References of "Bonfond, Bertrand"
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See detailEvidence for Auroral Emissions from Callisto's Footprint in HST UV Images
Bhattacharyya, Dolon; Clarke, John T.; Montgomery, Jordan et al

in Journal of Geophysical Research. Space Physics (in press)

Auroral emissions are expected from the footprint of Callisto in Jupiter's upper atmosphere owing to the known interaction of its atmosphere with Jupiter's magnetosphere, and from the observed auroral ... [more ▼]

Auroral emissions are expected from the footprint of Callisto in Jupiter's upper atmosphere owing to the known interaction of its atmosphere with Jupiter's magnetosphere, and from the observed auroral emissions from the footprints of the other three Galilean satellites. The mapping of Callisto along modeled magnetic field lines at Jupiter, however, places the expected footprint at the same latitude as the main auroral emissions, making it difficult to detect. We analyzed ultraviolet images of Jupiter taken using the HST/ACS instrument during a large observing campaign in 2007. Using a co-addition method similar to one used for Enceladus, we have identified a strong candidate for the footprint of Callisto on May 24, 2007. We tested this finding by applying the same co-addition technique to a nearly identical auroral configuration on May 30, 2007 when Callisto was behind Jupiter, not visible from Earth (CML = 22°; sub-Callisto system III longitude = 327°). By comparing the two co-added images, we can clearly see the presence of a strongly sub-corotating spot close to the expected Callisto footprint location on 24th May and its absence on 30th May. On the 24th Callisto was located in the current sheet. We also found a probable candidate on 26th May 2007 during which time Callisto was positioned below the current sheet. The measured location and intensity of the auroral emission provides important information about the interaction of Callisto with Jupiter's magnetic field, the corotating plasma, and the neutral and ionized state of the thin atmosphere of Callisto. [less ▲]

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See detailGeneration and Similarity of the Jovian Satellite Footprints
Bonfond, Bertrand ULiege

Conference (2017, December 14)

A long chain of processes connects the satellite auroral footprints to the moon-magnetosphere interaction from which they originate. These processes include Alfvén waves’ generation, filamentation ... [more ▼]

A long chain of processes connects the satellite auroral footprints to the moon-magnetosphere interaction from which they originate. These processes include Alfvén waves’ generation, filamentation, reflection, and bi-directional electron acceleration. The Io footprint is the most studied auroral footprint, because it is both the brightest one and the most isolated from other auroral emissions. It is made of at least three separate spots and an extended tail in the downstream direction. Early detections of the Europa and Ganymede footprints only identified single spots for these footprints, but re-analysis of the large dataset of Hubble Space Telescope images of the Jovian aurorae showed that they can also be made of multiple spots and display a tail. Moreover, the relative motion of these spots as a function of the location of the satellite is consistent with previous observations of the Io footprint, indicating that this dynamics corresponds to universal processes. Furthermore, a number of recent studies focused on the evolution of the brightness of these spots, with timescales ranging from minutes to days, and the signification of these changes will be reviewed. Finally, a discussion of the theoretical models explaining the footprint tails and their properties will be provided. [less ▲]

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See detailElectron Pitch Angle Distributions Along Field Lines Connected to the Auroral Region from ~25 to ~1.2 RJ Measured by the Jovian Auroral Distributions Experiment-Electrons (JADE-E) on Juno
Allegrini, Frederic; Bagenal, Fran; Bolton, Scott J et al

Poster (2017, December 13)

The Jovian Auroral Distributions Experiment (JADE) on Juno provides critical in situ measurements of electrons and ions needed to understand the plasma distributions and processes that fill the Jovian ... [more ▼]

The Jovian Auroral Distributions Experiment (JADE) on Juno provides critical in situ measurements of electrons and ions needed to understand the plasma distributions and processes that fill the Jovian magnetosphere and ultimately produce Jupiter’s bright and dynamic aurora. JADE is an instrument suite that includes two essentially identical electron sensors (JADE-Es) and a single ion sensor (JADE-I). JADE-E measures electron energy distributions from ~0.1 to 100 keV and provides detailed electron pitch angle distributions (PAD) at ~7.5° resolution. Juno’s trajectories in the northern hemisphere have allowed JADE to sample electron energy and pitch angle distributions on field lines connected to the auroral regions from as close as ~1.2 RJ all the way to distances greater than 25 RJ. Here, we report on the evolution of these distributions. Specifically, the PADs change from mostly uniform at distances greater than ~20 RJ, to butterfly from ~18 to ~12 RJ, to field aligned or pancake, depending on the energy, closer to Jupiter. Below ~1.5 RJ, electron beams and loss cones are observed. [less ▲]

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See detailJuno-UVS observation of the Io footprint: Influence of Io’s local environment and passage into eclipse on the strength of the interaction
Hue, Vincent; Gladstone, Randy; Greathouse, Thomas K et al

Poster (2017, December 13)

The Juno mission offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, built to ... [more ▼]

The Juno mission offers an unprecedented opportunity to study Jupiter, from its internal structure to its magnetospheric environment. Juno-UVS is a UV spectrograph with a bandpass of 70<λ<205 nm, built to characterize Jupiter’s UV emissions and provide remote sensing capacities for the onboard fields and particle instruments (MAG, Waves, JADE and JEDI). Juno’s orbit allows observing Jupiter from a unique vantage point above the poles. In particular, UVS has observed the instantaneous Io footprint and extended tail as Io enters into eclipse. This observation may better constrain whether the atmosphere of Io is sustained via volcanic activity or sublimation. Among other processes, the modulation of Io’s footprint brightness correlates to the strength of the interaction between the Io plasma torus and its ionosphere, which, in turn, is likely to be affected by the atmospheric collapse. UVS observed the Io footprint during two eclipses that occurred on PJ1 and PJ3, and one additional eclipse observation is planned during PJ9 (24 Oct. 2017). We present how the electrodynamic coupling between Io and Jupiter is influenced by changes in Io’s local environment, e.g. Io’s passage in and out of eclipse and Io’s traverse of the magnetodisc plasma sheet. [less ▲]

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See detailSystematic capture of MeV electron beams by MWR
Santos-Costa, Daniel; Bellotti, Amadeo; Janssen, Mike et al

Poster (2017, December 13)

Every ~ 53 days since August 2016, Juno swings by Jupiter and as the spacecraft spins along a polar orbit, measurements of Jupiter's microwave radiation are carried out at high data rates for several ... [more ▼]

Every ~ 53 days since August 2016, Juno swings by Jupiter and as the spacecraft spins along a polar orbit, measurements of Jupiter's microwave radiation are carried out at high data rates for several hours (~ 9 hours) with the Juno Microwave Radiometer (MWR). Within ~ 6 planetary radii (Rj) and from inside/outside the magnetospheric region, the thermal and synchrotron emissions are measured at high temporal and spatial resolutions. In this paper, we present a synthesis of the spatial distributions of the microwave radiation and discuss the similarities and differences observed at six wavelengths (1.3-50 cm). In addition to the thermal emission and synchrotron radiation from Jupiter's electron belt, unexpected signatures in MWR are either systematically or sporadically reported during perijove 1 (PJ1) and PJ3-PJ6. The preliminary results of a multi-instrument analysis of radio (MWR), extreme and far-ultraviolet auroral emissions (Juno UVS), field (Juno magnetometer), keV electrons (JEDI), and background radiation signatures in Juno's ASC and SRU instruments suggest that some of these signatures are consistent with the capture by MWR of synchrotron emission radiated by MeV electron beams, which may be associated with auroral activity. We subsequently describe in detail our data analysis and effort to model the synchrotron radiation from MeV electron beams to support our findings. [less ▲]

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See detailOverview of HST observa7ons of Jupiter’s ultraviolet aurora during Juno orbits 3 to 7
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege et al

Conference (2017, December 12)

Jupiter’s permanent ultraviolet auroral emissions have been systematically monitored from Earth orbit with the Hubble Space Telescope (HST) during an 8-month period. The Girst part of this HST large ... [more ▼]

Jupiter’s permanent ultraviolet auroral emissions have been systematically monitored from Earth orbit with the Hubble Space Telescope (HST) during an 8-month period. The Girst part of this HST large program (GO-14634) was meant to support the NASA Juno prime mission during orbits PJ03 through PJ07. The HST program will resume in Feb 2018, in time for Juno’s PJ11 perijove, right after HST’s solar and lunar avoidance periods. HST observations are designed to provide a Jovian auroral activity background for all instruments on-board Juno and for the numerous ground based and space based observatories participating to the Juno mission. In particular, several HST visits were programmed in order to obtain as many simultaneous observations with Juno-UVS as possible, sometimes in the same hemisphere, sometimes in the opposite one. In addition, the timing of some HST visits was set to take advantage of Juno’s multiple crossings of the current sheet and of the magnetic Gield lines threading the auroral emissions. These observations are obtained with the Space Telescope Imaging Spectrograph (STIS) in time-tag mode, they consist in spatially resolved movies of Jupiter’s highly dynamic aurora with timescales ranging from seconds to several days. Here, we present an overview of the present -numerous- HST results. They demonstrate that while Jupiter is always showing the same basic auroral components, it is also displaying an ever-changing auroral landscape. The complexity of the auroral morphology is such that no two observations are alike. Still, in this apparent chaos some patterns emerge. This information is giving clues on magnetospheric processes at play at the local and global scales, the latter being only accessible to remote sensing instruments such as HST. [less ▲]

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See detailA comparative examination of auroral acceleration processes at Jupiter and Earth as enabled by the Juno mission to Jupiter
Mauk, Barry; Haggerty, Dennis; Paranicas, Chris et al

Conference (2017, December 12)

Particle distributions observed by Juno’s Energetic Particle Detector Investigation (JEDI) at low altitudes over Jupiter’s polar regions are exceedingly diverse in directionality and in the shapes of ... [more ▼]

Particle distributions observed by Juno’s Energetic Particle Detector Investigation (JEDI) at low altitudes over Jupiter’s polar regions are exceedingly diverse in directionality and in the shapes of their 3-dimensional energy distributions. Asymmetric, bi-directional angular beams with broad energy distributions are often observed near Jupiter’s main auroral oval with considerable variability as to whether upward or downward intensities are the strongest. Signatures of upward and downward magnetic field-aligned potentials, with inferred potentials up to 100’s of kV are sometimes observed, but unlike at Earth, these potentials do not seem to be associated with the strongest discrete-like auroral emission intensities. Particle distributions have similarities to those observed at Earth over the various phenomenological auroral emission regions, but they are observed in unexpected places with respect to the strongest auroral emission regions, and the jovian distributions are much more energetic. We present a comparative examination of auroral acceleration processes observed at Earth and Jupiter in relation to the respective auroral emission regions. [less ▲]

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See detailAn overview of the first year of observations of Jupiter’s auroras by Juno-UVS with multi-wavelength comparisons
Gladstone, Randy; Greathouse, Thomas K; Versteeg, Maarten H et al

Conference (2017, December 12)

Juno’s Ultraviolet Spectrograph (Juno-UVS) has observed the Jovian aurora during eight perijove passes. UVS typically observes Jupiter for 10 hours centered on closest approach in a series of swaths, with ... [more ▼]

Juno’s Ultraviolet Spectrograph (Juno-UVS) has observed the Jovian aurora during eight perijove passes. UVS typically observes Jupiter for 10 hours centered on closest approach in a series of swaths, with one swath per Juno spin (~30s). During this period the spacecraft range to Jupiter’s aurora decreases from ~6 RJ to ~0.3 RJ (or less) in the north, and then reverses this in the south, so that spatial resolution changes dramatically. A scan mirror is used to target different features or raster across the entire auroral region. Juno-UVS observes a particular location for roughly 17 ms/swath, so the series of swaths provide snapshots of ultraviolet auroral brightness and color. A variety of forms and activity levels are represented in the Juno-UVS data–some have been described before with HST observations, but others are new. One interesting result is that the color ratio, often used as a proxy for energetic particle precipitation, may instead (in certain regions) indicate excitation of H2 by low-energy ionospheric electrons. Additional results from comparisons with simultaneous observations at x-ray, visible, and near-IR wavelengths will also be presented. [less ▲]

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See detailProbing Jupiter’s auroral radio sources with Juno
Imai, M.; Kurth, W. S.; Hospodarsky, G. B. et al

Conference (2017, December 12)

Jupiter is the major auroral radio source in our solar system, producing Jovian low-frequency radio emissions in a broad frequency range of 10 kHz to 40 MHz from both north and south polar regions of the ... [more ▼]

Jupiter is the major auroral radio source in our solar system, producing Jovian low-frequency radio emissions in a broad frequency range of 10 kHz to 40 MHz from both north and south polar regions of the planet. These sporadic nonthermal bursts have been monitored with the radio and plasma wave instrument (Waves) aboard the spinning Juno spacecraft in polar orbit about Jupiter since July 5, 2016. The Waves instrument is composed of one electric dipole antenna, one magnetic search coil sensor, and three on-board receivers that record the electric fields of waves from 50 Hz to 41 MHz and the magnetic fields of waves from 50 Hz to 20 kHz. Juno has three advantageous methods to determine the radio source locations and the beaming properties for the Jovian low-frequency radio emissions: (1) identifying emission frequency close to the local gyrofrequency at the source with in situ particle measurements through Juno's perijove surveys from pole to pole, (2) the spin-modulated spectral density recorded with Juno Waves to estimate the direction of arrival of incoming waves, and (3) with the aid of the Jovian radio beaming model, performing stereoscopic radio observations with Juno, Cassini, STEREO A, WIND, and Earth-based radio telescopes (e.g., LWA1 in New Mexico, USA, and NDA in Nançay, France) or investigating the statistical characteristics of Jovian radio occurrence by Juno. Because the three individual methods are self-consistent and complement each other, Juno observations are useful for determining the Jovian radio beam parameters and radio source locations, which can be traced along magnetic field lines onto Jupiter's atmosphere and further compared with the UV aurora taken by the Hubble Space Telescope. In this talk, we give a brief overview of early radio astronomy results from Juno, providing the recent results from these extended studies by means of the three methods. [less ▲]

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See detailFirst simultaneous observations of local moon aurora and the moon footprints in Jupiter’s polar aurora
Roth, Lorenz; Grodent, Denis ULiege; Gladstone, Randy et al

Conference (2017, December 12)

The interaction of the co-rotating magnetospheric plasma with Jupiter’s Galilean moons generates local perturbations and auroral emissions in the moons’ tenuous atmospheres. Alfvén waves are launched by ... [more ▼]

The interaction of the co-rotating magnetospheric plasma with Jupiter’s Galilean moons generates local perturbations and auroral emissions in the moons’ tenuous atmospheres. Alfvén waves are launched by this local interaction and travel along Jupiter’s field lines triggering various effects that finally lead to the auroral moon footprints far away in Jupiter’s polar regions. Within the large Hubble Space Telescope aurora program in support of the NASA Juno mission (HST GO-14634, PI D. Grodent), HST observed the local aurora at the moons Io and Ganymede on three occasions in 2017 while the Juno Ultraviolet Spectrograph simultaneously observed Jupiter’s aurora and the moon footprints. In this presentation, we will provide first results from the first-ever simultaneous moon and footprint observations for the case of Io. We compare the temporal variability of the local moon aurora and the Io footprint, addressing the question how much of the footprint variability originates from changes at the moon source and how much originates from processes in the regions that lie in between the moon and Jupiter’s poles. [less ▲]

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See detailA Study of Local Time Variations of Jupiter’s Ultraviolet Aurora using Juno-UVS
Greathouse, Thomas K; Gladstone, Randy; Versteeg, Maarten H et al

Conference (2017, December 12)

Juno’s Ultraviolet Spectrograph (Juno-UVS) offers unique views of Jupiter’s auroras never before obtained in the UV, observing at all local times (unlike HST observations, limited to the illuminated disk ... [more ▼]

Juno’s Ultraviolet Spectrograph (Juno-UVS) offers unique views of Jupiter’s auroras never before obtained in the UV, observing at all local times (unlike HST observations, limited to the illuminated disk). With Juno’s 2-rpm spin period, the UVS long slit rapidly scans across Jupiter observing narrow stripes or swaths of Jupiter’s poles, from 5 hours prior to perijove until 5 hours after perijove. By rotating a mirror interior to the instrument, UVS can view objects from 60 to 120 degrees off the spacecraft spin axis. This allows UVS to map out the entire auroral oval over multiple spins, even when Juno is very close to Jupiter. Using the first 8 perijove passes, we take a first look for local time effects in Jupiter’s northern and southern auroras. We focus on the strength of auroral oval emissions and polar emissions found poleward of the main oval. Some unique polar emissions of interest include newly discovered polar flare emissions that start off as small localized points of emission but quickly (10’s of sec) evolve into rings. These emissions evolve in such a way as to be reminiscent of raindrops striking a pond. [less ▲]

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See detailDawn Auroral Breakup at Saturn Initiated by Auroral Arcs: UVIS/Cassini Beginning of Grand Finale Phase
Radioti, Aikaterini ULiege; Grodent, Denis ULiege; Yao, Zhonghua ULiege et al

in Journal of Geophysical Research. Space Physics (2017)

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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 (2017), 213(1-4), 447-473

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 detailJovian aurora from Juno perijove passes: comparison of ultraviolet and infrared images
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Adriani, A. et al

Conference (2017, September 01)

The electromagnetic radiation emitted by the Jovian aurora extends from the X-Rays presumably caused by heavy ion precipitation and electron bremsstrahlung to thermal infrared radiation resulting from ... [more ▼]

The electromagnetic radiation emitted by the Jovian aurora extends from the X-Rays presumably caused by heavy ion precipitation and electron bremsstrahlung to thermal infrared radiation resulting from enhanced heating by high-energy charged particles. Many observations have been made since the 1990s with the Hubble Space Telescope, which was able to image the H2 Lyman and Werner bands that are directly excited by collisions of auroral electrons with H2. Ground-based telescopes obtained spectra and images of the thermal H3+ emission produced by charge transfer between H2+ and H+ ions and neutral H2 molecules in the lower thermosphere. However, so far the geometry of the observations limited the coverage from Earth orbit and only one case of simultaneous UV and infrared emissions has been described in the literature. The Juno mission provides the unique advantage to observe both Jovian hemispheres simultaneously in the two wavelength regions simultaneously and offers a more global coverage with unprecedented spatial resolution. This was the case. [less ▲]

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See detailJuno-UVS and Chandra Observations of Jupiter's Polar Auroral Emissions
Gladstone, G. R.; Kammer, J. A.; Versteeg, M. H. et al

Conference (2017, September 01)

New results are presented comparing Jupiter's auroras at far-ultraviolet and x-ray wavelengths, using data acquired by Juno-UVS and Chandra. The highly variable polar auroras (which are located within the ... [more ▼]

New results are presented comparing Jupiter's auroras at far-ultraviolet and x-ray wavelengths, using data acquired by Juno-UVS and Chandra. The highly variable polar auroras (which are located within the main auroral oval) track each other quite well in brightness at these two wavelengths. [less ▲]

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See detailDiscrete and broadband electron acceleration in Jupiter's powerful aurora
Mauk, B. H.; Haggerty, D. K.; Paranicas, C. et al

in Nature (2017), 549

The most intense auroral emissions from Earth's polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by ... [more ▼]

The most intense auroral emissions from Earth's polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by slowly evolving, powerful electric fields directed along the magnetic field lines that connect Earth's space environment to its polar regions. In contrast, Earth's less intense auroras are generally caused by wave scattering of magnetically trapped populations of hot electrons (in the case of diffuse aurora) or by the turbulent or stochastic downward acceleration of electrons along magnetic field lines by waves during transitory periods (in the case of broadband or Alfvénic aurora). Jupiter's relatively steady main aurora has a power density that is so much larger than Earth's that it has been taken for granted that it must be generated primarily by the discrete auroral process. However, preliminary in situ measurements of Jupiter's auroral regions yielded no evidence of such a process. Here we report observations of distinct, high-energy, downward, discrete electron acceleration in Jupiter's auroral polar regions. We also infer upward magnetic-field-aligned electric potentials of up to 400 kiloelectronvolts, an order of magnitude larger than the largest potentials observed at Earth. Despite the magnitude of these upward electric potentials and the expectations from observations at Earth, the downward energy flux from discrete acceleration is less at Jupiter than that caused by broadband or stochastic processes, with broadband and stochastic characteristics that are substantially different from those at Earth. [less ▲]

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See detailEvolution of the auroral signatures of Jupiter’s magnetospheric injections
Dumont, Maïté ULiege; Grodent, Denis ULiege; Bonfond, Bertrand ULiege et al

Conference (2017, September)

We report on the longitudinal and azimuthal motions of auroral signatures of Jupiter’s magnetospheric injections appearing in Hubble Space Telescope (HST) images in the northern and southern hemispheres ... [more ▼]

We report on the longitudinal and azimuthal motions of auroral signatures of Jupiter’s magnetospheric injections appearing in Hubble Space Telescope (HST) images in the northern and southern hemispheres. Based on HST spectral observations of time-tag mode and numerical simulations, we estimate the age of auroral signatures of plasma injections. [less ▲]

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See detailJuno Ultraviolet Spectrograph (Juno-UVS) Observations of Jupiter’s Aurora
Greathouse, T.; Veersteeg, M.; Hue, V. et al

Conference (2017, August 11)

The Juno Ultraviolet Spectrograph (UVS) is an imaging Rowland Circle spectrograph mounted on the Juno Spacecraft in orbit about Jupiter. Operating between 70 and 205 nm UVS was built to measure Jupiter’s ... [more ▼]

The Juno Ultraviolet Spectrograph (UVS) is an imaging Rowland Circle spectrograph mounted on the Juno Spacecraft in orbit about Jupiter. Operating between 70 and 205 nm UVS was built to measure Jupiter’s auroral and airglow emissions in the far- to extreme-ultraviolet spectral range (FUV-EUV range). These emissions provide a key link between the on board measurements of Jupiter’s magnetic field and particle populations within the intense Jovian magnetosphere and their interaction with Jupiter’s upper atmosphere.  The UV auroral emissions serve as a “witness plate” or “viewing screen” to some of the complex and powerful magnetospheric processes occurring there. We will present UV images, movies, and color ratio maps of both the northern and southern aurora and discuss how the many features evolve over time from the first Perijove on August 27, 2016 through the 7th Perijove planned on July 11, 2017. [less ▲]

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See detailThe tails of the satellite auroral footprints at Jupiter
Bonfond, Bertrand ULiege; Saur, J.; Grodent, Denis ULiege et al

in Journal of Geophysical Research. Space Physics (2017), 122

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint ... [more ▼]

The electro-magnetic interaction between Io, Europa and Ganymede and the rotating plasma that surrounds Jupiter has a signature in the aurora of the planet. This signature, called the satellite footprint, takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration. In the case of Io, these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon. A few examples of a tail for the Europa footprint have also been reported in the northern hemisphere. Here we present a simplified Alfvénic model for footprint tails and simulations of vertical brightness profiles for various electron distribution, which favour such a model over quasi-static models. We also report here additional cases of Europa footprint tails, in both hemispheres, even though such detections are rare and difficult. Furthermore, we show that the Ganymede footprint can also be followed by a similar tail. Finally, we present a case of a 320° long Io footprint tail, while other cases in similar configurations do not display such a length. [less ▲]

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

in Icarus (2017), 292(2017), 208217

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

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

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