to consecutive reconnection events at the flank of the magnetopause. The observations show that the open flux along the sequence increases when bifurcations appear. Magnetopause reconnection can lead to significant augmentation of the open flux within a couple of days and each reconnection event opens ∼10% of the flux contained within the polar cap. Additionally, the observations imply an overall length of the reconnection line of ∼4 hours of local time and suggest that dayside reconnection at Saturn can occur at several positions on the magnetopause consecutively or simultaneously. [less ▲]

Detailed reference viewed: 21 (5 ULg)
Full Text
Peer Reviewed
See detailThe auroral footprint of Enceladus on Saturn
Pryor, Wayne R; Rymer, Abigail M; Mitchell, Donald G et al

in Nature (2011), 472

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between ... [more ▼]

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. [less ▲]

Detailed reference viewed: 18 (5 ULg)
See detailThe Production of Titan's Ultraviolet Nitrogen Airglow
Stevens, Michael H.; Gustin, Jacques ULg; Ajello, J. M. et al

in AAS/Division for Planetary Sciences Meeting Abstracts #42 (2010, October 01)

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Titan's dayside limb on 22 June, 2009, obtaining high quality extreme ultraviolet (EUV) and far ultraviolet (FUV) spectra from a distance of ... [more ▼]

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Titan's dayside limb on 22 June, 2009, obtaining high quality extreme ultraviolet (EUV) and far ultraviolet (FUV) spectra from a distance of only 60,000 km (23 Titan radii). The observations reveal the same EUV and FUV emissions arising from photoelectron excitation and photofragmentation of molecular nitrogen (N[SUB]2[/SUB]) on Earth but with the altitude of peak emission much higher on Titan near 1000 km altitude. In the EUV, emission bands from the photoelectron excited N[SUB]2[/SUB] Carroll-Yoshino c[SUB]4[/SUB]'-X system and N I and N II multiplets arising from photofragmentation of N[SUB]2[/SUB] dominate, with no detectable c[SUB]4[/SUB]'(0,0) emission near 958 Å, contrary to many interpretations of the lower resolution Voyager 1 Ultraviolet Spectrometer data. The FUV is dominated by emission bands from the N[SUB]2[/SUB] Lyman-Birge-Hopfield a-X system and additional N I multiplets. We also identify several N[SUB]2[/SUB] Vegard-Kaplan A-X bands between 1500-1900 Å, two of which are located near 1561 and 1657 Å where C I multiplets were previously identified from a separate UVIS disk observation. We compare these limb emissions to predictions from a terrestrial airglow model adapted to Titan that uses a solar spectrum appropriate for these June, 2009 observations. Volume production rates and limb radiances are calculated, including extinction by methane and allowance for multiple scattering within the readily excited c[SUB]4[/SUB]'(0,v') system, and compared to UVIS observations. We find that for these airglow data only emissions arising from processes involving N[SUB]2[/SUB] are present. [less ▲]

Detailed reference viewed: 6 (1 ULg)
See detailSaturn's radio, UV and IR aurorae observed simultaneously by Cassini
Lamy, L.; Prangé, R.; Gustin, Jacques ULg et al

in European Planetary Science Congress 2010 (2010, September 01)

Not Available

Detailed reference viewed: 4 (1 ULg)
See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010, June 07)

Detailed reference viewed: 7 (2 ULg)
See detailSaturn's aurora seen by HST and UVIS
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2010, June 07)

Detailed reference viewed: 10 (3 ULg)
Full Text
See detailAuroral footprints; everywhere
Grodent, Denis ULg; Bonfond, Bertrand ULg; Radioti, Aikaterini ULg et al

Conference (2010, May 06)

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and ... [more ▼]

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and the Jovian magnetosphere causes strong Alfvénic perturbations which propagate along the magnetic field lines. On their way towards Jupiter’s polar regions, these perturbations accelerate charged particles which then interact with Jupiter’s ionosphere where they loose a fraction of their energy in the form of auroral emissions. Each of the three moons leaves an auroral footprint around the poles of Jupiter which departs from the bulk of the auroral emission. Their location is mainly controlled by the topology of the field lines and thus analysis of the auroral footprints provides information on the magnetic field itself. In that regard, the satellites auroral footpaths were used to highlight the presence of a strong magnetic anomaly in the northern hemisphere of Jupiter. Detailed inspection of the footprints’ brightness and morphology as a function of time reveals fundamental information on the interaction mechanisms near the moons, on the particles acceleration mechanisms as well as on the Jovian ionosphere. For example, it was suggested that the Io footprint actually consists of several spots resulting from successive steps in the perturbation propagation process. Another example is the finding of three different timescales in the variations of Ganymede’s footprint; each of them is pointing to a different part of the electromagnetic interaction between the moon’s mini-magnetosphere and the Jovian plasma. Several recent images of Saturn’s auroral regions obtained with Cassini/UVIS at high latitude show an obvious auroral spot at the predicted location of Enceladus’ footprint. This major finding demonstrates that the electromagnetic interaction between a moon and its parent planet is not unique to Jupiter but appears to be a common feature in planetary systems. [less ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
See detailAuroral footprints of tail reconnection at Jupiter and Saturn
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010, May 03)

Tail reconnection at Jupiter’s magnetosphere, has recently been shown to leave its signature in the aurora. The Hubble Space Telescope observed transient polar dawn spots on the Jovian aurora, with a ... [more ▼]

Tail reconnection at Jupiter’s magnetosphere, has recently been shown to leave its signature in the aurora. The Hubble Space Telescope observed transient polar dawn spots on the Jovian aurora, with a characteristic recurrence period of 2-3 days. Because of their periodic occurrence cycle and observed location, it is suggested that the transient auroral features are related to the precipitated, heated plasma during reconnection processes taking place in the Jovian magnetotail. Particularly, it is proposed that the transient auroral spots are triggered by the planetward moving flow bursts released during the process. A comparison of their properties with those of the <br />auroral spots strengthen the conclusion that they are signatures of tail reconnection. <br />Cassini recently revealed magnetotail reconnection events at Saturn similar to those observed at Jupiter. Based on the UVIS dataset we present transient features at Saturn’s polar auroral region, which are possible signatures of tail reconnection. We study their size, power, duration and duty cycle and we suggest possible triggering mechanisms associated with magnetotail dynamics. We compare these auroral emissions with those at Jupiter and we discuss how energy is transferred to the ionosphere during tail reconnection. [less ▲]

Detailed reference viewed: 12 (4 ULg)
See detailUVIS FUV spectra of Saturn’s aurora
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2010)

Detailed reference viewed: 10 (0 ULg)
See detailUltraviolet aurorae and dayglow in the upper atmospheres of terrestrial planets
Gérard, Jean-Claude ULg; Hubert, Benoît ULg; Gustin, Jacques ULg et al

in 38th COSPAR Scientific Assembly (2010)

Since its discovery in 2005 with the SPICAM spectrograph on board Mars Express, the Mars aurora has been further investigated. It is caused by sporadic soft electron precipitation whose signature is ... [more ▼]

Since its discovery in 2005 with the SPICAM spectrograph on board Mars Express, the Mars aurora has been further investigated. It is caused by sporadic soft electron precipitation whose signature is clearly observed in the FUV nightglow spectrum. The characteristics of the auroral electrons have been documented with parallel observations. Dayglow UV spectra have been collected with SPICAM over several seasons. The dependence of the intensity and peak altitude of the CO Cameron bands and CO2 + doublet emissions on latitude, local time and solar activity level have been investigated and compared with the results of a FUV Mars dayglow model. Far and Extreme ultraviolet spectra have been collected with the UVIS instrument during the flyby of Venus by Cassini, in a period a high solar activity. Their analysis shows the presence of OI, OII, NI, CI, CO and CO2 + emissions, some of them not previously identified in the Venus spectrum. The intensities will be compared with those observed with the HUT spectrograph during a period of low solar activity. The excitation processes of the observed features will be discussed. Scans of the intensity variation of several EUV bright emissions such as OII 83.4 nm, OI 98.9 nm and NI 120.0 nm multiplets across the sunlit disc will be compared with the calculations of a Venus dayglow model, including multiple scattering of optically thick transitions. [less ▲]

Detailed reference viewed: 12 (4 ULg)
See detailSaturn's secondary auroral ring
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2010)

Not Available

Detailed reference viewed: 3 (1 ULg)
See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2010)

Not Available

Detailed reference viewed: 1 (0 ULg)
Full Text
Peer Reviewed
See detailUVIS observations of the FUV OI and CO 4P Venus dayglow during the Cassini flyby
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Gustin, Jacques ULg et al

in Icarus (2010), 207

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of ... [more ▼]

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of the OI emissions at 130.4 and OI 135.6 nm, and of the bands of the CO fourth positive system which are dominated by fluorescence scattering. We compare the brightness observed along the UVIS foot track of the two OI multiplets with that deduced from a model of the excitation of these emissions by photoelectron impact on O atoms and resonance scattering of the solar 130.4 nm emission. The large optical thickness 130.4 nm emission is accounted for using a radiative transfer model. The airglow intensities are calculated along the foot track and found to agree with the observed 130.4 nm brightness within ˜10%. The modeled OI 135.6 nm brightness is also well reproduced by the model. The oxygen density profile of the VTS3 model is found to be consistent with the observations. We find that self-absorption of the (0, v″) bands of the fourth positive emission of CO is important and we derive a CO vertical column of about 6.4 × 10[SUP]15[/SUP] cm[SUP]‑2[/SUP] in close agreement with the value provided by the VTS3 empirical atmospheric model. [less ▲]

Detailed reference viewed: 26 (5 ULg)
Full Text
Peer Reviewed
See detailCharacteristics of Saturn’s FUV airglow from limb-viewing spectra obtained with Cassini-UVIS
Gustin, Jacques ULg; Stewart, Ian; Gérard, Jean-Claude ULg et al

in Icarus: International Journal of Solar System Studies (2010), 210

This study reports the analysis of far ultraviolet (FUV) limb spectra of the airglow of Saturn in the 1150–1850 Å spectral window, obtained with the Ultraviolet Imaging Spectrograph (UVIS) onboard Cassini ... [more ▼]

This study reports the analysis of far ultraviolet (FUV) limb spectra of the airglow of Saturn in the 1150–1850 Å spectral window, obtained with the Ultraviolet Imaging Spectrograph (UVIS) onboard Cassini, spanning altitudes from 1200 to 4000 km. The FUV limb emission consists of three main contributions: (1) H Ly-a peaking at 1100 km with a brightness of 0.8 kilo-Rayleighs (kR), (2) reflected sunlight longward of 1550 Å which maximizes at 950 km with 16.5 kR and (3) H2 bands in the 1150–1650 Å bandwidth, peaking at 1050 km reaching a maximum of 3.9 kR. A vertical profile of the local H2 volume emission rate has been derived using the hydrocarbon density profiles from a model of the Saturn equatorial atmosphere. It is well matched by a Chapman function, characterized by a maximum value of 3.5 photons cm-3 s-1 in the 800–1650 Å UV bandwidth, peaking at 1020 km. Comparisons between the observed spectra and a first-order synthetic airglow H2 model in the 1150–1650 Å bandwidth show that the spectral shape of the H2 bands is accounted for by solar fluorescence and photoelectron excitation. The best fits are obtained with a combination of H2 fluorescence lines and 20 eV electron impact spectra, the latter contributing 68% of the total H2 airglow emission. [less ▲]

Detailed reference viewed: 23 (4 ULg)
See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. W. et al

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

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007-2009 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. Selected movies will be presented with geometric overlays and in polar projections. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. Other movies show similar cusp-related structures that resemble the letter "Q" where a dynamical feature at right angles to the oval moves away from the cusp region. The 2008 day 201 movie also shows one bright "polar flare" inside the oval with a spectrally distinct signature indicating the presence of higher energy electrons. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. Several frames show emissions associated with the footprint of the Enceladus field line. We will discuss these features, their locations, and possible interpretations. [less ▲]

Detailed reference viewed: 6 (1 ULg)
Full Text
Peer Reviewed
See detailCorrection to ``Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations''
Radioti, Aikaterini ULg; Tomás, Ana Tomas; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

<A href="/journals/gl/gl0909/2009GL038676/">Abstract Available</A> from <A href="http://www.agu.org">http://www.agu.org</A>

Detailed reference viewed: 28 (6 ULg)
Full Text
Peer Reviewed
See detailEquatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations
Radioti, Aikaterini ULg; Tomás, Ana Teresa; Grodent, Denis ULg et al

in Geophysical Research Letters (2009), 36

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes ... [more ▼]

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes in the electron pitch angle distribution between the inner and middle magnetosphere (PAD boundary), indicative of electron diffusion. This region, magnetically maps to the equatorward diffuse emissions on both hemispheres. Whistler mode waves, observed simultaneously, can scatter electrons into the loss cone and lead to electron precipitation in the ionosphere. Based on simultaneous HST FUV and Galileo wave and electron data we test the conditions for electron scattering by whistler mode waves and derive the energy flux precipitated in the ionosphere. The comparison of the derived precipitation energy flux with the observed auroral brightness indicates that the energy contained in the PAD boundary can account for the auroral emissions. [less ▲]

Detailed reference viewed: 26 (5 ULg)