References of "Bonfond, Bertrand"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailAlfvén Wave Propagation in the Io Plasma Torus
Hinton, P. C.; Bagenal, F.; Bonfond, Bertrand ULiege

in Geophysical Research Letters (2019), 0(0),

Abstract Io, the most volcanically active body in the solar system, fuels a plasma torus around Jupiter with dissociation products of SO2 at a rate of ~1,000 kg/s. We use a combination of in situ Voyager ... [more ▼]

Abstract Io, the most volcanically active body in the solar system, fuels a plasma torus around Jupiter with dissociation products of SO2 at a rate of ~1,000 kg/s. We use a combination of in situ Voyager 1 data and Cassini Ultraviolet Imaging Spectrograph observations to constrain a diffusive equilibrium model of the Io plasma torus. The interaction of the Io plasma torus with Io launches Alfvén waves in both directions along magnetic field lines. We use the recent Juno-based JRM09 magnetic field model combined with our 3-D model of the Io plasma torus to simulate the propagation of Alfvén waves from the moon to the ionosphere of Jupiter. We map the location of multiple reflections of iogenic Alfvén waves between the northern and southern hemispheres. The location of the first few bounces of the Alfvén wave pattern match the Io auroral footprints observed by the Hubble Space Telescope. [less ▲]

Detailed reference viewed: 22 (3 ULiège)
See detailObservations of satellite footprints in Jupiter's Aurorae
Mura, A.; Adriani, A.; Altieri, F. et al

Conference (2018, December 12)

JIRAM (Jovian Infrared Auroral Mapper) on board Juno is an imager/spectrometer in the 2-5 um range. One imaging channel is designed to study the Jovian H3+ auroral emissions. Its high angular resolution ... [more ▼]

JIRAM (Jovian Infrared Auroral Mapper) on board Juno is an imager/spectrometer in the 2-5 um range. One imaging channel is designed to study the Jovian H3+ auroral emissions. Its high angular resolution, combined with the unique vantage point provided by Juno, allows JIRAM to observe the aurorae in unprecedented detail. Here we present the results from ~2 years of observations of the auroral footprints of the Galilean moons. These are bright spots and associated tail that appear in Jupiter’s ionosphere at the base of the magnetic field lines which sweep past Io, Europa, and Ganymede. The moons are obstacles in the path of Jupiter’s rapidly rotating magnetospheric plasma, and the resulting electromagnetic interaction launches Alfvén waves along the magnetic field towards Jupiter, where intense electron bombardment of the hydrogen atmosphere causes it to glow. Recent observations reveal for the first time that the footprint of Io is comprised of a regularly spaced array of emission features, extending downstream of the leading footprint. Contrary to the larger spots seen in lower resolution images, the small scale of these multiple features (~100 km) is incompatible with the simple paradigm of multiple Alfvén wave reflections. Additionally, observations of Io’s trailing tail well downstream of the main footprint reveal a pair of closely spaced parallel arcs, previously unresolved. The temperatures of the main spot and tail, retrieved with the JIRAM spectrometer, are lower than the main auroral oval. This could indicate that the emission is located at a deeper level, possibly caused by higher energy electrons. Ganymede’s footprint spots (main and secondary) appear as a pair of emission features that provide a remote measure of the size Ganymede’s magnetosphere, mapped from its distant orbit onto Jupiter’s magnetosphere. [less ▲]

Detailed reference viewed: 33 (2 ULiège)
See detailFlying through a Dawn Storm : an analysis of Juno-UVS images during PJ11
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

Poster (2018, December 11)

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at ... [more ▼]

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at Jupiter. An event with a total power emitted by the UV aurora in excess of 8.5 TW was even observed by Hisaki and the Hubble Space Telescope on May 21st 2016, during Juno’s approach of Jupiter. On February 7th 2018 (perijove 11, or PJ11), Juno’s ultraviolet imaging spectrograph, called Juno-UVS, observed the development of such a dawn storm, right before Juno flew right through the magnetic field line connected to this feature. The storm started around 13:15 UT as a limited enhancement of the main emission around midnight before slowly migrating and expanding on the dusk flank. As the brightness increased, the arc began to thicken and fork into two separate arcs. Simultaneously, the signatures of methane absorption of the UV light progressively intensified, indicative of a precipitation of increasingly energetic particles. Then, around 18:15 UT, Juno entered the field lines feeding the dawn storm. The remote auroral observations thus provide extremely valuable context information for the in-situ radio waves, particle and magnetic field observations gathered at this time. [less ▲]

Detailed reference viewed: 36 (3 ULiège)
Full Text
Peer Reviewed
See detailIn-Situ Observations Connected to the Io Footprint Tail Aurora
Szalay, J. R.; Bonfond, Bertrand ULiege; Allegrini, F. et al

in Journal of Geophysical Research: Planets (2018), 123(ja),

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10° to 120° along ... [more ▼]

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10° to 120° along the footprint tail. Juno's suite of magnetospheric instruments acquired detailed measurements of the Io footprint tail. Juno observed planetward electron energy fluxes of 70 mW/m2 near the Io footprint, and 10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Observed waves were primarily below the proton cyclotron frequency, yet identification of a definitive wave mode is elusive. Beyond 40° down the footprint tail, Juno observed depleted upward loss cones, suggesting the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7 RJ. For all transits, Juno observed fine structure on scales of 10s km, and confirmed independently with electron and waves measurements that a bifurcated tail can intermittently exist. [less ▲]

Detailed reference viewed: 39 (7 ULiège)
See detailObservations of Jupiter by the Juno Ultraviolet Spectrograph (Juno-UVS)
Greathouse, T. E.; Gladstone, G.R.; Hue, V. et al

Conference (2018, September 20)

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will ... [more ▼]

We present an overview of the science performed by Juno’s Ultraviolet Spectrograph, UVS, over the first 11 successful perijove sequences performed since orbital insertion on July 4th, 2016. We will discuss the measured local time dependence of Jupiter’s polar auroral emissions, simultaneous UV and H3+ observations and their correlations or lack thereof, evolution and morphology of Io’s magnetic footprint in Jupiter’s atmosphere, measurements concerning the spatial and temporal variation of high energy particles (>7 MeV) in the polar regions of Jupiter’s magnetosphere, and finally the production of a dataset that could be used to produce an all sky UV stellar atlas at wavelengths between 70 and 205 nm. [less ▲]

Detailed reference viewed: 26 (5 ULiège)
Full Text
Peer Reviewed
See detailA chemical survey of exoplanets with ARIEL
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2018)

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the ... [more ▼]

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ARIEL was conceived to observe a large number ( 1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H[SUB]2[/SUB]O, CO[SUB]2[/SUB], CH[SUB]4[/SUB] NH[SUB]3[/SUB], HCN, H[SUB]2[/SUB]S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives. [less ▲]

Detailed reference viewed: 45 (7 ULiège)
Full Text
Peer Reviewed
See detailPrecipitating electron energy flux and characteristic energies in Jupiter's main auroral region as measured by Juno/JEDI
Clark, G.; Tao, C.; Mauk, B. H. et al

in Journal of Geophysical Research. Space Physics (2018), 113(ja),

Abstract The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and ... [more ▼]

Abstract The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope (HST), but also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure – leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno/JEDI, an energetic particle instrument, we present these relationships for the 30 keV to 1 MeV electron population. Observations presented here show that the electron energy flux in the loss cone is a non-linear function of the characteristic or mean electron energy and supports both the predictions from Knight [1973] and MHD turbulence acceleration theories [e.g.,Saur et al., 2003]. Finally, we compare the in situ analyses of Juno with remote Hisaki observations and use them to help constrain Jupiter's atmospheric profile. We find a possible solution that provides the best agreement between these datasets is an atmospheric profile that more efficiently transports the hydrocarbons to higher altitudes. If this is correct, it supports the previously published idea [e.g., Parkinson et al. 2006] that precipitating electrons increase the hydrocarbon eddy diffusion coefficients in the auroral regions. [less ▲]

Detailed reference viewed: 26 (5 ULiège)
Full Text
See detailThe polar region of Jupiter’s aurora : barcode noise, conjugate flares and more...
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gladstone, Randy et al

Conference (2018, July 11)

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 ... [more ▼]

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 nm range, to explore the polar physics in two very different ways. In the first part of this presentation, we will analyze the rapid variations of the background noise caused by >10MeV electrons penetrating the instrument. In UV images, this rapidly varying signal takes the form of a barcode-like pattern. We will discuss the mapping, the altitude and the characteristic timescale of the “barcode events” in order to constrain the mechanisms giving rise to them. In the second part, we will compare simultaneous observations of the aurorae from the two hemispheres. One dataset comes from Juno-UVS while the other comes from the Hubble Space Telescope STIS instrument. We will show that most auroral features in one hemisphere have a clear counterpart in the other one. Among other examples, we will show evidence of conjugate flares in the active region of the two hemispheres. However, other strong brightness enhancements only show up in one hemisphere, without any echo in the other one. [less ▲]

Detailed reference viewed: 43 (4 ULiège)
See detailJUNO/MWR's supportive observations of downward field-aligned MeV electrons at Jupiter
Santos-Costa, Daniel; Kurth, William; Hospodarsky, George et al

in 42nd COSPAR Scientific Assembly (2018, July 01)

Since August 2016, the Juno MicroWave Radiometer (MWR) has continuously measured the radiation emitted by Jupiter and the surrounding environment, over a frequency range from 0.6 to 22 GHz, from Juno's ... [more ▼]

Since August 2016, the Juno MicroWave Radiometer (MWR) has continuously measured the radiation emitted by Jupiter and the surrounding environment, over a frequency range from 0.6 to 22 GHz, from Juno's highly elliptical 53-day polar orbit about Jupiter. The contributors to the strongest radio signals at the shorter frequencies are the thermal, cosmic microwave background, and synchrotron emission produced by the inner electron belt. Weaker but perceptible signatures in MWR are also reported at the shortest frequency during perijove 1 (PJ1) and PJ3-PJ11. Some of them are identified as a source of synchrotron emission produced by downward field-aligned MeV electrons in the middle magnetosphere. In this paper, we present a synthesis of the spatial distributions of the microwave radiation observed at six wavelengths. We focus on synchrotron emissions originating from regions beyond Io's plasma torus that we believe to be linked to auroral activity. To support our findings, we discuss the results of a multi-instrument analysis of radio (MWR, WAVES), field (Juno magnetometer), extreme and far-ultraviolet auroral emission (Juno/UVS), plasma and energetic electron (JADE, JEDI) datasets, and background radiation signatures in Juno's ASC instrument for PJ1. Our data analysis raises the question how electrons with energies of 10's of MeV are populating, transported, and accelerated within the middle magnetosphere to become part of the auroral current circuit at Jupiter. [less ▲]

Detailed reference viewed: 18 (1 ULiège)
See detailJuno-UVS observations of Jupiter's aurora and airglow emissions
Gladstone, R.; Mura, A.; Kurth, W. et al

in 42nd COSPAR Scientific Assembly (2018, July)

The Ultraviolet Spectrograph (UVS) on Juno observes Jupiter's northern and southern auroras for several hours each during every perijove pass. On each pass the 7°-long slit of UVS is used to observe the ... [more ▼]

The Ultraviolet Spectrograph (UVS) on Juno observes Jupiter's northern and southern auroras for several hours each during every perijove pass. On each pass the 7°-long slit of UVS is used to observe the jovian aurora in a series of swaths, with one swath for each 30-s spin of the Juno spacecraft. During these perijove periods, the range of Juno to the aurora drops from ˜6 R_J to ˜0.3 R_J (or less) in the north - and then reverses this in the south - so that spatial resolution and coverage change dramatically. A scan mirror points the UVS boresight at up to 30° from the Juno spin plane to enable targeting of different features or to build up context images by rastering over the auroral region. In addition, during the time period between observations of the northern and southern auroral regions, low-latitude airglow observations are possible. Since Juno perijove altitudes are only 3500-8000 km above the cloud tops, UVS is able to study Jupiter's airglow from within Jupiter's upper atmosphere. A variety of auroral forms and activity levels can be identified in the Juno-UVS data; some of these have been described before with HST observations, but others are new. One new result is that a large expanse of polar emissions may be excited by low-energy ionospheric electrons (and thus would be unrelated to precipitating particles). Recent results and comparisons with simultaneous Chandra observations at x-ray wavelengths will be presented here. In addition, we will also report on UVS airglow observations to date, with special attention to the Lyα emissions of atomic hydrogen. [less ▲]

Detailed reference viewed: 19 (2 ULiège)
See detailExploring Jupiter's Aurorae with the Chandra and XMM-Newton X-ray Observatories
Dunn, W.; Ray, L.; Kraft, R. et al

in 42nd COSPAR Scientific Assembly (2018, July)

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These ... [more ▼]

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These highly energetic emissions exhibit pulsations over timescales of 10s of minutes and change morphology, intensity and precipitating particle populations from observation to observation and pole to pole [e.g. Dunn et al. 2017]. Surrounding the soft X-ray emission there is an oval of hard X-ray bremsstrahlung from precipitating electrons. The acceleration process/es that allow Jupiter to produce these high-energy X-ray emissions remain poorly understood, but vary with solar wind conditions [Dunn et al. 2016; Kimura et al. 2016] and the soft X-ray emissions are expected to relate to processes on the boundary between Jupiter's magnetosphere and the solar wind.We present a decade of remote X-ray observations of Jupiter from 2007 to 2017 using the Earth-orbiting X-ray telescopes Chandra and XMM-Newton. We compare these high spatial and spectral resolution X-ray data with in-situ measurements of the solar wind and the Jovian magnetosphere conducted by NASA's New Horizons and Juno spacecraft. Analysing X-ray spectrograms and X-ray auroral videos we probe time-varying accelerations, precipitating particle populations and auroral morphologies and further connect these with their solar wind and in-situ drivers. Finally, we compare X-ray observations with UV observations to enrich multi-waveband connections and deepen our understanding of how Jupiter generates its highly energetic polar auroral precipitations. [less ▲]

Detailed reference viewed: 19 (3 ULiège)
See detailJuno's Investigation of Jupiter's Magnetosphere
Clark, G.; Gurnett, D.; Haggerty, D. et al

in 42nd COSPAR Scientific Assembly (2018, July)

Since its arrival in July of 2016, NASA's Juno spacecraft continues to return invaluable observations regarding Jupiter's dynamic magnetosphere. The polar orbiting spacecraft has an orbital period of 53.5 ... [more ▼]

Since its arrival in July of 2016, NASA's Juno spacecraft continues to return invaluable observations regarding Jupiter's dynamic magnetosphere. The polar orbiting spacecraft has an orbital period of 53.5 days, which takes it from just a few thousand kilometers above Jupiter's one-bar "surface" outward to over 100 jovian radii - cutting through Jupiter's polar region as well as its equatorial region. Although these regions are inherently coupled, in this talk we compartmentalize Juno's observations into the auroral and magnetospheric regions and briefly discuss their connections. One of Juno's primary science goals is to investigate the nature of Jupiter's aurora - the most powerful aurora in the solar system. Outfitted on the spacecraft are a suite of instruments dedicated to measuring the in situ plasma waves and magnetic fields, charged particles as well as remote sensing the ultraviolet and infrared signatures of the aurora. In concert, these observations have and continue to paint a fundamentally different view of the mechanisms producing the Jovian auroras. Juno's instruments are also sending back new and compelling observations of Jupiter's magnetospheric regions. Examples include: the discovery of a belt of heavy ions residing inside the main ring, new details regarding the magnetopause structure and dynamics, and a more comprehensive survey of the plasma sheet particle populations and dynamics. In this presentation we will briefly summarize some of the major findings from both the auroral and magnetospheric regions and discuss new mysteries and future anticipated observations from Juno. [less ▲]

Detailed reference viewed: 22 (1 ULiège)
See detailJuno Observations Connected to the Io Footprint Tail Aurora
Szalay, J. R.; Bonfond, Bertrand ULiege; Allegrini, F. et al

Conference (2018, July)

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10 ̊ to 120 ̊ along ... [more ▼]

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10 ̊ to 120 ̊ along the footprint tail. Juno’s suite of magnetospheric instruments allow for detailed measurements of a variety of physical parameters for the Io footprint tail. Juno observed planetward electron energy fluxes of ~70 mW/m2 near the Io footprint, and ~10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased down the tail. All observed electron distributions were broad in energy, possibly suggesting an Alfvénic acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Here, we discuss the JADE, UVS, Waves, and Magnetic field measurements taken during Juno’s transits through the Io footprint tail flux tubes during perijoves 5-7 and compare these measurements with existing theoretical models describing the tail formation. [less ▲]

Detailed reference viewed: 30 (1 ULiège)
See detailGemini-TEXES mid-infrared spectral observations of Jupiter's auroral regions: comparison with ultraviolet and near-infrared observations
Sinclair, J. A.; Orton, G. S.; Greathouse, T. K. et al

Conference (2018, July)

Jupiter exhibits auroral emission over a large range of wavelengths. Auroral emission at X-ray, ultraviolet and near-infrared wavelengths demonstrate the precipitation of ion and electrons in Jupiter’s ... [more ▼]

Jupiter exhibits auroral emission over a large range of wavelengths. Auroral emission at X-ray, ultraviolet and near-infrared wavelengths demonstrate the precipitation of ion and electrons in Jupiter’s upper atmosphere, at altitudes exceeding 350 km above the 1-bar level. Enhanced mid-infrared emission of stratospheric CH4, C2H2, C2H4 and further hydrocarbons is also observed coincident with Jupiter’s auroral regions. On March 17-19th 2017, we obtained spectral measurements of H2 S(1), CH4, C2H2, C2H4 and C2H6 emission of Jupiter’s high latitudes using TEXES on Gemini-North. This rare opportunity combines both the superior spectral resolving power of TEXES (R ≤ 85000) and the high-spatial diffraction-limited resolution (~2° latitude-longitude footprint at 70°N) provided by Gemini-North’s 8-metre primary aperture. The high spatial resolution has for the first time revealed transient spatial structure in the emission of CH4, C2H2 and C2H4 in Jupiter’s northern auroral region. From March 17th to 19th 2017, during a solar wind compression, a duskside brightening of these species was observed in the northern auroral region. We will present a retrieval analysis of these observations to demonstrate the altitudes in the atmosphere and the magnitude over which temperatures and hydrocarbon abundances were modified during this event. We will also compare the morphology of the mid-infrared emission with near-simultaneous (i) HST-STIS images of the ultraviolet auroral emission and (ii) IRTF-SpeX observations of the 3.42-μ m H3+ emission. [less ▲]

Detailed reference viewed: 22 (1 ULiège)
See detailGoings-on in Jupiter's auroras: Periodic emission within Jupiter’s main auroral oval and short timescale variations in the motion of the Ganymede footprpint
Nichols; Bonfond, Bertrand ULiege; Bunce, E. J. et al

Conference (2018, July)

In this presentation we discuss some results from a programme of Hubble Space Telescope observations of Jupiter’s FUV auroras obtained during 2016. In particular, we have discovered pulsating emission ... [more ▼]

In this presentation we discuss some results from a programme of Hubble Space Telescope observations of Jupiter’s FUV auroras obtained during 2016. In particular, we have discovered pulsating emission within Jupiter’s main auroral oval, providing evidence of the auroral signature of Jovian ULF wave processes. The form comprises a 1° × 2° spot located directly on the main emission, whose intensity oscillates with a period of ~10 min throughout the 45 min observation. The feature appears on the duskward edge of the discontinuity, maps to ~13– 14 h LT and ~20– 50 RJ, and rotates at around a half of rigid corotation. We show that the period of the oscillation is similar to the expected Alfvén travel time between the ionosphere and the upper edge of the equatorial plasma sheet in the middle magnetosphere, and we thus suggest that the pulsating aurora is driven by a mode confined to the low-density region outside the plasma sheet. We also discuss the discovery of short (10 min) timescale variations in the location of the Ganymede auroral footprint, which possibly indicate changes in the ambient plasma density near Ganymede. [less ▲]

Detailed reference viewed: 24 (1 ULiège)
See detailAuroral acceleration at Jupiter and its possible role in creating Jupiter’s uniquely energetic radiation belts
Mauk, B. H.; Haggerty, D. K.; Paranicas, C. P. et al

Conference (2018, July)

The electron acceleration processes that generate Jupiter’s uniquely powerful aurora are unexpectedly diverse. Broadband acceleration, likely stochastic, provides the greatest downward electron energy ... [more ▼]

The electron acceleration processes that generate Jupiter’s uniquely powerful aurora are unexpectedly diverse. Broadband acceleration, likely stochastic, provides the greatest downward electron energy fluxes over Jupiter’s main auroral regions. But electric potentials along the main auroral field lines are sometimes present, at times exceeding 400 kV in either the upward or downward directions. Huge downward electron energy fluxes are unexpectedly observed on the very same field lines where huge electric potentials are also accelerating downward energy beams of protons. Using the magnetic field-aligned potential directionality as a proxy for the directionality of magnetic field-aligned electric currents, the magnitude of the downward electron energy fluxes surprisingly does not seem to care about the directionality of the electric currents. But the directionality of the electric potentials does seem to play a role in determining the character of the broadband acceleration processes and particularly in the up-down asymmetries in the acceleration processes. Surprisingly, even over very intense UV aurora, the upward acceleration of electrons can be comparable and even greater than the downward acceleration. And more surprising still, the intensity of the upwardly accelerated electrons at MeV energies can be as much as 2 orders of magnitude greater than the intensity of Jupiter’s radiation belts. Based on that finding, we explore here the possibility that, at Jupiter, auroral acceleration represents the first acceleration step in the generation of Jupiter’s uniquely energetic radiation belts. [less ▲]

Detailed reference viewed: 28 (2 ULiège)
See detailStereoscopic observations of Jovian decametric radio arc s associated with ultraviolet auroras
Imai, Masafumi; Kurth, W.S.; Bonfond, Bertrand ULiege et al

Conference (2018, July)

Auroras in Jupiter’s polar regions show complex activity over a broad range of electromagnetic wavelengths. One of the auroral radio components, decametric radiation (DAM), dominates the frequency range ... [more ▼]

Auroras in Jupiter’s polar regions show complex activity over a broad range of electromagnetic wavelengths. One of the auroral radio components, decametric radiation (DAM), dominates the frequency range from a few to 40 MHz and is produced at a frequency very close to the local electron cyclotron frequency. Since Juno first began detecting sporadic DAM arcs on May 5, 2016, during the approach to Jupiter, the DAM radio arcs have been monitored in a frequency range of 3.5 to 40.5 MHz by several observatories. These include Juno at Jupiter, Cassini at Saturn, STEREO A at 1 AU, WIND at Earth, and Earth-based radio observatories (Long Wavelength Array Station One (LWA1) in New Mexico, USA, and Nançay Decameter Array (NDA) in France). We have carried out a visual survey of the spectral data to identify concurrent DAM radio arcs, from May 5, 2016, through September, 2017 (Cassini’s end-of-mission). We found six events for which two or more observers clearly captured the same group of arcs. In one of the events on December 3, 2016, Juno first captured a group of the DAM arcs around 4:00 UT and two intense arcs were later recorded in NDA spectrograms at 6:30 and 7:45 UT. On the same day from 13:44 to 14:24 UT, the Hubble Space Telescope (HST) observed a bright auroral arc at ultraviolet wavelengths with an emitted power of 20 to 25 GW, suggesting a possible link to the concurrently observed DAM arcs. In this paper, we show results from the stereoscopic DAM radio observations and compare with the ultraviolet auroras captured by HST. [less ▲]

Detailed reference viewed: 20 (1 ULiège)
See detailCombined Juno observations and modeling of the Jovian auroral electron interaction with the Jovian upper atmosphere
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Gladstone, G.R. et al

Poster (2018, July)

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s ... [more ▼]

The Juno mission provides a unique opportunity during each perijove pass to sample the downward electron flux at spacecraft altitude while observing far ultraviolet H2 and infrared H3+ emissions at Juno’s magnetic footprint. In addition, the ratio of the H2 spectral band absorbed by hydrocarbons to the unabsorbed portion of the spectrum (FUV color ratio) is often used as a proxy for the depth of the penetration of energetic electrons (relative to the hydrocarbon homopause). The relationship between the color ratio and the electron penetration has been simulated with a Monte Carlo model solving the Boltzmann transport equation. Analysis of concurrent FUV and IR images obtained during the first perijove (PJ1) suggests that the ratio of H3+ radiance to H2 unabsorbed emission is maximal in regions with low FUV color ratio. This result suggests that part of the H3+ column is lost in reactions with methane which converts H3+ into heavier ions. We also examine the observed relationship between the detailed morphology of the ultraviolet structures and of the associated UV color ratio, the total downward electron energy flux and its spectral characteristics. [less ▲]

Detailed reference viewed: 20 (2 ULiège)
See detailJuno Observations of Plasma Waves Associated with the Io Footprint Tail
Hospodarsky, G.B.; Kurth, W. S.; Elliott, S.S. et al

Conference (2018, July)

The Juno spacecraft has crossed magnetic flux tubes associated with the Io auroral footprint tail at a variety of downtail distances from the Io footprint spot. The Juno radio and plasma wave instrument ... [more ▼]

The Juno spacecraft has crossed magnetic flux tubes associated with the Io auroral footprint tail at a variety of downtail distances from the Io footprint spot. The Juno radio and plasma wave instrument (Waves) detects large amplitude electromagnetic waves during many of these crossings. These emissions are usually detected for just a few seconds to tens of seconds and high resolution Wave burst data show that peak amplitudes of these waves can reach about 1 V/m for the electric field and a few nT for the magnetic field. However, on the recent perijove 12 northern crossing, the Waves instrument detected an intense funnel shaped emission lasting for many minutes with intense lower frequency emission at the funnel apex. Initial analysis of these emissions suggest that these waves are propagating upward from Jupiter. The emission frequencies are well below the electron cyclotron frequency and the upper frequency appears to be cutoff at the electron plasma frequency, with an additional change in intensity also observed at the proton cyclotron frequency. We will discuss the details of these waves and examine possible wave modes. [less ▲]

Detailed reference viewed: 18 (1 ULiège)