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In the Jovian magnetosphere, quasi‐periodic phenomena, with quasi‐periods on the order of 10–60 min, are frequently identified using different data sets. These pulsations are a branch of ultra‐low frequency (ULF) waves, which are believed to play a crucial role in driving the energy circulation within Jupiter's magnetosphere. In this study, we utilize magnetic field data collected by Juno between 2016 and 2022 to perform a comprehensive global statistical analysis of the spatial distribution and periodic characteristics of ULF waves in the Jovian magnetosphere. Our findings reveal distinct periodic features observed at different latitudes and distances, providing valuable insights into the generation mechanisms of ULF waves. Furthermore, we establish a close relationship between the presence of these ULF wave fluctuations and the magnetospheric state, such as under conditions of solar wind compression. By combining contemporaneous ultraviolet aurora observations from the Hubble Space Telescope (HST) and magnetic field data obtained by Juno, we have discovered that the compressed magnetospheres exhibit more pronounced ULF waves and enhanced auroral activity. These results provide a global picture of the distribution, implying potential generation of ULF waves in the Jovian magnetosphere, and shedding light on the processes behind the 10–60‐min energy releases. Plain Language Summary: In the Jovian system, there are patterns of magnetic waves with periods of 10–60 min. These waves are part of a larger category called ultra‐low‐frequency waves and play an important role in how energy moves around Jupiter. Here, we study these waves using data collected by the Juno spacecraft from 2016 to 2022, investigating where these waves occur and how often they occur. The waves are different depending on the location and distance from Jupiter, which gives us clues about how they are created. These waves also appear to be more common when Jupiter's magnetic field is compressed by the solar wind. We have also combined data from the Hubble Space Telescope and Juno, and found that the compressed magnetic field leads to more of these waves and stronger auroras on Jupiter. This research helps us to understand how these 10–60‐min bursts of energy work in Jupiter's magnetosphere. Key Points: We investigate the spatial distribution and periodic characteristics of ultra‐low frequency (ULF) waves in the Jovian magnetosphereWe examine and compare the occurrence rate of ULF waves under different solar wind compression statesThe connection between ULF waves and auroral morphology provides key constraints on wave generation mechanisms [ABSTRACT FROM AUTHOR]

Jupiter's equatorial eastward zonal flows reach wind velocities of ∼100 m s−1, while on Saturn they are three times as strong and extend about twice as wide in latitude, despite the two planets being overall dynamically similar. Recent gravity measurements obtained by the Juno and Cassini spacecraft uncovered that the depth of zonal flows on Saturn is about three times greater than on Jupiter. Here we show, using 3D deep convection simulations, that the atmospheric depth is the determining factor controlling both the strength and latitudinal extent of the equatorial zonal flows, consistent with the measurements for both planets. We show that the atmospheric depth is proportional to the convectively driven eddy momentum flux, which controls the strength of the zonal flows. These results provide a mechanistic explanation for the observed differences in the equatorial regions of Jupiter and Saturn, and offer new understandings about the dynamics of gas giants beyond the Solar System. Plain Language Summary: In this study, we investigate the strong eastward jet around the equator of Jupiter and Saturn. Despite the planets being similar, Saturn's winds are stronger and cover a wider area in latitude. Recent spacecraft measurements revealed that Saturn's winds go much deeper into its interior than Jupiter's. Using numerical simulations, we find that the depth of the atmosphere is crucial in determining the strength and width of these winds. We show that the depth is related to a specific turbulent flow, dictating the strength of the jets. These findings explain why Jupiter and Saturn have different equatorial zonal wind patterns and provide new insights into the behavior of giant planets outside the Solar System. Key Points: Through 3D numerical simulations, we deduce that the flow depth of gas giants significantly influences their equatorial dynamicsEquatorial flows are driven by eddy fluxes perpendicular to the axis of rotation, and these fluxes are proportionate to the flow depthThe zonal flow depth of Jupiter and Saturn, inversely proportional to their 3:1 mass ratio, leads to the corresponding ratio in flow strength [ABSTRACT FROM AUTHOR]

The Juno spacecraft had previously observed intense high frequency wave emission, broadband electron and energetic proton energy distributions within magnetic flux tubes connected to Io, Europa, Ganymede, and their wakes. In this work, we report consistent enhancements in <46 keV energy proton fluxes during these satellite flux tube transit intervals. We find enhanced fluxes at discrete energies linearly separated in velocity for proton distributions within Io wake flux tubes, and both proton and electron distributions within Europa and Ganymede wake flux tubes. We propose these discrete enhancements to be a result of resonances between particles' bounce motion with standing Alfvén waves generated by the satellite‐magnetosphere interaction. We corroborate this hypothesis by comparing the bounce and field‐line resonance periods expected at the satellites' orbits. Hence, we find bounce‐resonant acceleration is a fundamental process that can accelerate particles in Jupiter's inner magnetosphere and other astrophysical plasmas. Plain Language Summary: The passage of the Galilean moons‐ Io, Europa, Ganymede, and Callisto, perturbs the plasma flow in Jupiter's magnetosphere, creating waves that travel from the moon and reflect off Jupiter's ionosphere. These waves have been proposed to accelerate charged particles, and such accelerated particles had been observed by the Juno spacecraft during its passage through magnetic field lines connected to the satellite wakes. In this work, we find instances when this acceleration occurs selectively at specific energies that have constant separation in speed. We propose that this selective acceleration is due to resonance between particle bounce motion and the waves arising from the satellite wake perturbation. Bounce‐resonant acceleration is a promising fundamental process which can accelerate particles in Jupiter's inner magnetosphere and other plasma systems with similar geometries. Key Points: Proton and electron flux enhancements in satellite and wake flux tubes often occur at discrete energies linearly separated in speedBroadband proton flux enhancements at <46 keV energies were also observed within satellite flux tube crossingsParticles can be accelerated via resonance between bounce motion and standing Alfvén waves generated by moon‐magnetosphere interactions [ABSTRACT FROM AUTHOR]

In 1995, the Galileo spacecraft traversed the wake of Io at ∼900 km altitude. The instruments onboard detected intense bi‐directional field‐aligned electron beams (∼140 eV–150 keV), embedded in a dense, cold and slow plasma wake (Nel ∼ 35,000 cm−3, Ti < 10 eV, V < 3 km/s). Similar electron beams were also detected along subsequent Galileo flybys. Using numerical simulations, we show that these electron beams are responsible for the formation of Io's dense plasma wake. We prescribe the composition of Io's atmosphere in S, O, SO and SO2, compute the atmospheric ionization by the beams with a parameterization adapted from study of auroral electrons at Earth, the plasma flow into Io's atmosphere with a Magneto‐Hydro‐Dynamic code, and the ion composition and temperature with a multi‐species physical chemistry code. Results reveal contrasting chemistries between the upstream and wake regions, leading to different ion compositions. The upstream chemistry is driven by the torus thermal electrons at 5 eV with SO2+ becoming the dominant ion because of electron‐impact ionization of the SO2 atmosphere. The wake chemistry is driven by the high‐energy electrons in the beams with S+ and SO+ becoming the dominant ions produced by dissociative‐ionization of SO2. We show that the wake ion composition is highly sensitive to the atmospheric composition. Juno, in its extended mission, will traverse Io's wake and determine its ion composition, which, compared with our numerical simulations will enable us to infer the detailed composition of the atmosphere. Plain Language Summary: Io, the inner‐most Galilean moon of Jupiter, is the most active volcanic body of the solar system. It has a tenuous atmosphere ultimately supplied by volcanic activity. The atmosphere is mainly composed of sulfur dioxide, oxygen, sulfur and sulfur monoxide, but its detailed composition, density and spatial distribution are still surprisingly poorly known. Between 1995 and 2001, the Galileo spacecraft made five close flybys of Io. The onboard instruments detected intense high‐energy electrons moving along Jupiter's magnetic field lines embedded in a remarkably dense ion wake (∼10 times denser than the surrounding plasma). Identifying the processes that generate this dense wake remains an outstanding issue. We utilize numerical simulations to demonstrate that the production of the dense ion wake is attributed to efficient ionization of Io's atmosphere by the electron beams. Our simulations reveal that the ion composition of the wake is highly sensitive to the atmospheric composition. The Juno spacecraft, currently in orbit around Jupiter, will conduct several flybys in Io's wake in 2023 and 2024 and determine its ion composition. Similar electron beams are likely present near other moons of Jupiter. Such beams have already been detected during a single flyby of Europa by the Juno probe. The Jupiter Icy Moon Explorer spacecraft is presently en route to Ganymede and Callisto, while the future Europa Clipper mission is scheduled to be launched to Europa in 2024. These missions will have the capacity to detect the presence of electron beams and plasma wakes similar to those observed at Io. Our numerical model serves as an effective tool for inferring the atmospheric composition and density of these moons as it predicts the ion composition and density of the wake based on the energy of the electron beams. Key Points: The Galileo spacecraft detected a dense and cold plasma wake downstream of Io and intense field‐aligned high‐energy electron beamsUsing numerical simulations, we show that this dense plasma wake is produced by the electron beams ionization of Io's atmosphereThe ion composition and density in the wake strongly depend on Io's atmospheric density and its neutral composition [ABSTRACT FROM AUTHOR]

The electromagnetic coupling between the Galilean satellites at Jupiter and the planetary ionosphere generates an auroral footprint, which is detected with high spatial resolution in the infrared L band by the Jovian InfraRed Auroral Mapper (JIRAM) onboard the Juno spacecraft. We report the JIRAM data acquired since 27 August 2016 until 23 May 2022, which are used to compute the average position of the footprint tracks of Io, Europa and Ganymede. The result of the present analysis help to test the reliability of magnetic field models, to calibrate ground‐based observations and to highlight the variability in the footprint positions, which can be used to probe the plasma environment at the orbit of the satellites. The determination of the plasma properties around the moons is particularly relevant to complement the Juno flybys of the moons during its extended mission, and to support the future Juice and Europa Clipper missions. Lastly, we report no clear evidence of the auroral footprint of Callisto, which is likely due to a combination of its low expected brightness and its position very close to the main Jovian aurora. Plain Language Summary: The Jovian InfraRed Auroral Mapper onboard the Juno spacecraft around Jupiter has now been gathering 6 years of observations. Here, we report the position of the auroral infrared emission associated with the orbital motion of Io, Europa and Ganymede. The position of this emission ‐ called footprint ‐ carries information on the magnetic field geometry and the distribution of charged particles along the magnetic field. Therefore, the footprint tracks provided here can be used to test and constrain magnetic field models, and to improve the calibration of ground based observations of Jupiter: this can help better understand the source region of the main Jovian aurora and its variations. Lastly, by surveying the data acquired over 40 Juno orbits, we point out variations in the footprint position, which reflect the variability in the plasma conditions near the moons: this monitoring may help determine the mass loading of the magnetosphere, which affects the intensity of the main aurora. The possibility of investigating the plasma environment at the orbit of the satellites is important to complement the satellite flybys performed during the extended mission of Juno and to support the future Juice and Europa Clipper missions, which are dedicated to the Galilean moons. Key Points: The position of the Io, Europa and Ganymede footprints based on Juno‐JIRAM observations are reported with unprecedented spatial resolutionThe positions of the footprints support the Juno‐based magnetic field models and the calibration of ground‐based observationThe transversal shift of the Ganymede footprint suggests variations of the plasmadisk; the shift appears to be correlated with local time [ABSTRACT FROM AUTHOR]

Using images at multiple mid‐infrared wavelengths, acquired in 2018 May using the Very Large Telescope Imager and Spectrometer (VISIR) instrument on ESO's Very Large Telescope (VLT), we study Jupiter's pole‐to‐pole thermal, chemical and aerosol structure in the troposphere and stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones and warm cloud‐free cyclonic belts persists throughout the mid‐latitudes, up to the polar boundaries, and evidence a strong correlation with the vertical maximum windshear and the locations of Jupiter's zonal jets. At high latitudes, VISIR images reveal a large region of mid‐infrared cooling poleward ∼64°N and ∼67°S extending from the upper troposphere to the stratosphere, co‐located with the reflective aerosols observed by JunoCam, and suggesting that aerosols play a key role in the radiative cooling at the poles. Comparison of zonal‐mean thermal properties and high‐resolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex. However, the southern stratospheric polar vortex is partly masked by a warm mid‐infrared signature of the aurora. Co‐located with the southern main auroral oval, this warming results from the auroral precipitation and/or joule heating which heat the atmosphere and thus cause a significant stratospheric emission. This high emission results from a large enhancement of both ethane and acetylene in the polar region, reinforcing the evidence of enhanced ion‐related chemistry in Jupiter's auroral regions. Plain Language Summary: A fundamental inquiry driving NASA's Juno mission was the investigation of the potential changes of Jupiter's famous banded structure below the top most clouds. As NASA's Juno spacecraft lacks instrumentation sensitive to the mid‐infrared, we have used the ground‐based Very Large Telescope Imager and Spectrometer (VISIR) on ESO's Very Large Telescope (VLT) to support the mission since 2016. The 2018 May data set provides a comprehensive view of Jupiter's pole‐to‐pole thermal, chemical, and aerosol structure; including the Great Red Spot; and the auroral‐related heating in the southern polar stratosphere. We show that the alternating pattern of cool cloudy zones and warm cloud‐free belts correlate to the zonal winds locations, extends from the equator to the boundary of the polar vortices (∼64°N and ∼67°S). Comparing this ground‐based data set with Juno observations, we show that the polar regions experience radiative cooling from the upper troposphere to the stratosphere, probably induced by the reflective polar aerosols, and confined at the poles by the polar vortices. However, the southern stratospheric polar vortex is partly masked by a large auroral emission, a signature of an interaction between the magnetosphere and stratosphere of Jupiter, which causes a ∼20 K warming as deep as the middle stratosphere. Excess hydrocarbons within the polar domain reinforces the evidence of enhanced ion‐related chemistry in Jupiter's auroral regions, resulting from charged particles precipitating from the top of the atmosphere to lower altitudes. Key Points: Jupiter's belt/zone thermal structure extends from the equator to the edge of the polar vortices and correlates with the zonal jetsThe cold polar vortices coincides with reflective aerosols, suggesting dynamical entrainment by the northernmost and southernmost jetsTemporal evolution of the southern auroral hotspot shows a stratospheric cooling after a solar wind compression event [ABSTRACT FROM AUTHOR]

Context. The Juno spacecraft has acquired exceptionally precise data on Jupiter's gravity field, offering invaluable insights into Jupiter's tidal response, interior structure, and dynamics, establishing crucial constraints. Aims. We aim to develop a new model for calculating Jupiter's tidal response based on its latest interior model, while also examining the significance of different dissipation processes for the evolution of its system. We studied the dissipation of dynamical tides in Jupiter by thermal, viscous, and molecular diffusivities acting on gravito-inertial waves in stably stratified zones and inertial waves in convection ones. Methods. We solved the linearised equations for the equilibrium tide. Next, we computed the dynamical tides using linear hydrodynamical simulations based on a spectral method. The Coriolis force is fully taken into account, but the centrifugal effect is neglected. We studied the dynamical tides occurring in Jupiter using internal structure models that respect Juno's constraints. We specifically looked at the dominant quadrupolar tidal components, and our focus is on the frequency range that corresponds to the tidal frequencies associated with Jupiter's Galilean satellites. Results. By incorporating the different dissipation mechanisms, we calculated the total dissipation and determined the imaginary part of the tidal Love number. We find a significant frequency dependence in dissipation spectra, indicating a strong relationship between dissipation and forcing frequency. Furthermore, our analysis reveals that, in the chosen parameter regime in which kinematic viscosity and thermal and molecular diffusivities are equal, the dominant mechanism contributing to dissipation is viscosity, exceeding both thermal and chemical dissipation in magnitude. We find that the presence of stably stratified zones plays an important role in explaining the high dissipation observed in Jupiter. [ABSTRACT FROM AUTHOR]

Based on a hybrid model of Europa's magnetospheric interaction, we provide context for the magnetic field perturbations observed by the Juno spacecraft during its only close flyby of the moon in September 2022. By systematically varying the incident flow conditions and the density profile of Europa's atmosphere, we demonstrate that the observed, large‐scale signatures of magnetic field draping are consistent with a dawn‐dusk asymmetry in the moon's neutral envelope. During the flyby, such an asymmetry would have enhanced the magnetic perturbations in Europa's anti‐Jovian hemisphere, explaining why the spacecraft already detected strong field line draping while still several moon radii away. Conversely, a reduced neutral density in the sub‐Jovian hemisphere can explain why the perturbations in the flow‐aligned field component remained nearly constant as Juno approached Europa. While a dawn‐dusk asymmetry in Europa's atmosphere has been predicted by theoretical work, our results provide the first in situ hints of its presence. Plain Language Summary: Located within Jupiter's magnetosphere, the small Galilean moon Europa is continuously exposed to a flow of magnetized plasma, traveling at a relative velocity of about 100 km/s. The deflection of this plasma around Europa generates perturbations to Jupiter's magnetic field, as observed for the first time in two decades during the flyby of the Juno spacecraft in 2022. The magnitude and extension of these magnetic perturbations are largely determined by the shape of Europa's atmosphere and ionosphere which represent obstacles to the incident magnetospheric plasma. To provide three‐dimensional context for the structure of Europa's magnetic environment at the time of the Juno flyby, we have applied a computer simulation to study the moon's interaction with the plasma flow. Comparison between modeled and observed magnetic fields suggests that, at the time when Juno collected these data, Europa's atmosphere may have been denser in the anti‐Jovian than in the Jupiter‐facing hemisphere. Theoretical predictions suggest such an asymmetry to be present in Europa's neutral envelope, partially generated by centrifugal and Coriolis forces acting on the gas molecules during the moon's rotation around Jupiter. Our study reveals first hints from a spacecraft flyby that such a hemispheric asymmetry may indeed exist in Europa's atmosphere. Key Points: By applying a hybrid model (kinetic ions, fluid electrons), we study Europa's interaction with Jupiter's magnetosphere during the Juno flybyA dawn‐dusk asymmetry in Europa's atmosphere can reproduce the large‐scale structure of the draping signatures seen by the Juno magnetometerThe spacecraft encountered the center of Europa's southern Alfven wing during ingress and the periphery of the northern wing during egress [ABSTRACT FROM AUTHOR]

Interchange instability is known to drive fast radial transport of particles in Jupiter's inner magnetosphere. Magnetic flux tubes associated with the interchange instability often coincide with changes in particle distributions and plasma waves, but further investigations are required to understand their detailed characteristics. We analyze representative interchange events observed by Juno, which exhibit intriguing features of particle distributions and plasma waves, including Z‐mode and whistler‐mode waves. These events occurred at an equatorial radial distance of ∼9 Jovian radii on the nightside, with Z‐mode waves observed at mid‐latitude and whistler‐mode waves near the equator. We calculate the linear growth rate of whistler‐mode and Z‐mode waves based on the observed plasma parameters and electron distributions and find that both waves can be locally generated within the interchanged flux tube. Our findings are important for understanding particle transport and generation of plasma waves in the magnetospheres of Jupiter and other planetary systems. Plain Language Summary: The centrifugal interchange instability, which has been observed in rapidly rotating planets, like Saturn and Jupiter, moves cold plasmas inside of the magnetosphere further away, and transports hotter, less dense plasmas toward the inner magnetosphere. These moving flux tubes have been observed at Jupiter together with plasma waves, but their detailed characteristics are not fully understood. In the present study, we use observations from the Juno spacecraft to report multiple representative interchange events and evaluate the properties of energetic particles and plasma waves. Furthermore, we use linear theory to calculate the growth rates of Z‐mode and whistler‐mode waves during these events. Our findings reveal the typical features of plasma waves and particles during interchange events, which provide important insights into particle transport and generation of plasma waves at Jupiter and possibly other magnetized planets in our solar system and beyond. Key Points: Several plasma transport events associated with interchange instability are identified alongside plasma waves using Juno observationsLinear growth rate analyses indicate that waves can be locally generated during interchange events due to anisotropic electron distributionsOur findings provide insights into electron transport and plasma wave dynamics during interchange events in planetary magnetospheres [ABSTRACT FROM AUTHOR]

At Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, except for Ganymede, they have been only remotely detected, using ground–based radio–telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the range of magnetic flux tubes which sustain the various Jupiter–satellite interactions, and in turn to sample in situ the associated radio emission regions. In this study, we focus on the detection and the characterization of radio sources associated with Io, Europa and Ganymede. Using electric wave measurements or radio observations (Juno/Waves), in situ electron measurements (Juno/JADE–E), and magnetic field measurements (Juno/MAG) we demonstrate that the Cyclotron Maser Instability (CMI) driven by a loss–cone electron distribution function is responsible for the encountered radio sources. We confirmed that radio emissions are associated with Main (MAW) or Reflected Alfvén Wing (RAW), but also show that for Europa and Ganymede, induced radio emissions are associated with Transhemispheric Electron Beam (TEB). For each traversed radio source, we determine the latitudinal extension, the CMI–resonant electron energy, and the bandwidth of the emission. We show that the presence of Alfvén perturbations and downward field–aligned currents are necessary for the radio emissions to be amplified. Plain Language Summary: At Jupiter, the auroras are much more intense and long‐lasting than on Earth, and some are influenced by Jupiter's three largest moons: Io, Europa, and Ganymede. We're particularly interested in the radio signals from these auroras. Until recently, these signals were mainly studied from a distance, using Earth‐based telescopes or spacecraft passing by Jupiter. However, since 2016, the Juno spacecraft has been orbiting Jupiter, flying through the auroral zone. Our study investigates the creation of these radio auroras using Juno's instruments to measure radio waves, particles, and magnetic fields. Our research strongly suggests that a phenomenon called the Cyclotron Maser Instability is the cause of these radio signals. This instability happens because some electrons are not coming back from Jupiter after causing Ultraviolet aurora on top of Jupiter's atmosphere. These radio signals are connected to the moons' ultraviolet auroras. Additionally, our research highlights the importance of specific perturbations in Jupiter's magnetic field, known as Alfvén perturbations, and currents that link Jupiter to these moons. This study deepens our understanding of Jupiter‐moon interactions and sheds light on Jupiter's fascinating auroras. Key Points: All Jupiter‐moon radio emissions are shown to be similarly triggered by the CMIThe crossed radio sources are colocated with either MAW, RAW or TEB footprintsThe crossed radio sources coincide with downward field‐aligned currents and Alfvén perturbations [ABSTRACT FROM AUTHOR]

On 29 September 2022 Juno's low‐light sensitive Stellar Reference Unit (SRU) captured a high‐resolution (256–340 m/pixel) broadband (450–1,100 nm) visible image of Europa's icy surface during the first close flyby of the Jovian moon since Galileo's last encounter in 2000. Collected at a sub‐spacecraft altitude of 412 km while the surface was illuminated only by Jupiter‐shine (incidence angle: 48–51°), the SRU image reveals a 3 × 104 km2 region between ∼0°–6°N and 43.5°–51°W in remarkable detail at the highest resolution to date. Prior coverage by Galileo under high‐sun conditions at 1 km resolution led to the characterization of the terrain as ridged plains with undifferentiated linea. The SRU image reveals a much richer and more complex picture. Intricate networks of cross‐cutting ridges and lineated bands surround an intriguing 37 km (east‐west) by 67 km (north‐south) chaos feature with a concentric fracture system, depressed matrix margins, and low‐albedo materials potentially associated with brine infiltration. The morphology and local relief of the chaos feature are consistent with formation in the collapse of ice overlying a salt‐rich lens of subsurface water. Low‐albedo deposits, similar to features previously associated with hypothesized cryovolcanic plume activity, flank nearby ridges. The SRU's high‐resolution view of many types of features in a single image allows us to explore their regional context and greatly improve the geologic mapping of this part of Europa's surface. The image reveals several relatively youthful features in a potentially dynamic region, providing baselines for candidate locations that future missions can investigate for present day surface activity. Plain Language Summary: On 29 September 2022, the Juno spacecraft performed the first close flyby of Jupiter's icy moon Europa in generation. The low‐light sensitive Juno SRU navigation camera was used to photograph a part of the surface that was lit only by sunlight scattered off Jupiter, from a spacecraft‐to‐surface distance of 412 km. This innovative use of a high‐resolution star camera designed to detect dim stars produced Juno's highest resolution image of Europa, and provides the highest resolution coverage of the targeted region to date. The imaged area is revealed to be incredibly complex and rich with many different types of terrains and features. Dark stains that may be associated with plumes, and an area of ice shell disruption nicknamed "the Platypus," are compelling targets for future missions to investigate possible present day surface activity. Key Points: Juno's Stellar Reference Unit imaged Europa's surface at high resolution while it was illuminated by Jupiter‐shineThe image reveals a feature‐rich region between 0°–6°N and 43.5°–51°W with hints of relatively recent activityA young 37 km by 67 km chaos feature and some low‐albedo deposits adjacent to double ridges may be associated with subsurface liquid water [ABSTRACT FROM AUTHOR]

On 29 September 2022 the Juno spacecraft flew within 354 km of Europa's surface while several instruments probed the moon's surroundings. During the close flyby, radio occultations were performed by collecting single‐frequency Doppler measurements. These investigations are essential to the study of Europa's ionosphere and represent the first repeat sampling of any set of conditions since the Galileo era. Ingress measurements resulted in a marginal detection with a peak ionospheric density of 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude. A more significant detection emerged on egress, with a peak density of 6,000 ± 3,000 cm−3 (3σ) at 320 km altitude. Comparison with Galileo measurements reveals a consistent picture of Europa's ionosphere, and confirms its dependence on illumination conditions and position within Jupiter's magnetosphere. However, the overall lower densities measured by Juno suggest a dependence on time of observation, with implications for the structure of the neutral atmosphere. Plain Language Summary: On 29 September 2022, NASA's Juno spacecraft flew very close to Jupiter's moon Europa. During the encounter, a radio occultation experiment was performed, where radio signals are exchanged between the spacecraft and ground stations as the former sets behind or rises from the moon as seen from the Earth. The scope of this experiment was studying the ionosphere of Europa, a layer of electrons and ions surrounding the moon. The Juno measurements confirmed the presence of the layer, with a structure similar to the one observed by the Galileo mission in the late 1990s. Key Points: Europa's ionosphere was detected from Juno's X‐band Doppler data via NASA's Deep Space Network during a close encounter in 2022Peak densities were 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude during ingress and 6,000 ± 3,000 cm−3 (3σ) at 320 km during egressThe Juno ionospheric profiles are consistent with Galileo measurements, and show a dependence on solar zenith and magnetospheric ram angles [ABSTRACT FROM AUTHOR]

Optical remote sensing observations have suggested that the top layer of Europa's icy surface is heavily affected by external weathering agents. To model and understand these effects, it is necessary to characterize the environment as fully as possible. In this paper, we focus on one agent in the environment (energetic electrons). We show Juno electron data from its 2022 Europa flyby and other time periods. While the Juno sensor used here (Jupiter Energetic Particle Detector Instrument) was not designed to obtain high quality electron data in an intense radiation environment, it is possible to extract information such as how Europa blocks energetic particles from accessing some of the surrounding space. The decrease in charged particle flux in Europa's wake provides an upper limit on the precipitation fluxes of the same particles. We also report that electron pitch angle distributions near Europa for the single energy channel considered here are time variable and not isotropic. Plain Language Summary: We present energetic electron data obtained when the Juno spacecraft crossed the plasma wake of the moon Europa in 2022. A major goal of this work is to estimate the amount of blockage of MeV electrons near the moon to inform radiation estimates for future Europa orbiters and landers. While the Jupiter Energetic Particle Detector Instrument does not directly detect particles between 1 and 20 MeV, using knowledge gained since the instrument began obtaining data we were able to estimate that about 80% of the particles in question are blocked by Europa in its wake at low altitude. Research on the weathering of Europa's surface by electrons is also discussed. Key Points: Jupiter Energetic Particle Detector Instrument electron data relevant to Europa are presentedWe estimate Europa's blockage causes an ∼80% reduction of ∼1–20 MeV electrons in the immediate plasma wakePitch angle distributions are computed from 70 keV electron data and show time variability [ABSTRACT FROM AUTHOR]

We compare Hubble Space Telescope observations of Jupiter's FUV auroras with contemporaneous conjugate Juno in situ observations in the equatorial middle magnetosphere of Jupiter. We show that bright patches on and equatorward of the main emission are associated with hot plasma injections driven by ongoing active magnetospheric convection. During the interval that Juno crossed the magnetic field lines threading the complex of auroral patches, a series of energetic particle injection signatures were observed, and immediately prior, the plasma data exhibited flux tube interchange events indicating ongoing convection. This presents the first direct evidence that auroral morphology previously termed "strong injections" is indeed a manifestation of magnetospheric injections, and that this morphology indicates that Jupiter's magnetosphere is undergoing an interval of active iogenic plasma outflow. Plain Language Summary: Auroras, known as the "Northern (or Southern) Lights" on Earth, are spectacular manifestations of energetic processes occurring in the space environment of a planet. The behavior of Jupiter's magnetosphere is dominated by the planet's rapid rotation, along with the centrifugally‐driven outflow of plasma (ionized gas) originating from active volcanoes on the moon Io. A prominent auroral feature on Jupiter has for many years been interpreted as a sign that Jupiter's magnetosphere is undergoing active convection, in which plasma from Io "falls" away from the planet, to be replaced by hot, relatively empty "bubbles" known as injections, moving inward. This feature comprises prominent patches of bright emission that are often observed in Jupiter's auroras, though the evidence associating them with injections has been largely circumstantial. Here we show that the NASA Juno spacecraft flew through such injections in the equatorial magnetosphere on magnetic field lines mapping to a cluster of auroral patches as observed by HST. The Juno data also indicated the interval was characterized by signatures of convection and outflow of plasma originating from Io. This demonstrates that auroral patches are signatures of injections, and that auroral emissions are an important tool for diagnosing the behavior of planetary magnetospheres. Key Points: Bright FUV auroral patches on Jupiter are associated with magnetospheric injections and magnetospheric convectionHubble Space Telescope and Juno equatorial data show a cluster of patches is magnetically conjugate with energetic particle injectionsThe interval also exhibits flux tube interchange and lagging magnetic field associated with plasma mass outflow [ABSTRACT FROM AUTHOR]

The first orbits around Jupiter of the Juno spacecraft in 2016 revealed a symmetric structure of multiple cyclones that remained stable over the next 5 years. Trajectories of individual cyclones indicated a consistent westward circumpolar motion around both poles. In this paper, we propose an explanation for this tendency using the concept of beta‐drift and a "center‐of‐mass" approach. We suggest that the motion of these cyclones as a group can be represented by an equivalent sole cyclone, which is continuously pushed by beta‐drift poleward and westward, embodying the westward motion of the individual cyclones. We support our hypothesis with 2D model simulations and observational evidence, demonstrating this mechanism for the westward drift. This study joins consistently with previous studies that revealed how aspects of these cyclones result from vorticity‐gradient forces, shedding light on the physical nature of Jupiter's polar cyclones. Plain Language Summary: The Juno spacecraft arrived at Jupiter in 2016, revealing a unique atmospheric phenomenon. Each of the poles of Jupiter is inhabited by a symmetrically structured group of cyclones, where a ring of cyclones surrounds one cyclone close to the pole. The collective observations of these cyclones over 5 years show that although they are relatively stable, they generally drift in the westward direction a few degrees per year. Here, we investigate the mechanism driving this drift by examining the cyclones as a group. This "center‐of‐mass" approach masks the interactions between the cyclones and only considers trends that happen simultaneously on all cyclones. Using model simulations, we show that the motion of a group's "center of mass" can be captured by a sole equivalent cyclone, pushed poleward and westward by the "beta‐drift" effect, which is known to contribute to the motion of tropical cyclones on Earth. This westward force on the group as a whole is thus suggested as the driver of the observed westward drift. We conclude by presenting observational evidence supporting this hypothesis. Key Points: The mean westward circumpolar motion of Jupiter's northern and southern polar cyclones is analyzed and explained by the β‐drift effectSimulations show that the "center of mass" of a group of cyclones behaves like one equivalent cyclone, moving poleward‐westward under β‐driftThis center‐of‐mass approach is applied to the Juno data, implying that the cyclones' collective β‐drift drives their observed westward drift [ABSTRACT FROM AUTHOR]

During its polar orbits around Jupiter, Juno often crosses the boundaries of the Jovian magnetosphere (namely the magnetopause and bow shock). From the boundary locations, the upstream solar wind dynamic pressure can be inferred, which in turn illustrates the state of compression or relaxation of the system. The aim of this study is to examine Jovian radio emissions during magnetospheric compressions, in order to determine the relationship between the solar wind and Jovian radio emissions. In this paper, we give a complete list of bow shock and magnetopause crossings (from June 2016 to August 2022), and the associated solar wind dynamic pressure and standoff distances inferred from Joy et al. (2002, https://doi.org/10.1029/2001JA009146). We then select two sets of magnetopause crossings with moderate to strong compression of the magnetosphere for two case studies of the response of the Jovian radio emissions. We confirm that magnetospheric compressions lead to the activation of new radio sources. Newly activated broadband kilometric emissions are observed almost simultaneously with compression of the magnetosphere, with sources covering a large range of longitudes. Decametric emission sources are seen to be activated more than one rotation later only at specific longitudes and dusk local times. Finally, the activation of narrowband kilometric radiation is not observed until the magnetosphere is in its expansion phase. Key Points: This paper provides a list of the Jovian magnetosphere boundary crossings by the Juno spacecraft from June 2016 to August 2022Jovian magnetospheric compressions lead to increased bKOM radio emissions (immediately) and DAM on the dusk sector (more than one rotation later)nKOM radio emission appears later during relaxation phase of the compression [ABSTRACT FROM AUTHOR]

We use the Kelvin‐Helmholtz instability (KHI) condition with particle and magnetic field observations from Jovian Auroral Distributions Experiment and MAG on Juno along the dawn flank of Jupiter's magnetosphere. We identify the occurrence of magnetopause crossings that show evidence of being KH (Kelvin‐Helmholtz) unstable. When estimating the k vector to be parallel to the velocity shear, we find that 25 of 62 (40%) magnetopause crossings satisfy the KHI condition. When considering the k vector of the maximum growth rate through a solid angle approach, we find that 60 of 62 (97%) events are KH unstable. This study shows evidence of KH waves at Jupiter's dawn flank, including primary drivers such as high velocity shears and changes in plasma pressure. Signatures of magnetic reconnection were also observed in ∼25% of the KH unstable crossings. We discuss these results and their implication for the prevalence of KHI at Juno's dawn magnetopause as measured by Juno. Plain Language Summary: The Kelvin‐Helmholtz instability occurs when a boundary separating two fluids of different densities is perturbed and these fluids are moving at different speeds, directions, or both. The difference in speeds across the perturbed boundary that separates the fluids creates wave structures as these fluids diffuse into each other. The Kelvin‐Helmholtz instability may be observed at the boundary that separates a planetary magnetic field (magnetosphere) from the stream of charged particles emitted by the Sun (solar wind); this boundary is known as the magnetopause. This instability is confirmed to occur at Earth and Saturn, but is not confirmed at Jupiter. This study analyzes the properties of the plasma and magnetic field in Jupiter's magnetosphere and the surrounding solar wind to identify signatures of the Kelvin‐Helmholtz instability. We find that out of 62 occurrences where the Juno spacecraft crosses the magnetopause, 25 events signify that the Kelvin‐Helmholtz instability is possible—primarily due to large differences in velocities—and 37 events do not. Key Points: There is evidence of Kelvin‐Helmholtz instability (KHI)‐driven waves along Jupiter's dawn flank magnetopause during the Juno prime mission24 (38.7%) crossings satisfied the KHI condition and 38 (61.3%) crossings did not satisfy the KHI conditionMagnetopause crossings that satisfied the KHI condition had, in general, larger velocity shears than those that did not [ABSTRACT FROM AUTHOR]

Jupiter's auroral emission is a spectacular phenomenon that provides insight into energy release processes related to the coupling of its magnetosphere and ionosphere. This energy release is influenced by solar wind conditions. Using joint observations from Juno and the Hubble Space Telescope (HST), we statistically investigate the relationship between auroral power and current sheet variations under different solar wind conditions. In this study, we reveal that during global main auroral brightening events that are closely connected to solar wind compressions, the dawn side current sheet is substantially thinner than during times when a quiet auroral morphology is present. Furthermore, the total current intensity in the current sheet is found to increase under solar wind compression conditions compared to the quiet period. These findings provide important observational evidence for how magnetospheric dynamics driven by solar wind behavior affect auroral activity, deepening our understanding of the coupling between Jupiter's magnetosphere and ionosphere. Plain Language Summary: Jupiter, the largest planet in our solar system, has a fascinating and powerful auroral emission that can help us understand the interactions between its magnetic field and the charged particles in its atmosphere. These auroral emissions are influenced by solar wind conditions, which are streams of charged particles coming from the Sun. In this study, we used observations from the Juno spacecraft and the Hubble Space Telescope to investigate the relationship between Jupiter's auroral emissions and changes in the planet's magnetic field. We found that during periods of increased solar wind pressure, the magnetic field layer, known as the current sheet, becomes thinner compared to times when the aurora is quiet. These findings offer valuable evidence of how Jupiter's magnetic field is affected by solar wind behavior and improve our understanding of the relationship between the planet's magnetic field and its aurora. This research helps us better comprehend the complex processes occurring in Jupiter's magnetosphere and can potentially enhance our knowledge of similar phenomena occurring on other planets. Key Points: The features of the current sheet in Jupiter's dawnside magnetosphere are highly relevant to auroral contextsDuring a solar wind compression event, the dawnside current sheet becomes substantially thinner than during quiet timesThe total current intensity of the current sheet is much higher during solar wind compression events than the quiet times [ABSTRACT FROM AUTHOR]

We characterize the precipitating electrons accelerated in the Europa‐magnetosphere interaction by analyzing in situ measurements and remote sensing observations recorded during 10 crossings of the flux tubes connected to Europa's auroral footprint tail by Juno. The electron downward energy flux, ranging from 34 to 0.8 mW/m2, exhibits an exponential decay as a function of downtail distance, with an e‐folding factor of 7.4°. Electrons are accelerated at energies between 0.3 and 25 keV, with a characteristic energy that decreases downtail. The electron distributions form non‐monotonic spectra in the near tail (i.e., within an angular separation of less than 4°) that become broadband in the far tail. The size of the interaction region at the equator is estimated to be 4.2 ± 0.9 Europa radii, consistent with previous estimates based on theory and UV observations. Plain Language Summary: The space environment close to Jupiter is dominated by the magnetic field of the giant planet in a so‐called magnetosphere. The four Galilean moons, including Europa, orbit deep inside the Jovian magnetosphere and therefore constantly interact with the rapidly rotating plasma flow made of charged particles trapped by the magnetic field of the giant planet. The interaction between moons and plasma generates electromagnetic waves, accelerate particles and produce emissions at various wavelengths, including bright UV auroral spots and tails in the atmosphere of Jupiter. In this work, we present 10 events where the Juno spacecraft observed both in situ and remotely the acceleration of electrons due to the interaction between the icy moon Europa and the magnetospheric environment. We characterize the properties of the accelerated electrons. In particular, we find that acceleration is maximum near the moon itself, and that two distinct families of electron distributions exist. Key Points: Juno unambiguously observed 10 events of downward electron acceleration from Europa at various downtail separations with the moonPrecipitating energy fluxes decrease exponentially as a function of downtail distance from the moon, with an e‐folding of 7.4°Two types of electron distributions exist: non‐monotonic in the near tail and broadband in the far tail [ABSTRACT FROM AUTHOR]

We use data from the plasma and energetic particle instruments on the Juno spacecraft, JADE and JEDI, to study the equatorial pitch angle distributions of energetic protons within Jupiter's inner magnetosphere during Juno's prime mission from 2016 to 2021. Averaging over all observations made by Juno within M‐shell bins between M = 6 and M = 30, we find protons at energies between 10 and 50 keV are predominantly field‐aligned at all M‐shells. In contrast, those at energies above 200 keV transition from being predominantly field‐aligned at M = 20 to having pancake‐like distributions at M < 10. We find the observed distributions are consistent either with charge exchange of protons with neutral toroidal clouds, or with adiabatic acceleration of protons originating from Jupiter that are transported inward from the middle magnetosphere. Plain Language Summary: Protons are seen throughout Jupiter's magnetosphere. Where these protons come from and how they evolve is not well understood. Previous observations by the Galileo spacecraft showed that protons in the vicinity of Europa have properties consistent with charge exchange with a neutral species, which effectively removes the charged particles from the magnetosphere. Using data from the Juno spacecraft, we survey proton distributions at different energies. Although charge exchange remains a plausible explanation for the observations, another possibility is that the distribution is a result of adiabatically transporting the protons through Jupiter's magnetic field. Key Points: 10–50 keV protons at Jupiter are predominantly field‐aligned at M‐shells between M = 7 and M = 20Normalized pitch angle distributions of >200 keV protons show evidence of adiabatic acceleration during inward radial transportObserved proton distributions could result from charge‐exchange with neutrals or conservation of adiabatic invariants during transport [ABSTRACT FROM AUTHOR]

Juno observations show dust halo near Mars, contributing to Zodiacal light, the source of which is yet to be known. It is interesting for scientists to understand whether dust primarily comes from the Martian moons. Here, we investigate Phobos/Deimos as likely sources of interplanetary dust near Mars. Incoming dust at the Martian moons impact their surface and produce ejecta, a part of which can escape easily to space. Results of escaping mass rates are presented and compared with incoming mass rates through a parameter called mass escape ratio. The results show higher ratio for a wide range of particles, inferring a large amount of effective mass loss from the moons. From whatever is lost, smaller particles (<0.1 µm) can escape, while larger particles are influenced by the gravitational pull of Mars. Furthermore, from the larger particles, those with sizes greater than critical size (i.e. ∼10 µm) remain in a ring/torus for a specific lifetime and afterwards, they get released from the gravitational effect of Mars. Since, incoming dust creates the ejecta continuously from Phobos/Deimos, the process of the release of particles after the lifetime is also continuous. On the other side, flux of interplanetary dust is derived from Juno observations of dust impact rates between 1 and 5 au heliocentric distance. An increase in the flux observed by Juno around 1.5 au and the results of larger, continuous escaping mass from the moons indicate Phobos and Deimos to be the local sources of dust bands observed by Juno spacecraft. [ABSTRACT FROM AUTHOR]

Juno's highly inclined orbits provide opportunities to sample high‐latitude magnetic field lines connected to the orbit of Io, among the other Galilean satellites. Its payload offers both remote‐sensing and in‐situ measurements of the Io‐Jupiter interaction. These are at discrete points along Io's footprint tail and at least one event (12th perijove) was confirmed to be on a flux tube Alfvénically connected to Io, allowing for an investigation of how the interaction evolves down‐tail. Here we present Alfvén Poynting fluxes and field‐aligned current densities along field lines connected to Io and its orbit. We explore their dependence as a function of down‐tail distance and show the expected decay as seen in UV brightness and electron energy fluxes. We show that the Alfvén Poynting and electron energy fluxes are highly correlated and related by an efficiency that is fully consistent with acceleration from Alfvén wave filamentation via a turbulent cascade process. Plain Language Summary: Io and Jupiter are electrodynamically coupled resulting in the Io footprint tail. This is one of the most persistent, stable, and recognizable features of Jupiter's aurora. The Juno spacecraft routinely samples magnetic field lines connected to Io's orbit, allowing for an investigation of this powerful coupling. We use data recorded by Juno to estimate a proxy for the strength of this interaction, that is, electromagnetic energy, and show its dependence downstream of Io and how the interaction decays. We further show that the available electromagnetic energy and electron energy are intimately linked, suggesting a transfer of energy between wave and particles. This is the basis upon which electrons end up precipitating into Jupiter's upper atmosphere and generate some of the brightest auroras. Key Points: Alfvénic Poynting fluxes and electron energy fluxes are highly correlated on magnetic field lines connected to Io's orbitThe efficiency in the Main Alfvén Wing is ∼10%, fully consistent with Alfvén wave filamentation via a turbulent cascade processField‐aligned current densities are quantified and exhibit a decay in magnitude down‐tail of Io [ABSTRACT FROM AUTHOR]

We report some of the most intense Z‐mode and O‐mode observations obtained by the Juno spacecraft while in orbit about Jupiter in a low to mid‐latitude region near the inner edge of the Io torus. We have been able to estimate the density of the plasma in this region based on the lower frequency cutoff of the observed Z‐mode emission. The results are compatible with the electron density measurements of the Jovian Auroral Distributions Experiment (JADE), on board the Juno spacecraft, if we account for unmeasured cold plasma. Direction‐finding measurements indicate that the Z‐ and O‐mode emission have distinct source regions. We have also used the measured phase space density of the JADE and the Jupiter energetic particle detector instruments to calculate estimated local growth rates of the observed O‐mode and Z‐mode emission assuming a loss cone instability and quasilinear analysis. The results suggest the emissions were observed near, but not within, a source region, and the free energy source is consistent with a loss cone. We have thus carried out the quasilinear wave analysis of the assumed remote Z‐ and O‐mode wave growths. It is shown that the remotely generated waves, propagated through an inhomogeneous medium to the satellite location, may account for the observed wave characteristics. The importance of Z‐mode in accelerating electrons in the inner Jovian magnetosphere makes these new wave mode confirmations at Jupiter of particular interest. Key Points: Intense Z‐mode and O‐mode in the Jovian inner magnetosphere yield important plasma parametersDirection finding suggests that each mode is from a different source regionQuasilinear wave analysis of in‐situ phase space density provides wave growth temporal development [ABSTRACT FROM AUTHOR]

Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter's magnetotail provides an almost ideal environment to study high-energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high-energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts. [ABSTRACT FROM AUTHOR]

The driver of energetic electron precipitation into Ganymede's atmosphere has been an outstanding open problem. During the Juno flyby of Ganymede on 7 June 2021, Juno observed significant downward‐going electron fluxes inside the bounce loss cone of Ganymede's polar magnetosphere. Concurrently, Juno detected intense whistler‐mode waves, both in the quasi‐parallel and highly oblique directions with respect to the magnetic field line. We use quasi‐linear model to quantify energetic electron precipitation driven by quasi‐parallel and very oblique whistler‐mode waves, respectively, in the vicinity of Ganymede. The data‐model comparison indicates that in Ganymede's lower‐latitude (higher‐latitude) polar region, quasi‐parallel whistler‐mode waves play a dominant role in precipitating higher‐energy electrons above ∼100s eV (∼1 keV), whereas highly oblique waves are important for precipitating lower‐energy electrons below 100s eV (∼1 keV). Our result provides new evidence of whistler‐mode waves as a potential primary driver of precipitating energetic electrons into Ganymede's atmosphere. Plain Language Summary: During the Juno flyby of Ganymede on 7 June 2021, the Juno spacecraft detected energetic electrons precipitating into Ganymede's atmosphere. Simultaneously, Juno detected intense electromagnetic whistler‐mode waves in the vicinity of Ganymede. We use a physics‐based model to quantify the role of the observed whistler‐mode waves in energetic electron precipitation. The comparison between the Juno observation and modeling results reveals that whistler‐mode waves potentially play a dominant role in precipitating energetic electrons into Ganymede's atmosphere over a broad energy range from tens of eV to several hundred keV. Our findings are potentially important for understanding the loss process of energetic electrons in Ganymede's magnetosphere, as well as the generation of Ganymede's diffuse aurora. Key Points: We provide new evidence of whistler‐mode waves as a potential primary driver of precipitating energetic electrons into Ganymede's atmosphereThis finding is potentially important for the generation of aurora and the loss of energetic electrons in the vicinity of GanymedeJuno observations and quasi‐linear modeling are used to quantify energetic electron precipitation driven by whistler‐mode waves [ABSTRACT FROM AUTHOR]

Context. The Juno spacecraft has obtained highly accurate tidal Love numbers, which provide important constraints on the tidal response and interior structure of Jupiter. Aims. In order to exploit these observations, it is necessary to develop an approach to accurately calculate the tidal response of Jupiter for a given interior model and to investigate the role of the interior structure. Methods. We directly solve the linearized tidal equations of a compressible, self-gravitating, rotating, and viscous fluid body using a pseudo-spectral method. The Coriolis force is fully taken into account, but the centrifugal effect is neglected. We are able to simultaneously obtain the real and imaginary parts of the tidal Love numbers for a given planetary interior model. Results. We calculated the tidal responses for three simplified interior models of Jupiter which may contain a compact rigid core or an extended dilute core. All of the models we consider can explain the fractional correction ∆k22 ≈ −4% due to dynamical tides, but they all have difficulties reconciling the observed ∆k42 ≈ −11% for the high-degree tidal Love number. We show that the Coriolis force significantly modifies gravity modes in an extended dilute core at the tidal frequency relevant to the Galilean satellites. We demonstrate that the existence of a thin stable layer in the outer region would also influence the tidal responses of Jupiter. [ABSTRACT FROM AUTHOR]

We present the first estimation of the energy cascade rate in Jupiter's magnetosheath (MS). We use in situ observations from the Jovian Auroral Distributions Experiment and the magnetometer investigation instruments on board the Juno spacecraft, in concert with two recent compressible models, to investigate the cascade rate in the magnetohydrodynamic (MHD) scales. While a high level of compressible density fluctuations is observed in the Jovian MS, a constant energy flux exists in the MHD inertial range. The compressible isothermal and polytropic energy cascade rates increase in the MHD range when density fluctuations are present. We find that the energy cascade rate in Jupiter's magnetosheath is at least 2 orders of magnitude (100 times) smaller than the corresponding typical value in the Earth's magnetosheath. [ABSTRACT FROM AUTHOR]

The first observation of possible transient luminous events (TLEs) on Jupiter was reported recently. Whereas initiation of elves on Jupiter has been theoretically studied before, the possibility of sprite streamer inception on Jupiter has not been investigated yet. Here we critically review the literature concerned with TLEs on Jupiter. Subsequently, we report on development of a numerical model for modeling of magnetized streamers in presence of Jupiter's strong magnetic field. The model utilizes the knowledge provided by recent observations of Jupiter's lightning and magnetic field by the Juno spacecraft. It is demonstrated that sprite streamer inception under realistic atmospheric conditions on Jupiter is possible. Plain Language Summary: Transient luminous events are large scale (thousands of cubic kilometers) gas discharges produced at low air densities at high altitudes in the Earth's atmosphere. These events are driven by intense lightning discharges in underlying thunderstorms at tropospheric altitudes. Recently the first observation of lightning‐related transient luminous events in Jupiter's ionosphere was reported. Considering Jupiter's conditions, we present here the first modeling of filamentary plasma structures called streamers that are known to produce the brightest optical emissions among different types of transient luminous events in the Earth's atmosphere. In contrast the streamer plasma in Jupiter's atmosphere is strongly magnetized. Key Points: Inception of sprite streamers under realistic atmospheric conditions on Jupiter is possibleDue to Jupiter's strong magnetic field at altitudes where possible transient luminous events emerge, the gas discharge plasma is magnetizedContribution of H2 photoionization due to extreme ultraviolet emissions from atomic helium to streamer propagation is negligible [ABSTRACT FROM AUTHOR]

Reflected sunlight observations from the Ultraviolet Spectrograph (UVS) on the Juno spacecraft were used to study the distribution of acetylene (C2H2) at Jupiter's south pole. We find that the shape of the C2H2 absorption feature varies significantly across the polar region, and this can be used to infer spatial variability in the C2H2 abundance. There is a localized region of enhanced C2H2 absorption which coincides with the location of Jupiter's southern polar aurora; the C2H2 abundance poleward of the auroral oval is a factor of 3 higher than adjacent quiescent, non‐auroral longitudes. This builds on previous infrared studies, which found enhanced C2H2 abundances within the northern auroral oval. This suggests that Jupiter's upper‐atmosphere chemistry is being strongly influenced by the influx of charged auroral particles and demonstrates the necessity of developing ion‐neutral photochemical models of Jupiter's polar regions. Plain Language Summary: The Ultraviolet Spectrograph on the Juno mission to Jupiter measures ultraviolet sunlight that is reflected from the planet's upper atmosphere and these observations can be used to measure the abundances of different gases in the stratosphere. In this paper, we study the spatial distribution of the molecule acetylene at Jupiter's south pole. We find that there is a significant increase in the acetylene abundance at the location of Jupiter's southern aurora. This suggests that the charged particles that travel along magnetic field lines toward Jupiter's poles and produce bright auroral emission also have a strong influence on the chemistry of Jupiter's upper atmosphere. Key Points: Ultraviolet reflected sunlight observations from Juno Ultraviolet Spectrograph were used to study the distribution of C2H2 at Jupiter's south poleFrom the changes in the spectral shape, we infer enhanced C2H2 absorption within the southern auroral ovalJupiter's atmospheric chemistry at the poles is strongly influenced by the influx of charged auroral particles [ABSTRACT FROM AUTHOR]

Ability to quantify variations in magnetic field topology and density within Jupiter's magnetosphere is an important step in understanding the overall structure and dynamics. The Juno spacecraft has provided a rich data set in the dawnside magnetosphere. The recent Grid Agnostic MHD for Extended Research Applications (GAMERA) global simulation study by Zhang et al. (2021, https://doi.org/10.1126/sciadv.abd1204) showed a highly structured plasmadisc with closed magnetic field lines mapped between the outer dawn‐tail flank and the high‐latitude polar region. To test these model predictions, we examined Juno's magnetic field data and electron/energetic particle data to categorize portions of orbits 1–15 into one of three regions based on plasma confinement: the flux pileup region, the intermediate region, and the plasmadisc region. For each region we examined periodicities from magnetic field fluctuations and particle density fluctuations on the 1–10 hr time scale. Periodicities on this time scale could relate to internal (e.g., plasmadisc structure) or external processes (e.g., Kelvin‐Helmholtz vortices). Similar analysis was performed on the GAMERA simulation with the data split into two regions, an outer (150 > R > 60) region and an inner (R < 60) region. Finally, using published density moments from Huscher et al. (2021, https://doi.org/10.1029/2021JA029446), we compared the relative density variations of the Juno moments and the GAMERA simulation to further understand the overall structure and dynamics of the plasmadisc. The agreement between data and simulation supports the existence of such a highly structured plasmadisc. Plain Language Summary: A very complex and poorly understood problem of Jupiter is the structure and dynamics of the planet's space environment (i.e., "magnetosphere"), due to its sheer size and unique internal ionized gas (i.e., plasma) sourced from the moon, Io. Thanks to the Juno mission, we are able to analyze data from previously unexplored regions around the planet. It has been demonstrated using Voyager data that ionized gas from Io formed a plasma disc‐like structure around the planet in the equatorial plane, becoming less confined in the outer regions. Computer simulations showed a similar structure. In order to investigate this structure, we utilized magnetic field data and particle data from the Juno spacecraft. This data was analyzed to understand the occurrence of regular fluctuations in the magnetic field and gas density, and to understand spatial domains where regular fluctuations occur. Similar analysis was done on magnetic field and density data from simulations for comparison. We found relations between the Juno data and simulation data that suggest a much more variable and structured plasma disc as well as a region in the dawn/tail flank that is magnetically connected to the high latitude polar region. Key Points: Three‐regions with different plasma confinement characteristics have been identified in Jupiter's dawn to postmidnight magnetosphereComparison of Juno data and Grid Agnostic MHD for Extended Research Applications simulations suggest a very structured plasmadiscPeriodicities in 1–4 hr range could be related to plasmadisc structure [ABSTRACT FROM AUTHOR]

In this work, we present the most updated catalog of Io hot spots based on Juno/JIRAM data. We find 242 hot spots, including 23 previously undetected. Over the half of the new hot spots identified, are located at high northern and southern latitudes (>70°). We observe a latitudinal variability and a larger concentration of hot spots in the polar regions, in particular in the North. The comparison between JIRAM and the most recent Io hot spot catalogs listing power output (Veeder et al., 2015, https://doi.org/10.1016/j.icarus.2014.07.028; de Kleer, de Pater, et al., 2019, https://doi.org/10.3847/1538-3881/ab2380), shows JIRAM detected 63% and 88% of the total number of hot spots, respectively. Furthermore, JIRAM observed 16 of the 34 faint hot spots previously identified. JIRAM data revealed thermal emission from 5 dark pateræ inferred to be active from color ratio images, thus confirming that these are hot spots. Plain Language Summary: We mapped the hot spot distribution on Io's surface by analyzing the images acquired by the JIRAM instrument onboard the Juno spacecraft. We identified 242 hot spots, including 23 not present in other catalogs. A large number of the new hot spots identified are in the polar regions, specifically in the northern hemisphere. The comparison between our work and the most recent and updated catalog reveals that JIRAM detected 82% of the most powerful hot spots previously identified and half of the intermediate‐power hot spots, thus showing that these are still active. JIRAM detected 16 out of the 34 faint hot spots previously reported. The resolution of JIRAM may not have been sufficient to detect these faint hot spots, or activity might have faded or stopped. Key Points: We produced a new Io hot spot map based on Juno/JIRAM dataWe identified 242 hot spots, including 23 previously undetectedThe latitudinal hot spot distribution is uneven with a larger concentration at the poles [ABSTRACT FROM AUTHOR]

On 7 June 2021 the Juno spacecraft visited Ganymede and provided the first in situ observations since Galileo's last flyby in 2000. The measurements obtained along a one‐dimensional trajectory can be brought into global context with the help of three‐dimensional magnetospheric models. Here we apply the magnetohydrodynamic model of Duling et al. (2014, https://doi.org/10.1002/2013ja019554) to conditions during the Juno flyby. In addition to the global distribution of plasma variables we provide mapping of Juno's position along magnetic field lines, Juno's distance from closed field lines and detailed information about the magnetic field's topology. We find that Juno did not enter the closed field line region and that the boundary between open and closed field lines on the surface matches the poleward edges of the observed auroral ovals. To estimate the sensitivity of the model results, we carry out a parameter study with different upstream plasma conditions and other model parameters. Plain Language Summary: In June 2021 the Juno spacecraft flew close to Ganymede, the largest moon of Jupiter, and explored its magnetic and plasma environment. Ganymede's own magnetic field forms a magnetosphere, which is embedded in Jupiter's large‐scale magnetosphere, and which is unique in the solar system. The vicinity of Ganymede is separated into regions that differ in whether the magnetic field lines connect to Ganymede's surface at both or one end or not at all. These regions are deformed by the plasma flow and determine the state of the plasma and the location of Ganymede's aurora. We perform simulations of the plasma flow and interaction to reveal the three‐dimensional structure of Ganymede's magnetosphere during the flyby of Juno. The model provides the three‐dimensional state of the plasma and magnetic field, predicted locations of the aurora and the geometrical magnetic context for Juno's trajectory. These results are helpful for the interpretation of the in situ and remote sensing obtained during the flyby. We find that Juno did not cross the region with field lines that connect to Ganymede's surface at both ends. Considering possible values for unknown model parameters, we also estimate the uncertainty of the model results. Key Points: Our magnetohydrodynamic model illustrates the state of Ganymede's magnetosphere during Juno's flyby and locates its trajectory outside closed field linesThe location of the open‐closed‐field line‐boundary is predicted and matches the poleward edges of the aurora as observed by JunoWe investigate model uncertainties caused by incomplete knowledge of upstream conditions and other parameters [ABSTRACT FROM AUTHOR]

On 7 June 2021 the Juno spacecraft passed through the Ganymede magnetosphere, with a closest approach altitude of 1,046 km. The Jovian Auroral Distributions Experiment‐Ion (JADE‐I) sensor observed ionospheric ions, consisting of O2+, O+, H2+, H+, and H3+. These ions were outflowing, with no bi‐directional flow except possibly near the magnetopause. Relative ion densities with respect to time agree the electron density determined by the Waves instrument, but are ∼2.5 times larger. The light ions appear to be in hydrostatic equilibrium because the altitude profile is generally symmetric between 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. Plain Language Summary: On 7 June 2021 the Juno spacecraft passed through the Ganymede magnetosphere, with a closest approach altitude of 1,046 km. During this flyby, the Jovian Auroral Distributions Experiment‐Ion (JADE‐I) sensor observed ions flowing out from the ionosphere. The JADE‐I observations are the first direct measurement of the composition of the ionospheric ions. This is an important measurement since there is currently not consensus of the composition. These ionospheric ions consist of O2+, O+, H2+, H+, and H3+. The different species have different altitude profiles. The light ions altitude profile is generally symmetric between 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. Key Points: First in situ, ion composition observations of Ganymede's outflowing ionosphereLow energy ions consist of O2+, O+, H2+, H+, and H3+Light ions and heavy have different altitude profiles and spatial profiles [ABSTRACT FROM AUTHOR]

On 7 June 2021, Juno crossed the orbital path of Jupiter's moon Ganymede, flying within 1,046 km of the surface. Juno's low‐light‐sensitive Stellar Reference Unit (SRU) navigation camera captured an image of the satellite's dark side in a region of Xibalba Sulcus illuminated solely by Jupiter‐shine. Collected at high incidence angle with 670–920 m/pixel resolution, the image reveals terrain morphology, ejecta, and numerous small craters that cannot be discerned in the Voyager imagery used for the USGS global geologic map of Ganymede. The Juno data enable improved mapping of Ganymede's surface and reinterpretation of material and crater ages in a region previously characterized as light "undivided" material due to poor image resolution. The illumination conditions achieved by the SRU observation geometry also reveal the detailed morphology of a 270‐km elongated bright feature in this area. These newly resolved features contribute to an improved understanding of Ganymede's complex history. Plain Language Summary: On 7 June 2021, the Juno spacecraft flew within about 1,000 km of the surface of Jupiter's largest moon, Ganymede. The Mission used their sensitive navigation camera to photograph the moon's dark side where it was lit only by scattered sunlight from Jupiter. This new imaging approach revealed multiple surface features, including a patchwork of different surface textures (such as grooved terrain), several craters, and ejecta deposits. These features had not been visible in images collected by previous spacecraft. Well‐resolved details of the surface structure help us understand Ganymede's history and the processes responsible for how it appears today. One feature may either be ejecta from a very distant crater or scars from the pieces of a broken up comet that collided with Ganymede. Key Points: Juno's Stellar Reference Unit imaged Ganymede at high resolution and incidence angle while the surface was illuminated by Jupiter‐shineGrooved material, ejecta, and multiple craters are now resolved, enabling improved mapping of a 2 × 105 km2 region in Xibalba SulcusThe unique morphology of a possible 270‐km scar from comet fragments, or a highly isolated distal ray from Tros, is revealed [ABSTRACT FROM AUTHOR]

During the Juno orbit 34 Ganymede encounter, the ultraviolet spectrograph mapped UV sunlight reflected by Ganymede from a closest approach altitude of 1,044 km, allowing us to study spatial variations in Ganymede's far ultraviolet reflectance at higher resolution than has previously been possible. We find that a characteristic signature of water ice seen around 165 nm in laboratory spectra is absent over much of the observed area, but is detectable in the north high latitude region. We suggest that the spectral difference between the high latitudes and other icy regions, such as Tros crater, may be explained by the presence of additional UV‐absorbing contaminants such as NH3 at lower latitudes. We also note a decrease in the relative reflectance of the high latitude regions at wavelengths >190 nm, which may be the start of a previously observed ozone absorption feature. Plain Language Summary: The ultraviolet spectrograph (UVS) instrument on the Juno spacecraft observed ultraviolet sunlight reflected by the surface of Jupiter's largest moon, Ganymede. Although we know from previous observations that Ganymede's surface contains a large amount of water ice, we found that Ganymede does not reflect ultraviolet light in the way we expected: while water ice is very reflective at ultraviolet wavelengths longer than 165 nm, Ganymede's surface does not reflect well at these wavelengths. The northern high latitudes were found to be more reflective than the low latitudes, suggesting that the polar regions are more water‐ice rich than parts of the surface closer to the equator. The bright Tros crater, which is known to contain a large amount of water ice, had a low UV reflectance, which we suggest may be due to UV‐absorbing material trapped within the ice there. These results will be useful for planning future investigations of Ganymede's surface composition by the UVS instrument on the upcoming JUICE mission, which will tour all three of Jupiter's icy moons before entering orbit around Ganymede. Key Points: Juno ultraviolet spectrograph mapped UV sunlight reflected by Ganymede's surface during the Juno orbit 34 Ganymede flybyThe UV signature of pure water ice was detected in the north polar regions but not within other ice‐rich regions including Tros craterAdditional absorption features observed may be related to ammonia and ozone [ABSTRACT FROM AUTHOR]

We report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on 7 June 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant timevariability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m−2 are required for its OI 1,356 Å emission making Ganymede a very poor auroral emitter. Plain Language Summary: Jupiter's moon Ganymede is the largest moon in the solar system and the only known moon with an intrinsic magnetic field and two auroral ovals around its north and south poles. Earth also possesses two auroral ovals, which are bands of emission around its poles. This emission is also referred to as northern and southern lights. We use the Hubble Space Telescope to observe Ganymede's aurora around the time when NASA's Juno spacecraft had a close flyby at Ganymede. We find that the brightness of the northern and southern ovals alternate in intensity with a period of 10 hr. Additionally, we derive that an energy flux of several tens of milli‐Watt per square meter is necessary to power the auroral emission. This energy flux comes from energetic electrons accelerated in the vicinity of Ganymede. Key Points: Hubble Space Telescope observations of Ganymede's orbitally trailing hemisphere on 7 June 2021 in support of Juno flybyBrightness ratio of northern and southern auroral ovals oscillates such that the oval facing the Jovian plasma sheet is brighterOscillation suggests the aurora is driven by magnetic stresses coupling the moon's magnetic field to the surrounding Jovian plasma sheet [ABSTRACT FROM AUTHOR]

The Juno spacecraft has been in orbit around Jupiter since 2016. Two flybys of Ganymede were executed in 2021, opportunities realized by evolution of Juno's polar orbit over the intervening 5 years. The geometry of the close flyby just prior to the 34th perijove pass by Jupiter brought the spacecraft inside Ganymede's unique magnetosphere. Juno's payload, designed to study Jupiter's magnetosphere, had ample dynamic range to study Ganymede's magnetosphere. The Juno radio system was used both for gravity measurements and for study of Ganymede's ionosphere. Remote sensing of Ganymede returned new results on geology, surface composition, and thermal properties of the surface and subsurface. Plain Language Summary: The evolution of Juno's orbit around Jupiter made it possible to execute a close and a distant flyby of Ganymede in 2021. The geometry of the close pass allowed Juno to enter Ganymede's unique magnetosphere. Juno's remote sensing instruments observed a significant area of Ganymede's surface and subsurface with higher resolution than Voyager or Galileo. Key Points: Juno passed Ganymede on 7 June 2021 at an altitude of approximately 1,000 km, the closest any spacecraft has come since the Galileo mission ended in 2003The path of Juno's trajectory allowed the spacecraft to pierce Ganymede's unique magnetosphere and map a swath of its surface and subsurfaceThe geometry of the flyby is described for the close pass in June and a more distant pass (approximately 50,000 km) on 20 July 2021 [ABSTRACT FROM AUTHOR]

The JEDI instrument made measurements of energetic charged particles near Ganymede during a close encounter with that moon. Here we find ion flux levels are similar close to Ganymede itself but outside its magnetosphere and on near wake and open field lines. But energetic electron flux levels are more than a factor of 2 lower on polar and near‐wake field lines than on nearby Jovian field lines at all energies reported here. Flux levels are relevant to the weathering of the surface, particularly processes that affect the distribution of ice, since surface brightness has been linked to the open‐closed field line boundary. For this reason, we estimate the sputtering rates expected in the polar regions due to energetic heavy ions. Other rates, such as those related to radiolysis by plasma and particles that can reach the surface, need to be added to complete the picture of charged particle weathering. Plain Language Summary: This paper uses Juno data to quantify the levels of energetic charged particle flux near Jupiter's moon Ganymede. We have computed energy spectra (energy vs. charged particle intensity) for electrons, protons, oxygen and sulfur ions, from a near encounter of Ganymede by the Juno spacecraft in June 2021. Particle fluxes may be important for weathering processes on Ganymede, such as the sputtering of water ice in the top layer. The distribution of water ice in the upper layer of Ganymede's surface does not appear to be consistent with sublimation alone, so questions remain about which processes are dominant in shaping the ice distribution. Quantification of the flux levels is also needed for planning, for example, for ESA's JUICE mission, expected to orbit Ganymede in the future. Key Points: We present energy spectra from energetic charged particle data from Juno's close flyby of Ganymede in 2021We find a drop in electron fluxes on polar field lines compared to the surrounding region whereas ion fluxes are similar in both regionsWe compute sputtering rates to evaluate particle weathering, as a step toward understanding the distribution of Ganymede's surface ice [ABSTRACT FROM AUTHOR]

In June 2021, the Juno spacecraft executed a close flyby of Ganymede. During the encounter, Juno passed behind Ganymede for 15 min as observed from Earth, providing the geometry to conduct a radio occultation experiment to probe Ganymede's tenuous ionosphere. X‐band and Ka‐band radio links were transmitted from Juno to antennas at the Deep Space Network. Electrons encountered along the radio propagation path advance the signal's phase and a linear combination the two frequencies allows for a direct measurement of the electron content along the propagation path. On occultation ingress, an ionosphere peak of 2,000 ± 500 (1‐σ) cm−3 near the surface was observed. On occultation egress, no statistically significant ionosphere was detected. Ingress observation viewed where Ganymede's intrinsic magnetic field lines are open whereas egress observation viewed where the field lines are closed, implying electron impact ionization plays a key role in the generation of the ionosphere. Plain Language Summary: Juno conducted a flyby of Ganymede, the largest Galilean moon of Jupiter, on 7 June 2021. During the flyby, the Juno spacecraft set behind Ganymede as observed by the Earth. Juno's radio signals were captured by the Deep Space Network during this time to make radio occultation measurements of Ganymede's ionosphere. Elevated electron density was measured on occultation ingress but no statistically significant ionosphere was detected on egress. These results are consistent with Galileo's radio occultation observations and provide insight into the generation mechanisms of Ganymede's ionosphere. Key Points: A dual‐frequency radio occultation experiment of Ganymede's ionosphere was conducted with the Juno spacecraft on 7 June 2021Ingress observed an ionosphere with peak density 2,000 ± 500 (1‐σ) cm−3 but no statistically significant signature was detected on egressIngress detection occurred in the open field line region, where higher electron impact ionization rates may increase the electron density [ABSTRACT FROM AUTHOR]

We investigate the small‐scale magnetic field fluctuations and their associated turbulent nature in the Io flux tube (IFT) connected to Io's footprint tail (IFPT). Our study is based on the recent magnetic field measurements by the Juno spacecraft during the PJ12 Juno flyby. Here, we are interested in understanding what type of turbulence is consistent with the fluctuations in the quasi‐dispersionless frequency range of 0.2–800 Hz as observed by Sulaiman et al. (2020), https://doi.org/10.1029/2020GL088432. Knowledge of the turbulent fluctuations is important to constrain the acceleration mechanisms for ions and electrons in the IFT. In this work, we suggest that the observed temporal fluctuations in the spacecraft frame correspond to Doppler‐shifted spatial fluctuation structured perpendicular to the background magnetic field. This would imply an alternative reinterpretation of the spectral index of the observed magnetic power spectral density to be potentially the result of weak‐MHD and sub‐ion scale kinetic Alfvén wave turbulence in the low‐frequency regime. Our theoretical modelings show that turbulence can be driven both in the torus region and at high‐latitudes rendering results in agreement with the Juno measurements. Calculated turbulence heating rates are consistent with observed energy fluxes in the IFT and represent efficient drivers for particle acceleration. Moreover, a widening of the IFPT structure with respect to the IFT extent is consistent with propagating dispersive Alfvén waves modified by kinetic effects on their group velocities. Key Points: Low‐frequency Juno observations in the Io flux tube (IFT) tail represent structures perpendicular to background magnetic fieldMagnetic field fluctuations observed in the Io footprint tail (IFPT) are consistent with weak‐MHD and sub‐ion kinetic Alfvén wave turbulenceDispersion effects on group velocity of Alfvén waves widens the IFT consistent with the observed width of the IFPT [ABSTRACT FROM AUTHOR]

We analyze magnetic data obtained during northern high‐altitude traversals of Jovian middle magnetosphere (MM) field lines during the first 10 inbound data‐taking passes of the Juno spacecraft for azimuthal field perturbations associated with magnetosphere‐ionosphere coupling currents. Full traversals across the MM region occur on all 10 passes at radial distances ∼7 to 16 RJ (T1 traversals), followed in four cases by reversed traversals (T2) at ∼4 to 7 RJ. Signatures of upward field‐aligned currents were observed in all cases, closely collocated with the statistical main auroral oval when mapped along field lines to the ionosphere. Two T1 sheets carry currents ∼10 MA per radian of azimuth in ionospheric colatitudinal layers ∼1.2°, closely comparable with the ∼8.5 MA rad−1 theoretical model value of Cowley et al. (2008, https://doi.org/10.5194/angeo-26-4051-2008). The other T1 sheets typically carry half this current ∼5.1 MA rad−1 in layers half the width ∼0.56°, thus with comparable current densities ∼425 nA m−2. The T2 currents are smaller ∼3.4 MA rad−1 with current densities ∼120 nA m−2, a difference that may relate to locations on opposite sides of the main oval as reflected in near‐contemporaneous ultraviolet observations, though ionospheric field strengths are not greatly different. Comparison with northern near‐periapsis currents observed inside ∼2 RJ on the same passes by Kotsiaros et al. (2019, https://doi.org/10.1038/s41550-019-0819-7) yields a cross‐correlation coefficient ∼0.7 with our T1 currents, though Kotsiaros et al.'s mean current value of ∼3.8 MA rad−1 is somewhat less than our overall mean T1 value ∼6.2 MA rad−1. The differences may have spatial, temporal, or methodological origins. Key Points: Upward field‐aligned currents ∼400 nA m−2 are seen at high altitudes (r ∼ 4–16 RJ) on northern auroral field lines on 10 inbound Juno passesSheets in opposite longitude sectors carry factor ∼2 different mean currents, the larger ∼4 to 10 MA rad−1 being comparable with model valuesLow‐altitude (r < ∼2 RJ) auroral currents reported on the same passes are correlated (R ∼ 0.7) but overall lower in magnitude ∼4 MA rad−1 [ABSTRACT FROM AUTHOR]

Jupiter's magnetic field is tilted by ∼10° with respect to the planet's spin axis, and as a result the Jovian plasma sheet passes over the Galilean satellites at the jovigraphic equator twice per planetary rotation period. The plasma and magnetic field conditions near Ganymede's magnetosphere therefore change dramatically every ∼5 hr, creating a unique magnetosphere‐magnetosphere interaction, and on longer time scales as evidenced by orbit‐to‐orbit variations. In this paper, we summarize the typical magnetic field conditions and their variability near Ganymede's orbit as observed by the Galileo and Juno spacecraft. We fit Juno data from orbit 34, which included the spacecraft's close Ganymede flyby in June 2021, to a current sheet model and show that the magnetospheric conditions during orbit 34 were very close to the historical average. Our results allow us to infer the upstream conditions at the time of the Juno Ganymede flyby. Plain Language Summary: Ganymede is the only moon in the solar system with an intrinsic magnetic field. This field forms a bubble in space around the moon, called a magnetosphere, that is itself contained within Jupiter's magnetosphere. The magnetic field and plasma conditions within Ganymede's magnetosphere can be used to infer information about the satellite's atmosphere, ionosphere, and interior. It is therefore important to understand the interaction between Ganymede's magnetosphere and the Jovian environment in the same way that we study the effects of space weather on the Earth. Here we analyze Galileo magnetic field measurements from Jupiter's magnetosphere in the region near Ganymede's orbit to establish the typical magnetic field magnitude and direction. We discuss the average conditions as well as the nature of the variability that occurs due to dynamic processes occurring in Jupiter's magnetosphere. This information provides useful context for analyzing data from Juno's recent flyby of Ganymede, which we show occurred during typical magnetospheric conditions. Key Points: The magnetic field magnitude and direction upstream of Ganymede vary strongly with longitudeTemporal variations in the magnetosphere also influence Ganymede's upstream field conditionsJuno's Ganymede flyby occurred during typical magnetospheric conditions [ABSTRACT FROM AUTHOR]

Understanding Jupiter's present‐day interior structure and dynamics is key to constraining planetary accretion models. In particular, the extent of stable stratification (i.e., non‐convective regions) in the planet strongly influences long‐term cooling processes, and may record primordial heavy element gradients from early in a planet's formation. Because the Galileo entry probe measured a subsolar helium abundance, Jupiter interior models often invoke an outer stably stratified region due to helium rain. Additionally, Juno gravity data suggest a deeper, potentially stratified dilute core extending halfway through the planet. However, fits to Jupiter's gravitational data are non‐unique, and outstanding uncertainty over the equations of state for hydrogen and helium remain. Here, we use high‐resolution numerical magnetohydrodynamic simulations of Jupiter's magnetic field to place constraints on the extent of stable stratification within the planet. We find that compared to traditional interior models, an upper stably stratified layer between 0.9 and 0.95 Jupiter radii (RJ) helps to explain both Jupiter's dipolar magnetic field and zonal winds. In contrast, an extended dilute core that is entirely stably stratified (no convective layers) yields significantly worse fits to both. However, our models with extended deep stratification still generate dipolar magnetic fields if an upper stratified region is also present. Overall, we find that a planet with a dilute core i.e., strongly stably stratified is increasingly challenging to reconcile with Jupiter's magnetic field and winds. Thus if a dilute core is present, alternative modalities such as a fully convective dilute core, a complex multilayered interior structure, or double diffusive convection may be required. Plain Language Summary: Giant planets like Jupiter provide important clues to how the solar system formed. Jupiter is often thought of as a dynamic and well‐mixed ball of hydrogen and helium gas that has been convectively cooling for billions of years. However, data from the NASA Juno Mission spacecraft suggests large regions of the planet may actually be "stably stratified," that is, not convective. Understanding the extent of this process is important since it would affect how Jupiter's temperature cools over time, and may challenge our ideas of how giant planets are formed. In this paper, we simulate the fluid dynamics of Jupiter's interior to investigate two potential stable regions: (a) an upper region (potentially due to helium rain, where helium and hydrogen separate like oil and water) and (b) a lower stratified region corresponding to the so‐called "dilute core," which may extend halfway through the planet. We find that the upper stable layer helps explain both Jupiter's magnetic field and winds. In contrast, the lower stratified region does not explain either unless the upper stable layer is also present. Our results have implications for the present‐day interior dynamics of giant planets, as well as their past formation and evolution. Key Points: Numerical dynamo models provide important constrains on Jupiter's interiorAn upper stably stratified layer (SSL) (e.g., helium rain) helps explain Jupiter's magnetic field and windsA fully stratified dilute core is inconsistent with Jupiter's field and winds, unless there is also an upper SSL [ABSTRACT FROM AUTHOR]

We present a survey of electron conics over Jupiter's high latitude regions utilizing 22.6 hr of data from the Jovian Auroral Distribution Experiment electron instrument aboard NASA's Juno spacecraft during science orbits 01 and 03-30. We observed electron conics for about 2.5% of this time and characterized them into three types based on their direction of motion along Jupiter's magnetic field lines: upward, downward, and bidirectional. We observed the upward electron conics most often and at energies of 0.057–80.1 keV, while we observed the downward electron conics least often and at energies of 0.073–1.2 keV. We observed bidirectional electron conics mostly around the same times and places as the upward electron conics having energies of 0.081–49.6 keV. We observed all electron conic types to occur mostly at altitudes 0.3–0.4 RJ and local times 15–16 hr. Furthermore, we observed all electron conic types to have energies greater than 0.7 keV below an altitude of 0.5 RJ and over the main auroral region. [ABSTRACT FROM AUTHOR]

The Juno spacecraft has been collecting data to shed light on the planet's origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter's zonal gravitational field. Here, we analyze 22 Juno's gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10–50 cm/s at 900–1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions. Juno spacecraft experienced unknown accelerations near the closest approach to Jupiter. Here, the authors show that Jupiter's axially symmetric, north-south asymmetric gravity field measured by Juno is perturbed by a time-variable component, associated to internal oscillations. [ABSTRACT FROM AUTHOR]