References of "Grodent, Denis"
     in
Bookmark and Share    
See detailThe variability of auroral emissions on Jupiter and Saturn
Clarke; Nichols; Gérard et al

Conference (2009, July 27)

Detailed reference viewed: 3 (0 ULiège)
See detailNews from outer worlds
Grodent, Denis ULiege

Conference (2009, July 27)

Detailed reference viewed: 5 (0 ULiège)
Full Text
Peer Reviewed
See detailThe auroral footprint of Ganymede
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Radioti, Aikaterini ULiege et al

in Journal of Geophysical Research. Space Physics (2009), 114(A07212),

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede ... [more ▼]

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede footprint. Based on an analysis of ultraviolet images obtained with the Hubble Space Telescope we demonstrate that the auroral footprint surface matches a circular region in Ganymede's orbital plane having a diameter of 8 to 20 RG. Temporal analysis of the auroral power of Ganymede's footprint reveals variations of different timescales: 1) a 5 hours timescale associated with the periodic flapping of Jupiter's plasma sheet over Ganymede, 2) a 10 to 40 minutes timescale possibly associated with energetic magnetospheric events, such as plasma injections, and 3) a 100 s timescale corresponding to quasi-periodic fluctuations which might relate to bursty reconnections on Ganymede's magnetopause and/or to the recurrent presence of acceleration structures above Jupiter's atmosphere. These three temporal components produce an auroral power emitted at Ganymede's footprint of the order of ~0.2 GW to ~1.5 GW. [less ▲]

Detailed reference viewed: 83 (50 ULiège)
Full Text
Peer Reviewed
See detailThe Io UV footprint: Location, inter-spot distances and tail vertical extent
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

in Journal of Geophysical Research. Space Physics (2009), 114

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by ... [more ▼]

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by an auroral curtain, called the tail, extending more than 90° longitude in the direction of planetary rotation. We use recent Hubble Space Telescope images of Jupiter to analyze the location of the footprint spots and tail as a function of Io's location in the jovian magnetic field. We present here a new IFP reference contour---the locus of all possible IFP positions---with an unprecedented accuracy, especially in previously poorly covered sectors. We also demonstrate that the lead angle - the longitudinal shift between Io and the actual IFP position - is not a reliable quantity for validation of the interaction models. Instead, the evolution of the inter-spot distances appears to be a better diagnosis of the Io-Jupiter interaction. Moreover, we present observations of the tail vertical profiles as seen above the limb. The emission peak altitude is ~900 km and remains relatively constant with the distance from the main spot. The altitudinal extent of the vertical emission profiles is not compatible with precipitation of a mono-energetic electron population. The best fit is obtained for a kappa distribution with a characteristic energy of ~70 eV and a spectral index of 2.3. The broadness of the inferred electron energy spectrum gives insight into the physics of the electron acceleration mechanism at play above the IFP tail. [less ▲]

Detailed reference viewed: 71 (18 ULiège)
Full Text
Peer Reviewed
See detailVariation of different components of Jupiter's auroral emission
Nichols, J. D.; Clarke, J. T.; Gérard, Jean-Claude ULiege et al

in Journal of Geophysical Research. Space Physics (2009), 114

The Hubble Space Telescope (HST) data set obtained over two campaigns in 2007 is used to determine the long-term variability of the different components of Jupiter's auroras. Three regions on the planet's ... [more ▼]

The Hubble Space Telescope (HST) data set obtained over two campaigns in 2007 is used to determine the long-term variability of the different components of Jupiter's auroras. Three regions on the planet's disc are defined: the main oval, the low-latitude auroras, and the high-latitude auroras. The UV auroral power emitted from these regions is extracted and compared to estimated solar wind conditions projected to Jupiter's orbit from Earth. In the first campaign the emitted power originated mainly from the main oval and the high-latitude regions, and in the second campaign the high-latitude and main oval auroras were dimmer and less variable, while the low-latitude region exhibited bright, patchy emission. We show that, apart from during specific enhancement events, the power emitted from the poleward auroras is generally uncorrelated with that of the main oval. The exception events are dawn storms and compression region enhancements. It is shown that the former events, typically associated with intense dawnside main oval auroras, also result in the brightening of the high-latitude auroras. The latter events associated with compression regions exhibit a particular auroral morphology; that is, where it is narrow and well defined, the main oval is bright and located ~1° poleward of its previous location, and elsewhere it is faint. Instead there is bright emission in the poleward region in the postnoon sector where distinct, bright, sometimes multiple arcs form. [less ▲]

Detailed reference viewed: 15 (5 ULiège)
Full Text
Peer Reviewed
See detailCorrection to ``Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations''
Radioti, Aikaterini ULiege; Tomás, Ana Tomas; Grodent, Denis ULiege 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: 35 (6 ULiège)
Full Text
Peer Reviewed
See detailResponse of Jupiter's and Saturn's auroral activity to the solar wind
Clarke, J. T.; Nichols, J.; Gérard, Jean-Claude ULiege et al

in Journal of Geophysical Research. Space Physics (2009), 114

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter and ... [more ▼]

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter and Saturn are driven primarily by internal processes, with the main energy source being the planets' rapid rotation. Prior observations have suggested there might be some influence of the solar wind on Jupiter's aurorae and indicated that auroral storms on Saturn can occur at times of solar wind pressure increases. To investigate in detail the dependence of auroral processes on solar wind conditions, a large campaign of observations of these planets has been undertaken using the Hubble Space Telescope, in association with measurements from planetary spacecraft and solar wind conditions both propagated from 1 AU and measured near each planet. The data indicate a brightening of both the auroral emissions and Saturn kilometric radiation at Saturn close in time to the arrival of solar wind shocks and pressure increases, consistent with a direct physical relationship between Saturnian auroral processes and solar wind conditions. At Jupiter the correlation is less strong, with increases in total auroral power seen near the arrival of solar wind forward shocks but little increase observed near reverse shocks. In addition, auroral dawn storms have been observed when there was little change in solar wind conditions. The data are consistent with some solar wind influence on some Jovian auroral processes, while the auroral activity also varies independently of the solar wind. This extensive data set will serve to constrain theoretical models for the interaction of the solar wind with the magnetospheres of Jupiter and Saturn. [less ▲]

Detailed reference viewed: 74 (14 ULiège)
Full Text
See detailThe location and topology of electron beams in Io‘s wake
Jacobsen, Sven; Saur, Joachim; Neubauer, Friz et al

Conference (2009, April 22)

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned ... [more ▼]

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned electron beams for the individual flyby scenarios. Io continuously generates MHD waves by disturbing the Jovian magnetoplasma. Currents carried by Alfvén waves propagate predominantly along the magnetic field lines. The waves accelerate electrons as the number of charge carriers decreases on their way to Jupiter. These energetic electrons precipitate into the Jovian ionosphere, visible as prominent Io footprint emission in the Jovian aurora. On the other hand electrons have to be accelerated upward to form the beams measured by Galileo. Unlike the beam formation, the position and spatial structure of these beams has been poorly discussed. We adopt our 3D MHD model initial conditions to the individual flyby scenario and determine the spatial morphol- ogy of beams in Io’s orbital plane. We compare our findings to Galileo observations and find very good agreement. Moreover, we use our model to further investigate in detail a recent concept which involves cross-hemisphere electron beams to explain certain auroral features of the Io footprint emission such as a leading spot and secondary spots [Bonfond et al., 2008]. Our results indicate that besides geometrical properties, such as Io’s position in the torus, the incoming plasma density controls the travel path and topology of an electron beam. [less ▲]

Detailed reference viewed: 9 (1 ULiège)
Full Text
Peer Reviewed
See detailEquatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations
Radioti, Aikaterini ULiege; Tomás, Ana Teresa; Grodent, Denis ULiege 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: 40 (10 ULiège)
Full Text
Peer Reviewed
See detailObservations of Jovian polar auroral filaments
Nichols, J. D.; Clarke, J. T.; Gérard, Jean-Claude ULiege et al

in Geophysical Research Letters (2009), 36

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ... [more ▼]

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ~100 kR spanning the highly variable region poleward of the main oval. This observation, made using Hubble Space Telescope images, is significant since no coherent structures have previously been observed in Jupiter's very high latitude auroral region, and it may help shed light on the dynamics of Jupiter's under-explored magnetotail. PAFs have been observed in 4 sets of observations over 6 days in 2007, and their occurrence appears to be independent of impinging solar wind conditions. The feature comprises two components: the section toward noon remains fixed in orientation toward the sun, while the anti-sunward section rotates. We estimate overall rotation rates of ~0--45% of corotation, values which may indicate the rotation rate of Jupiter's polar ionosphere and tail lobes. [less ▲]

Detailed reference viewed: 27 (8 ULiège)
Full Text
Peer Reviewed
See detailTransient auroral features at Saturn: Signatures of energetic particle injections in the magnetosphere
Radioti, Aikaterini ULiege; Grodent, Denis ULiege; Gérard, Jean-Claude ULiege et al

in Journal of Geophysical Research. Space Physics (2009), 114

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from ... [more ▼]

We report for the first time transient isolated auroral spots at Saturn's southern polar region, based on Hubble Space Telescope (HST) FUV images. The spots last several minutes and appear distinct from the rest of the auroral emissions. We study two sets of HST and Cassini observations during which Cassini instrumentation detected signatures of energetic particle injections close to the region where, on the same day, HST observed transient auroral spots. On the basis of the simultaneous remote and in situ observations, we discuss the possibility that the transient features are associated with the dynamical processes taking place in the Kronian magnetosphere. Given the limitations in the available observations, we suggest the following possible explanations for the transient aurora. The injection region could directly be coupled to Saturn's ionosphere by pitch angle diffusion and electron scattering by whistler waves, or by the electric current flowing along the boundary of the injected cloud. The energy contained in the injection region indicates that electron scattering could account for the transient aurora process. [less ▲]

Detailed reference viewed: 43 (20 ULiège)
Full Text
Peer Reviewed
See detailCharacteristics of Saturn's polar atmosphere and auroral electrons derived from HST/STIS, FUSE and Cassini/UVIS spectra
Gustin, Jacques ULiege; Gérard, Jean-Claude ULiege; Pryor, Wayne et al

in Icarus: International Journal of Solar System Studies (2009), 200

Ultraviolet (UV) spectra of Saturn's aurora obtained with the Hubble Space Telescope Imaging Spectrograph (STIS), the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Far Ultraviolet Spectroscopic ... [more ▼]

Ultraviolet (UV) spectra of Saturn's aurora obtained with the Hubble Space Telescope Imaging Spectrograph (STIS), the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Far Ultraviolet Spectroscopic Explorer (FUSE) have been analyzed. Comparisons between the observed spectra and synthetic models of electron-excited H[SUB]2[/SUB] have been used to determine various auroral characteristics. Far ultraviolet (FUV: 1200 1700 Å) STIS and UVIS spectra exhibit, below 1400 Å, weak absorption due to methane, with a vertical column ranging between 1.4×10[SUP][/SUP] and 1.2×10[SUP][/SUP]cm[SUP][/SUP]. Using the low-latitude Moses et al. [Moses, J.I., Bézard, B., Lellouch, E., Feuchtgruber, H., Gladstone, G.R., Allen, M., 2000. Icarus, 143, 244 298] atmospheric model of Saturn and an electron energy H[SUB]2[/SUB] column relationship, these methane columns are converted into the mean energy of the primary precipitating electrons, estimated to lie in the range 10 18 keV. This result is confirmed by the study of self-absorption with UVIS and FUSE extreme ultraviolet (EUV: 900 1200 Å) spectra. Below 1200 Å, it is seen that transitions connecting to the v[SUP][/SUP]<2 vibrational levels of the H[SUB]2[/SUB] electronic ground state are partially self-absorbed by H[SUB]2[/SUB] molecules overlying the auroral emission. Because of its low spectral resolution (Ë 5.5 Å), the UVIS EUV spectrum we analyzed does not allow us to unequivocally determine reasonable ranges of temperatures and H[SUB]2[/SUB] columns. On the other hand, the high spectral resolution (Ë 0.2 Å) of the FUSE LiF1a and LiF2a EUV spectra we examined resolve the H[SUB]2[/SUB] rotational lines and makes it possible to determine the H[SUB]2[/SUB] temperature. The modeled spectrum best fitting the FUSE LiF1a observation reveals a temperature of 500 K and self-absorption by a H[SUB]2[/SUB] vertical column of 3×10[SUP][/SUP]cm[SUP][/SUP]. When converted to energy of precipitating electrons, this H[SUB]2[/SUB] column corresponds to primary electrons of Ë 10 keV. The model that best fits the LiF2a spectrum is characterized by a temperature of 400 K and is not self-absorbed, making this segment ideal to determine the H[SUB]2[/SUB] temperature at the altitude of the auroral emission. The latter value is in agreement with temperatures obtained from H3+ infrared polar spectra. Self-absorption is detectable in the LiF2a segment for H[SUB]2[/SUB] columns exceeding 6×10[SUP][/SUP]cm[SUP][/SUP], which sets the maximum mean energy determined from the FUSE observations to Ë 15 keV. The total electron energy range of 10 18 keV deduced from FUV and EUV observations places the auroral emission peak between the 0.1 and 0.3 mubar pressure levels. These values should be seen as an upper limit, since most of the Voyager UVS spectra of Saturn's aurora examined by Sandel et al. [Sandel, B.R., Shemansky, D.E., Broadfoot, A.L., Holberg, J.B., Smith, G.R., 1982. Science 215, 548] do not exhibit methane absorption. The auroral H[SUB]2[/SUB] emission is thus likely located above but close to the methane homopause. The H[SUB]2[/SUB] auroral brightness in the 800 1700 Å bandwidth varies from 2.9 kR to 139 kR, comparable to values derived from FUV Faint Object Camera (FOC) and STIS images. [less ▲]

Detailed reference viewed: 64 (22 ULiège)
Full Text
Peer Reviewed
See detailAltitude of Saturn's aurora and its implications for the characteristic energy of precipitated electrons
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Gustin, Jacques ULiege et al

in Geophysical Research Letters (2009), 36

Images of Saturn's aurora at the limb have been collected with the Advanced Camera for Surveys on board the Hubble Space Telescope. They show that the peak of Saturn's nightside emission is generally ... [more ▼]

Images of Saturn's aurora at the limb have been collected with the Advanced Camera for Surveys on board the Hubble Space Telescope. They show that the peak of Saturn's nightside emission is generally located 900-1300 km above the 1-bar level. On the other hand, methane and H[SUB]2[/SUB] columns overlying the aurora have been determined from the analysis of FUV and EUV spectra, respectively. Using a low-latitude model, these columns place the emission layer at or above 610 km. One possibility to solve this apparent discrepancy between imaging and spectral observations is to assume that the thermospheric temperature in the auroral region sharply increases at a higher pressure level than in the low-latitude regions. Using an electron transport code, we estimate the characteristic energy of the precipitated electrons derived from these observations to be in the range 1-5 keV using a low latitude model and 5-30 keV in case of the modified model. [less ▲]

Detailed reference viewed: 25 (2 ULiège)
See detailSaturn Auroral Images and Movies from Cassini UVIS
Pryor, Wayne; Esposito, L.W.; Stewart, A.I.F. et al

Conference (2009)

Cassini’s Ultraviolet Imaging Spectrograph (UVIS) has completed five <br />years of study of Saturn’s atmosphere and auroras. Two long slit spectral channels are <br />used to obtain EUV data from 56.3 ... [more ▼]

Cassini’s Ultraviolet Imaging Spectrograph (UVIS) has completed five <br />years of study of Saturn’s atmosphere and auroras. Two long slit spectral channels are <br />used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 <br />spatial pixels along each slit are combined with slit motion to construct spectral images of <br />Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. <br />In 2008-2009 UVIS obtained data with the spacecraft well out of Saturn’s ring plane, <br />permitting UVIS to obtain a number of short movies of the rotating auroral structures. <br />In some movies a cusp-like feature is present near noon inside the oval. One movie from <br />2008 day 201 shows parallel linear features on the day side almost at right angles to <br />the main auroral oval that appear, then lengthen, separate in the middle, and then fade <br />away. The same movie also shows one bright "polar flare" inside the oval. A few of <br />the most recent images were obtained at sufficiently close range that 2 spacecraft slews <br />were needed to completely cover the oval. These images provide almost 100 pixels of <br />information across the oval and clearly show multiple arcs of emission on the main oval <br />and scattered emissions inside the oval. We will discuss these features, their locations, and <br />possible interpretations. We also report on a search for an Enceladus auroral footprint <br />on Saturn. [less ▲]

Detailed reference viewed: 16 (2 ULiège)
Peer Reviewed
See detailEvolution of Saturn's Bright Polar Aurora
Stallard, T.; Grodent, Denis ULiege; Badman, S. V. et al

Conference (2009)

Observations of Saturn's infrared aurorae have shown that in addition to the main auroral oval, which is believed to be associated with the solar wind, there are significant polar emissions. Ground-based ... [more ▼]

Observations of Saturn's infrared aurorae have shown that in addition to the main auroral oval, which is believed to be associated with the solar wind, there are significant polar emissions. Ground-based infrared observations of Saturn have been able to show that there is a general level of raised emission across the entire polar region, in a similar way to that seen at Jupiter. However, with direct observations of the aurora made from orbit around Saturn by the Cassini-VIMS instrument, this aurora was shown to be more than a relative generalised brightening in the infrared. Instead, a unique auroral feature was observed to occur, appearing as a large region of bright polar emission, positioned poleward of 82 degrees latitude. This Bright Polar Aurora emission is significantly different from the recently observed subrotating Q-branch auroral emission seen in both the ultraviolet and infrared, as it is separated from the main auroral oval by a region of low emission. This effectively produces a cap of bright aurora inside the main auroral oval, surrounded by a dark ring that separates the two aurorae. Here, we take a more detailed look at this cap of emission and examine the way the auroral feature develops with time. Bright Polar Aurora emission has been observed in two separate VIMS images. A more detailed analysis of the polar emission shows that each of these images in fact differs in structure; the first has auroral emission across the whole polar cap >82 degrees, but within the second the emission is concentrated on the dusk side. While the dramatic in-filling of the polar cap is not seen within any UV observations, the Hubble Space Telescope has observed transitory duskward auroral features within the polar cap, in a similar location to the duskward feature seen in the infrared. Using ground-based infrared observations, which allow a Bright Polar Aurora event to be broken into shorter timescale steps, it is possible analyse the progression of the infrared auroral emission with time, connecting the morphology seen within the two VIMS images with those in the ultraviolet. [less ▲]

Detailed reference viewed: 13 (0 ULiège)
Full Text
Peer Reviewed
See detailSaturn's equinoctial auroras
Nichols, J. D.; Badman, S. V.; Bunce, E. J. et al

in Geophysical Research Letters (2009), 36

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 ... [more ▼]

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 degrees smaller than the southern, indicating that Saturn's polar ionospheric magnetic field, measured for the first time in the ionosphere, is similar to 17% larger in the north than the south. Despite this, the total emitted UV power is on average similar to 17% larger in the north than the south, suggesting that field-aligned currents (FACs) are responsible for the emission. Finally, we show that individual auroral features can exhibit distinct hemispheric asymmetries. These observations will provide important context for Cassini observations as Saturn moves from southern to northern summer. Citation: Nichols, J. D., et al. (2009), Saturn's equinoctial auroras, Geophys. Res. Lett., 36, L24102, doi: 10.1029/2009GL041491. [less ▲]

Detailed reference viewed: 39 (4 ULiège)
Full Text
See detailAuroral Processes
Kurth, W. S.; Bunce, E. J.; Clarke, J. T. et al

in Dougherty, M. K.; Esposito, L. W.; Krimigis, S. M. (Eds.) Saturn from Cassini-Huygens (2009)

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number ... [more ▼]

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number of campaigns were coordinated with the Hubble Space Telescope such that Cassini could provide either ground truth on the impinging solar wind or in situ measurements of magnetospheric conditions leading to qualitative and sometimes quantitative relationships between the solar wind influence on the intensity, the morphology and evolution of the auroras, and magnetospheric dynamics. The Hubble UV images are enhanced by Cassini’s own remote sensing of the auroras. Cassini’s in situ studies of the structure and dynamics of the magnetosphere discussed in other chapters of this book provide the context for understanding the primary drivers of Saturn’s auroras and the role of magnetospheric dynamics in their variations. Finally, Cassini’s three dimensional prime mission survey of the magnetosphere culminates in high inclination orbits placing it at relatively small radial distances while on auroral field lines, providing the first such in situ observations of auroral particles and fields at a planet other than Earth. The new observations have spawned a number of efforts to model the interaction of the solar wind with the magnetosphere and how such dynamics influence the auroras. [less ▲]

Detailed reference viewed: 15 (0 ULiège)
See detailCharacteristics of Saturn's polar atmosphere and auroral electrons derived from HST/STIS, FUSE and Cassini/UVIS spectra
Gustin, Jacques ULiege; Pryor, W.; Feldman, P. et al

Poster (2008, December 01)

Ultraviolet spectra of Saturn's aurora obtained with the Hubble Space Telescope Imaging Spectrograph (STIS), the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Far Ultraviolet Spectroscopic ... [more ▼]

Ultraviolet spectra of Saturn's aurora obtained with the Hubble Space Telescope Imaging Spectrograph (STIS), the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Far Ultraviolet Spectroscopic Explorer (FUSE) have been compared to synthetic spectra of electron-excited H2 in order to derive various auroral characteristics, such as the energy of the primary precipitating electrons and the H2 temperature at the altitude of the aurora. Two physical processes have been exploited: the absorption by hydrocarbons in the FUV and H2 self-absorption in the EUV. We find energies in the range 10-18 keV, which locates Saturns's aurora between 0.1 and 0.3 μ bar. We also determined that the auroral H2 emission is characterized by a temperature of ~400K, consistent with temperatures measured in the infrared, but much higher than what is expected from equatorial atmospheric models. These new results bring valuable constraints on both polar atmospheric models and theoretical studies of the ionosphere-magnetosphere coupling. [less ▲]

Detailed reference viewed: 37 (5 ULiège)
See detailThe Ultraviolet Spectrograph (UVS) on Juno
Gladstone, G. R.; Persyn, S.; Eterno, J. et al

Conference (2008, December 01)

Juno, a NASA New Frontiers mission, plans for launch in August 2011, a 5-year cruise (including a flyby of Earth in October 2013 for a gravity boost), and 14 months around Jupiter after arriving in August ... [more ▼]

Juno, a NASA New Frontiers mission, plans for launch in August 2011, a 5-year cruise (including a flyby of Earth in October 2013 for a gravity boost), and 14 months around Jupiter after arriving in August 2016. The spinning (2 RPM), solar-powered Juno will study Jupiter from a highly elliptical orbit, in which the spacecraft (for about 6 hours once every 11 days) dives down over the north pole, skims the outermost atmosphere, and rises back up over the south pole. This orbit allows Juno avoid most of the intense particle radiation surrounding the planet and provides an excellent platform for investigating Jupiter's polar magnetosphere. Part of the exploration of Jupiter's polar magnetosphere will involve remote sensing of the far-ultraviolet H and H2 auroral emissions, plus gases such as methane and acetylene which add their absorption signature to the H2 emissions. This hydrocarbon absorption can be used to estimate the energy of the precipitating electrons; since more energetic electrons penetrate deeper into the atmosphere and the UV emissions they produce will show more absorption. Juno will carry an Ultraviolet Spectrograph (UVS) to make spectral images of Jupiter's aurora. UVS is a UV imaging spectrograph sensitive to both extreme and far ultraviolet emissions in the 70-205~nm range that will characterize the morphology and spectral nature of Jupiter's auroral emissions. Juno UVS consists of two separate sections: a dedicated telescope/spectrograph assembly and a vault electronics box. The telescope/spectrograph assembly contains a telescope which feeds a 0.15-m Rowland circle spectrograph. The telescope has an input aperture 40à 40~mm2 and uses an off-axis parabolic primary mirror. A flat scan mirror situated at the front end of the telescope (used to target specific auroral features at up to ±30° perpendicular to the Juno spin plane) directs incoming light to the primary. The light is then focused onto the spectrograph entrance slit, which has a 'dog- bone' shape 6° long, in three 2° sections of 0.2°, 0.05°, and 0.2° width (projected onto the sky). Light entering the slit is dispersed by a toroidal grating which focuses the UV bandpass onto a curved microchannel plate (MCP) cross delay line (XDL) detector with a solar blind UV- sensitive CsI photocathode, which makes up the instrument's focal plane. Tantalum shielding surrounds the detector assembly to protect the detector and the adjacent detector electronics from high-energy electrons. The main electronics box is located in the Juno vault. Inside are two redundant high-voltage power supplies (HVPS), two redundant low-voltage power supplies, the command and data handling (C&DH) electronics, heater/actuator activation electronics, scan mirror electronics, and event processing electronics. An overview of the UVS design and scientific performance will be presented. [less ▲]

Detailed reference viewed: 146 (9 ULiège)
See detailThe variation of different components of Jupiter's auroral emission
Nichols, J.; Clarke, J.; Gérard, Jean-Claude ULiege et al

Conference (2008, December 01)

In this paper we use the extensive HST data set obtained over two month-long campaigns in 2007 to determine the long term variability of the different components of Jupiter's auroras. We define three ... [more ▼]

In this paper we use the extensive HST data set obtained over two month-long campaigns in 2007 to determine the long term variability of the different components of Jupiter's auroras. We define three regions on the planet's disc, i.e. the main oval, the low latitude, and high latitude auroras, and extract the UV auroral power emitted therefrom. The high latitude region was also further divided into the polar inner and polar outer regions. We discuss the temporal variation of these parameters with reference to the auroral morphology and estimated solar wind conditions projected to Jupiter's orbit from data obtained at Earth orbit. We show that the auroral morphology was very different between the first and second campaigns. In the first campaign the emitted power originated mainly from the main oval and the high latitude regions, which roughly correlated, and exhibited enhancements that are suggested to be associated with compression regions. In the second campaign the high latitude and main oval auroras were generally dimmer overall and less variable, while the low latitude region was populated with bright, patchy emission. We show that a particular auroral morphology is probably associated specifically with compression regions, i.e. over longitudes greater than approx. 180 degrees the main oval is bright and located approx. 1 degree poleward of its previous location, while over smaller longitudes the main oval is not bright or well defined. Instead there is bright emission originating from the contiguous poleward region in the afternoon/dusk sector where bright, sometimes multiple arcs form. It remains unclear, however, whether this state is a response to the initial shock or some other event within the rapidly-varying compression regions. We also show that the dawn storm events, typically associated with intense dawn side main oval auroras also result in the brightening of the high latitude auroras, even to the very highest latitude components, which presumably map to a very different region of the magnetosphere. However, apart from the dawn storms and bright poleward arcs in the afternoon/dusk sector, the power emitted from the poleward auroras is generally uncorrelated with that of the main oval. [less ▲]

Detailed reference viewed: 25 (3 ULiège)