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

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

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

Nasa’s JUNO spacecraft, now in its extended mission, is finally passing through the Io plasma torus (IPT) taking in situ measurements of the plasma environment using the JUNO-JADE instrument. Through September of 2025 we will have almost 40 passes through the IPT of JUNO observations. Further, there is recent evidence from ground based optical telescopes that Io recently had a major eruption increasing neutral emission close to Io around Thanksgiving of 2022 (C. Schmidt, personal communication, 2022). We have been developing a nominal torus model based on in situ plasma measurements from previous missions, emission modeling of UV spectra, and ground based optical emission derived plasma parameters. Physical chemistry modeling informs our model and is another point of comparison. We use Phipps & Bagenal (2021) to define the centrifugal equator, along with the newest JUNO based magnetic field model (Connerney et al. 2022), and using diffusive equilibrium to find the plasma distribution along a magnetic field line. We will compare our IPT model with observations from JUNO before, during, and after the Thanksgiving 2022 eruption. We will compare JUNO observations with a physical chemistry model of the IPT to constrain the source rate, radial transport diffusion coefficient, transport timescale, and how these vary throughout the eruption.

We study Jupiter’s magnetic field and plasma parameters during Juno’s prime mission, using data from Juno’s FGM magnetometer and ion measurements from the Jovian Auroral Distributions Experiment Ion (JADE-I) sensor on Juno. We compare the observed poloidal magnetic field and plasma density, angular velocity and temperature profiles, with predictions from the Nichols et al. (2015) axisymmetric magnetic vector potential model. This magnetodisc model balances the j x B force of the azimuthal magnetodisc currents with the outwards forces of the plasma pressure gradient, plasma pressure anisotropy and the centrifugal force associated with the rotating plasma. By varying the model parameters for each orbit we model how Jupiter’s mass outflow rate, plasma angular velocity and ‘hot’ and ‘cold’ plasma temperatures and densities vary throughout Juno’s prime mission. We further examine how changes in magnetospheric conditions are related to variations in the magnetosphere–ionosphere coupling parameters, in particular by studying the azimuthal and radial currents and the ionospheric field-aligned current density.

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

We present simultaneous Juno and Hubble Space Telescope of Jupiter's far-ultraviolet auroras obtained as part of a programme of observations covering 3 years of Juno's Extended Mission. We show that bright, expanded dusk-side southern main emission is associated with large-scale convection dynamics, dusk-side main emission arcs are associated with field-aligned currents, and equatorward diffuse emission and patches are associated with plasma injections in the middle magnetosphere occurring within intervals of enhanced plasma density, ongoing interchange motion and magnetospheric convection. These results shed light on the relation between the main auroral emission and magnetosphere-ionosphere coupling currents, and radial force balance in the magnetosphere. We also report on unusually bright and expanded southern auroral emissions observed during PJ 43.

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

We present a discrete observation of diverse plasma populations and evidence of closed magnetic topology at Jupiter’s polar cap. Two distinct populations of protons are observed over Jupiter’s southern polar cap: a ~1 keV core population and ~1-300 keV dispersive conic population at 6-7 Jovian radii planetocentric distance. We find the 1 keV core protons are likely the seed population for the higher-energy dispersive conics. Transient wave-particle heating in a “pressure-cooker” process is likely responsible for this proton acceleration. The plasma characteristics and composition during this period show Jupiter's polar-most field lines can be topologically closed, with conjugate magnetic footpoints connected to both hemispheres. Finally, these observations demonstrate energetic protons can be accelerated into Jupiter's magnetotail via wave-particle coupling.

Juno made a close flyby of Ganymede and flew through its magnetosphere on June 7, 2021. This flyby included a crossing of Ganymede’s upstream magnetopause on the outbound segment of the spacecraft transit. We present plasma and magnetic field observations near that magnetopause crossing from Juno’s Jovian Auroral Distributions Experiment (JADE; McComas et al. 2017) and magnetometer (MAG; Connerney et al. 2017), respectively. JADE observed enhanced electron fluxes, including heated, streaming electrons, some with bi-directional pitch angle distributions, as Juno crossed the magnetopause current layer (MCL) as identified by the magnetic field observations. The acceleration of cold ions, both protons and heavy ions originating from Ganymede, was observed on approach to the magnetopause along with a likely mixing of ions from Ganymede and Jupiter’s plasma sheet within the MCL. These observations are used to examine the physics of plasma interactions at this boundary, including evidence that magnetic reconnection, considered a key driver of magnetospheric dynamics at Ganymede, was occurring along the magnetopause at that time.

Jupiter’s aurora is complex and dynamic, with a large number of distinct auroral features and regions generated by multiple phenomena. Of these features, Io’s auroral signature is one of the most persistent and identifiable aurora, with a rich observational history spanning decades of remote observations. Since Juno arrived at Jupiter, providing in-situ transits through flux tubes directly connected to Io’s auroral emissions, its diverse set of instruments have revealed an even more complex and dynamic picture of Io’s auroral interaction. In this presentation, we report on Juno observations of precipitating electron fluxes connected to 18 crossings of Io’s footprint tail aurora, over altitudes of 0.15 to 1.1 Jovian radii (RJ). We will highlight how the strength of precipitating electron fluxes is dominantly organized by “Io-Alfvén tail distance”, the angle along Io’s orbit between Io and an Alfvén wave trajectory connected to the tail aurora. We will discuss how these fluxes were best fit with an exponential as a function of down-tail extent with an e-folding distance of 21˚, the acceleration region altitude likely increases down-tail, and most of the parallel electron acceleration sustaining the tail aurora occurs above 1 RJ in altitude. Finally, we will highlight how Juno has likely transited Io’s Main Alfvén Wing fluxtube, observing a characteristically distinct signature with precipitating electron fluxes ~600 mW/m2 and an acceleration region extending as low as 0.4 RJ in altitude.

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

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

The Io Torus plasma is mostly composed of singly and multi-charged S and O ions. These ions interact with the neutrals of Io’s atmosphere (S, O, SO2 and SO) through symmetrical (i.e. O+ + O => O + O+) and asymmetrical (i.e. S++ + O => S + O++) charge-exchanges. Charge-exchange cross-sections were estimated in Johnson & Strobel, 1982 and McGrath & Johnson, 1989 at 60 km/s (the plasma corotation velocity in Io’s frame), and are used in numerical simulations of the torus/neutral cloud interaction (i.e. Delamere and Bagenal, 2003). Dols et al., 2008 proposed numerical simulations of the multi-species chemistry interaction at Io using these cross-sections at 60 km/s. The plasma/atmosphere interaction at Io is strong and the flow velocity and ion temperature are drastically reduced close to Io (v < 10 km/s). Thus, velocity-dependent charge-exchange cross-sections are critical for such numerical simulations and their effect on the local plasma and neutral supply at Io should be explored. We propose to revisit the calculation of ion/neutral charge-exchange cross-sections following Johnson & Strobel, 1982’s approach for plasma velocities relevant to the local interaction at Io (V=10-120 km/s). More sophisticated calculations were proposed in McGrath & Johnson, 1989 but both publications offered very few details about their procedure. We will illustrate the effect of using velocity-depend charge-exchange cross-sections in numerical simulations of the multi-species plasma/atmosphere interaction at Io. More generally, this presentation aimed at providing an incentive for the community to expand the work of McGrath & Johnson, 1989. Johnson & Strobel, Charge-exchange in the Io torus and exosphere, JGR, 87,1982 McGrath & Johnson, Charge exchange cross sections for the Io plasma torus, JGR, 94, 1989 Delamere & Bagenal, Modeling variability of plasma conditions in the Io torus, JGR, 108, 2003 Dols, Delamere, Bagenal, Kurth, Paterson, A multi-species chemistry model of Io’s local interaction with the plasma torus, JGR, 113, 2008

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

The plasma interaction with Io’s atmosphere results in at least a ton per second of escaping neutrals. Most of these neutrals supply extended neutral clouds along Io's orbit and eventually become ionized and accelerated to corotation with Jupiter, populating the Io plasma torus as well as spreading out to fill Jupiter’s vast magnetosphere. About half to two-thirds of the plasma torus ions charge-exchange with the extended neutral clouds and leave the torus as energetic neutral atoms, passing Europa’s orbit. Energetic neutrals are also produced directly in the plasma-atmosphere interaction, escaping with sufficient speed to reach Europa’s orbit before being ionized. The iogenic ions that are accelerated to high energies in the middle magnetosphere ultimately move back inward, again crossing Europa’s orbit. We present estimates of the fluxes of these various iogenic populations and how much oxygen, sulfur and sodium might be hitting Europa.

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