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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 detailJupiter’s magnetopause: A search for wave and reconnection signatures
Bonfond, Bertrand ULg; Kivelson, M. G.; Khurana, K. K. et al

Conference (2014, September 12)

Surface waves and magnetic reconnection are two key processes taking place at the planetary magnetopause. They allow the coupling, through energy (and particle) transfer, of the interplanetary medium and ... [more ▼]

Surface waves and magnetic reconnection are two key processes taking place at the planetary magnetopause. They allow the coupling, through energy (and particle) transfer, of the interplanetary medium and the magnetosphere. The relative importance of large scale Dungey reconnection and viscous interaction (including small-scale intermittent reconnection associated with Kelvin-Helmholtz vortices) are expected to be different at Jupiter compared to the Earth’s case. Such differences would be due to the combination of a) a weaker solar wind pressure and Alfvén velocity as the distance to the Sun increases, b) a high-β plasma sheet, originating from Io’s outgassing, which inflates the Jovian magnetosphere, c) the rapid rotation of the planet relative to its size (e.g. Desroche et al. 2012). Here we analyse the signatures of wave activity and reconnection on the magnetopause of Jupiter, based on magnetic field and energetic particle measurements from the successive spacecraft that explored the Jovian system. Up to now, 7 spacecraft equipped with a magnetometer have crossed the Jovian magnetopause: Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Galileo and Cassini. We make use of several normal direction finding techniques, such as the Minimum Variance Analysis, in order to identify waves and Kelvin-Helmholtz vortices. As far as the reconnection is concerned, small scale signatures of flux-tube events (FTEs) had been identified by Walker and Russell (1985), based on a limited data-set from the Pioneers’ and Voyagers’ fly-bys. Here we will extend this search to the extensive dataset from all the missions that explored Jupiter’s system. [less ▲]

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See detailHighlights of the 2014 Jupiter observing campaign by multi - spectral remote sensing using space telescopes
Kimura, T.; Badman, S.; Tao, C. et al

Conference (2014, September 11)

From January to April 2014, two observing campaigns by multi-wavelength remote sensing from X-ray to radio were performed to uncover energy transport process in Jupiter’s plasma environment using space ... [more ▼]

From January to April 2014, two observing campaigns by multi-wavelength remote sensing from X-ray to radio were performed to uncover energy transport process in Jupiter’s plasma environment using space telescopes and ground-based facilities. These campaigns were triggered by the new Hisaki spacecraft launched in September 2013, which is an extremely ultraviolet (EUV) space telescope of JAXA designed specifically for planetary observations. In the first campaign in January, Hubble Space Telescope made imaging of far ultraviolet (FUV) aurora with a high special resolution (0.08”) through two weeks while Hisaki continuously monitored aurora and plasma torus emissions in EUV wavelength with a high temporal resolution (1 min<). We discovered new magnetospheric activities from the campaign data: e.g., internally-driven type auroral brightening associated with hot plasma injection, and plasma and electromagnetic filed modulations in the inner magnetosphere externally driven by the solar wind modulation. The second campaign in April was performed by Chandra X-ray Observatory, XMM newton, and Suzaku satellite simultaneously with Hisaki. Relativistic auroral accelerations in the polar region and hot plasma in the inner magnetosphere were captured by the X-ray space telescopes simultaneously with EUV monitoring of aurora and plasma torus. In this presentation, we show remarkable scientific results obtained these campaigns mainly focusing on Jupiter’s aurora. [less ▲]

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See detailWeakening of Jupiter’s main auroral emission in response to magnetospheric hot plasma injections
Badman, Sarah; Bonfond, Bertrand ULg; Fujimoto, M. et al

Conference (2014, September 11)

We present images of Jupiter’s northern UV aurorae taken by the Hubble Space Telescope as part of a large observing campaign in January 2014. The high time resolution observations allow the dynamics of ... [more ▼]

We present images of Jupiter’s northern UV aurorae taken by the Hubble Space Telescope as part of a large observing campaign in January 2014. The high time resolution observations allow the dynamics of the different components of the aurorae to be observed. Particular features of interest are large regions of diffuse emission, which occurred equatorward of the main oval, enveloping the auroral footprint of Ganymede. These diffuse, low latitude emissions are caused by the injection of hot plasma from the outer magnetosphere, a process which has previously been related to interchange between the flux tubes from the outer magnetosphere and outward-moving flux tubes loaded with iogenic plasma. Over the two-week observing interval the auroral signatures of two large injection events were observed, while the main oval generally decreased in intensity. We suggest that the overall dimming of the main oval results from the weakening of the corotation-enforcement currents that drive the main emission, following the replacement of the radially-stretched, mass-loaded flux tubes by more dipolar flux tubes containing rarefied hot plasma. [less ▲]

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See detailJupiter's equatorward auroral features : Possible signature of magnetospheric injections
Dumont, Maïté ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

Conference (2014, September)

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties ... [more ▼]

We investigate the characteristics of ultraviolet auroral features located equatorward of the main emission appearing in the Hubble Space Telescope (HST) images obtained in 2000-2007. Several properties of the auroral emissions are analyzed. The mapped radial position and System III longitude of the observed auroral features are in good agreement with those of the injections observed in the equatorial plane by Galileo. Finally, we discuss the processes causing auroral signatures of injections. This comparative study demonstrates that the structures under study are most probably related to magnetospheric injections and sheds light to the mechanism involved in the magnetosphere-ionosphere dynamics. [less ▲]

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See detailSpectral mapping of the FUV Jovian aurora and electron energy distribution
Gérard, Jean-Claude ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2014, September)

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build ... [more ▼]

Observations have been made with the Hubble Space Telescope in the timetag mode using the STIS long slit. During the 40 min of the observations, the slit spatially scanned the polar regions to build spectral maps of the jovian aurora. The emission is composed of the HI Lyman-alpha line and the H2 Lyman and Werner bands. The shorter wavelengths are partly absorbed by the methane layer overlying the bulk of the auroral emission. Since the CH4 absorption cross section drastically drops above 140 nm, the longer wavelengths are not absorbed and the intensity directly reflects the precipitated energy flux carried by the electrons. Maps of the intensity ratio of the two spectral regions will be presented, together with the associated auroral electron energy. These values will be compared with those expected from current magnetosphere-ionosphere model. They will provide input into 3-D modeling of the auroral heat source into the high-latitude Jovian upper atmosphere. [less ▲]

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See detailSaturn’s elusive nightside polar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2014)

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

Conference (2014, April 29)

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

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

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See detailSaturn’s elusive transpolar arc
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2014, April)

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See detailThe Ultraviolet Spectrograph on NASA’s Juno Mission
Gladstone, G Randal; Persyn, Steven C.; Eterno, John S. et al

in Space Science Reviews (2014)

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These ... [more ▼]

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS. [less ▲]

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See detailDynamics of the aurora at Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Badman, Sarah et al

Conference (2014, February 19)

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See detailMagnetospheric Science Objectives of the Juno Mission
Bagenal, Fran; Adriani, A.; Allegrini, F. et al

in Space Science Reviews (2014)

In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and enture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we ... [more ▼]

In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and enture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets. [less ▲]

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See detailSolarWind and Internally Driven Dynamics: Influences on Magnetodiscs and Auroral Responses
Delamere; Bagenal; Paranicas et al

in Space Science Reviews (2014)

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

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

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

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

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See detailAurorae at Jupiter: a selection of recent results
Bonfond, Bertrand ULg

Scientific conference (2013, December 17)

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See detailMagnetopause Boundary Normal Analysis at Jupiter and Saturn: Evidence of Kelvin Hemholtz Vorticies
Stauffer, Blake Hughes; Delamere, Peter A; Ma, Xuanye et al

Poster (2013, December 10)

Identification of surface waves and Kelvin Hemholtz (KH) vorticies at the magnetopause boundary at Jupiter and Saturn is critical to understanding interaction between the solar wind and their planetary ... [more ▼]

Identification of surface waves and Kelvin Hemholtz (KH) vorticies at the magnetopause boundary at Jupiter and Saturn is critical to understanding interaction between the solar wind and their planetary magnetospheres. The rapid rotation of those planets coincides with a co-rotating plasma that creates an asymmetry between the formation and evolution of surface waves on either side of the sub-solar point. Minimum variance analysis and other techniques are performed on hundreds of select crossings of Saturn's magnetopause from 2004 to 2012 by the Cassini spacecraft and 47 crossings at Jupiter's magnetopause by the Galileo spacecraft. It is compared to the boundary normals of a simple magnetopause model. The wide range in angular difference between the model and the analysis is evidence of the presence of KH instability vorticies at the magnetopause boundary. Furthermore, boundary crossings from the magnetosheath into the magnetosphere on the dusk flanks are dominated by shallower angles, consistent with MHD simulations of variable shear flows on the dayside magnetopause boundary. [less ▲]

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See detailThe 2-3 minutes periodicity in the polar aurora and the magnetosphere of Jupiter
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Poster (2013, December 10)

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer ... [more ▼]

The main aurora at Jupiter is related to the middle magnetosphere and the corotation breakdown of the magnetospheric plasma. On the other hand, the polar regions either magnetically map to the outer magnetosphere or correspond to field lines open to the interplanetary medium and most of the auroral emissions from this region are still poorly understood. Among these polar auroral emissions are the flares, dramatic brightenings of several million square kilometers over a couple of minutes. Two previously reported observations of the southern hemisphere showed that these flares can be quasi-periodic with a re-occurrence time of 2-3 minutes. Here we report results from the Hubble Space Telescope campaign carried out in 2012-2013 with the STIS FUV instrument in time-tag mode (PI: D. Grodent). This campaign consisted in alternating observations of the two hemispheres. Based on the analysis of this dataset, we confirm that these quasi-periodic flares are ubiquitous and occur in both hemispheres. Moreover, in at least one case, these flares appear to occur in phase in both hemispheres. We compare the characteristics of these flares with those of the relativistic electron bursts observed by the Ulysses spacecraft with the HET instrument. We find that 2-3 minutes quasi-periodic burst are much more frequent than previously reported and that they magnetically map to the same auroral area as the flares. We conclude that these two phenomena are most probably related and arise from a common origin. [less ▲]

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See detailSaturn’s UV aurora: the (high latitude) point of view of Cassini
Grodent, Denis ULg; Bonfond, Bertrand ULg; Gustin, Jacques ULg et al

Conference (2013, December 09)

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of ... [more ▼]

The high latitude vantage point of Cassini and its short distance to Saturn give rise to a unique opportunity for obtaining exceptional spectral images of the aurorae, along with in situ observations of the associated particles and magnetic field. Cassini’s T83 flyby of Titan significantly changed the inclination of the spacecraft’s orbit and marked the beginning of the XXM inclined phase 1 which will last until March 16, 2015. We will give an overview of the auroral emissions observed so far with the UVIS camera on board Cassini. In particular we will link the morphology of the aurora with specific magnetospheric processes, such as dayside reconnection and auroral bifurcations, nightside reconnection, hot plasma injections. We will also take advantage of the view from nearly above the poles to describe the overall shape and size of the aurora, which are expected to respond to the solar wind conditions. Moreover, this presentation will focus on small-scale features, which can only be observed by an instrument close enough to the planet. We will also present movies of these observations, allowing us to explore the auroral dynamics at various timescales. This information will be used to identify the various mechanisms at play in Saturn’s magnetosphere. [less ▲]

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See detailHow could the Io footprint disappear?
Hess, Sébastien; Bonfond, Bertrand ULg; Delamere, Peter

in Planetary and Space Science (2013), 89

The interaction of Io with the Jovian magnetosphere is the best known – and the most intense – case of satellite-magnetosphere interaction. The interaction involves a power of more than a TeraWatt, a few ... [more ▼]

The interaction of Io with the Jovian magnetosphere is the best known – and the most intense – case of satellite-magnetosphere interaction. The interaction involves a power of more than a TeraWatt, a few percent of which are transferred to electrons. These electrons precipitate in the Jovian ionosphere where they light-up bright auroral emissions (several 100's kR to a few 1000's kR). The brightness of the Io-controlled UV auroras is known to vary, due to the Jovian magnetic field tilt, which induces longitudinal variations, and due to the Io torus ever changing parameters (possibly due to Io's volcanic activity), which induce a temporal variation. As Io-controlled UV auroras have been monitored for a long time, the variation of their brightness is well-documented, and the typical amplitude of these variations has been established. However, on June, 7th 2012 an unusual event occurred in the plasma torus surrounding Io, which triggered its own UV emissions on Jupiter in a region mapping to Io's orbit. When Io reached that region, Io's auroral footprint disappeared, its brightness dimming by at least a factor of three to be below the background aurora brightness. Both the auroral event at such a low latitude and the Io footprint disappearance are events that have never been observed before and should be quite rare. However, the question of how the bright Io footprint becomes that weak remains. From a theoretical point-of-view, the Io-Jupiter interaction has been widely studied. In the 80's, it was shown that Alfvén waves are radiated from Io, carrying currents to Jupiter. In the late-2000's, studies showed that dispersive Alfvén waves were likely to cause the acceleration of the electrons powering the auroral emissions, although Io-scale Alfvén waves should be non-dispersive. More recently, a model was built which permits one to compute the ratio between dispersive and non-dispersive waves in the auroral region for satellite-magnetosphere interactions, and thus the brightness of the related aurorae. We use this model to investigate which variation of the interaction parameters could lead to the Io footprint disappearance. [less ▲]

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