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We present plasma observations from a previously unexplored wake region of Ganymede’s magnetosphere obtained by the Jovian Auroral Distributions Experiment (JADE) onboard the Juno spacecraft as it flew by Ganymede on June 7th, 2021. This region is highlighted by 1) plasma deflection well downstream of Ganymede's magnetopause, consistent with magnetic field perturbations, 2) plasma composition that is a mix of that in Jupiter’s adjacent plasma sheet or in Ganymede's magnetosphere, and 3) proton, heavy ion and electron distributions that are compressed compared to both adjacent regions. We derive ion and electron velocity distributions, pitch angles, temperatures, and densities inthis newly explored region of Ganymede’s magnetosphere.

Water-group gas continuously escapes from Jupiter’s icy moon Europa in both charged and neutral states. The neutral species form co-orbiting populations of particles, or neutral toroidal clouds, eventually becoming ionized to be incorporated into the Jovian plasma environment. In September 2022, Juno performed a close flyby at ~350 km, an altitude less than the satellite’s radius, allowing it to make direct observations of water-group pickup-ions originating from the moon’s surface. These observations, along with more remote measurements by Juno of Europa-genic water-group pickup ions, provide critical constraints on the evolution and loss processes of Europa’s icy surface. We will present direct observations of water-group pickup-ions from Europa in the context of understanding the breakdown and evolution of Europa’s surface ice.

On 7 June 2021 the Juno spacecraft passed through the Ganymede magnetosphere, with a closest approach altitude of 1046 km. While in the magnetosphere, the Jovian Auroral Distributions Experiment-Ion (JADE-I) sensor observed outflowing ionospheric ions. These are the first in situ observations of the ionospheric ion mass composition. The outflowing ions consist of O2+, O+, H2+, H+, and H3+. Ion densities estimated from the measurements agree with the electron density determined by the Waves instrument to within a factor of 2.5. The light ions appear to be in hydrostatic equilibrium, and the altitude profile is generally symmetric between the inbound and outbound legs of the flyby. H3+ ions are an exception to this, with the ratio of H3+/H2+ being ~a factor 4 lower on the outbound than the inbound leg. The heavy ions have higher densities outbound than inbound. The outflowing flux of light ions peak near closest approach, but the heavy ions peak outbound of the flyby.

During its 53-day polar orbit around Jupiter, Juno often crosses the boundaries of the Jovian magnetosphere, namely the magnetopause and bow shock, as well as the plasma disc (located at the centrifugal equator). The positions of the magnetopause and bow shock allow us to determine the dynamic pressure of the solar wind (using both the updated model of Joy et al. 2002 by Ranquist et al., 2020 and/or in situ data) which allows us to infer magnetospheric compression or relaxation, while the observations of plasma disc perturbations allows us to infer magnetospheric reconfigurations.The aim of this study is to examine Jovian radio emissions during magnetospheric perturbations. We then use our analysis to determine the relationship between the solar wind and Jovian radio emissions (observed and emitted from different regions of the magnetosphere, from different mechanisms, and at different wavelengths from kilometers to decameters).In this presentation, we show case studies for each typical case (bow shock, magnetopause and plasma disk crossings) and show that the activation of new radio sources is related to magnetospheric disturbances. By performing a statistical study of these crossings, we show the relationship between the activation of new radio sources (emission intensity and extension, source positions) and the solar wind (dynamic pressure, magnetic intensity, …). The final aim is to be able to use observations of planetary radio emission as a proxy for the solar wind conditions.

Jupiter’s plasma sheet is understood to be dominated by Io-genic material, mostly in various charge states of sulfur and oxygen. This material moves radially away from Jupiter, filling its magnetosphere. The material in the plasma sheet interacts with Europa and Ganymede, which are also sources of magnetospheric pickup ions, mostly in the form of both atomic and molecular hydrogen and oxygen. Juno’s plasma instrument JADE, the Jovian Auroral Distributions Experiment, has provided the first comprehensive in-situ observations of the composition of Jupiter’s plasma sheet with its Time-of-Flight mass-spectrometry capabilities. Here, we present observations of the magnetospheric composition in the Europa-Ganymede region of Jupiter’s magnetosphere. We highlight how Europa-genic material is often present and at times can be the dominant population for certain atomic masses, revealing a more complex and compositionally diverse magnetosphere than previously thought.

Water-group gas continuously escapes from Jupiter’s icy moons to form co-orbiting populations of particles, or neutral toroidal clouds. We report the first observations of H2+ pickup ions in Jupiter’s magnetosphere from 13-18 Jovian radii, confirming the presence of a neutral H2 toroidal cloud. Pickup ion densities are consistent with an advecting Europa-genic cloud source. As the observed H2+ ions are originally produced from H2 lost from Europa, the abundance of detected ions allows us to determine that ~1 kg/s of neutral H2 is lost from Europa. Hence, these observations presented here for the first time directly measure ions from a neutral H2 toroidal cloud at Jupiter, prove the cloud provides an additional plasma source in Jupiter’s magnetosphere, and provide the most direct constraints on Europa’s loss of neutral H2 via observations of the neutral toroidal cloud’s primary loss process – pickup ions.

Measurements by Juno as the spacecraft flew by Ganymede on June 7th of 2021 from the JADE instrument when combined with images from UVS of the aurora can be used to significantly advance our knowledge of the atmosphere and ionosphere. JADE measures the ion outflow composition that results from downgoing plasma electrons in the polar cap region and also measures the downward electrons associated with the reconnection at the boundary of Ganymede’s magnetosphere with the Jupiter magnetosphere. Modeling can help to check the consistency between the electron energy influx in the polar cap and the resulting ionospheric outflow and can also be used to set constraints on how reconnected electrons form the auroral atmosphere and the auroral emissions measured by UVS.

The velocity distribution functions (VDFs) of pickup He+ ions near a Coronal Mass Ejection (CME) are expected to be extremely variable due to the specific source particle distributions and the interactions with the shock passage, turbulence, and large scale magnetic structures. One of the most eminent examples is the shock injection process. Around interplanetary (IP) shocks, significant abundance enhancements of He+ pickup ions over He++ ions of solar wind origin (e.g., Chotoo et al., 2000) provided compelling evidence that the source population for the energetic particle population is not the solar wind itself, but rather the pickup ion population that contains more particles beyond the injection threshold due to the difference in VDF. However, due to the lack of high-resolution measurements of pickup ion’s energy and phase space densities, their kinetics are not well understood.In this study, VDFs of He+ pickup ions are investigated for a typical quasi-perpendicular shock observed in the heart of the helium focusing cone. In order to calculate the VDFs of helium ions, pulse height information from each ion event in the PLasma And SupraThermal Ion Compostion (PLASTIC) instrument (Galvin et al., 2008) on the Solar Terrestrial Relations Observatory (STEREO) was utilized. During each electrostatic analyzer energy-per-charge (E/q) step (128 steps, 435.6 ms each), PLASTIC stores 512 raw pulse height events including E/q, time-of-flight, total energy, and arrival direction. This allows us to reproduce partial 3-dimensional VDFs for various ion species with ~2° angular resolution (Taut et al., 2018). Moreover, the concentration of He+ ions in the helium focusing cone increased the count rate significantly, and provided enough counting statistics to achieve 10 min cadence.The IP shock that we focus on was driven by a coronal mass ejection producing a fast mode shock. Our study focuses on two regions: (1) VDFs within the CME sheath in the shock downstream, and (2) VDFs in the magnetic cloud. VDFs are analyzed in terms of particle heating/cooling, acceleration/deceleration, and pitch angle diffusion. The connectivity to the shock will also be investigated. In the far downstream region, correlation between the VDFs and the ambient magnetic field activities (the power spectra and the Alfvénic activity) are discussed in terms of how they modify the He+ pitch angle distributions.References:Chotoo, K., et al. (2000), The suprathermal seed population for corotating interaction region ions at 1 AU deduced from composition and spectra of H+, He++, and He+ observed on Wind, doi:10.1029/1998JA000015.Taut, A., et al. (2018), Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff, doi: 10.1051/0004-6361/201731796.Galvin, A.B., Kistler, L.M., Popecki, M.A. et al. The Plasma and Suprathermal Ion Composition (PLASTIC) Investigation on the STEREO Observatories. Space Sci Rev 136, 437–486 (2008). https://doi.org/10.1007/s11214-007-9296-x

Jupiter’s aurora is complex and dynamic, with a large number of distinct auroral features and regions generated by multiple phenomena. Of these features, Io’s auroral signature is one of the most persistent and identifiable aurora, with a rich observational history spanning decades of remote observations. Since Juno arrived at Jupiter, providing in-situ transits through flux tubes directly connected to Io’s auroral emissions, its diverse set of instruments have revealed an even more complex and dynamic picture of Io’s auroral interaction. In this presentation, we report on Juno observations of precipitating electron fluxes connected to 18 crossings of Io’s footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). We will highlight how 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. We will discuss how these fluxes were best fit with 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 most of the parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. Finally, we will highlight how 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.

The CubeSat Mission for studying Solar Particles is a NASA Science Mission Directorate and Heliophysics Division funded 6U Interplanetary CubeSat Science Mission. CuSP is scheduled to launch in mid-2020 as a secondary payload on the SLS EM -1 (Exploratory Mission One) flight. CuSP is a pathfinder mission for Space Weather Research as it will be the first heliophysics science mission to be placed in heliocentric orbit outside the influence of the Earth's magnetosphere. CuSP features three complementary, miniaturized sensors to address two science objectives: study the sources and acceleration mechanisms of solar and IP particles in near-Earth orbit, and support space weather research by determining proton radiation levels during SEP events and identifying properties of ST ions that could help predict the arrival of strong CME-driven IP shock waves that produce geomagnetic storms.

Using 30 inbound passes through the Jovian system, we combine measurements from the fields and particles instruments on the Juno spacecraft to survey the properties of Jupiter's plasma disk. Juno's orbit is particularly useful for exploring the variation in plasma conditions with latitude as well as radial distance (from ~10 to ~50 RJ). We present basic plasma properties (composition, density, temperature, velocity, magnetic field strength) to make maps of the plasma environment. Also show that on some of the 53-day orbits the plasma sheet has regular structure (density having roughly Gaussian distribution with latitude and decreasing with distance) but there are also highly irregular orbits with low or erratic density distributions.

The ice giant planets provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields and wide-ranging Alfvénic and sonic Mach numbers on magnetospheric processes. The geometries of the solar wind–magnetosphere interaction at the ice giants vary dramatically on diurnal timescales due to the large tilt of the magnetic axis relative to each planet's rotational axis and the apparent off-centred nature of the magnetic field. There is also a seasonal effect on this interaction geometry due to the large obliquity of each planet (especially Uranus). Within situobservations at Uranus and Neptune limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize these unique magnetospheres and test hypotheses related to the magnetic structures and the distribution of plasma observed. Yet many questions regarding magnetospheric structure and dynamics, magnetospheric coupling to the ionosphere and atmosphere, and potential interactions with orbiting satellites remain unanswered. Continuing to study and explore ice giant magnetospheres is important for comparative planetology as they represent critical benchmarks on a broad spectrum of planetary magnetospheric interactions, and provide insight beyond the scope of our own Solar System with implications for exoplanet magnetospheres and magnetic reversals.This article is part of a discussion meeting issue ‘Future exploration of ice giant systems'.

In this presentation, we exploit the charge-dependent nature of field-aligned potentials in Jupiter’s polar cap auroral region to infer the charge states of energetic oxygen and sulfur. To-date, there are very limited and sparse measurements of the > 50 keV oxygen and sulfur charge states, yet many studies have demonstrated their importance in understanding the details of various physical processes, such as, X-ray aurora, ion-neutral interactions in Jupiter’s neutral cloud and particle acceleration theories. In this contribution, we develop a technique to determine the most abundant charge states associated with heavy ions in Jupiter’s polar magnetosphere. We find that O+ and S++ are the most abundant and therefore iogenic in origin. The results are important because they provide 1) strong evidence that soft X-ray sources are likely due to charge stripping of magnetospheric ions and; 2) a more complete spatial map of the oxygen and sulfur charge states, which is important for understanding how the charge- and mass-dependent physical processes sculpt the energetic particles throughout the Jovian magnetosphere.

On February 7th 2018, during Juno’s 11th perijove observation sequence, Juno’s ultraviolet spectrograph (Juno-UVS) unveiled the development of a dawn storm in Jupiter's aurorae. These auroral events consist of spectacular brightenings of the midnight to dawn sector of the main emissions at Jupiter. At the end of the sequence, Juno crossed the magnetic field lines connected to this dawn storm, unraveling some of the processes giving rise to these spectacular events. All in situ instruments detected a sharp transition as the spacecraft entered the dawn storm at an altitude of approximately 5RJ in the southern hemisphere. The particle fluxes detected by the JADE and JEDI instruments, including electrons and ions, increased dramatically. A strong flux of penetrating radiation was also detected by the UVS instrument. The Alfvén waves spectrograms derived from the MAG instrument also show a clear transition between a quiet and an extremely active regime as the spacecraft entered the dawn storm. Furthermore, the orientation of the magnetic field showed a very strong perturbation, associated with intense currents. And, finally, intense bKOM emissions were also observed during this time interval. Combined with the remote sensing observations of the aurora, these datasets strongly suggest that Juno witnessed a strong magnetospheric reconfiguration that started in the magneto-tail and then evolved toward dawn as the planet rotated.

Jupiter’s UV and X-ray aurorae were first discovered in 1979 by Voyager 1 and the Einstein Observatory, respectively. The auroral morphology comprises an oval ring of UV and high energy, or “hard”, X-rays and both emissions are produced by the same population of energetic electrons (Branduardi-Raymont et al., 2008). As the electrons precipitate into the gas giant’s atmosphere, they can excite molecular and atomic hydrogen that will then release UV photons while returning back to the ground state. The electrons can also emit bremsstrahlung radiation in the X-ray waveband as they are slowed and deflected by the molecules in the atmosphere. Within this oval is a second source of X-ray emissions with lower energies, as well as diffuse UV emissions. These “soft” X-rays are the result of ions charge exchanging with neutrals in Jupiter’s atmosphere. Observational and theoretical studies seem to favour an iogenic origin for these ions (e.g. Wibisono et al., 2020; Cravens et al., 1995), however, there are instances where the spectrum is better fit by the inclusion of solar wind ions (Dunn et al., 2020). The ion emissions also often pulse with periods of tens of minutes (e.g. Gladstone et al., 2002; Jackman et al., 2018). The aurora in both wavebands is responsive to changing conditions inside and outside of Jupiter’s magnetosphere (Grodent et al., 2018). For example, the dawnside main emission of the UV aurora is dim and thin when the magnetosphere is undisturbed and contains very little plasma. The appearance of dawn storms, or short-lived brightenings in the dawnside main oval emission, is associated with tail reconnection events (Yao et al., in review) and is usually accompanied by a distinct enhancement equatorward of the main emission towards the dusk sector. This feature is caused by strong injections of magnetospheric plasma (Mauk et al. 2002). A solar wind compression results in a very bright and defined main oval in the dawn sector and bright poleward emissions in the dusk sector. Previous studies have shown that the X-ray aurora brightens during solar wind compressions but it can also do so during intervals of quiet solar wind, possibly suggesting control by sources internal to the magnetosphere (Dunn et al., 2020). However, signatures in the X-rays that point to mass loading and injection events having happened have not yet been identified. Juno’s 22nd perijove on 12 September 2019 was supported by remote observations of Jupiter from XMM-Newton, Chandra, the Hubble Space Telescope and Hisaki. XMM-Newton undertook an unprecedented 405 ks-long campaign between 8 and 14 September 2019 and recorded the X-ray aurora changing its behaviour throughout this time (see Figures 1-3). The spacecraft made 3 orbits around the Earth during this time hence why there are 3 sets of spectra and lightcurves and the gaps in the lightcurves are due to XMM-Newton perigee passages. Images of the UV aurora from Hubble show dawn storms and injection events at least twice during those six days. Hisaki data also show that the Io Plasma Torus and EUV aurora were responding to internally driven processes around this time. Juno’s location at local midnight allowed it the perfect opportunity to confirm whether tail reconnection had happened and detect plasmoids that may have been shot back towards Jupiter. We present our findings of how these mass loading and magnetospheric plasma injection events leave their marks on the timing and spectral properties of the X-ray aurora. Figure 1: XMM-Newton EPIC-pn spectra (crosses on panel A) and EPIC light travel time shifted lightcurves (panel C) of Jupiter’s X-ray aurora from 8-10 September 2019. The spectrum is best fitted with an atomic charge exchange model for an iogenic (sulphur and oxygen) plasma population and a power law continuum. Panel B shows the theoretical spectra of the models used which were then convolved with the instrument response to give the black lines that are plotted over the data in panel A. The aurora is very bright during the first XMM-Newton orbit with a high flux above 1 keV in the spectrum and the corresponding lightcurve shows some regular pulsations. Figure 2: Same format as Figure 1 but for 10-12 September 2019. There is an increased amount of soft X-ray emissions in the second orbit with very dim hard X-ray emissions. Bright flares were emitted at ~02:00 and ~22:00 UT on 11 September and strong quasi-periodic pulsations in the aurora occurred during much of this orbit. Figure 3: Same format as Figure 1 but for 12-14 September 2019. The spectrum for the final orbit now illustrates a decreased amount of soft X-ray emissions and brightened hard X-ray emissions; the lightcurve shows that the aurora had stopped pulsating. References Branduardi‐Raymont, G. et al. (2008), Spectral morphology of the X‐ray emission from Jupiter's aurorae, J. Geophys. Res., 113, A02202, doi:10.1029/2007JA012600 Cravens, T.E. et al. (1995), Auroral oxygen precipitation at Jupiter, J. Geophys. Res., 100 (A9), 17153– 17161. doi:10.1029/95JA00970. Dunn, W.R. et al. (2020). Comparisons between Jupiter's X‐ray, UV and radio emissions and in‐situ solar wind measurements during 2007. Journal of Geophysical Research: Space Physics, 125, e2019JA027222. https://doi.org/10.1029/2019JA027222 Gladstone, G.R. et al. (2002). A pulsating auroral X-ray hot spot on Jupiter. Nature, 415, 1000–1003. https://doi.org/10.1038/4151000a Grodent, D. et al. (2018). Jupiter's aurora observed with HST during Juno orbits 3 to 7. Journal of Geophysical Research: Space Physics, 123, 3299– 3319. https://doi.org/10.1002/2017JA025046 Jackman, C.M. et al. (2018). Assessing quasi‐periodicities in Jovian X‐ray emissions: Techniques and heritage survey. Journal of Geophysical Research: Space Physics, 123, 9204– 9221. https://doi.org/10.1029/2018JA025490 Mauk, B.H. et al. (2002). Transient aurora on Jupiter from injections of magnetospheric electrons. Nature, 415, 1003-1005. https://doi.org/10.1038/4151003a Wibisono, A.D. et al. (2020). Temporal and spectral studies by XMM‐Newton of Jupiter's X‐ray auroras during a compression event. Journal of Geophysical Research: Space Physics, 125, e2019JA027676. https://doi.org/10.1029/2019JA027676 Yao, Z.H. et al. (in review). Reconnection and Dipolarization Driven Auroral Dawn Storms and Injections, J. Geophys. Res. Space Physics

Jupiter’s unique x-ray aurora is driven by the same processes as Earth’s: Heavy ion scattering by electromagnetic waves., Jupiter’s rapidly rotating, strong magnetic field provides a natural laboratory that is key to understanding the dynamics of high-energy plasmas. Spectacular auroral x-ray flares are diagnostic of the most energetic processes governing magnetospheres but seemingly unique to Jupiter. Since their discovery 40 years ago, the processes that produce Jupiter’s x-ray flares have remained unknown. Here, we report simultaneous in situ satellite and space-based telescope observations that reveal the processes that produce Jupiter’s x-ray flares, showing surprising similarities to terrestrial ion aurora. Planetary-scale electromagnetic waves are observed to modulate electromagnetic ion cyclotron waves, periodically causing heavy ions to precipitate and produce Jupiter’s x-ray pulses. Our findings show that ion aurorae share common mechanisms across planetary systems, despite temporal, spatial, and energetic scales varying by orders of magnitude.

International audience; We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field lines connected to Europa's FPT. We find that electrons in the range ~0.4 to ~25 keV, with a characteristic energy of 3.6 ± 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at ~36 mW/m2, while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm-3 and 1.8 ± 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 ± 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> ~5-10 MeV electrons) increased during the Europa FPT crossing.

We compare Chandra and XMM-Newton X-ray observations of Jupiter during 2007 with a rich multi-instrument data set including upstream in situ solar wind measurements from the New Horizons spacecraft, radio emissions from the Nancay Decametric Array and Wind/Waves, and ultraviolet (UV) observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. Non-Io decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterize three types of X-ray aurorae: hard X-ray bremsstrahlung main emission, pulsed/flared soft X-ray emissions, and a newly identified dim flickering (varying on short time scales, but quasi-continuously present) aurora. For most observations, the X-ray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by iogenic plasma. However, the brightest X-ray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. X-ray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power > 1 TW) and X-ray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim, and UV main emission power was also lower (

We present Juno observations between 03:00 to 06:00 UT on day-of-year 86, 2017 that link electrons in Jupiter's polar magnetosphere to images of transient, enhanced UV emissions in Jupiter's dawn a...

International audience; 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 (J. Outside that region, the >100-keV electrons contribute to most (>~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.

Jupiter’s ultraviolet (UV) aurora, the most powerful and intense in the solar system, is caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Electrons from ~50 eV to ~100 keV are characterized over the auroral regions by the Jovian Auroral Distributions Experiment (JADE) on Juno. Investigating the characteristics of electron distributions at these energies is critical for understanding the source population for the electrons that produce Jupiter’s UV aurora and the mechanisms that accelerated them to keV and MeV energies. In this study, we present a survey of electron distributions and moments derived from JADE in Jupiter’s polar magnetosphere. We quantify the electron properties (e.g. density and temperature) and explore similarities and differences in their distributions over several Juno perijove passes, focusing on regions near the main emission.

The ion radiation belts just above the surface of the giant planets Jupiter and Saturn have recently been observed for the first time with Juno and Cassini. The relevant physical processes differ from Earth’s inner proton belt. Jupiter’s innermost ion belt consists of protons, oxygen, and sulfur ions. A comparison of Juno particle and plasma data with numerical modeling supports that these ions are occasionally transported from the magnetosphere across the main ring of Jupiter. It has been suggested earlier that this ring is populated through the stripping of energetic neutral atoms that are produced in the magnetosphere. This process is found to be too slow to populate the belt. After radial transport, the new ions lose energy in the tenuous ring halo inward of the main ring. This gives rise to an unusual spectral shape that rises from 100keV to 1MeV. Neutralization of the ions in the ring grains acts slower and eventually removes Saturn’s innermost belt differs from Jupiter’s and Earth’s inner belts in the sense that Saturn’s rings are too dense and extended to allow radial transport of magnetospheric ions into the innermost belt. Saturn’s ion belts are therefore thought to be exclusively populated by cosmic ray tertiary particles from the CRAND process. While the source is different, the losses are similar as at Jupiter, namely interaction with the tenuous D-ring and the planetary exosphere. This interaction shows in the proton pitch angle distribution and has been used to constrain the scale height of Saturn’s exosphere that is difficult to do otherwise.

This whitepaper identifies important science questions that can be answered through exploration of the Jupiter System, with emphasis on the questions that can be addressed by the Europa Clipper Mission. We advocate for adding Jupiter System Science to the mission after launch when expanding the scientific scope will not affect the development cost., Comment: White Paper submitted to the Astrobiology and Planetary Science Decadal Survey

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 degrees to 120 degrees 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 similar to 70mW/m(2) near the Io footprint and similar to 10mW/m(2) 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 broad 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 degrees down the footprint tail, Juno observed depleted upward loss cones, suggesting that the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7R(J). For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed independently with electron and wave measurements that a bifurcated tail can intermittently exist. Plain Language Summary The Juno spacecraft crossed regions magnetically connected to auroral structures associated with Jupiter's moon Io on multiple occasions. The transits covered longitudinal separations of approximately 10 degrees to 120 degrees along Io's auroral tail. Juno's suite of instruments acquired detailed measurements of these auroral structures. Juno directly observed the electrons that sustain these auroral features before they crash into the atmosphere and generate the brilliant aurora. The flux of these electrons decreased as Juno transited the tail farther from Io's longitude. While there are two main explanations for Io's auroral signatures, the nature of the observed electrons in this work favors one mechanism over the other. When Juno was far from Io's longitude, the observations suggest that the spacecraft was below the point at which the electrons are accelerated into the atmosphere. For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed that a bifurcated tail can intermittently exist.

Recent results of the first ever orbit through Jupiter's auroral region by NASA's Juno spacecraft did not show evidence of coherent acceleration in the auroral or polar region. However, in this letter, we show energetic particle data from Juno's Jupiter Energetic-particle Detector Instrument instrument during the third auroral pass that exhibits conclusive evidence of downward parallel electric fields in portions of Jupiter's polar region. The energetic particle distributions show inverted-V ion and electron structures in a downward electric current region with accelerated peaked distributions in hundreds of keV to ~1 MeV range. The origin of these large electric potential structures is investigated and discussed within the current theoretical framework of current-voltage relationships at both Earth and Jupiter. Parallel electric fields responsible for accelerating particles to maintain the aurora/magnetospheric circuit appear to be a common phenomenon among strongly magnetized planets with conducting ionospheres; however, their origin and generation mechanisms are subjects of ongoing research.

A Hot Flow Anomaly (HFA) is created when an interplanetary current sheet interacts with a planetary bow shock. Previous studies have reported observing HFAs at Earth, Mercury, Venus, Mars and Saturn. During Juno's approach to Jupiter, a number of its instruments operated in the solar wind. Prior to crossing into Jupiter's magnetosphere, Juno observed an HFA at Jupiter for the first time. This Jovian HFA shares most of the characteristics of HFAs seen at other planets. The notable exception is that the Jovian HFA is significantly larger than any HFA seen before. With an apparent size greater than 2 × 106 km the Jovian HFA is orders of magnitude larger than those seen at the other planets. By comparing the size of the HFAs at the other planets with the Jovian HFA, we conclude that HFAs size scales with the size of planetary bow shocks that the interplanetary current sheet interacts with.

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.