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The Jupiter Energetic Particle Detector Instrument (JEDI) on the Juno mission detects energetic electrons from the tens of keV to almost 1 MeV and energetic ions from the tens of keV to about 10 MeV or more. The population at higher energies, e.g., > 1 MeV electrons, while relatively small in number can add non-insignificant counts in the energy range JEDI is designed to detect as foreground. For example, a band is often seen in the electron spectrograms around 200 keV that is believed to be due to higher energy electrons that for various reasons only deposit a fraction of their energy in the detector. To apply a correction to this, Mauk et al. [JGR, 2018] have developed a procedure for correcting the JEDI-measured electron spectra contaminated with high-energy foreground electrons that penetrate the detector. Using this procedure, one can extract an energy spectrum from the tens of keV to 1 MeV that corrects for both penetrators and the loss of JEDI efficiency just below 1 MeV. The corrected spectra can also be extended above 1 MeV by making use of the penetrator counts, but uncertainties exist in creating a high-energy tail. In addition, JEDI proton data may also be contaminated with ions. To extract accurate electron spectra that extend to high energies and understand the response to penetrating protons, one would need to better understand the response of the detector to those high-energy electrons and protons. Characterization of energetic particles above 1 MeV can enable a study of energetic particles’ dynamics and structure as a function of latitude and L-shell and help evaluate different theories for loss and acceleration mechanisms. It is also a critical step in reducing uncertainties in the Jovian radiation models, assisting in understanding Juno data, and impacting future missions to Jupiter. A series of comprehensive and realistic Geant4 simulations have been performed to obtain the Geometric Factors (GFs) of JEDI as functions of the energy and the angles of incoming electrons and protons at a breadth that is not feasible through laboratory measurements. The results of the simulations are presented in this paper. The GFs are used to convert the count rate measurements to more physically meaningful particle flux spectra. Here, we also show the long-term trend of thus-obtained electron and proton spectra during Juno’s PJ 1 to 24.

Saturn’s kilometric radio (SKR) and energetic neutral atom (ENA) emissions are important remote diagnostics of the planet’s magnetospheric dynamics, intensifying during periods of global-scale plasma injection, and displaying characteristic planetary periodicity (e.g. Ye et al., 2011, Kinrade, Bader et al., 2021). Here we focus on the narrowband emissions between 5-40 kHz, thought to originate near density gradients at the edges of the plasma torus (e.g. Gurnett et al., 1981, Ye et al., 2009), and test the hypothesis that narrowband SKR production might be enhanced by inward-moving plasma following global injection events. Global scale ENA signatures have been associated with both 5 and 20 kHz nSKR emissions, particularly at dusk-evening local times (e.g. Wing et al., 2020, Wu et al., 2021) where plasma injections are expected to have moved inwards through the magnetosphere, possibly triggering interchange instabilities (e.g. Mitchell et al., 2015, Azari et al., 2018, Kinrade et al., 2020). Figure A: A calibrated and re-binned Cassini INCA image of Saturn’s equatorial ENA emission (24-55 keV Hydrogen, X-Y plane). This dataset and the open-source repository location are detailed in Bader & Kinrade, et al. (2020). We use a new set of calibrated equatorial ENA projections - captured by the Cassini INCA - to test the relationship between Saturn’s ENA and narrowband SKR emissions. The narrowband SKR emission intensity peak often coincides with the rotation of ENA enhancement through the dusk local time sector, complementing the findings of Wing et al. (2020). We test for radial distance dependence by constraining ENA keograms over a set of distances and local time sectors covering the edges of the plasma torus, and quantify the relative timing of nSKR enhancements through correlation of the ENA intensity with flux density in the 5 and 20-40 kHz emission bands. We also observe periods of strong 5 kHz SKR emission when the ENA emission is absent, even during times of favourable viewing, indicating that this relationship is complex (e.g. Wu et al., 2022). These results contribute towards our developing picture of how global plasma injection events can influence Saturn’s inner magnetosphere, linking together two valuable sources of remotely-sensed global emissions, the ENAs and SKR. Figure B: A re-working of the Wang et al. (2010) narrowband SKR example from 2007 (left-hand SKR polarisation shown in top panel), plus a keogram of the median ENA intensity between 1-20 RS (bottom panel). Some viewing artefacts remain here in this pre-published version of the ENA keogram (DOY 073 and 078), but the persistence of the rotating ENA enhancement over several days is clear. INCA projection / SKR viewing geometry are best on DOY 076 when Cassini was high above the north hemisphere ( > 50º latitude) at a range of ~ 30 RS. The bursts of narrowband SKR coincide with the ENA enhancement rotating through the dusk local time sector. This work is timely given the expected arrival of the JUICE mission at Jupiter in 2031, which carries an advanced ENA camera. ENA emissions have already been detected from Jupiter and the Io and Europa plasma torii by instruments onboard Cassini and JUNO (e.g. Mauk et al., 2003; 2020), and the arrival of JUICE will provide an opportunity to replicate this analysis, comparing the much-different Jovian ENA and associated radio emissions with those of Saturn’s neutral-dominated magnetosphere. References Azari et al. (2018), Interchange Injections at Saturn: Statistical Survey of Energetic H+Sudden Flux Intensifications, JGR Space Physics, https://doi.org/10.1029/ 2018JA025391. Bader, Kinrade et al. (2020), A complete dataset of equatorial projections of Saturn's energetic neutral atom emissions observed by Cassini-INCA, JGR Space Physics, https://doi.org/10.1029/2020JA028908. Gurnett et al. (1981), Narrowband electromagnetic emissions from Saturn's magnetosphere, Nature, https://www.nature.com/articles/292733a0. Kinrade et al. (2020), Tracking Counterpart Signatures in Saturn's Auroras and ENA Imagery During Large‐Scale Plasma Injection Events, JGR Space Physics, https://doi.org/10.1029/2019JA027542. Kinrade, Bader et al. (2021), The Statistical Morphology of Saturn’s Equatorial Energetic Neutral Atom Emission, Geophysical Research Letters, https://doi.org/10.1029/2020GL091595. Mauk et al. (2003), Energetic neutral atoms from a trans-Europa gas torus at Jupiter, Nature, https://www.nature.com/articles/nature01431. Mauk et al. (2020), Juno Energetic Neutral Atom (ENA) Remote Measurements of Magnetospheric Injection Dynamics in Jupiter's Io Torus Regions, JGR Space Physics, https://doi.org/10.1029/2020JA027964. Mitchell et al. (2015), ‘Injection, Interchange, and Reconnection: Energetic Particle Observations in Saturn’s Magnetosphere’ in Magnetotails in the Solar System, https://doi.org/10.1002/9781118842324.ch19. Wang et al. (2010), Cassini observations of narrowband radio emissions in Saturn's magnetosphere, JGR Space Physics, https://doi.org/10.1029/2009JA014847. Wing et al. (2020), Periodic Narrowband Radio Wave Emissions and Inward Plasma Transport at Saturn's Magnetosphere, The Astronomical Journal, https://doi.org/10.3847/1538-3881/ab818d. Wu et al. (2021), Statistical Study on Spatial Distribution and Polarization of Saturn Narrowband Emissions, The Astrophysical Journal, https://doi.org/10.3847/1538-4357/ac0af1. Wu et al., (2022), Reflection and Refraction of the L-O Mode 5 kHz Saturn Narrowband Emission by the Magnetosheath, Geophysical Research Letters, https://doi.org/10.1029/2021GL096990. Ye et al., (2009), Source locations of narrowband radio emissions detected at Saturn, JGR Space Physics, https://doi.org/10.1029/2008JA013855.

Pitch angle distribution of energetic particles can be used to understand the global topology of field lines (connected on both ends to the planet, connected on both ends to the moon or connected on one end to the moon and the other end to the planet etc.). The pitch angle distributions on field lines connected on one end to the moon can also be used to gauge the speed at which the field lines are convecting past a moon. The Galileo spacecraft flew by the Galilean moons multiple times and explored the charged particle distributions in their vicinities. In this paper we will revisit the data of the Energetic Particles Detector EPD onboard Galileo in terms of pitch angle distributions for various energy channels for different ion species and electrons in the energy range from 15 keV up to several tens of MeV. We analyzed the Europa flybys E11, E12, E14, E15, E26.; Ganymede flybys G2, G7, G8, G28, G29; Callisto flybys C3, C9, C10. We will show how different the energy-dependent pitch angle distributions are upstream and downstream of the moons and how different those distributions are between electrons and the various ions. Electron PADs near Europa are trapped for energies of several 100 keV while for lower energies the PAD shapes are uncertain. Dropout signatures indicate that charged particles are lost in the moons' tenuous exospheres and onto their surface. PADs near Ganymede showed bi-directional electron distributions for low energies upstream and trapped for higher energies while PADs of protons and heavy ions are more isotropic. Inside Ganymede’s magnetosphere trapped distributions have been observed when the S/C was connected to closed field lines. The signal-to-noise ratio of energetic electron and ion fluxes near Callisto is a factor of 10 lower than for Europa. PADs near the moon are less clear compared to the other Galilean satellites. Bi-directional ion PADs close to the moon have been observed.

Icy bodies are the most numerous and diverse bodies in the Solar System, but only a few have been visited yet by space probes. Some of these icy bodies, mostly giant planet satellites like Callisto, are called ocean worlds as they likely host most of the liquid water of our Solar System within sub-glacial oceans [Sotin & Tobie 2004]. The presence of liquid water under the icy crusts of these bodies raises questions relative to exobiology. In the coming years and decades, these ocean worlds will be the focus of major planetary science missions, firstly with JUICE (ESA, launch scheduled in April 2023) and Europa Clipper (NASA, launch scheduled in October 2024) which will be targeting the Galilean moons, then with still conceptual missions as we speak such as (i) Uranus Orbiter and Probe and (ii) Enceladus Orbilander. Despite not being the prime target of any of these missions, Callisto will be investigated by JUICE and Europa Clipper through multiple flybys. One way to get information about Callisto’s sub-glacial ocean is to look at the moon’s surface, which may highlight markers of past or current activity and could lift the veil on its chemical composition. Spectroscopy is a powerful technique for such study, especially in the near-infrared domain where spectral signatures of H2O-ices, silicates, salts are detectable. Consequently, in preparation for future infrared spectroscopic data, and specifically those of the infrared imaging spectrometer MAJIS of the JUICE mission, a ground-based campaign was led with an instrument sharing some similar and also complementary characteristics: SINFONI (SINgle Faint Object Near-infrared Investigation), which was mounted on the UT4 of the VLT at ESO. Here we present the results derived from the analysis and the modeling of four full-disk observations acquired with this instrument. SINFONI combines an integral field spectrometer operating with different gratings with an adaptive optics module [Eisenhauer et al. 2003]. Our four observations were performed using the H+K grating, ranging from 1.46 µm to 2.41 µm, with a spectral resolution R = 1.500, but each spectrum acquired was automatically resampled in order to get a spectral sampling of 5 x 10-4 µm. The campaign took place from January 2015 from March 2016, and the observations were acquired near the opposition to optimize the angular resolution with Callisto’s angular diameter close to 1.5 arcsec. As SINFONI’s field of view is 0.8 x 0.8 arcsec2 divided into 64 x 64 pixels, one observation actually corresponds to a mosaic of ten overlapping acquisitions, as described in a paper about Ganymede using the exact same technique [Ligier et al. 2019]. All in all, after removing the high solar incident angle pixels we could not recover after applying photometric corrections (basically all pixels above latitude 60°, north and south), our dataset covers approximately 70% of Callisto’s entire surface with a spectral and spatial sampling (~40 km/pix) which allow to detect and map the spectral absorptions that may exist in this wavelength range of the Callisto’s spectrum. Spatial resolution is in par with that of the partial Callisto mosaic from the NIMS imaging spectrometer of the NASA Galileo probe. The first results obtained concerns the physical properties of the moon’s surface directly derived from the reduction process and the photometric corrections; one obtains satisfactory results using the qualitative photometric model of Oren-Nayar, which is a generalization of the Lambertian model with the surface roughness (σ) as only additional parameter [Oren & Nayar 1994]. In the case of our study, the best results were obtained with ranging between 17° and 19° whatever the observation. These values are much lower than the values in the 30° – 45° range provided by previous studies [Buratti 1991, Domingue & Verbiscer 1997], however these values were obtained through the modeling of the solar phase curve via the Hapke model [Hapke 1984, Hapke 1986] using a combination of telescopic observations and Voyager data; the major differences between the approaches make the respective results hard to compare (our data are < 10° emergence angle). Our second result concerns the global shape and spectral signatures in the surface spectra: overall, they are much flatter and more distorted than those of Europa and Ganymede, especially the quite large 2-µm H2O-ice band. To the exception of crystalline ice absorptions at ~1.50 µm, ~1.57 µm, ~1.65 µm and the 2-µm band, Callisto does not show other clear signatures (figure 1). However, very subtle signature(s), like the one at ~2.21 µm (figure 1), might actually be observed and are being investigated to confirm the detection(s). If confirmed it could suggest the presence of hydrated materials like salts or silicates. We will address this point during the meeting. Figure 1: Comparison between Ganymede’s (blue) and Callisto’s (red) mean spectrum of the entire dataset. And lastly our third main result comes from spectral modeling, where both linear and non-linear unmixing were performed. Unlike previous studies on Ganymede and Europa [Ligier et al. 2019, Ligier et al. 2016], the linear model shows that all of Callisto’s spectra are satisfactorily modeled without needing any hydrated salt and that the only two constituents would be (i) a darkening agent, with abundances always exceeding 80% even for the iciest spectra, and (ii) multiple grain sizes of the crystalline form of H2O-ice, with an average abundance of 7% and exhibiting a strong latitudinal gradient for the smallest grains typical of the influence of the Jovian magnetospheric environment (figure 2). Such a low concentration overall of H2O-ice challenged us about the legitimacy of the linear unmixing approach, so we decided to run the Shkuratov non-linear unmixing model [Shkuratov et al. 1999]. Tests are ongoing but very preliminary results show that the overall concentration of the crystalline ice should be much higher than the 7% coming from the linear model and hence much more representative of what should be the surface composition of an icy satellite. By the time of the meeting, we will be able to present the final results of the study. Figure 2: Distribution of the smallest grains of crystalline ice.

Jupiter’s moon Callisto is exposed to a highly dynamic magnetospheric environment. During a full synodic period, properties of the local magnetospheric field and thermal plasma environment change by an order of magnitude, and Callisto’s resulting interaction with the ambient plasma displays a strong variability. In this study, we combine results from the AIKEF hybrid and GENTOo test-particle models to constrain the variability of energetic particle dynamics and quantify their flux onto the top of Callisto’s atmosphere during a synodic period. For three positions of Callisto with respect to the center of the Jovian current sheet (at maximum distance above, maximum distance below, and embedded within), we model the interaction between Callisto’s atmosphere/ionosphere, its induced field, and ambient magnetospheric plasma environment, and we trace energetic ions (hydrogen, oxygen, and sulfur) and electrons through the perturbed electromagnetic fields. Our findings highlight the important role that Callisto's interaction with the low energy magnetospheric plasma and signatures associated with the moon’s induced field have on shaping the dynamics and flux patterns of the high-energy particles, which may play a role in the asymmetric ionization of, and energy deposition into, Callisto's neutral atmosphere.

For the Europa Clipper mission, the radiation environment of Jupiter will be measured by a dedicated Radiation Monitoring (RadMon) subsystem, which will provide mission accumulated Total Ionizing Dose (TID) and instantaneous electron flux measurements at a 1-Hz cadence in multiple energy ranges. The radiation monitoring subsystem is comprised of a stand-alone sensor assembly along with distributed TID assemblies at various locations on the spacecraft. The TID measurements will provide the critical information about the overall radiation levels relevant to the electronic’s degradation over time and the electron flux data can serve as a proxy for the Internal ElectroStatic Discharge (IESD) environment by measuring the >~1 MeV electron environment. In addition, the radiation monitoring subsystem data will be augmented by serendipitous radiation data from science instruments onboard. This will be made possible by careful modeling and analysis of opportunistic background data from the following instruments (as we envisioned now): Europa Imaging System (EIS), Europa-Ultraviolet Spectrograph (Europa-UVS), Mapping Imaging Spectrometer for Europa (MISE), MAss Spectrometer for Planetary EXploration (MASPEX), Plasma Instrument for Magnetic Sounding (PIMS), and SUrface Dust Analyzer (SUDA). Based on the current understanding, these instruments would be most sensitive to > 1 MeV electrons. As such, the high energy electron data obtained by the radiation monitoring subsystem will be qualitatively and quantitively enhanced by the high energy electron data acquired by the instruments. The holistic radiation monitoring program for the mission will be an extensive collaboration among many teams across the flight and payload systems. Although the radiation monitoring subsystem itself is an engineering resource for the mission, the collective data from the mission can be also used to improve the scientific understanding of the Jovian magnetosphere and the high energy electron environment near Europa, where the motion of charged particles is perturbed by the local electromagnetic environment. The data will also help understand the radiation modification of surface compounds, which will subsequently help guide lab experiments to aid in understanding the origin and evolution of surface materials. In this paper, we will discuss the science made possible by these high energy electron measurements. Examples of potential science from the Europa Clipper mission include: Quantification of trapped electron fluxes spatially (e.g., by R, lat, and LT) Assessment of time variations of the radiation belts of Jupiter High-energy (>10 MeV) electron populations and physical mechanism for energization Physical mechanism for a C-22 like storm Radiation level range in stretched field line region of Jupiter (outward of Ganymede's orbit) Level of precipitation of electron flux and dose into Europa as a function of surface region Role of energetic electrons in surface modifications, e.g., radiolysis, sputtering, etc.

The Galileo mission was the first to orbit Jupiter and lasted from 1995 to 2003. Its data set is unique even compared to contemporary data from the Juno mission since Galileo had an equatorial orbi...

Remote observations clearly show that soft X-ray emissions at Jupiter concentrate poleward of the main oval forming a so-called “hot spot” (Gladstone et al., 2002; Dunn et al., 2016). One hypothesis proposes that the X-rays are likely produced from precipitating energetic heavy ions that become fully stripped via interactions in Jupiter’s upper atmosphere; however, the details regarding the ion source and acceleration mechanism(s) of the soft X-ray (~2 keV) component is still an active area of research. NASA’s Juno mission – a Jupiter polar orbiting spacecraft – is shedding light onto this mystery with in situ observations of the energetic particle environment over the poles, and coordinated observing campaigns with Earth-orbiting X-ray observatories, e.g., Chandra and XMM-Newton. Recent ideas supported by Juno data include: 1) pitch angle scattering of energetic ions via electromagnetic ion cyclotron waves in the outer magnetosphere (Yao et al., 2021); and 2) acceleration of ions to several MeV over Jupiter’s poles via field-aligned electric potentials (Clark et al., 2017; Haggerty et al., 2017; Clark et al., 2020; Yao et al., 2021). New techniques have been recently developed to push the capabilities of Juno’s Jupiter Energetic particle Detector Instrument (JEDI) to measure the > 10 MeV ions (Westlake et al., 2019; Kollmann et al., 2020). In this presentation, we utilize these techniques to characterize the precipitating fluxes of > 10 MeV ions over Jupiter’s polar region with the goal of better understanding the sources of Jupiter’s X-ray auroral emissions.

Saturn's magnetosphere is an efficient emitter of energetic neutral atoms (ENAs), created through charge exchange of energetic ions with the extended neutral cloud originating from the icy moon Enceladus. We present an analysis using the complete image set captured by Cassini’s Ion Neutral Camera (INCA) to characterise Saturn’s average ENA morphology. Concentric tori are formed around the planet by oxygen and hydrogen ENAs, with intensity peaks between 7-10 Rs radial distance, with a ~1-2 Rs dayside offset. Nightside intensity is brighter than the dayside, likely the result of enhancements following large-scale plasma injections from the magnetotail, and influence of the noon-midnight electric field. Global intensity is clearly modulated with the near-planetary rotation period. This Cassini-era profile of Saturn's ENA emission advances our understanding of how volcanic moons can influence plasma dynamics in giant magnetospheres and is timely ahead of the planned JUICE mission, which carries the first dedicated ENA detector to Jupiter.

Observations of energetic neutral atoms (ENAs) are a useful tool for analyzing ion and neutral abundances in planetary magnetospheres. They are created when hot plasma, originating for example from magnetic reconnection sites, charge-exchanges with the ambient neutral population surrounding the planet. The motion of ENAs is not governed by the magnetic field, allowing remote imaging. During the Cassini mission, the Ion Neutral Camera (INCA) of the Magnetosphere Imaging Instrument (MIMI) collected vast amounts of hydrogen and oxygen ENA observations of Saturn's magnetosphere from a variety of different viewing geometries. In order to enable investigations of the morphology and dynamics of Saturn's ring current, it is useful to re-bin and re-project the camera-like views from the spacecraft-based perspective into a common reference frame. We developed an algorithm projecting INCA's ENA observations into a regular grid in Saturn's equatorial plane. With most neutrals and ions being confined into an equatorial rotating disc, this projection is quite accurate in both spatial location and preservation of ENA intensity, provided the spacecraft is located at large enough elevations. Such projections were performed for all INCA ENA data from the Cassini Saturn tour; the data is available for download together with a Python routine flagging contaminated data and returning detailed spacecraft geometry information. The resulting dataset is a good foundation for investigating for example the statistical properties of Saturn's ring current and its complicated dynamics in relation to other remote and in situ observations of, for example, auroral emissions and magnetotail reconnection events.

On 10 January 2001, Cassini briefly entered into the magnetosphere of Jupiter, en route to Saturn. During this excursion into the Jovian magnetosphere, the Cassini Magnetosphere Imaging Instrument/Charge‐Energy‐Mass Spectrometer detected oxygen and sulfur ions. While Charge‐Energy‐Mass Spectrometer can distinguish between oxygen and sulfur charge states directly, only 95.9 ± 2.9 keV/e ions were sampled during this interval, allowing for a long time integration of the tenuous outer magnetospheric (~200 RJ) plasma at one energy. For this brief interval for the 95.9 keV/e ions, 96% of oxygen ions were O+, with the other 4% as O2+, while 25% of the energetic sulfur ions were S+, 42% S2+, and 33% S3+. The S2+/O+ flux ratio was observed to be 0.35 (±0.06 Poisson error)., Key Points Cassini measured the relative charge state abundances of 95.9 keV/e oxygen and sulfur in the outer magnetosphere (~200 RJ) of JupiterThe flux of 95.9 keV/e O+ was higher than that of S2+, with S2+ being the most abundant charge state among sulfur ionsThe relative abundances of 95.9 keV/e heavy ions are compared to thermal ions in the inner to middle magnetosphere

Ganymede's surface exhibits great geological diversity, with old dark terrains, expressed through the surface composition, which is known to be dominated by two constituents: H2O-ice and an unidentified darkening agent. In this paper, new investigations of the composition of Ganymede's surface at global scale are presented. The analyses are derived from the linear spectral modeling of a high spectral resolution dataset, acquired with the near-infrared (1.40–2.50 μm) ground-based integral field spectrometer SINFONI (SINgle Faint Object Near-IR Investigation) of the Very Large Telescope (VLT hereafter) located in Chile. We show that, unlike the neighboring moon Europa, photometric corrections cannot be performed using a simple Lambertian model. However, we find that the Oren-Nayar (1994) model, generalizing the Lambert's law for rough surfaces, produces excellent results. Spectral modeling confirms that Ganymede's surface composition is dominated by H2O-ice, which is predominantly crystalline, as well as a darkening agent, but it also clearly highlights the necessity of secondary species to better fit the measurements: sulfuric acid hydrate and salts, likely sulfates and chlorinated. A latitudinal gradient and a hemispherical dichotomy are the strongest spatial patterns observed for the darkening agent, the H2O-ice, and the sulfuric acid: the darkening agent is by far the major compound at the equator and mid-latitudes (≤ ± 35°N), especially on the trailing hemisphere, while the H2O-ice and the sulfuric acid are mostly located at high latitudes and on the leading hemisphere. This anti-correlation is likely a consequence of the bombardment of the constituents in the Jovian magnetosphere which are much more intense at latitudes higher than ±35°N. Furthermore, the modeling confirms that polar caps are enriched in small, fresh, H2O-ice grains (i.e. ≤50 μm) while equatorial regions are mostly composed of larger grains (i.e. ≥200 μm, up to 1 mm). Finally, the spatial distribution of the salts is neither related to the Jovian magnetospheric bombardment nor the craters. These species are mostly detected on bright grooved terrains surrounding darker areas. Endogenous processes, such as freezing of upwelling fluids going through the ice shell, may explain this distribution. In addition, a small spectral residue that might be related to brines and/or hydrated silica-bearing minerals are located in the same areas.

The polar orbit of Juno at Jupiter provides a unique opportunity to observe high‐latitude energetic particle injections. We measure energy‐dispersed impulsive injections of protons and electrons. Ion injection signatures are just as prevalent as electron signatures, contrary to previous equatorial observations. Included are previously unreported observations of high‐energy banded structures believed to be remnants of much earlier injections, where the particles have had time to disperse around Jupiter. A model fit of the injections used to estimate timing fits the shape of the proton signatures better than it does the electron shapes, suggesting that electrons and protons are different in their abilities to escape the injection region. We present ultaviolet observations of Jupiter's aurora and discuss the relationship between auroral injection features and in situ injection events. We find, unexpectedly, that the presence of in situ particle injections does not necessarily result in auroral injection signatures., Key Points High‐latitude observations at Jupiter reveal features of injections (L < 15 RJ) and associated auroral signatures not previously reportedIncluded are a near equality of electron and ion injections, puzzling differences between their signatures and signatures of old injectionsThere is no one‐to‐one correspondence between the in situ particle and auroral signatures of injections, contrary to literature expectations

We have conducted experiments to better understand the extent to which radiation-induced color changes observed at near-ultraviolet through near-infrared wavelengths for various salts could provide insight into the composition of the nonice material(s) on the surface of Europa's trailing hemisphere. Salts of NaCl, KCl, Na2SO4, partially hydrated MgSO4, partially hydrated FeSO4, Na2CO3, and CaCO3 were irradiated with 1020 electrons/cm2 at room temperature; the electron energy was 40 keV. This is equivalent to ~100,000 years of exposure to electrons at Europa in this energy range, or to an equivalent few thousand years of exposure to electrons of at least ~100 eV, a conservative estimate for the lowest energy electrons capable of producing color centers. Each salt either browned, darkened, and/or developed color centers. Most salts also developed a probable colloidal band near 600 nm that would be expected to be much weaker or non-existent in materials at the temperature of Europa's surface. The ultraviolet through near-infrared telescopic spectra of Europa's trailing hemisphere is most consistent with a linear mixture of irradiated MgSO4·nH2O with a few percent of another salt that exhibits a color center near 600 nm (either Na2SO4·nH2O, Na2CO3, CaCO3, or KCl). Other irradiated salts exhibit spectral features that limit their abundances in the nonice material on the trailing hemisphere, with the abundance of NaCl, because of its strong color centers, limited to not more than approximately 10%.

The inner boundary of Saturn's electron radiation belts, near the planet's A‐ring (∼2.27 Rs), is studied using Cassini's Proximal orbit measurements. We find that variable convective flows transport energetic electrons to the A‐ring, which absorbs them instantaneously, forming the inner belt boundary. These flows are also responsible for a variable and longitudinally asymmetric boundary configuration. Pre‐noon, the boundary oscillates towards and away from the A‐ring with a two‐week period. Post‐noon, it maps persistently near the F‐ring (∼2.32 Rs) and coexists with localized MeV electron intensity enhancements (microbelts). We propose that the microbelts contain electrons in drift resonance with corotation, trapped in local‐time confined trajectories which result from the aforementioned convective flows. The microbelts' collocation with the F‐ring implies either a local, secondary electron production due to Galactic Cosmic Ray collisions with F‐ring dust, or an enhanced resonant electron trapping due to an electrodynamic interaction between the F‐ring and Saturn's magnetosphere.

The events and their comparison to previous works are located on the Deep Blue Data Repository under doi:10.7302/Z2WM1BMN (https://deepblue.lib.umich.edu/data/concern/data_sets/3n203z679) or can be received through email contact with A. R. Azari.

The existence of planetary radiation belts with relativistic electron components means that powerful acceleration mechanisms are operating within their volume. Mechanisms that bring charged particles planetward toward stronger magnetic fields can cause their heating. On the basis that electron fluxes in Saturn’s radiation belts are enhanced over discrete energy intervals, previous studies have suggested that rapid inward plasma flows may be controlling the production of their most energetic electrons. However, rapid plasma inflows languish in the planet’s inner magnetosphere, and they are not spatially appealing as a mechanism to form the belts. Here we show that slow, global-scale flows resulting from transient noon-to-midnight electric fields successfully explain the discretized flux spectra at quasi- and fully relativistic energies, and that they are ultimately responsible for the bulk of the highest energy electrons trapped at Saturn. This finding is surprising, given that plasma flows at Saturn are dominated by the planetary rotation; these weak electric field perturbations were previously considered impactful only over a very narrow electron energy range where the magnetic drifts of electrons cancel out with corotation. We also find quantitative evidence that ultrarelativistic electrons in Jupiterʼs radiation belts are accelerated by the same mechanism. Given that similar processes at Earth drive a less efficient electron transport compared to Saturn and Jupiter, the conclusion is emerging that global-scale electric fields can provide powerful relativistic electron acceleration, especially at strongly magnetized and fast-rotating astrophysical objects.

The dedicated Energetic Neutral Atom (ENA) imager on the Cassini spacecraft provided indispensable measurements of magnetospheric processes at Saturn. At Jupiter, Cassini provided only a few serendipitous ENA images as the spacecraft flew by Jupiter at large radial distances. The Juno spacecraft, now in a polar orbit around Jupiter, carries no ENA camera, but the energetic particle JEDI instrument is sensitive to ENA’s with energies > 50 keV, provided there are few charged particles in the environment to mask their presence. Even with limited ENA capabilities, the Juno mission has revealed important differences between Saturn and Jupiter with regard to how charged ions are lost from these magnetospheric systems. Specifically, a major contribution to ENA emissions at Jupiter come from Jupiter’s polar atmosphere. These ENAs likely arise from energetic ions that nearly precipitate in the auroral zone, only to mirror magnetically within the atmosphere where they charge exchange with atoms in Jupiter’s upper atmosphere. Cassini did not observe this precipitating component at Saturn despite the abundance of quality ENA measurements obtained there. We conclude that ion precipitation into Jupiter’s atmosphere is competitive with other loss processes. In contrast, in the Saturn system, it is likely that losses associated with the dense neutral gas populations near the equator dominate the loss of energetic particles.

Energetic particles (>∼25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the low‐energy magnetosphere measurements system, one of the three sensors of the magnetosphere imaging instrument on board the Cassini spacecraft, during a period of ∼14 years (2004–2017). It is found that energetic particles, especially ions, are also common in Saturn's magnetosheath. A clear inward (toward Saturn) gradient in the electron differential flux is identified, suggestive of magnetospheric sources. Such an inward gradient does not appear in some of the ion channels. We conclude that Saturn's magnetopause acts as a porous barrier for energetic electrons and, to a lesser extent, for energetic ions. A dawn‐dusk asymmetry in the gradient of particle flux across the magnetopause is also identified, with a gradual decrease at the dawn and a sharp decrease at the dusk magnetopause. It is also found that magnetic reconnection enhanced flux levels just outside of the magnetopause, with evidence suggesting that these particles are from magnetospheric sources. These findings strongly suggest that Saturn's magnetosphere is most likely the main source of energetic particles in Saturn's magnetosheath and magnetosphere leakage is an important process responsible for the presence of the energetic particles in Saturn's magnetosheath.

We present multi-instrument Juno observations on day-of-year 86, 2017 that link particles and fields in Jupiter’s polar magnetosphere to transient UV emissions in Jupiter’s northern auroral region known as dawn storms. Juno ranged from 42ºN - 51ºN in magnetic latitude and 5.8 – 7.8 jovian radii (1 RJ = 71,492 km) during this period. These dawn storm emissions consisted of two separate, elongated structures which extended into the nightside, rotated with the planet, had enhanced brightness (up to at least 1.4 megaRayleigh) and high color ratios. The color ratio is a proxy for the atmospheric penetration depth and therefore the energy of the electrons that produce the UV emissions. Juno observed electrons and ions on magnetic field lines mapping to these emissions. The electrons were primarily field-aligned, bi-directional, and, at times, exhibited sudden intensity decreases below ∼10 keV coincident with intensity enhancements up to energies of ∼1000 keV, consistent with the high color ratio observations. The more energetic electron distributions had characteristic energies of ∼160 – 280 keV and downward energy fluxes (∼70 – 135 mW/m2) that were a significant fraction needed to produce the UV emissions for this event. Magnetic field perturbations up to ∼0.7% of the local magnetic field showing evidence of upward and downward field-aligned currents, whistler mode waves, and broadband kilometric radio emissions were also observed along Juno’s trajectory during this timeframe. These high latitude observations show similarities to those in the equatorial magnetosphere associated with dynamics processes such as interchange events, plasma injections, and/or tail reconnection.

Jupiter is surrounded by intense and energetic radiation belts, yet most of the available in-situ data, in volume and quality, were taken outside of Europa's orbit, where radiation conditions are n...

Saturn's magnetosphere is an efficient emitter of Energetic Neutral Atoms (ENAs), given the presence of an extended neutral cloud around the planet that originates from the icy moon, Enceladus. The ENA emission is symptomatic of the global circulation of plasma in Saturn's magnetosphere. Energetic ions are injected from the outer magnetosphere following magnetotail dynamics and reconnection events. These ions then charge exchange with the neutral cloud, which is mostly confined to the spin plane, resulting in ENA production. The global ENA emission is dynamic, displaying sudden brightening on the nightside, and discrete rotating enhancements which circle the planet for many hours as energetic ions drift with the bulk plasma flow. These latter features have been linked with rotating signatures in the ultraviolet auroras, suggesting coupling via some transient system of field-aligned currents that forms following injection events. Indeed these injection events occur so often as to form Saturn’s dawn auroral arc. Our characterization of the ENA emission at Saturn is made possible using imagery from the Ion-Neutral Camera (INCA) that flew onboard Cassini. Observations were made over the entire mission lifetime. We present for the first time a statistical analysis of the complete INCA image set, using equatorial projections of the flux distribution to reveal the time-averaged morphology of Saturn's ENAs. We used a comprehensive data processing and equatorial projection algorithm to calibrate, clean and filter for all high inclination orbit days. In the final average pictures, many of the projected pixels consist of between tens to hundreds of days continuous exposure, all captured with a line-of-sight > 50° elevation (above the projection plane) and within 30 RS distance from the spacecraft. We find clear toroidal ENA distributions in O and H, and all INCA energy bands, with the emission dropping off sharply inside 5 RS radial distance in all cases. Average peak intensities occur at radial distances from ~7 RS (O, 170-230 keV) to ~10 RS (H, 24-55 keV). All toroids are offset towards the dayside by several RS, most clearly in the 24-55 keV H image, with a maximum intensity at ~13-14 RS from the planet centre on the dayside, compared to only ~10 RS on the nightside. The H ENA distribution is also enhanced around midnight local times, as previously observed in an early morphological study of 2007 data by Carbary et al. [2008], a net effect associated with reconnection return flows and transient ENA enhancements in this sector. We also explore possible organisation of the average global ENA intensity by Saturn’s rotating current systems associated with planetary period oscillations (PPOs, e.g., Provan et al. [2018]). We find that the ENA intensity is statistically modulated by periodic changes in expected plasma sheet thickness as controlled by field-aligned current interactions, a pattern evident in both north and south rotating system frames. With a thicker plasma sheet, more energetic ions are available to charge exchange within the background neutral cloud, and the LOS integral measure increases as a result (and vice versa). In this long-term picture, this effect may dominate over other possible PPO modulation effects on the appearance or evolution of transient ENA injection signatures.

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.

Observations of energetic neutral atoms (ENAs) are a useful tool for analyzing ion and neutral abundances in planetary magnetospheres. Saturn's magnetosphere is dominated by high densities of water group neutrals which originate from the icy moon Enceladus and are confined close to the equatorial plane due to the planet's rapid rotation rate. Hot plasma populations are mainly created by magnetotail reconnection events and driven inward with the subsequent magnetic field dipolarization to form a so-called "injection". As this hot plasma interacts with the ambient neutral population, charge exchange creates ENAs whose motion is not governed by the magnetic field anymore, such that they can be observed remotely allowing us to image Saturn's ring current on a global scale. Over the course of the Cassini mission, the Ion Neutral Camera (INCA) of the Magnetosphere Imaging Instrument (MIMI) collected vast amounts of hydrogen and oxygen ENA observations of Saturn's magnetosphere from a variety of different viewing geometries. In order to enable statistical investigations of the morphology and dynamics of Saturn's ring current, it is useful to re-bin and re-project the camera-like views from the spacecraft-based perspective into a common reference frame. We developed an algorithm which projects ENA observations by the MIMI-INCA instrument into a regular grid in Saturn's equatorial plane, spanning from -30 to +30 Saturn radii in the XKSMAG and YKSMAG axes of the Kronocentric Solar Magnetic (KSMAG) reference frame with a resolution of 2 pixels per Saturn radii. With most neutrals and ions being confined into an equatorial rotating disc, this projection is quite accurate in both spatial location and measured ENA intensity, provided the spacecraft is located at large enough perpendicular distances from the equatorial plane such that the viewing angle is not too flat. The INCA dataset can exhibit several different kinds of contamination: sunlight entering the detector may lead to artificial intensifications, and bit errors during data transmission may result in wrong count numbers. High ENA fluxes may exceed the limit up to which the instrument calibration is valid, and energetic ion beams bypassing the high voltage deflector and entering the detector may lead to artifacts not representing the actual ENA intensity. Many of these events have been identified by the instrument team and tables are available with INCA calibration files, but ion contamination events were so far not identified - we developed an algorithm identifying these to complement previous exclusion lists. Our dataset of projections includes all days during which Cassini was located at >4 RS off the equatorial plane, and will be provided as a zip archive of daily files in .fits format. A Python routine for loading these files into a useful array format will be provided, returning not only ENA intensity data but also various geometric information detailing the spacecraft's location as well as data quality flags. This allows the user to easily set validity constraints depending on the spacecraft distance from and elevation above each pixel and highlights which exposures may be contaminated. The resulting dataset is a good foundation for investigating the statistical properties of Saturn's ring current as well as its complicated dynamics in relation to other remote and in situ observations of, for example, auroral emissions and magnetotail reconnection events.

During its more than 13 years in orbit, the Cassini spacecraft detected a large number of plasma and energetic charged particle injections in Saturn's inner magnetosphere. In the corotating frame of the planet, the plasma contained within an injection moves radially inward with the component particles gaining energy. The highest energy particles in the injection experience stronger gradient‐curvature drifts in the longitudinal direction and can drift out of the main body of the injection. We have used these drift‐out effects to estimate the inflow speed of 19 injections by surveying cases from the available plasma data. We find that the average inflow speed from our sample is 22 km/s, and the values are well distributed between 0 and 50 km/s, with a few higher estimates. We have also computed the radial travel distance of interchange events and found that these are typically one to two Saturn radii. We discuss the implications of these quantifications on our understanding of transport.

This study examines the bombardment of energetic magnetospheric electrons onto Ganymede as a function of Jovian magnetic latitude. We use the output from a three-dimensional, hybrid model to constr ...

The moon Dione orbits Saturn at 6.2 Saturn radii RS deep in the Kronian magnetosphere. In situ studies of the moon-magnetosphere interaction processes near Dione were possible with the Cassini/Huygens mission which flew by close to Dione five times at distances between 99 and 516 km. In addition, Cassini crossed Dione's L-shell more than 400 times between 2004 and 2017 and documented the variability of Saturn's magnetosphere. Different flyby geometries allowed to study the interaction processes upstream, in the low-energy wake, and above the north pole of Dione. We describe here the energetic particle measurements from the Low Energy Magnetospheric Measurement System (LEMMS), part of the Magnetosphere Imaging Instrument (MIMI) onboard Cassini. We also use hybrid simulation results from “A.I.K.E.F.” to interpret the signatures in the particle fluxes. This paper is a continuation of Krupp et al. (2013, https://doi.org/10.1016/j.icarus.2013.06.007) and Kotova et al. (2015, https://doi.org/10.1016/j.icarus.2015.06.031). The key results are as follows: (1) Saturn's magnetosphere at Dione's orbit is highly variable with changes in energetic charged particle fluxes by 1–2 orders of magnitude. (2) The dropout signatures near Dione are basically consistent with a fully absorbing obstacle, but some features point to more complex interaction processes than plasma and energetic particle absorption. (3) Absorption signatures are found to be asymmetric with respect to the orientation of the moon, indicative of the presence of radial drift components for electrons. (4) The deepest absorption signatures were observed at the edge of the low-energy wake pointing to gradient-B drifts strongest in that part of the interaction region.

The 2007-2009 solar minimum was the longest of the space age. We present the first of two companion papers on Chandra and XMM-Newton X-ray campaigns of Jupiter through February-March 2007. We find that low solar X-ray flux during solar minimum causes Jupiter's equatorial regions to be exceptionally X-ray dim (0.21 GW at minimum; 0.76 GW at maximum). While the Jovian equatorial emission varies with solar cycle, the aurorae have comparably bright intervals at solar minimum and maximum. We apply atomic charge exchange models to auroral spectra and find that iogenic plasma of sulphur and oxygen ions provides excellent fits for XMM-Newton observations. The fitted spectral S:O ratios of 0.4-1.3 are in good agreement with in situ magnetospheric S:O measurements of 0.3-1.5, suggesting that the ions that produce Jupiter's X-ray aurora predominantly originate inside the magnetosphere. The aurorae were particularly bright on 24-25 February and 8-9 March, but these two observations exhibit very different spatial, spectral, and temporal behavior; 24-25 February was the only observation in this campaign with significant hard X-ray bremsstrahlung from precipitating electrons, suggesting this may be rare. For 8-9 March, a bremsstrahlung component was absent, but bright oxygen O(6+)lines and best-fit models containing carbon, point to contributions from solar wind ions. This contribution is absent in the other observations. Comparing simultaneous Chandra ACIS and XMM-Newton EPIC spectra showed that ACIS systematically underreported 0.45- to 0.6-keV Jovian emission, suggesting quenching may be less important for Jupiter's atmosphere than previously thought. We therefore recommend XMM-Newton for spectral analyses and quantifying opacity/quenching effects.

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...

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.

The Jovian polar regions produce X-rays that are characteristic of very energetic oxygen and sulfur that become highly charged on precipitating into Jupiter’s upper atmosphere. Juno has traversed the polar regions above where these energetic ions are expected to be precipitating revealing a complex composition and energy structure. Energetic ions are likely to drive the characteristic X-rays observed at Jupiter (Haggerty et al., 2017; Houston et al., 2018; Kharchenko et al., 2006). Motivated by the science of X-ray generation, we describe here Juno JEDI measurements of ions above 1 MeV, and demonstrate the capability of measuring oxygen and sulfur ions with energies up to 100 MeV. We detail the process of retrieving ion fluxes from pulse width data on instruments like JEDI (called “puck’s”; Clark et al., 2016; Mauk et al., 2013) as well as details on retrieving very energetic particles (>20 MeV) above which the pulse width also saturates. The Juno JEDI instrument is shown to have the unplanned capability to measure heavy ions to energies as high as 100 MeV. As such, the JEDI instrument has the capability to measure those ions needed to generate polar X-rays at Jupiter. (> 10’s of MeV O and/or S). We present analysis that involves separating these very energetic ions into the group that is trapped (i.e., part of the very high latitude radiation belts) and the group that is precipitating and might be linked to observed X-rays.

The Jovian current sheet is the main repository of Jupiter’s magnetospheric plasma. Spatial variations in its thickness and therefore its plasma content are poorly understood because thickness determination requires a knowledge of the motion of the current sheet relative to the observing spacecraft which is hard to get. Recently, we have developed a new technique that uses the timings of any three consecutive current sheet crossings to determine the instantaneous motion of Jupiter’s current sheet relative to the spacecraft. Next by using this technique and modeling the magnetic field and electron density dataset in terms of Harris current sheet type equilibria we can estimate the thickness and plasma content of the Jovian current sheet over all local times and radial distances. Our modeling of Juno and Galileo magnetic field data shows that in all local times the current sheet thickness increases with radial distance. We also find that the Jovian current sheet is highly asymmetric in local time, being at its thinnest in the dawn sector and the thickest in the dusk sector. The current sheet thickness on the dayside is comparable to that in the dusk sector. The nightside current sheet is intermediate in its thickness to the dawn and the dusk sectors.We show that the increase in the thickness of the current sheet with radial distance can be explained in terms of the increasing temperature and therefore the plasma beta of the current sheet with radial distance. However what causes the sharp local time variations of the current sheet is not yet fully understood. We will discuss several models of plasma transport and redistribution in Jupiter’s magnetosphere that can create local time differences in the plasma content and therefore the current sheet thickness. These models have testable implications for the structure of the magnetosphere (open versus closed, convective versus diffusive transport of plasma etc.).

We present results from a three-dimensional diffusion theory model, which solves the time dependent Fokker-Planck equation with physical terms representing energizing, source and loss processes to interpret key features in the radial and angular distributions of > 1 keV-energy electrons at Saturn. Cassini observations of eV-keV electron Pitch-Angle Distributions (PADs) at Saturn have revealed a spatial structuring, with little temporal and longitudinal dependence, that can be broken up into three distinct regions [1]: (1) a region dominated by field-aligned PADs from ~12-15 Rs, (2) a transition region from ~8-12 Rs in which butterfly distributions are typically observed, and (3) a region inside ~8 Rs dominated by trapped PADs. Past studies have explained field-aligned PADs by the presence of field aligned currents and acceleration mechanisms in the auroral region [2], while pancake profiles would be the result of inward adiabatic transport [3]. It was argued that energetic electrons are adiabatically energized during inward motion and their PADs would radially evolve from field-aligned (> 15 Rs) to butterfly to pancake/isotropic inside ~8 Rs [4,5,6]. Although Cassini had unveiled Enceladus' dense and extended neutral cloud, little had been done regarding the role of neutrals on the distributions of electrons. We have subsequently combined multi-instrument data analyses of Cassini observations (particle, field and waves) and a diffusion theory model of charged particle fluxes to test the scenarios of the origins and radial evolution of electrons' PADs in the region ~2-15 Rs. In our work, Cassini CAPS/ELS, MIMI/LEMMS and MAG are used to both constrain the model at its boundary conditions and discuss our simulation results with in-situ data. Our radial transport is initially constrained by MIMI/LEMMS observations of micro-signatures [7] and assumed to be adiabatic [8]. Our simulation results show that the adiabatic transport cannot entirely explain the radial and angular features of energetic electrons within the ~2-15 Rs region. The coupling of different mechanisms is required into our model to obtain better agreements with in-situ data. The implementation of a supra-thermal electron population at high-latitudes appears to be a reasonable source of magnetospheric particles beyond ~9 Rs. While impact-ionization and Bremsstrahlung are insignificant mechanisms for > 1 keV-energy electrons, coulomb collisions with neutrals efficiently alter the electron distributions inside ~9 Rs. The drastic depletion observed in the electron fluxes inside ~9-10 Rs is partially explained by the interaction of electrons with neutrals. To pursue our understanding of radial and angular distributions of > 1 keV electrons inside ~7-8 Rs, we are currently investigating the role of dust, cold plasma and waves. Interactions with dust and plasma particles seem to have limited effects. Past studies showed that wave-particle interactions at Saturn are inconclusive [9,10]. Nonetheless, we propose to revisit the role of waves at Saturn as only the interaction with whistler mode chorus waves was examined and the role of coupled processes not discussed. We will thus present our latest results of the interactions of neutrals, dust and plasma environments, and electromagnetic waves with Saturn’s energetic electron population from a physics-based modeling approach. [1] Clark et al., PSS, Volume 104, 2014 [2] Saur et al, Nature, Volume 439 (7077), 2006 [3] Paranicas et al., GRL, Volume 34 (2), 2007 [4] Rymer et al., JGR, Volume 113 (A1), 2008 [5] Schippers et al., JGR, Volume 113 (A7), 2008 [6] Rymer et al, PSS, Volume 57 (14-15), 2009 [7] Roussos et al., JGR, Volume 112 (A6), 2007 [8] Kollmann et al., JGR, Volume 123, 2018 [9] Lorenzato et al., JGR, Volume 117, 2012 [10] Shprits et al., JGR, Volume 117, 2012

Saturn's morningside auroras consist mainly of rotating, transient emission patches, following periodic reconnection in the magnetotail. Simultaneous responses in global energetic neutral atom (ENA) emissions have been observed at similar local times, suggesting a link between the auroras and large‐scale injections of hot ions in the outer magnetosphere. In this study, we use Cassini's remote sensing instruments to observe multiple plasma injection signatures within coincident auroral and ENA imagery, captured during 9 April 2014. Kilometric radio emissions also indicate clear injection activity. We track the motion of rotating signatures in the auroras and ENAs to test their local time relationship. Two successive auroral signatures—separated by ~4 hr UT—form postmidnight before rotating to the dayside while moving equatorward. The first has a clear ENA counterpart, maintaining a similar local time mapping throughout ~9 hr observation. Mapping of the ionospheric equatorward motion post‐dawn indicates a factor ~5 reduction of the magnetospheric source region's radial speed at a distance of ~14‐20 RS, possibly a plasma or magnetic boundary. The second auroral signature has no clear ENA counterpart; viewing geometry was relatively unchanged, so the ENAs were likely too weak to detect by this time. A third, older injection signature, seen in both auroral and ENA imagery on the nightside, may have been sustained by field‐aligned currents linked with the southern planetary period oscillation system, or the re‐energization of ENAs around midnight local times. The ENA injection signatures form near magnetic longitudes associated with magnetotail thinning.