Juno has transformed our view of Jupiter through major discoveries about its interior structure, origin, and evolution; atmospheric dynamics and composition; magnetic dynamo; and polar magnetosphere. The natural evolution of Juno’s polar orbit brings new regions within reach with every close passage to Jupiter, as the inbound equator crossing marches ever closer to the giant planet. The 1^st extended mission began in August 2021 and provided the first close flybys of Io, Europa and Ganymede since the Galileo mission.  The second extended mission (EM2) begins in October 2025 and last 3 years.  The new mission provides opportunities for Juno to unexplore new regions in the Jovian system, and to follow up on Juno’s discoveries made during its prime and 1^st extended missions.  The Juno spacecraft and instruments are in excellent health. During EM2, Juno will dive deep within Jupiter's inner radiation belts where the rings and inner moons reside. EM2 provides an opportunity for a thorough investigation of these components and their complex interaction, providing a unique data set to compare with other giant planet ring systems, including the ice giants. The migration of the periapsis northward creates an opportunity to explore in-situ Jupiter's ring-moon system, investigate Jupiter’s northern hemisphere and the unexplored regions of Jupiter's distant southern magnetospheric boundaries. During EM2, Juno’s polar perijoves will provide the opportunity to continue the exploration of Jupiter’s circumpolar cyclones over a wide range of altitudes/depths via imagery, occultations and microwave sounding. Radio science occultations will icharacterize the upper atmosphere to levels as deep as 0.5 bar. EM2 gravity passes over the north polar region will constrain the depth and mass of the polar cyclones and will also be compared to MWR's sounding of the same..  Juno’s 2^nd extended mission proposal is currently being reviewed.  An overview of the new opportunities provided with EM2 will be presented. 

How to cite: Bolton, S.: The Juno 2nd Extended Mission, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-158, https://doi.org/10.5194/epsc-dps2025-158, 2025.

The Jovian magnetodisk refers to a thin disc of plasma and electric current near the equatorial plane of Jupiter’s magnetosphere. It serves as an “energy converter” within Jupiter’s planetary system, receiving rotational energy from Jupiter’s interior and upper atmosphere and converting it into the thermal and kinetic energy of the magnetospheric plasma. Juno’s in-situ observations of fields (MAG) and charged particles (JADE and JEDI) provide valuable data for revealing the structure and dynamics of the magnetodisk. 

By examining this dataset, we developed an empirical model of the magnetodisk, capturing the distributions of its magnetic field, electric current, and plasma. The results show that: (a) heavy ions dominate both the number density and pressure; (b) the number density and pressure of all species decrease with radial distance; (c) the temperature increases with radial distance for electrons and heavy ions, but decreases for protons; (d) on average, the parallel pressure exceeds the perpendicular pressure for all species; and (e) the magnetodisk exhibits strong local time asymmetry.

Based on this model, we investigated the equilibrium and stability of the magnetodisk. On average, the magnetodisk is in radial force balance, with the dominant forces being the inward magnetic stress and the outward plasma anisotropy force. However, signatures of ongoing non-equilibrium activity are also detected, ranging from global-scale magnetic dipolarization down to ion- and electron-scale plasma waves. A detailed data survey indicates that anisotropy in the pitch-angle distributions of charged particles plays a key role in these processes, both in determining marginal equilibrium states and in controlling the growth of plasma instabilities. A theoretical model incorporating this aspect could provide a better description of the magnetodisk and its role in the dynamics of the magnetosphere.

How to cite: Liu, Z.-Y., Andre, N., and Blanc, M.: Structure and Dynamics of the Jovian Magnetodisk Seen by Juno, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-26, https://doi.org/10.5194/epsc-dps2025-26, 2025.

Radio occultation measurements from the Galileo, Voyager, and Pioneer missions have unveiled many mysteries in the Jovian ionosphere. The altitudinal structure of the Jovian ionosphere appears to be highly variable, although it is difficult to distinguish if the variability is spatial or temporal; and clear evidence of non-solar produced local time and latitudinal trends are observed. We present a quantitative analysis of all available sub-auroral radio occultation data, including new data from Juno, showing that the ionosphere’s vertical structure depends strongly on local time, longitude, and magnetic field geometry. Consequently, we investigate the key drivers of spatially variable plasma transport at non-auroral latitudes, namely: ambipolar diffusion, equatorial electrodynamics, and neutral wind-driven field-aligned flows. Our results indicate that neutral wind-driven field-aligned transport effectively organizes the observed electron density profiles, where model predictions of upward or downward plasma motion corresponds to higher (>1500 km) or lower (<1000 km) ionospheric peaks, respectively. This suggests that altitudinal structure of the non-auroral Jovian ionosphere may be temporally stable but spatially variable. However, highly variable ionospheric structure persists in the dusk ionosphere in regions where no plasma motion is predicted. The complexity of this variability will be discussed further in our presentation.

How to cite: Agiwal, O., Moore, L., Withers, P., Felici, M., Coffin, D., Mueller-Wodarg, I., and Bloch, T.: Unraveling Jupiter's Enigmatic Ionosphere from Galileo and Juno Radio Occultations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1194, https://doi.org/10.5194/epsc-dps2025-1194, 2025.

Low latitude field-aligned current systems have been well documented at the Earth and reported at Saturn. Here we presented a comprehensive analysis of Juno magnetic field measurements in the low-latitude region within 1 Jovian radii from the surface of Jupiter. After removing the internal magnetic field (and its time variations) as well as the large-scale magnetodisk field, our analysis revealed a “sandwich” structure in the azimuthal component of the Jovian magnetic field, Bphi, with day-night asymmetries: on the dayside, Bphi is positive at mid-to-low latitudes but reverses sign at high latitudes; on the other hand, the pre-dawn side between 3am and 6am features a negative band of Bphi in the low-latitude region.

Based on the observed spatial structures, we propose a day-night asymmetric low-latitude field-aligned current (FAC) system at Jupiter: currents flow from the northern to the southern hemisphere along low-latitude magnetic field lines on the dayside, and reverse direction on the pre-dawn side. These FACs are closed via ionospheric Pedersen currents, forming meridional current loops. We will also discuss the Ohmic heating associated with this current system in the Jovian upper atmosphere.

How to cite: Zhang, W., Cao, H., Connerney, J., Bloxham, J., and Khurana, K.: Low latitude field-aligned currents (FACs) at Jupiter: perspective from Juno MAG , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-454, https://doi.org/10.5194/epsc-dps2025-454, 2025.

Juno in-situ observations provide insightful data on plasma, electric, and magnetic fields associated with Jovian decametric (DAM) emission, while remote-sensing observations have the advantage of large spatial and temporal scales. Combining these two perspectives may help us understand the dynamic processes of DAM radiation. In this work, we present an Io-DAM emission continued intermittently for at least 2 hours combining Juno in-situ observation and remote-sensing observation from Wind and Stereo-A. The Io-DAM emission evolved from three discrete narrow arcs to one mixed broad arc within 11 minutes in remote-sensing dynamic spectra. This Io-DAM source is located at a lead angle of 6° from the main Alfvén wing spot (MAW) lasting for the observation. Juno/JADE detected peaks of electron energy fluxes and showed the loss-cone distribution in the upgoing direction. We set a series of resonant circles to estimate the maximum growth rate 8*10^-4, which yields an electron energy range of 0.2–3 keV and an emission angle of 84°-88°. Meanwhile, we infer the properties of the source region of the event from the remote-sensing observations at 1 AU. The inversed results on electron energy, emission angle, and source locations are consistent with the Juno in-situ observations, which may indicate the consistent properties of this Io-DAM event over 2-hour observational intervals. This consistency also reinforces the reliability of the remote sensing inversion method. Our work contributes to the establishment of long-term stereoscopic remote monitoring, addressing limitations in local observational coverage and enhancing our understanding of the dynamic processes of DAM emission.

How to cite: Zheng, R., Wang, Y., and Wang, C.: A Jovian decametric emission event observed locally by Juno and remotely by Wind and STEREO-A at 1 AU, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-287, https://doi.org/10.5194/epsc-dps2025-287, 2025.

Introduction. Jupiter's ultraviolet aurora frequently shows a number of arcs between the dusk-side polar region and the main emission, which are denoted as “bridges” (Figure 1, left).  Thus far, the only dedicated study of the auroral bridge was part of a Master’s thesis which analysed three images of the aurora taken by the Space Telescope Imaging Spectrograph (STIS) instrument aboard the Hubble Space Telescope (HST) that contained bridges. The bridges were found to map to the dusk-side magnetosphere between 10 and 22 magnetic local time (MLT) and be largely confined to radial distances greater than 60 RJ. Other works have identified the appearance of dusk-side polar arcs with compression by the solar wind, though these conclusions were based a limited number of observations, and the origins of auroral bridges remain poorly understood.

Methods. We present a largely automated detection and statistical analysis of bridges over 248 HST-STIS observations, alongside a multi-instrument study of crossings of magnetic field lines connected to bridges by the Juno spacecraft during its first 30 perijoves. The detection of bridges in the large number of HST images is performed automatically using a bespoke arc-tracing algorithm (Figure 1, right), which is combined with manual arc designations and a random-forest filter to provide a model test accuracy of 82%. In the Juno-UltraViolet-Spectrograph (Juno-UVS) images, bridge locations (and hence bridge-crossing timestamps) were identified manually to avoid the introduction of artefacts of the automated method.

Results. Bridges are observed to arise on timescales of ~2 hours, can persist over a full Jupiter rotation, and are conjugate between hemispheres. The appearance of bridges is strongly associated with compression of the magnetosphere by the solar wind (Figure 2, left); there is a clear distinction between green points (cases where the magnetosphere was compressed) and red points (cases where the magnetosphere was uncompressed) in the total detected bridge length. Low-altitude bridge crossings are associated with upward-dominated, broadband electron distributions (Figure 2, left), consistent with Zone-II (Mauk et al. 2020; doi:10.1029/2019JA027699) aurorae, notable since similar regions in Earth and Saturn’s aurorae show no appreciable emission. Bridge crossings are also associated with plasma-wave bursts observed by Juno-Waves, in agreement with existing theoretical models for the generation of polar-region aurorae. Electron populations associated with crossings of field lines threading the main emission by Juno also become more downward-dominated when separate bridges are present in the nearby aurora. Figure 2 (right) shows that main emission crossings where bridges are present in the aurora (green) did not show the same bridge-like/Zone-II upward-travelling population of electrons as cases where no separate bridge was observed in the aurora (orange), which indicates that the “bridge” aurora was merely spatially indistinguishable from the main emission in these latter cases.

Conclusions. Combining these two sets of results, bridges are identified as Zone-II aurorae that have become spatially separated from the Zone-I aurorae under the influence of the solar wind. In the absence of separate bridges in the polar region, the main emission takes on a decidedly mixed Zone-I-II character (bidirectional electrons, plasma-wave bursts) which become uniquely Zone-I-like when bridges are present. This is consistent with the previously observed adjacency of the auroral Zone-I and Zone-II; the gap between the two is thus observed to increase during solar wind compression. The solar wind is thus implied to be able to exert a considerable influence on Jupiter’s internally driven magnetosphere that is reflected in the morphology of its aurora.

Figure 1: (left) An image of the northern jovian UV aurora captured by HST during the GO-15638 campaign (exposure ID: odxc01okq). A 15°-by-15° grid in System-III longitude and planetocentric latitude is included; the System-III longitude of certain meridians are given in white, and certain planetocentric latitudes in magenta. The average subsolar longitude during this exposure (170°) is denoted by a solid yellow line, and the positions of the dawn and dusk hemispheres are included to guide the reader. The approximate location of the polar collar is enclosed by red dashed lines, and that of the noon active region by a green dashed ellipse. Bridges are highlighted with yellow arrows. (right) Results of the bridge-detection algorithm after filtering. Red lines denote arcs accepted by the filter, and grey the arcs that have been discarded. The seed point of each arc is given in magenta. Manually designated arcs are given in yellow. White contours give the region of validity of the JRM33 flux-equivalence mapping along closed field lines.

Figure 2: (left) Detected average expansion of the main emission vs. the total detected magnetosphere-mapped bridge length for each northern HST-STIS series considered in this work. Negative expansions imply a contracted main emission. Bridge-length error bars are determined as described in Appendix A. Green crosses denote those cases where the magnetosphere was compressed, and red pluses those cases where the magnetosphere was uncompressed; grey points denote cases where the compression state of the magnetosphere is unknown. The least-squares best fit is given by the solid blue line. (right) Median-average properties of dusk-side (12<MLT<18), low-altitude (<3 RJ) bridge crossings (red, solid) and main-emission crossings, both with (green, dotted) and without (orange, dashed) local bridges, observed by Juno. From top to bottom: JEDI electron flux vs. pitch angle profiles; Waves-E LFR-Lo spectral intensity. The shaded regions denote the 25-to-75th percentile range.

How to cite: Head, L., Grodent, D., Bonfond, B., Sulaiman, A., Moirano, A., Sicorello, G., Elliott, S., Vogt, M., Louis, C., Kruegler, N., and Vinesse, J.: Jupiter's ultraviolet auroral bridge: the influence of the solar wind on polar auroral morphology, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-3, https://doi.org/10.5194/epsc-dps2025-3, 2025.

We present global temperature and density maps of Jupiter’s upper atmosphere from 15 nights of observation on Keck/NIRSPEC across 2022-2025 in support of the Juno mission. On average, each night provides ~12,000 pole-to-pole, L-band spectra over approximately 100 degrees of longitude. Within these spectra are emissions from the dominant molecular ion, H₃⁺, which yield column-averaged temperatures and column-integrated densities at local noon. We find a median equatorial temperature of 760 ± 75 K, with night-to-night variation up to 130 K over a year. Temperatures decrease monotonically from pole to equator, consistent with the aurora being the primary source of heating at low latitudes. Mean auroral temperatures are approximately equal in the north and south, 1100  ± 100 K, and are far more variable—up to 300 K on long timespans. Our density map reveals the same highly structured features as presented in the Stallard et al. H₃⁺ global emission map, proving this depleted emission is caused by low density regions of the upper atmosphere. Additionally, it highlights the permanence of these structures in Jupiter’s upper atmosphere due to their persistence for nearly 30 years.  

Long thought to be a highly variable system, we present the highest spatial resolution, first global, and first multi-epoch maps of Jupiter’s upper atmosphere which reveal morphologies that are remarkably consistent over year- to decades-long timespans. With our maps we contribute further evidence of the magnetosphere-ionosphere control seen in previous H₃⁺ emission maps, and tie their features to longstanding magnetically-controlled density variations. Observed pole-to-pole temperature structure is consistent in time and attributed to the redistribution of auroral energy.

Stallard, T. S. et al. (2018). Identification of Jupiter’s magnetic equator through H₃⁺ ionospheric emission. NatAs 2018 2:10, 2(10), 773–777. https://doi.org/10.1038/s41550-018-0523-z

**This material is based upon work supported by Future Investigators in NASA Earth, Space Science, and Technology Grant 80NSSC23K1637 and Keck Key Strategic Mission Support Grants 80NSSC22K095 and 80NSSC25K7727.

How to cite: Roberts, K., Moore, L., Melin, H., O'Donoghue, J., Stallard, T., Knowles, K., Schmidt, C., Tiranti, P., Agiwal, O., Mohamed, K., and Thomas, E.: Jupiter’s Stable Upper Atmosphere: Mapping Long-term Temperature Trends and Ionospheric Density Structures, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-368, https://doi.org/10.5194/epsc-dps2025-368, 2025.

Many current models of plasma transport in the Jovian equatorial plasma disk (magnetodisk) consider it to be azimuthally symmetric over radial distances extending from the outer edge of the Io torus (6 Jovian radii) to about 50 Jovian radii. But there are also many pieces of evidence pointing to a local time asymmetry in this system at such radial distances, and in the upper atmosphere to which it is coupled. In the magnetosphere, local-time asymmetries have been detected in the thickness of the magnetodisk and in high-energy particle fluxes; observations of magnetodisk radial and azimuthal current systems show that they vary with local time, in such a way that their divergence in the disk plane feeds a system of field-aligned currents similar to the so-called Region 2 currents observed at Earth. At ionospheric altitudes, local time asymmetries are systematically observed in the main auroral emissions, and have also been observed in neutral and ion winds detected in the near infrared by Earth-based telescopes. Finally, deep in the magnetosphere, local time asymmetries have been observed during ground-based surveys of the Io torus, as well as by JAXA’s Hisaki spacecraft observations which suggested they are modulated by the solar wind pressure. Many of these observed asymmetries have been interpreted as the result of a large-scale dawn-to-dusk electric field generated across the magnetospheric cavity by its interaction with the Solar Wind and which would be superimposed to the dominant corotation electric field. 

Despite this many pieces of evidence, no consistent model of this electric field, its generation and its penetration to different magnetospheric radial distances and ionospheric latitudes exists yet. In this study, we attempt to fill this gap by developing a simple semi-analytical model of electric fields, plasma convection and current flows in the Jovian ionosphere and magnetosphere, adapting models developed in the Earth case. We feed our model with the latest measurement of ionospheric resistive properties and magnetospheric magnetic field content. We calculate the latitudinal and local time distributions of the electrostatic potential and field-aligned currents for two particular cases, an abrupt onset of an external dawn-dusk electrostatic potential across the polar cap and a steady dawn-dusk potential, as well as various time variable external electric field, based on Solar Wind observation at the location of Jupiter. We compare these cases to the measurement of the electrostatic potential associated with the above mentioned observations of local time asymmetries, and find that observations fit well with a rapid forcing from the Solar Wind enabling an important penetration of the electric field inside the magnetosphere. 

How to cite: Devinat, M., Liu, Z.-Y., Blanc, M., Nakamura, Y., Wang, Y., Al-Saati, S., Clément, N., Yuan, C., Kamran, A., André, N., and Senior, C.: Local-time Variations In The Jovian System And Possible Connections To Solar Wind/Magnetosphere Interactions, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1592, https://doi.org/10.5194/epsc-dps2025-1592, 2025.

Resulting from the precipitation of magnetospheric particles into the upper atmosphere, planetary aurorae form an image of the dynamics of the magnetosphere and its coupling with the ionosphere and atmosphere. Hence, exploring the upper atmospheres of the Solar System's giant planets allows us to test our theories of the magnetosphere-ionosphere-thermosphere-atmosphere (MITA) interactions under very different conditions. At Jupiter, the coupling between the magnetosphere and the ionosphere has been the subject of numerous studies since the discovery of the Jovian ultraviolet (UV) aurorae by Voyager 1 in 1979 (Broadfoot et al., 1979). Each auroral feature arises from the precipitation of charged particles (mostly electrons) accelerated by a different magnetospheric process. The penetration depth of precipitating electrons in the atmosphere depends directly on their energy, and it is thus possible to use the absorption of UV light by the various hydrocarbons in the deepest layers to estimate their mean energy.

In this study, we compute the energy of the electrons precipitating in the auroral regions of Jupiter using observations from Juno’s UltraViolet Spectrograph (Juno-UVS), with the electron transport model TransPlanet (Lilensten et al., 1989; Benmahi et al., 2024). We compare the correlation between the H₂ brightness and the electron energy to those predicted by several theoretical models to constrain the acceleration mechanisms that produce each auroral feature. Indeed, observational studies have established that such a correlation exists for some features but not others (Gérard et al., 2016), thus indicating that several acceleration processes are at play at Jupiter.

We find that most of the data recorded by Juno-UVS is well calibrated, but in some unique circumstances (especially times of very localized intense emissions) the calibration for some wavelength ranges can be unreliable due to higher order instrumental effects. To circumvent this problem, we define a new color ratio between unabsorbed and absorbed wavelengths. Utilizing these results, we can locate the specific Juno orbits and auroral regions most affected by the instrument effects which make the nominal color ratio values less accurate. Using the new ratio and the corresponding relationship between color ratio and energy of the precipitating electrons, we map the brightness and the electron energy (see fig 1) for each Juno orbit for both hemispheres. We will show results of how this new color ratio and the energies inferred from the modeling compare to the previous method. We then compute the correlation between H₂ brightness and electron energy and determine if they follow a relation resembling the one predicted by Knight (1973), or not. These results thus constitute a test for the various explanations that were put forward to explain the complex morphology of the Jovian aurorae.

Figure 1 Electron energy map obtained from the CR(E) relation for an electron population with a kappa distribution of energies for the northern auroral region during PJ6. The subsolar longitude is marked by the yellow cross.

Bibliography :

Broadfoot et al., Science (1979), doi:10.1126/science.204.4396.979.

Lilensten et al., Annales Geophysicae. 7, 83–90 (1989).

Benmahi et al., A&A. 685, A26 (2024).

J.-C. Gérard et al., Planetary and Space Science. 131, 14–23 (2016).

Knight, Planetary and Space Science. 21, 741–750 (1973).

How to cite: Vinesse, J., Bonfond, B., Benmahi, B., Moirano, A., Grodent, D., Greathouse, T., Hue, V., Gérard, J.-C., Sicorello, G., Head, L., and Gladstone, R.: Characterizing Auroral Acceleration Mechanisms at Jupiter: Statistical Analyses of Juno-UVS-Derived Electron Energies., EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-758, https://doi.org/10.5194/epsc-dps2025-758, 2025.

Jupiter’s poleward (Zone II) main aurora exhibits bi-directional electron acceleration; upward acceleration dominates but downward acceleration generates strong aurora. During Juno’s first perijove (PJ1), the upward acceleration manifested as narrow electron angular beams (within ~5° of the magnetic field) over the 30-1200 keV energy range of Juno’s Jupiter Energetic Particle Detector Investigation (JEDI).  These beams can be simply connected (non-uniquely) to >10 to perhaps 100’s of MeV electrons that penetrated the radiation shielding of the camera head of the Magnetometer Investigation’s Advanced Stellar Compass (ASC).  The most intense of those multiple MeV populations are shown to have been highly directional and propagating upwards. How auroral processes generate such beams is unknown.  With azimuthal symmetry assumed (not demonstrated here), these beams provided >10²⁶ s^-1 of >30 keV electrons to Jupiter’s vast magnetosphere.  That southern auroral source alone can completely replenish the >30 keV electron population within Jupiter’s vast magnetosphere, between 15 and 80 RJ, within 3.5 Earth days. The auroral source therefore may represent a critical and perhaps dominating source of energetic electrons to Jupiter’s magnetosphere and perhaps Jupiter’s electron radiation belts. (See Mauk et al., 2024)

Mauk, B. H., Ma, Q., Becker, H. N., Jørgensen, J. L., Denver, T., Connerney, J. E. P., et al. (2024). Upward, MeV-class electron beams over Jupiter's main aurora. Geophysical Research Letters, 51, e2024GL108799. https://doi.org/10.1029/2024GL108799

How to cite: Mauk, B., Ma, Q., Becker, H., Jørgensen, J., Denver, T., Connerney, J., Allegrini, F., Bagenal, F., Bolton, S., Clark, G., Haggerty, D., Kollmann, P., and Paranicas, C.: Upward, MeV-class electron beams over Jupiter’s Main Aurora;A critical seed population for Jupiter’s uniquely energetic radiation belts, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-776, https://doi.org/10.5194/epsc-dps2025-776, 2025.

Since the discovery of Jupiter’s auroral footprints linked to the Galilean moons - Io, Europa, Ganymede, and Callisto - extensive efforts have been made to unravel the mechanisms behind these unique features, which have no direct analog on Earth. These auroral emissions arise from interactions between Jupiter’s magnetic field, co-rotating iogenic plasma, and the moons themselves, generating disturbances that propagate as Alfvén waves along magnetic field lines. Further insights into these aurorae have been made possible by NASA’s Juno mission, which has provided unprecedented access to Jupiter’s polar regions and significantly advanced our understanding of auroral processes and the coupling between the planet’s ionosphere and its moons. Central to this progress is the Jovian InfraRed Auroral Mapper (JIRAM), which combines an L-band imager (3.3–3.6 μm) with a spectrometer spanning the 2–5 μm range. Throughout the mission, JIRAM has provided numerous high-spatial-resolution images of H₃⁺ infrared emissions associated with the footprints of Io, Europa, and Ganymede, revealing fine-scale structures and enhancing our understanding of their morphology and the electrodynamic processes that shape them. Nonetheless, the spectral properties of these features remain poorly characterized.

This study investigates the infrared signatures observed by JIRAM’s spectrometer at the footprint locations. We analyze L-band images and spectra acquired during perijove (PJ) passes 1 through 40. The images provide the spatial context necessary to identify the spectra corresponding to the auroral footprints driven by Io, Europa, and Ganymede, which are the primary focus of this work. From these spectra, we derive key parameters such as the temperature and column density of H₃⁺ across the distinct spots that make up the footprints: the Main Alfvén Wing (MAW) spot, formed at the magnetic foot of Alfvén waves directly connected to the moon; the Reflected Alfvén Wing (RAW) spot, generated by wave reflection on the density gradient at the plasma sheet boundary; and the Transhemispheric Electron Beam (TEB) spot, produced by electrons accelerated away from Jupiter and precipitating into the opposite hemisphere (Figures 1 and 2).

Figure 1. JIRAM image-slit composite maps of the southern Io footprint, created by combining L-band images from (a) PJ 14 on July 7, 2018 (scanning session from 07:01:44 to 07:11:46) and (b) PJ 27 on June 2, 2020 (scanning session from 12:07:16 to 12:08:19), with simultaneously measured spectral slits (green lines). Red lines indicate the trajectories of the footprints, while red squares mark the positions of the footprints in the first and last images of the sequence, as predicted by the Con2020 magnetic field model.

Figure 2. JIRAM image-slit composite maps of the southern Ganymede footprint obtained from (a) PJ 33 on April 15, 2021, in the scanning session from 00:42:55 to 00:45:55, (b) PJ 8 on September 2, 2017, in the scanning session from 00:06:06 to 00:22:43, and (c) PJ 15 on November 8, 2020, in the scanning session from 03:25:19 to 03:34:51. Red lines indicate the trajectories of the footprints, while red squares mark the positions of the footprints in the first and last images of the sequence, as predicted by the Con2020 magnetic field model.

Here, we present the results of the analysis of the auroral footprints of Io and Ganymede (Figure 3), where JIRAM spectra sampled all three considered spots. We also compare the derived parameters with those from previous JIRAM spectral studies of the main aurora, providing a better understanding of how the footprints relate to the main emissions. The MAW spots of the Io and Ganymede footprints exhibit H₃⁺temperatures and abundances comparable to those previously observed along the main auroral ovals. The Io footprint's MAW shows H₃⁺ temperatures ranging from 750 K to 1070 K and column densities between 0.47 and 1.6 x 10¹³ cm^-2, while the Ganymede footprint's MAW displays H₃⁺temperatures ranging from 860 K to 1230 K and column densities between 4.3 and 9.2 x 10¹² cm^-2. Similarly, the RAWs of both footprints reveal H₃⁺ temperatures and abundances consistent with those found in the main aurora. In contrast, the TEB structures show divergent behaviors: the Io footprint’s TEB is approximately 75 K hotter than its MAW, whereas the TEB in Ganymede’s footprint is about 70–90 K cooler. These thermal profiles indicate that the TEBs associated with Io and Ganymede form at different altitudes in Jupiter’s upper atmosphere - above the MAW and RAW for Io, but below them for Ganymede - pointing to possible differences in magnetosphere-ionosphere coupling processes between the different moon-aurora systems.

Figure 3. Retrieved values of H₃⁺ temperature and column density from the inversion of the JIRAM mean spectra of the MAW and TEB of the footprints of Io (a,b) and Ganymede (c,d).

How to cite: Castagnoli, C., Moirano, A., Mura, A., Adriani, A., Altieri, F., Dinelli, B. M., Migliorini, A., Noschese, R., Sordini, R., Tosi, F., and Plainaki, C.: Jupiter's Moon-Induced Infrared Aurorae: Spectral Insights from Juno's JIRAM, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-627, https://doi.org/10.5194/epsc-dps2025-627, 2025.

A striking feature of Jupiter’s aurora are the emissions induced by the Galilean satellites. Their auroral footprints represent the ionospheric signature of the electromagnetic interaction between the Galilean moons and Jupiter's co-rotating magnetospheric plasma. We present a new high-resolution view of the auroral footprints of Io and Europa in the near-infrared, as observed by the Near-Infrared Spectrograph (NIRSpec) onboard the James Webb Space Telescope (JWST). We report measurements of ionospheric H₃⁺ spectral radiance, total emission, column-averaged temperature and ion density, as well as the spectral radiance from lower altitude CH₄.

The H₃⁺ spectral radiance for both footprints is found to be primarily driven by the ion densities, as opposed to the local thermospheric temperature, with significant variability on the timescales of ∼30 minutes observed in both the H₃⁺ temperature (∼50%) and density (∼500%) at the core of the Io spot. A spatially confined cold structure was uniquely seen, localised to the centre of the Io spot, with extremely high H₃⁺ densities and surrounded by a “halo” of relatively hot and less dense H₃⁺ extending into the footprint tail. The variability in the ionization of H₃⁺ at the Io spot is likely driven by changes in the precipitating electron flux and energy creating H₃⁺ across different altitudes, therefore sampling various regions of the ionosphere’s altitudinal temperature profile, and/or NIRSpec’s changing observing geometry is revealing different vertical extents of the footprint. There are also suggestions of a similar, yet less extreme, cold and dense population of H₃⁺ associated with the Europa footprint.   

Our findings highlight the unique insights gained from analysing the near-infrared emissions from the auroral footprints of the Galilean moons. Such observations can supply valuable context for the in-situ measurements acquired by Juno as it traversed within the moons’ orbits during its prime and extended missions, as well as to support future investigations made by JUICE and Europa Clipper.

How to cite: Knowles, K., Melin, H., Stallard, T., O'Donoghue, J., Moore, L., Schmidt, C., Tiranti, P., Roberts, K., Thomas, E., and Johnson, R.: Following Jupiter's Satellite Footprints with JWST, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-727, https://doi.org/10.5194/epsc-dps2025-727, 2025.

The interaction between the four major moons of Jupiter - Io, Europa, Ganymede and Callisto - and the Jovian magnetic field generates satellite-induced auroral emissions, called footprints. These are caused by electrons precipitating into the ionosphere by wave-particle interaction with the Alfvén waves that are generated by the plasma flow impinging onto the moon. The position and inter-spot distance of the footprints mirror the shape of the wave-fronts of these Alfvén waves, whose propagation is mainly affected by the magnetic field and plasma density. Consequently, the footprint implicitly contains information on those quantities.

The Juno mission has been providing high-quality observations of the Io footprint in the infrared (IR) and ultraviolet (UV) bands since 2016. We propose an overview of the Io footprints from Juno’s perspective, with the goal of showing how the footprint can be used 1) to monitor the plasma conditions near the moon, and 2) to investigate the structure of the Jovian ionosphere. For the first aspects, we use the IR and UV observations of the Io footprint to constrain the density and temperature of the Io Plasma Torus around Jupiter from 2016 to 2022. To support this survey, we also include the radio occultations performed by the radio tracking systems, as they are sensitive to the electron content of the Io Plasma Torus. For the second goal, we are investigating the UV vertical profile of the Io footprint, which combines information about the hydrocarbon distribution in the upper atmosphere with the energy distribution of the precipitating particles. We will show how to determine the presence of methane, ethane and acetylene using the UV spectrum measured by Juno, and how to derive the energy distribution of the precipitating electrons from the vertical profile of the emission.

How to cite: Moirano, A., Bonfond, B., Mura, A., Hue, V., Caruso, A., Benmahi, B., Grodent, D., Head, L. A., Gérard, J.-C., Sicorello, G., Vinesse, J., Greathouse, T., Casajus, L. G., Tortora, P., and Zannoni, M.: The moon-induced auroral emissions at Jupiter: a natural probe of the atmosphere and magnetosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-947, https://doi.org/10.5194/epsc-dps2025-947, 2025.

INTRODUCTION
Io’s atmosphere is spatially variable, with evidence for a higher-density molecular SO₂ atmosphere bound to low-to-mid latitudes (Strobel & Wolven 2001) and global atomic coronae made of atomic S and O (Ballester et al. 1987). Interactions between Io’s atmosphere and electrons trapped by Jupiter’s magnetic field produce auroral emissions. Compared to the icy Galilean satellites Europa, Ganymede and Callisto, Io’s aurora have been studied much more extensively. These include both observations taken from Earth (e.g., Ballester et al. 1987; Roesler et al. 1999; Retherford et al. 2000; Bouchez et al. 2000; Schmidt et al. 2023) and during spacecraft fly-bys by Galileo (Geissler et al. 1999, 2001), Cassini (Geissler et al. 2004) and New Horizons (Retherford et al. 2007). Spatially resolved observations from these fly-bys and some UV observations from Earth orbit revealed distinctive emission morphologies, including bright spots at equatorial latitudes located near the sub and anti-Jovian longitudes, a diffuse global coronal glow and emissions from volcanic plumes. We combined high-resolution spectral observations of Io’s visible aurora in eclipse taken over six nights between 2022 and 2024 to characterize both the variability in the aurora and their connection to some of the physical properties of Jupiter’s plasma sheet.

OBSERVATIONS
Visible wavelength observations of aurora from the Galilean satellites require them to be eclipsed by Jupiter in order to suppress reflected sunlight from their surfaces. Eclipse observations from the ground require Jupiter to be near quadrature with Earth, permitting observers to view either the ingress (western quadrature) or egress (eastern quadrature) phases of the eclipse. We observed Io during six different eclipses between 2022 and 2024 using the High Resolution Echelle Spectrometer (HIRES), an instrument on the Keck I telescope at the summit of Maunakea with a resolving power of around 30,000. On five of these nights we observed Io during eclipse ingress and on the one remaining night during eclipse egress. We used a slit with a width of 1.722′′, which was wider than Io’s angular size on the sky, allowing the instrument to operate as a high-resolution imaging spectrometer for the monochromatic atomic auroral emissions. Each spectrum was a 5-minute integration with approximately 3 minutes of overhead between the end of one integration and the start of the next, yielding a high-cadence time series. We developed a data calibration pipeline (described in detail in Milby et al. 2024) which carefully characterizes and removes the background, isolating the auroral emissions despite often bright scattered light from Jupiter.

RESULTS
Prior to our observations, only six visible wavelength atomic auroral emissions had been identified at Io: the forbidden oxygen emissions at 557.7, 630.0 and 636.4 nm, the sodium doublet at 589.0 and 589.6 nm and the potassium line at 766.4 nm. The quality of the HIRES data combined with careful background subtraction allowed us to detect 13 additional lines at a signal-to-noise ratio greater than 2, tripling the number of optical emissions detected from Io’s eclipse atmosphere. Figure 1 shows an example of each of the emission lines identified in the HIRES spectra.

We used this set of emission lines in conjunction with both broadband and narrowband images of Io in eclipse taken by Cassini (Geissler et al. 2004) to map the locations of the emissions and connect them to discrete auroral features. The identification of additional atomic oxygen lines provides a powerful diagnostic for determining whether the auroral emission originated due to electron impact on atomic or molecular species. Schmidt et al. (2023) interpreted the 630.0∕557.7 nm emission ratio as evidence for emission from an atomic oxygen column. We updated our auroral emission model to include cross sections for electron impact on SO₂ and modeled the emission at 557.7, 777.4 and 844.6 nm from atmospheres composed of just O, a combination of O and SO₂, and finally a combination of O, SO₂ and O2, which we used as an isoelectronic proxy for SO. We found the three species atmosphere fit the data within the uncertainties assuming excitation by canonical 5 eV electrons.

The high cadence of the HIRES observations allowed us to explore the connection between the ambient electron density and the auroral brightness. We found the connection to be ambiguous, suggesting that plasma bombardment at Io is varies significantly beyond what simple modulation of the magnetic geometry provides.

Time permitting, we will provide a preview of preliminary conclusions of a similar time-series analysis of Europa’s optical aurora.

Figure 1. Auroral emissions from Io in eclipse including both new emissions and those previously detected at 557.7, 589.0, 589.6, 630.0, 636.4 and 766.4 nm. Note that each image is displayed using an individually scaled colormap in order to optimize the dynamic range available to the dimmer emissions. Wireframe globes show Io’s physical orientation at the time of the observation. Figure from Milby et al. (under review).

REFERENCES
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Bouchez, A. H., Brown, M. E., & Schneider, N. M. 2000, Icarus, 148, doi: 10.1006/icar.2000.6518
Geissler, P., McEwen, A., Porco, C., et al. 2004, Icarus, 172, doi: 10.1016/j.icarus.2004.01.008
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Milby, Z., de Kleer, K., & Schmidt, C. under review, The Planetary Science Journal
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How to cite: Milby, Z., de Kleer, K., and Schmidt, C.: New Optical Aurora Detections at Io and Implications for Interactions with the Jovian Plasma Environment, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1044, https://doi.org/10.5194/epsc-dps2025-1044, 2025.

Jupiter hosts the most intense electron radiation belts in our solar system—so energetic that relativistic electrons emit synchrotron radiation detectable at radio wavelengths. However, direct in-situ measurements of these belts are exceptionally challenging: the high fluxes of instrument-penetrating (ultra)relativistic electrons interfere with particle detectors, masking key information on energy spectra and angular distributions. As a result, remote sensing of synchrotron radiation has long been the primary method for probing the inner belts, with temporal variations in the observed radio emissions offering critical insight into the physical mechanisms shaping this extreme environment. Such variations have been observed on timescales ranging from days to years and have been linked to both external drivers—such as solar wind pressure changes, solar EUV control of Jovian upper atmosphere dynamics, and cometary impacts—and internal processes, including pitch-angle scattering by moons like Amalthea.

A fundamental limitation of synchrotron observations, however, is their integrated nature: even when spatial resolution is achieved, the signal combines emissions from a wide range of magnetic distances and electron energies along the line of sight. This complicates efforts to localize variability and disentangle overlapping physical processes. The Juno mission, with more than 65 close passes through Jupiter’s radiation environment between 2016 and 2025, presents a unique opportunity to complement remote observations with in-situ measurements of the same system. Although Juno's instruments (JADE, JEDI) cannot resolve spectra of >1 MeV electrons in the synchrotron-emitting region, the intensity of those instrument-penetrating electrons serves as a reliable proxy for tracking their content at different distances.

By subtracting a long-term average belt model from individual Juno passes, we extract the residual signal and track its temporal variations as a function of L-shell. This analysis reveals two dynamically distinct regions, separated near the orbit of Amalthea (L ~2.3), with largely decoupled variability. Both regions exhibit recurring quasi-periodic variations on ~100-day timescales, though often out of phase. In the outer belts (L > 2.3), this mid-term modulation is superimposed on a longer-term trend that develops into a flux minimum around the time of the solar minimum. The long-term perturbation propagates inward from Io’s orbit (L ~6) toward Amalthea over roughly one year. Surprisingly, a comparison with synchrotron belt variations observed by the Goldstone-Apple Valley Radio Telescope (GAVRT) shows a stronger correlation with the outer belt region, despite the inner belts dominating the synchrotron signal. These findings highlight the value of long-term, multi-instrument monitoring and provide a framework for interpreting remotely observed radiation belts in extrasolar systems, such as brown dwarfs.

How to cite: Roussos, E., Kollmann, P., Krupp, N., Paranicas, C., Hao, Y., Plainaki, C., Grassi, D., Kao, M., Pei-Chun Tsai, B., and Clark, G.: Probing Jupiter’s Inner Radiation Belts: Multi-Timescale Variability Revealed by Juno, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-415, https://doi.org/10.5194/epsc-dps2025-415, 2025.

The Juno spacecraft, currently in orbit around Jupiter, provides a unique opportunity to investigate the planet’s atmospheric and ionospheric structure through radio occultation experiments. This study presents an analysis of radio signals transmitted between Juno and Earth-based antennas as the spacecraft passes behind Jupiter’s limb, offering vertical profiles of electron density in the ionosphere with unprecedented resolution.

A radio occultation experiment utilizes the precise tracking of a spacecraft’s radio signal as it is occulted by a planetary body from the line of sight of a ground-based antenna. As the signal propagates through the planetary atmosphere, it experiences bending and phase delay due to refractive index gradients. The passage of the radio signal through Jupiter’s ionosphere induces a frequency-dependent Doppler shift, superimposed on the non-dispersive contributions from the neutral atmosphere and spacecraft dynamics.

Juno's radio science subsystem employs a dual-frequency link, involving coherent X-band (8.4 GHz) and Ka-band (32 GHz) signals transmitted to Earth. By exploiting a linear combination of the sky frequencies recorded at the ground antenna in the two bands, it is possible to isolate the downlink dispersive effect, which is proportional to the integrated electron content along the ray path. This enables the retrieval of accurate vertical electron density profiles through an inversion process based on a ray-tracing technique, assuming Jupiter’s ionosphere to be oblate and axially symmetric. Additionally, an uncertainty quantification has been carried out  through a Monte Carlo simulation, providing confidence intervals for each altitude level above Jupiter’s 1 bar reference ellipsoid.

Within the Juno extended mission, starting from July 2023 radio occultations of Jupiter have been occurring at a cadence of approximately one per month, near perijove. In this context, we report on a series of occultation events spanning multiple perijoves, with particular attention to the most recent experiments that probed high latitudes near the auroral zone close to Jupiter’s north pole. Understanding auroral effects is essential for characterizing the coupling between Jupiter’s magnetosphere and ionosphere, and for evaluating their broader impact on the dynamics and thermal structure of the planet’s upper atmosphere.

Our findings contribute to the growing understanding of Jupiter’s upper atmosphere, demonstrating the unique capabilities of dual-frequency radio occultations and paving the way for future ionospheric studies in support of upcoming exploration missions such as JUICE and Europa Clipper.

How to cite: Caruso, A., Gomez Casajus, L., Coffin, D., Buccino, D., Smirnova, M., Galanti, E., Gramigna, E., Parisi, M., Togni, A., Zannoni, M., Tortora, P., Park, R. S., Kaspi, Y., Withers, P., Hubbard, W., Orton, G., Steffes, P., and Bolton, S.: Characterization of Jupiter’s Ionosphere using Juno’s Radio Occultation Measurements, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-621, https://doi.org/10.5194/epsc-dps2025-621, 2025.

We present the Jovian Atmospheric Model Making Ionospheric EStimates (JAMMIES), a new model for Jupiter's non-auroral ionosphere. JAMMIES is a 2D model of Jupiter’s non-auroral ionosphere that solves the ion continuity and momentum equations in a dipole coordinate system. It was recently adapted from SAMI2 (Huba+2000), a model that has successfully reproduced numerous ionospheric features on Earth. JAMMIES incorporates neutral atmospheric inputs from a new general circulation model, JTIM (Mueller-Wodarg+2024), and defines its grid based on the updated JRM33 magnetic field model (Connerney+2022). JAMMIES is able to reproduce structures globally in H₃⁺ column density co-located with the long unexplained H₃⁺ Dark Ribbon: a lack of emission from the dominant molecular ion — H₃⁺ — coincident with Jupiter’s magnetic equator (Stallard+2018). We present how JAMMIES is able to recreate this ionospheric feature via Earth-like interhemispheric electrodynamic transport or neutral-wind driven-motion along magnetic field lines. We also present how we use JAMMIES to model electron density altitude profiles measured at dawn and dusk from radio occultations using the Galileo and Juno spacecrafts. Electron density altitude profiles from radio occultations are highly variable with no obvious systematic trends (Mendillo+2022). We find that much of that variability is captured in JAMMIES as a result of wind-driven field aligned plasma transport. Neutral winds from JTIM have strong westward zonal components and converge towards the equator. When combined with Jupiter’s complex magnetic geometry, this results in irregular patterns of effective upward and downward plasma transport, which are broadly consistent with observed plasma distributions. Additional modifications follow from vertical plasma drifts arising from electrodynamic interactions near the magnetic equator. The fact that plasma dynamics driven by a single neutral wind pattern can reproduce radio occultation morphologies from both the Galileo and Juno eras (spanning 30 years) suggests that Jupiter’s ionosphere is remarkably stable. Future JAMMIES simulations will further investigate this stability through comparisons with additional datasets and will enhance modeling capabilities by incorporating expanded chemistry and self-consistent plasma temperature calculations.

How to cite: Mohamed, K., Agiwal, O., Moore, L., Huba, J., Martinis, C., and Müeller-Wodarg, I.: Modeling Jupiter’s Ionosphere: Reproduction of Global H3+ Density Maps, and Electron Density Profiles from Galileo and Juno, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-913, https://doi.org/10.5194/epsc-dps2025-913, 2025.