Robert J. Wilson

The Jovian magnetosheath plays a key role in modulating the interaction between the solar wind and Jupiter's magnetosphere. It also serves as a natural laboratory for studying fundamental plasma processes, such as turbulence, magnetic reconnection, and kinetic instabilities. Here, we introduce a data set of magnetosheath proton plasma properties derived from 9 years of Juno JADE‐I observations, including plasma density, temperature, and 3‐D bulk velocity. Covering both the equatorial dawn sector and the mid‐to‐high latitude dusk sector, the data set consists of 443 magnetosheath intervals longer than 1 hr. In total, it contains 233.2 days of observations and 317,719 data points, spanning from Juno's arrival at Jupiter to the end of the first extended mission. An overview of the data set and related statistical properties is presented to demonstrate its effectiveness and usefulness. The magnetosheath flow drapes around the magnetopause and accelerates as it moves tailward. The dawn sector plasma exhibits lower density and temperature but higher velocity than the dusk sector. These differences may result from local time effects, variations in distance from the subsolar magnetopause, and/or solar cycle modulation. This data set has strong potential to advance our understanding of Jupiter's magnetosheath through a wide range of future applications.

The Juno mission has elucidated magnetosphere processes, structure, and dynamics via multi‐instrument plasma and magnetic field observations. In this study, these instruments are used to identify magnetic reconnection during the Juno extended mission from a survey of 490 magnetopause crossings at the mid‐latitude southern dusk magnetopause. This survey spans distances of 30–99 R _J , 14–20 local time, and 30°–65° in southern latitude. We identify reconnection outflow jets, plasma heating, and Hall magnetic fields as reconnection signatures while independently applying the Swisdak and Walén relations to each magnetopause crossing. Additionally, eastward versus westward interplanetary magnetic field (IMF) conditions are compared in this context. The results show that magnetic reconnection is most likely to occur during eastward IMF at the mid‐latitude dusk magnetopause due to favorable magnetic shear conditions. The identified eastward IMF reconnection events strongly adhere to the Walén relation, showing signatures of Alfvénic flow perturbations.

The space environment around the Galilean moons is important for understanding the interaction of the magnetospheric plasma with their magnetosphere (in the singular case of Ganymede), their atmospheres and surfaces. Juno's orbital evolution brought the spacecraft close to the orbits of Ganymede and Callisto on multiple occasions over several years. We present a survey of plasma conditions (density, temperature, composition, flows, and magnetic field) near the orbits of these moons to illustrate the variability of these plasma properties. Statistics of their median and percentile values quantify the ranges of parameters experienced by the moons.

In Jupiter's magnetosphere, a key question is how plasma is transported outward from its source near Io to the distant magnetotail. Since 2016, the plasma disk has been extensively observed by the Juno mission. Using plasma data from the JADE instrument, we perform an analysis revealing significant temporal variation. For different Juno orbits, plasma disk observations are categorized as either enhanced or depleted based on plasma density, with extreme cases showing variations exceeding an order of magnitude. For plasma disk crossings by Juno, density enhancements and fluctuations in plasma density and magnetic field profiles are correlated, suggesting that flux tube interchange is triggered by increase in the plasma source from Io. Juno's in situ measurements show a correlation with remotely sensed Io torus ribbon brightness from the IoIO telescope, suggesting that the average plasma transport time from Io to the plasma disk between 10 and 30 is around 40 days.

In October 2024, the Juno spacecraft observed an extreme compression of Jupiter's magnetosphere. This event pushed the magnetosheath into an unprecedented distance of only 30 Jupiter radii from Jupiter. This suggests an enhanced Solar Wind (SW) dynamic pressure (DynP), that was likely produced from a coronal mass ejection after an X1.8 class solar flare. The compression brought the magnetosheath, observed at a high southern latitude, to the closest distance ever observed from Jupiter. Using data from multiple instruments on Juno to identify magnetosheath signatures, it is shown that Juno had many encounters with the magnetosheath as it moved inward from apojove to perijove. This included many short‐lived encounters that were not readily identifiable from a single data set. From model estimates, a SW DynP of around 1.2 is suggested for this event, consistent with previous upper estimates observed in the vicinity of Jupiter's orbital path. Remote imaging suggests the magnetosphere remained compressed for several days after this event. The event raises the possibility that Jupiter's magnetosphere on the dayside could potentially shrink inside of Callisto's orbital path, and that if Callisto happened to be on the dayside of Jupiter at the time (although it was on the nightside during this event), it could find itself outside of the jovian magnetosphere and exposed directly to the SW.

Using the methodology of Cowley et al. ( https://doi.org/10.1029/2025JA033993 ), we employ ∼8 years of Juno azimuthal magnetic field data to derive colatitude profiles of Jupiter's nightside (17‐05 hr via midnight) ionospheric equatorward Pedersen current from near the magnetic pole to inner magnetosphere field lines at 18° colatitude, from which we quantify large‐scale field‐aligned currents on spatial scales ∼1°. Polar‐tail Pedersen currents are ∼1–2 MA per radian of azimuth, with regions of downward and upward currents of order tens nA m ⁻² . Stronger downward currents ∼50–200 nA m ⁻² flow in an outer magnetosphere layer that is wider at dusk (∼7°) than at dawn (∼2°), with peak Pedersen currents near the outer/middle magnetosphere boundary reaching ∼12 MA rad ⁻¹ at dusk falling to ∼2.5 MA rad ⁻¹ at dawn. Upward currents of order hundreds of nA m ⁻² flow on middle magnetosphere field lines across which the Pedersen current falls to small values. The Pedersen currents are also combined with Juno/JADE‐I plasma angular velocity measurements to determine Jupiter's effective ionospheric height‐integrated Pedersen conductivity, together with the power input to thermospheric heating. Outer magnetosphere effective conductivities are ∼0.4 mho at dusk, falling to ∼0.25 mho at midnight, and ∼0.1 mho pre‐dawn. No significant increase in conductivity is found in the middle magnetosphere region of strong upward current, suggesting that thermospheric winds closely track the plasma velocity in this region. Latitude‐integrated powers show a similar dusk‐dawn asymmetry, with a total nightside power per hemisphere of ∼370 TW, of which ∼55% is input to thermospheric heating and 45% to the magnetospheric plasma.

Saturn's magnetosphere is continuously supplied with neutrals from the Enceladus plume and the icy rings, which undergo ionization and charge‐exchange to form a complex water‐group plasma environment. While the Cassini Plasma Spectrometer (CAPS) instrument has provided extensive compositional information, detailed separation of individual water‐group ion species in time‐of‐flight (TOF) data has not previously been achieved. In this study, we perform forward modeling of CAPS‐IMS energy‐per‐charge (E/Q) and TOF spectra obtained between 2004 and 2012 to resolve O ⁺ , OH ⁺ , H ₂ O ⁺ , and H ₃ O ⁺ and to characterize their plasma properties, including number density, temperature, and thermodynamic κ. Our results demonstrate that O ⁺ is the dominant thermal ion species throughout Saturn's magnetosphere, comprising up to ∼70% of the total ion population beyond ∼5 Saturn radii (R _S ). In contrast, molecular ions such as OH ⁺ , H ₂ O ⁺ , and H ₃ O ⁺ dominate closer to Enceladus but rapidly dissociate into atomic ions between ∼5 and 10 R _S . This radial region is also characterized by the steepest increase in plasma flow speed, which rises from ∼40% to ∼80% of rigid corotation. Simultaneously, ion velocity distributions approach Maxwell–Boltzmann equilibrium, as indicated by high kappa values. These findings provide new constraints on the ion–neutral chemistry that regulates the balance between molecular and atomic ions in Saturn's magnetosphere. They also emphasize the critical role of the 5–10 R _S region as a transition zone for both plasma composition and dynamics. Our results refine previous CAPS‐based studies and underscore the need to incorporate seasonal variability and ionospheric coupling into future global models of Saturn's plasma environment.