Scott J. Bolton

A surface wave is a mechanical wave propagating along the interface between two media, such as the magnetopause. Planetary magnetopause surface waves influence mass and energy circulation in interplanetary space, magnetospheres, and coupled ionospheres and atmospheres. Although surface waves have been extensively investigated on Earth and Saturn, their characteristics on Jupiter require further investigation. Our analysis of Juno in situ data reveals periodic magnetopause crossings consistent with a large‐scale surface‐wave interpretation. The Doppler‐shifted source‐period range overlaps a 13.7‐min auroral periodicity observed by the Hubble Space Telescope on the same day. This correspondence motivates a hypothesized link between magnetopause surface waves and polar auroral pulsations that remains to be tested with simultaneous observations, field‐line mapping, and precipitation diagnostics. The occurrence of surface waves in Jupiter’s rapidly rotating, strongly magnetized environment further suggests that such waves are a broadly shared feature of planetary magnetospheres and may contribute to energy coupling under diverse conditions.

Interchange instability plays a critical role in driving mass and plasma transport within Jupiter's inner and middle magnetospheres. In this study, we present a superposed epoch analysis of 160 interchange events to quantify their characteristic signatures of magnetic fields, particles, and plasma waves using Juno data from 2016 to 2024. Interchange events are characterized by rapid magnetic field enhancements, strong depletion in low‐energy particles, pronounced enhancements in higher‐energy particles, and associated plasma wave activity. The threshold energy separating particle depletion from enhancement increases with radial distance for electrons across M‐shells of ∼8–20, while remaining nearly constant for protons beyond M‐shell ≈10. Accompanying plasma wave activity, including Z‐mode, whistler‐mode, and electron cyclotron harmonic emissions, exhibits distinct spectral characteristics. Along event boundaries, predominantly electrostatic waves consistent with lower hybrid drift waves are observed. These results demonstrate that interchange instability plays an important role in plasma transport and wave generation in Jupiter's magnetosphere.

Jupiter displays the brightest auroras in the solar system, driven by intensely varying energetic electrons that accelerate into the atmosphere. Here, we provide a comprehensive formalism that accurately describes the bimodality of observed auroral electron acceleration regimes. We demonstrate that the occurrence of the two dominant auroral regimes—broadband and monoenergetic—is dictated by specific characteristic plasma length scales, namely, the relationship between the transverse length scale and the electron inertial length. Furthermore, in contrast to the long-standing acceptance that Alfvén waves responsible for auroral electron acceleration exclusively originate at distant equatorial regions, we demonstrate that they can be locally generated at Jupiter’s low altitudes. From this understanding, we find that locally generated, low-altitude Alfvén waves can be directly responsible for accelerating the most intense auroral electrons at Jupiter. These findings establish that the low-altitude acceleration region can itself become a source of Alfvén waves rather than merely a sink for wave energy, thus altering the standard picture of global magnetospheric energy transfer in strongly magnetized planets.

We report observations of a low energy (<2 keV), trapped electron population near Jupiter's magnetic equator made by the Jovian Auroral Distributions Experiment (JADE) on Juno. Electron intensity peaks around the location of the minimum magnetic field magnitude along the field line that is connected to Juno. Pitch angle distributions peak at 90° with an average FWHM of 64°. The energy distributions have a power spectral slope of −0.74 on average with a roll‐over at ∼500 eV and a cutoff at ∼1–2 keV. There is no ordering of the peak intensity with altitude or latitude, although the peak is lower in intensity between 220° and 280° System III west longitude. There is a significant correlation between 15–70 keV ion rates and the peak electron intensity. The energy distribution of these electrons is consistent with secondary electrons created from the interaction of energetic particles with the upper atmosphere.

We report on new observations of Io upwelling thermal emission over the range of 0.6–22 GHz acquired with the Juno Microwave Radiometer in December 2023 and February 2024. The microwave emission spectrum from the surface of Io is retrieved from the calibrated brightness temperatures by characterizing and removing reflections from the sky. The surface appears to exhibit specular reflection in the microwave, suggesting a relatively smooth surface on 100 km spatial scales (apart from visible topography), like Earth's land and ocean surfaces. The real part of the dielectric constant is found to be in the range of 2–4; constrained by overlapping observations on the surface from two viewing geometries. This relatively low value is consistent with a density of 0.7–1.1 g/cm ³ of the surface layer (2 . Alternately, relatively fresh lava flows (<5 years) or heat vents covered by a cooling crust on the order of 10 m over about 10% of the surface area can also explain the spectral gradient.

The mechanism driving ion outflow from Jupiter's auroras remains to be determined. outflow has been observed with highly field‐aligned pitch angles consistent with acceleration by high‐altitude electrostatic potential structures. However, the cold ionospheric ions require a pre‐acceleration mechanism to reach Jupiter's large escape speed and access the potential structures. Here we present case studies of outflow coincident with intense ion cyclotron waves (ICWs). We invoke resonant wave heating to suggest a causality between the two phenomena. We further investigate Landau resonance with auroral electron beams as a plausible source of free energy using cold plasma theory, finding that electron energies between 10 and 100 keV produce results consistent with ICW observations. and ICWs are likewise present, which we suggest indicates that Jovian ion outflow is a multi‐species process.

Unlike Earth, where whistler‐mode chorus is generally observed outside the plasmasphere and hiss is predominantly confined within it, Jupiter's magnetosphere frequently hosts both wave modes simultaneously. Using Juno observations, we present a global survey of whistler‐mode waves at Jupiter, demonstrating that both chorus and hiss are prevalent over 6 < M < 13, with chorus confined to lower latitudes and hiss extending to higher latitudes. Based on the observed wave and plasma characteristics, we apply physics‐based global diffusion modeling to assess the separate and combined effects of chorus and hiss waves on energetic electron dynamics. The simulations show that, near regions of peak wave activity, chorus waves lead to net electron losses below ∼1 MeV while producing acceleration at higher energies. Hiss waves primarily drive electron losses, but in combination with chorus waves, they can also enable electron acceleration above ∼1 MeV at specific pitch angles.

Auroral emissions play a critical role in coupling the magnetosphere and atmosphere at magnetized planets. At Jupiter, isolated auroral patches equatorward of the main auroral oval have been associated with magnetospheric injections, yet the key conditions driving these emissions remain unclear. Here we combine in situ particle and wave measurements and remote-sensing auroral observations from Juno to uncover the origins of Jupiter’s patchy aurora. By examining both low-altitude and equatorial crossings, our results reveal that not all injections lead to auroral enhancements. Instead, auroral patches arise directly from electron precipitation driven by wave-particle interactions, while injections play a supportive role in facilitating wave growth and electron precipitation. These findings highlight the central role of plasma waves in auroral generation and in coupling Jupiter’s magnetosphere and ionosphere, providing broader implications for wave-driven auroral processes across planetary magnetospheres.