Publications of Bertrand Bonfond
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See detailReconnection- and Dipolarization-Driven Auroral Dawn Storms and Injections
Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege; Clark, G. et al

in Journal of Geophysical Research: Space Physics (2020), 125(8),

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the ... [more ▼]

Jupiter displays many distinct auroral structures, among which auroral dawn storms and auroral injections are often observed contemporaneously. However, it is unclear if the contemporaneous nature of the observations is a coincidence or part of an underlying physical connection. We show six clear examples from a recent Hubble Space Telescope campaign (GO-14634) that each display both auroral dawn storms and auroral injection signatures. We found that these conjugate phenomena could exist during intervals of either relatively low or high auroral activity, as evidenced by the varied levels of total auroral power. In situ observations of the magnetosphere by Juno show a strong magnetic reconnection event inside of 45 Jupiter radii (RJ) on the predawn sector, followed by two dipolarization events within the following 2 hr, coincident with the auroral dawn storm and auroral injection event. We therefore suggest that the auroral dawn storm is the manifestation of magnetic reconnection in the dawnside magnetosphere. The dipolarization region is mapped to the auroral injection, strongly suggesting that this was associated with the auroral injection. Since magnetic reconnection and dipolarization are physically connected, we therefore suggest that the often-conjugate auroral dawn storm and auroral injection events are also physically connected consequences. ©2020. The Authors. [less ▲]

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See detailA New Framework to Explain Changes in Io's Footprint Tail Electron Fluxes
Szalay, J. R.; Allegrini, F.; Bagenal, F. et al

in Geophysical Research Letters (2020), 47(18), 2020089267

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). The strength of precipitating electron fluxes is ... [more ▼]

We analyze precipitating electron fluxes connected to 18 crossings of Io's footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). The strength of precipitating electron fluxes is dominantly organized by “Io-Alfvén tail distance,” the angle along Io's orbit between Io and an Alfvén wave trajectory connected to the tail aurora. These fluxes best fit an exponential as a function of down-tail extent with an e-folding distance of 21°. The acceleration region altitude likely increases down-tail, and the majority of parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. We do not find a correlation between the tail fluxes and the power of the initial Alfvén wave launched from Io. Finally, Juno has likely transited Io's Main Alfvén Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes 600 mW/m2 and an acceleration region extending as low as 0.4 RJ in altitude. [less ▲]

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See detailEnergy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission
Allegrini, Frédéric A.; Mauk, Barry H.; Clark, George B. et al

in Journal of Geophysical Research: Space Physics (2020), 125(4), 2019027693

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the ... [more ▼]

Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies ( 100 eV to 1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (\textless10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of 51. A refined current sheet model will likely bring this boundary closer to the expected 20–30 RJ. Outside that region, the \textgreater100-keV electrons contribute to most (\textgreater 70–80\%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model. [less ▲]

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See detailEnergetic Particles and Acceleration Regions Over Jupiter's Polar Cap and Main Aurora: A Broad Overview
Mauk, Barry H.; Clark, George B.; Gladstone, G. Randall et al

in Journal of Geophysical Research: Space Physics (2020), 125(3), 2019027699

Previous Juno mission event studies revealed powerful electron and ion acceleration, to 100s of kiloelectron volts and higher, at low altitudes over Jupiter's main aurora and polar cap (PC; poleward of ... [more ▼]

Previous Juno mission event studies revealed powerful electron and ion acceleration, to 100s of kiloelectron volts and higher, at low altitudes over Jupiter's main aurora and polar cap (PC; poleward of the main aurora). Here we examine 30–1200 keV JEDI-instrument particle data from the first 16 Juno orbits to determine how common, persistent, repeatable, and ordered these processes are. For the PC regions, we find (1) upward electron angle beams, sometimes extending to megaelectron volt energies, are persistently present in essentially all portions of the polar cap but are generated by two distinct and spatially separable processes. (2) Particle evidence for megavolt downward electrostatic potentials are observable for 80 of the polar cap crossings and over substantial fractions of the PC area. For the main aurora, with the orbit favoring the duskside, we find that (1) three distinct zones are observed that are generally arranged from lower to higher latitudes but sometimes mixed. They are designated here as the diffuse aurora (DifA), Zone-I (ZI(D)) showing primarily downward electron acceleration, and Zone-II (ZII(B)) showing bidirectional acceleration with the upward intensities often greater than downward intensities. (2) ZI(D) and ZII(B) sometimes (but not always) contain, respectively, downward electron inverted Vs and downward proton inverted Vs, (potentials up to 400 kV) but, otherwise, have broadband distributions. (3) Surprisingly, both ZI(D) and ZII(B) can generate equally powerful auroral emissions. It is suggested but demonstrated for intense portions of only one auroral crossing, that ZI(D) and ZII(B) are associated, respectively, with upward and downward electric currents. [less ▲]

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See detailAlfvénic Acceleration Sustains Ganymede's Footprint Tail Aurora
Szalay, Jamey R.; Allegrini, Frederic; Bagenal, Fran et al

in Geophysical Research Letters (2020), 47(3), 2019086527

Integrating simultaneous in-situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvénic acceleration mechanisms are responsible for ... [more ▼]

Integrating simultaneous in-situ measurements of magnetic field fluctuations, precipitating electrons, and ultraviolet auroral emissions, we find that Alfvénic acceleration mechanisms are responsible for Ganymede's auroral footprint tail. Magnetic field perturbations exhibit enhanced Alfvénic activity with Poynting fluxes of 100 mW/m2. These perturbations are capable of accelerating the observed broadband electrons with precipitating fluxes of 11 mW/m2, such that Alfvénic power is transferred to electron acceleration with 10 efficiency. The UV emissions are consistent with in-situ electron measurements, indicating 13 ± 3 mW/m2 of precipitating electron flux. Juno crosses flux tubes with both upward and downward currents connected to the auroral tail exhibiting small-scale structure. We identify an upward electron conic in the downward current region, possibly due to acceleration by inertial Alfvén waves near the Jovian ionosphere. In concert with in-situ observations at Io's footprint tail, these results suggest that Alfvénic acceleration processes are universally applicable to magnetosphere-satellite interactions. [less ▲]

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See detailProton Acceleration by Io's Alfvénic Interaction
Szalay, J. R.; Bagenal, F.; Allegrini, F. et al

in Journal of Geophysical Research: Space Physics (2020), 125(1), 2019027314

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked ... [more ▼]

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvénic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfvén waves associated with Io's Main Alfvén Wing. The inferred high-latitude proton acceleration region spans 0.92.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfvén waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of 13 h, likely due to wave-particle interactions. The tail populations are split into a wake-like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti-Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfvén waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvénic interaction is bifurcated. [less ▲]

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See detailJovian dawn storms and terrestrial auroral substorms: similarities and differences
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, Randy et al

Conference (2019, September 18)

Juno's polar orbit allows us to contemplate a complete view of the Jovian aurorae for the first time. Here we mainly use observations from the ultraviolet spectrograph (Juno-UVS) in order to study one of ... [more ▼]

Juno's polar orbit allows us to contemplate a complete view of the Jovian aurorae for the first time. Here we mainly use observations from the ultraviolet spectrograph (Juno-UVS) in order to study one of the most spectacular features of Jupiter's aurorae: the dawn storms. Many of the properties of the dawn storms observed by Juno-UVS are similar to those of terrestrial substorms. [less ▲]

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See detailRecent Juno-UVS Observations of Jupiter's Auroras
Gladstone, Randy; Greathouse, Thomas; Versteeg, Maarten et al

Conference (2019, September 18)

Juno’s polar orbit provides excellent vantage pointsfor studying Jupiter’s bright and highly-variable far-ultraviolet (FUV) auroral emissions [1-3]. The Juno mission is a little over halfway through its ... [more ▼]

Juno’s polar orbit provides excellent vantage pointsfor studying Jupiter’s bright and highly-variable far-ultraviolet (FUV) auroral emissions [1-3]. The Juno mission is a little over halfway through its primary mission, and here we review some of the interesting results found so far by the Ultraviolet Spectrograph (UVS) instrument [4] during perijoves 1 and 3-21. [less ▲]

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See detailEnergy flux and characteristic energy of electrons over Jupiter's main auroral emission
Allegrini, Frederic; Mauk, Barry; Clark, George et al

Conference (2019, September 01)

Jupiter's powerful aurorae are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. These electrons are characterized over the ... [more ▼]

Jupiter's powerful aurorae are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. These electrons are characterized over the auroral regions by the Jovian Auroral Distributions Experiment (JADE) and the Jupiter Energetic particle Detector Instrument (JEDI) on Juno. Derived energy spectra and pitch angle distributions help us understand how these aurorae are created and powered. Corresponding ultraviolet emissions from reconstructed images taken by the Ultraviolet Spectrograph (UVS) on Juno give us the context and allow us to match the electron observations with their impact on the atmosphere. In this study, we show how the electron energy flux and characteristic energy vary from the polar region, over the main emission, and equatorward of the main emission in relationship with the UV emissions. We focus on the closest passes which range from 1.25 to 2 RJ. We find that while the >30 keV electrons dominate the energy flux in the polar regions and equatorward of the main emission, there is a region near the maximum UV brightness where: i) the characteristic energy decreases from more than 100 keV to less than 10 keV and ii) the maximum contribution to, or a significant fraction of, the total downward energy flux comes from <30 keV electrons. This pattern is present in all eight perijove passes for which JADE and JEDI have the best pitch angle coverage. <P /> [less ▲]

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See detailAre Dawn Storms Jupiter's auroral Substorms?
Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege; Gladstone, R. G. et al

Poster (2019, June)

There are multiple evidences that mass and energy rarely circulate smoothly in planetary magnetospheres. To the contrary, these systems tend to accumulate them until they fall out of balance through ... [more ▼]

There are multiple evidences that mass and energy rarely circulate smoothly in planetary magnetospheres. To the contrary, these systems tend to accumulate them until they fall out of balance through reconfiguration events. The source of mass and the source of energy can differ, as well as the trigger that initiates the collapse. However, despite some fundamental differences between the planets, the auroral signatures of the global reconfigurations bear many similarities that inform us on the common physical processes at play. For the first time, Juno has granted us a complete and global picture of one type of such reconfigurations, the auroral dawn storms, from their initiation to their vanishing. Juno actually captured views of dawn storms at different stages of development in approximately half of the cases. For example, on PJ11 and PJ16, Juno-UVS caught the brief appearence of small elongated spots located poleward of the main emission in the midnight sector. In both cases, a few hours later, the main emission began to brighten and broaden in the same sector. Then the main arc split into two parts, one moving towards the pole and the other moving equatorward. The whole feature also started to rotate towards the dawn sector, progressively accelerating to co-rotation. On PJ6, Juno-UVS observations missed the beginning of the event, but they allowed us to examine the next phase. After the broadening and the splitting of the main emission, the outer arc transformed unto large blobs. During the same time interval, subsequent Hubble Space Telescope images confirmed that the blobs kept on evolving, forming latitudinally extended fingers. All these auroral features resemble auroral morphologies observed at Earth during substorms. The Jovian elongated spots look like terrestrial poleward boundary intensifications (PBIs), the poleward motion of the arc indicates a dipolarisation/current disruption and the blobs in the outer emissions suggest massive plasma injections. [less ▲]

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See detailJupiter is alive! HST observations of Jupiter's aurora during Juno orbits 18, 19 and 20.
Grodent, Denis ULiege; Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege et al

Conference (2019, June)

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the ... [more ▼]

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the different components of Jupiter's UV aurora provide information on the evolution of the overall state of the portion of the Jovian magnetosphere to which they connect. During the present medium-size HST campaign (HST GO-15638, cycle 26), precession of the line of apsides of Juno's orbit makes it possible to probe different regions of the magnetosphere, compared to Juno orbits during previous HST cycles. Solar wind dynamics and internal processes are known to have strong influence on Jupiter's aurora, but their relative contributions and the way they couple with each other are still under debate. Cycle 26 falls during the expected minimum of the 11-year solar activity cycle. Current measurements suggest that the solar activity is already exceptionally low, with very few solar events, like CMEs, reaching Jupiter. This provides an unprecedented opportunity to observe Jupiter's aurora during a period when its magnetosphere is mainly controlled by internal processes, therefore revealing Jupiter's natural "breathing." The present HST campaign is meant to observe Jupiter's bright FUV auroral emissions in time-tag imaging mode during Juno orbits 18 to 22 (Feb-Sep 2019). We focus on the 5-day periods prior to and during Junos perijove, when Juno is sampling the current sheet region within 60 RJ, which is expected to contain the plasma source responsible for most bright auroral components, but is in a location where these aurorae cannot be observed with Juno-UVS. We sample Jupiter's emissions at a frequency of ~1 HST visit per Jovian rotation, with typically 10 HST visits for each of the 5 Juno orbits. Here we present preliminary results inferred from HST observations and concurrent Juno in situ data, obtained during Juno orbits 18, 19 and 20. [less ▲]

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See detailJupiter is alive!
 HST observations of Jupiter's aurora during Juno orbits 18, 19 and 20. (Invited)
Grodent, Denis ULiege; Yao, Zhonghua ULiege; Bonfond, Bertrand ULiege et al

Conference (2019, June)

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the ... [more ▼]

The terawatts of ever-changing ultraviolet auroral emissions that are always observed with HST at both poles of Jupiter demonstrate that Jupiter's planetary system is “alive.” The characteristics of the different components of Jupiter's UV aurora provide information on the evolution of the overall state of the portion of the Jovian magnetosphere to which they connect. During the present medium-size HST campaign (HST GO-15638, cycle 26), precession of the line of apsides of Juno's orbit makes it possible to probe different regions of the magnetosphere, compared to Juno orbits during previous HST cycles. Solar wind dynamics and internal processes are known to have strong influence on Jupiter's aurora, but their relative contributions and the way they couple with each other are still under debate. Cycle 26 falls during the expected minimum of the 11-year solar activity cycle. Current measurements suggest that the solar activity is already exceptionally low, with very few solar events, like CMEs, reaching Jupiter. This provides an unprecedented opportunity to observe Jupiter's aurora during a period when its magnetosphere is mainly controlled by internal processes, therefore revealing Jupiter's natural "breathing." The present HST campaign is meant to observe Jupiter's bright FUV auroral emissions in time-tag imaging mode during Juno orbits 18 to 22 (Feb-Sep 2019). We focus on the 5-day periods prior to and during Junos perijove, when Juno is sampling the current sheet region within 60 RJ, which is expected to contain the plasma source responsible for most bright auroral components, but is in a location where these aurorae cannot be observed with Juno-UVS. We sample Jupiter's emissions at a frequency of ~1 HST visit per Jovian rotation, with typically 10 HST visits for each of the 5 Juno orbits. Here we present preliminary results inferred from HST observations and concurrent Juno in situ data, obtained during Juno orbits 18, 19 and 20. [less ▲]

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See detailOn the relation between Jovian aurorae and the loading/unloading of the magnetic flux: simultaneous measurements from Juno, HST and Hisaki (Invited)
Yao, Zhonghua ULiege; Grodent, Denis ULiege; Kurth, W. S. et al

Conference (2019, June)

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in-situ measurements of magnetic field, particles and radio waves from the ... [more ▼]

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in-situ measurements of magnetic field, particles and radio waves from the Juno Spacecraft in the outer magnetosphere, from ~ 60 RJ to 80 RJ during March 17 to 22, 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which strongly correlate with electron energization and auroral intensifications. Magnetic reconnection events are identified during both the loading and unloading periods, indicating that reconnection and unloading are independent processes. The loading/unloading processes also correlate with MeV heavy ion fluxes, implying a potential role in Jovian X-ray emissions. [less ▲]

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See detailA brightening of Jupiter’s auroral 7.8-μm CH 4 emission during a solar-wind compression
Sinclair, J. A.; Orton, G. S.; Fernandes, J. et al

in Nature Astronomy (2019)

Enhanced mid-infrared emission from CH4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the ... [more ▼]

Enhanced mid-infrared emission from CH4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the neutral stratosphere of Jupiter are coupled; however, the exact nature of this coupling is unknown. Here we present a time series of Subaru-COMICS images of Jupiter measured at a wavelength of 7.80 μm on 11–14 January, 4–5 February and 17–20 May 2017. These data show that both the morphology and magnitude of the auroral CH 4 emission vary on daily timescales in relation to external solar-wind conditions. The southern auroral CH 4 emission increased in brightness temperature by about 3.8 K between 15:50 ut, 11 January and 12:57 ut, 12 January, during a predicted solar-wind compression. During the same compression, the northern auroral emission exhibited a duskside brightening, which mimics the morphology observed in the ultraviolet auroral emission during periods of enhanced solar-wind pressure 4,5 . These results suggest that changes in external solar-wind conditions perturb the Jovian magnetosphere in such a way that energetic particles are accelerated into the planet’s atmosphere, deposit their energy as deep as the neutral stratosphere, and modify the thermal structure, the abundance of CH 4 or the population of energy states of CH 4 . We also find that the northern and southern auroral CH 4 emission evolved independently between the January, February and May images, as has been observed at X-ray wavelengths over shorter timescales 6 and at mid-infrared wavelengths over longer timescales 7 . © 2019, The Author(s), under exclusive licence to Springer Nature Limited. [less ▲]

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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 ▲]

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See detailContemporaneous Observations of Jovian Energetic Auroral Electrons and Ultraviolet Emissions by the Juno Spacecraft
Gérard, Jean-Claude ULiege; Bonfond, Bertrand ULiege; Mauk, B. H. et al

in Journal of Geophysical Research: Space Physics (2019), 124(11), 8298--8317

We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ... [more ▼]

We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ultraviolet spectrograph (UVS) spectral imager H2 emission intensities at locations magnetically conjugate to the spacecraft using the JRM09 model. We use UVS images as close in time as possible to the electron measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) instrument. The upward electron flux generally exceeds the downward component and shows a broadband energy distribution. Auroral intensity is related to total precipitated electron flux and compared with the energy-integrated JEDI flux inside the loss cone. The far ultraviolet color ratio along the spacecraft footprint maps variations of the mean energy of the auroral electron precipitation. A wide diversity of situations has been observed. The intensity of the diffuse emission equatorward of the main oval is generally in fair agreement with the JEDI downward energy flux. The intensity of the ME matches exceeds or remains below the value expected from the JEDI electron energy flux. The polar emission may be more than an order of magnitude brighter than associated with the JEDI electron flux in association with high values of the color ratio. We tentatively explain these observations by the location of the electron energization region relative to Juno's orbit as it transits the auroral region. Current models predict that the extent and the altitude of electron acceleration along the magnetic field lines are consistent with this assumption. [less ▲]

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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 ▲]

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See detailElectron and ion particle acceleration regimes observed by Juno over Jupiter's main aurora
Mauk, Barry; Haggerty, Dennis; Paranicas, Chris et al

Conference (2018, September 01)

Over Jupiter's most intense main aurora, the Juno spacecraft has identified up to four different particle acceleration regimes at energies above 30 keV. Some of these regimes are very different than any ... [more ▼]

Over Jupiter's most intense main aurora, the Juno spacecraft has identified up to four different particle acceleration regimes at energies above 30 keV. Some of these regimes are very different than any of the particle acceleration regimes observed over Earth's auoras. We explore here the relationships between these different regimes and their similarities and differences to those at Earth. <P /> [less ▲]

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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 ▲]

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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 ▲]

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