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A comprehensive catalog of 1,589 Saturn magnetosheath traversals by Cassini between 2004 and 2012 was used to perform a statistical study of mirror mode (MM) waves and assess their role in influencing magnetic reconnection at the magnetopause (MP). MM waves have been observed in many planetary magnetospheres and magnetosheaths, comets and the solar wind. Understanding the conditions under which they grow and dominate can reveal their role in influencing plasma dynamics. Using a thresholding method on both magnetic field and plasma data, MM wave candidates can be identified. The magnetic field characteristics and occurrence distributions of these waves against different locations and conditions were found. MM waves were found from 4 to 19 hr local time (partly due to data coverage), and distances of 0–12 RS ${\mathrm{R}}_{\mathrm{S}}$ from the magnetopause (MP). The occurrence of MM dips was more frequent near the MP and magnetosheath flanks, analogous to the Jovian system. MM dips exhibited a minimum field strength saturation ∼ ${\sim} $ 0.5 nT, with the largest dip inferred to be in mirror‐stable plasma. Notably, larger amplitude MM dips were typically found nearer the MP boundary which increases Δβ ${\Delta }\beta $ across the boundary thus increasing the magnetic shear necessary for the onset of MP reconnection. Thus, MM waves may be important in plasma dynamics near Saturn's magnetopause. Plain Language Summary: Mirror mode waves (MM waves) are fluctuations in plasma density and magnetic fields that move with the bulk flow. They are commonly observed by spacecraft around planetary magnetospheres and other space environments. Their growth occurs when the plasma temperature perpendicular‐to‐magnetic‐field is greater than some threshold of the temperature parallel‐to‐magnetic‐field direction. After reaching saturation, some MM structures can remain stable for a long time. These waves can transfer energy between particles and electromagnetic fields, and could also influence more energetic events like magnetic reconnection. This study investigates the nature and role of mirror mode waves in Saturn's magnetosheath and surroundings. Key Points: Mirror mode (MM) dips at Saturn occur more frequently near the magnetopause (MP) and magnetosheath flanks, akin to the Jovian systemMM dips saturated at a field strength ∼ ${\sim} $0.5 nT. 83% of dips were in mirror stable region, whilst 46% peaks were in mirror unstable regionLarge MM dips enhance Δβ across the MP boundary, limiting the range of magnetic shear to near anti‐parallel for MP reconnection to occur [ABSTRACT FROM AUTHOR]

Understanding of wave environments is critical for the understanding of how particles are accelerated and lost in space. This study shows that in the vicinity of Europa and Ganymede, that respectively have induced and internal magnetic fields, chorus wave power is significantly increased. The observed enhancements are persistent and exceed median values of wave activity by up to 6 orders of magnitude for Ganymede. Produced waves may have a pronounced effect on the acceleration and loss of particles in the Jovian magnetosphere and other astrophysical objects. The generated waves are capable of significantly modifying the energetic particle environment, accelerating particles to very high energies, or producing depletions in phase space density. Observations of Jupiter's magnetosphere provide a unique opportunity to observe how objects with an internal magnetic field can interact with particles trapped in magnetic fields of larger scale objects.

Juno performed two close flybys of Io and found enhanced field‐aligned proton fluxes are absorbed by Io. These protons are absorbed at mass input rates comparable to previous estimates for hydrogen losses from Io, hence Jupiter is likely the source of hydrogen at Io. The conditions necessary for this to occur are: (a) formation of Alfvén waves at Io, (b) wave‐particle coupling to energize protons, (c) anti‐planetward transport of ions due to the magnetic mirror force and/or parallel acceleration, and (d) strong sub‐Alfvénic interaction slowing the flow connected to Io's fluxtube allowing for sufficient travel time for energized ions to transit to Io. The derived slowdown of ≤12% the upstream value is linked to filamentation within the Alfvén wing. This mechanism is likely operating at all strongly interacting satellites and provides an avenue to transfer material from a planetary body to its satellites, including exoplanets and brown dwarfs. Plain Language Summary: Juno performed two close flybys of Jupiter's moon Io, where it observed highly directional charged hydrogen streaming along magnetic field lines. These protons hit Io and the overall influx of them is sufficient to account for previously observed proton losses from Io. Therefore, Io's protons are not from Io's interior and instead provided from Jupiter and its charged particle environment. Furthermore, the observations allow for an estimation of the speed at which plasma flows across Io, which is found to be reduced to ≤12% of the flow speed upstream from Io. These processes are likely operating at similarly interacting bodies throughout our solar system and other solar systems far from the Sun. Key Points: Io's Alfvénic interaction provides a mechanism to transport ∼10's g s−1 of Jovian hydrogen ions to Io's polesThis mechanism is a universal process that can operate at any satellite‐planet system with adequate interaction conditionsPlasma flow within Io's Alfvén wing is slowed to ≤12% of its upstream value, allowing for filamentation [ABSTRACT FROM AUTHOR]

On days 2023‐364 and 2024‐034, the Juno spacecraft made close passages of Jupiter's moon Io, at altitudes of about 1,500 km. Data obtained from the first flyby, when the spacecraft was on magnetic field lines connected to both Jupiter and Io, revealed deep flux decreases. In addition, Juno's energetic particle detectors observed tens to hundreds of keV electron and proton beams. Such beams could be generated near Jupiter on field lines associated with Io. The second encounter occurred in the plasma wake and a more modest flux decrease was observed. Furthermore, data from both encounters suggest a spatially extensive decrease in >1 MeV electrons that includes regions inward of Io's orbit. In the immediate vicinity of Io, signatures of absorption likely dominate the data whereas diffusion and wave‐particle interactions are expected to be needed to understand MeV electron data in the wider spatial region around Io. Plain Language Summary: Jupiter's magnetospheric plasma overtakes Io in its orbit. This causes a cavity to be formed over the hemisphere of Io that leads its orbital motion. Within this cavity subtle details of the plasma and energetic charged particle environment can be extracted from the signal, usually dominated by radiation at these distances. Examples include beams traveling in the direction from Jupiter to the moon, with little evidence of reflection at Io. Another major finding of this work is that there is a large region both along Io's orbit and even radially inward of it with a lower level of MeV electron flux. Guided by previous modeling, the most likely candidates for shaping the data are absorption by the moon, wave‐particle interactions that can scatter particles into Jupiter's atmosphere, and diffusion. Key Points: Deep flux decreases over Io and in its immediate wake caused by losses to the moon's surface were observed in Juno JEDI dataJuno JEDI detected narrow field‐aligned beams of electrons and protons directed toward Io's north poleMoon absorption and wave‐particle interactions may explain the loss of >1 MeV electrons that extend both inward and outward of Io's orbit [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]

Author(s): B. H. Mauk (corresponding author) [1]; D. K. Haggerty [1]; C. Paranicas [1]; G. Clark [1]; P. Kollmann [1]; A. M. Rymer [1]; S. J. Bolton [2]; S. M. [...]