Zhonghua Yao

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.

Context . The Jovian magnetopause is a highly dynamic boundary that experiences substantial deformation driven by interactions with the co-rotating internal plasma and the solar wind, leading to the development and propagation of wave activity along the boundary. Aims . This study aims to analyse in situ magnetic field measurements to detect wave activity along the magnetopause and identify the physical processes responsible for the observed perturbations. Methods . We applied five boundary analysis techniques to magnetic field data from seven different spacecraft to infer the local magnetopause normal. The resulting normals were then compared with a model of the magnetopause in order to detect surface wave activity and characterise its propagation direction. Results . We identified tailward-propagating waves along the Jovian magnetopause and linked them to solar wind interactions, with signatures probably associated with the Kelvin–Helmholtz instability. Conclusions . Magnetic field measurements provide robust statistical evidence of tailward-propagating perturbations on both flanks of Jupiter’s magnetopause regardless of the analysis method used.

Enceladus is a key source of plasma and neutrals in Saturn’s magnetosphere through its active south polar plume, which drives complex dust–plasma interactions and modifies the local environment. In this paper, we investigate electron density perturbations near Saturn’s moon Enceladus using Cassini observations from 12 targeted flybys that sampled the upstream and downstream regions. Electron densities are derived from the upper hybrid resonance frequencies detected by the Radio and Plasma Wave Science (RPWS) instrument, and energetic electron intensities are obtained from the Low Energy Magnetospheric Measurement System (LEMMS) of the Magnetospheric Imaging Instrument. Flybys are classified as upstream or downstream encounters, enabling a direct comparison of spatial variations. The results reveal a pronounced upstream–downstream asymmetry in RPWS electron density. Downstream flybys exhibit strong depletions near Enceladus, with anomalies reaching up to ∼60 cm ⁻³ below background levels, whereas upstream flybys display only modest variations of a few cm ⁻³ . The magnitude of dropouts in the downstream region also depends on flyby geometry. These observations are consistent with the presence of plume-generated dust and Alfvén wings downstream and offer insight into the spatial scale of the interaction region. In contrast, LEMMS energetic electron observations show no clear upstream–downstream asymmetry, with intensity dropouts occurring in both geometries. This may indicate that cold and energetic electron populations exhibit different behaviors influenced by physical processes operating on different spatial scales in the vicinity of Enceladus.

Jupiter’s magnetospheric current sheet is predominantly shaped by rapid rotation and internal plasma sources, yet its structure is also influenced by the surrounding solar wind. It provides a natural laboratory for understanding how a rotation-dominated current sheet maintains its global organization while accommodating external forcing. Using Juno observations together with analytical modeling, we investigate both the global geometry and small-scale irregularities of this system. Our analysis indicates that Jupiter’s current sheet exhibits a wavy “ballerina-skirt” morphology analogous to that of the heliospheric current sheet. Beyond this large-scale similarity, statistical analysis of magnetic polarity distributions provides the first direct observational evidence for Jovian current sheet hinging, identifying a characteristic distance of ∼30 R _J . Small-scale structures associated with external perturbations are likewise more frequently observed beyond this hinging distance. The correspondence between boundaries in large-scale geometry and small-scale activity indicates a physical transition: ∼30 R _J separates a rotation-dominated inner region from an outer region governed by the complex interplay between internal subcorotating plasma dynamics and external solar wind forcing. The structural parallels with the heliospheric current sheet, together with multiscale deviations from this baseline morphology, illustrate how Jupiter’s magnetospheric current sheet operates and maintains organization under coupled internal and external drivers, offering a framework for understanding other rapidly rotating magnetized plasma systems.

Jupiter has the largest planetary magnetosphere in our solar system, and the rapid planetary rotation imposes a strong centrifugal force on the iogenic plasmas, forming a rotating magnetodisc. An inside-out compression of the magnetopause is expected on the dayside, while in the tail region, the interaction near magnetopause is poorly understood. By comparing particle and wave features near the magnetopause at different distances, we reveal quasi-planetary rotation periodic magnetic depressions in the magnetosheath near the magnetopause at dawnside (local time ∼6 h) at about 100 R _J and post-midnight (local time ∼3 h) at about 200 R _J . Accompanied by the magnetic depressions, energetic particle enhancements were observed, suggesting acceleration processes on the boundary. The strong magnetic perturbations and energetic particle enhancements are likely consequences of magnetospheric flow compression on the boundary. Particularly, the Voyager 2 observations made at about 200 R _J in the tail provide key clues in understanding Jovian magnetotail dynamics and flow circulations.

Juno observations have revealed that Jupiter's polar cusps are displaced toward dusk and even the nightside, contradicting the Earth‐derived paradigm that is confined to narrower ranges near noon. These findings underscore the overlooked influence of planetary rotation on magnetospheric dynamics, exposing a critical gap in current theoretical frameworks. Using global magnetohydrodynamic (MHD) simulations, we show that high‐altitude cusps reside on the dusk hemisphere at both Saturn and Jupiter, consistent with Juno data at Jupiter and distinct from Earth's near‐noon‐centered cusps. Controlled experiments with artificially increased Earth rotation rates demonstrate a systematic duskward shift of cusp local time, transitioning from noon to afternoon (Saturn‐like) and dusk (Jupiter‐like) sectors. We propose the corotation‐to‐convection speed ratio as a unifying parameter that captures this duskward displacement across different planets. This unified framework explains gas‐giant magnetospheres, offering potential applications to other rapidly rotating systems, such as ice giants, early Earth, and exoplanets.

Saturn’s magnetosphere, shaped by solar wind interaction with its dipole field, differs from Earth’s due to faster rotation and Enceladus’s internal plasma sources. An ongoing focus of investigation is how the internal plasma sources and rapid rotation result in a different global magnetospheric configuration. The magnetospheric cusp, a crucial interaction region between solar wind and planetary magnetic field, serves as an indicator of global magnetic configuration. Here we utilize Cassini observations from 2004 to 2010 to study dawn-dusk asymmetry in Saturn’s cusp distribution and extend the number of cusp events from about 11 reported in previous studies to 67. We find peak occurrence in the post-noon sector and signatures extending to post-dusk (near 20 local time), resembling recent observations of Jupiter’s post-dusk cusp. We further examine magnetic topology using high-resolution magnetohydrodynamic simulations to visualize the cusp asymmetry. This is consistent with previous studies, but our simulations provide a more detailed view of Saturn’s magnetic topology near the magnetopause. This asymmetry of cusp distribution demonstrates how rapid rotation and internal plasma sources fundamentally alter magnetospheric configuration, offering insights for understanding other rotating planetary systems within and beyond the solar system.

Jovian magnetospheric dynamics are often believed to be mainly controlled by internal elements such as Jupiter's strong and fast‐rotating magnetic moment and Io's abundant volcanic escape, as these internal elements are powerful enough to control the magnetospheric dynamics, contrary to the internal elements of the earth's magnetosphere. On the other hand, the significant influence of external processes has been revealed by observations such as dawn‐dusk asymmetries, indicating the complexity of the driver of Jovian magnetospheric dynamics. To further contrast the influence of internal and external processes, it is essential to explore the effect of external processes on the Jovian magnetosphere. For this purpose, this study investigated the magnetic field in Jupiter's dawn outer magnetosphere and identified several current sheet crossing events displaying apparent north‐south asymmetry. The magnetic field shows a significant difference in variation rate, and the current sheet direction can change by more than 45 degrees while the tendency of variation in the identified events is changeable and hard to conclude. The word “apparent” is used in this paper to show that the apparent asymmetry displayed in data represents the change of the environment, containing the variations of current system and plasma flow, instead of a global asymmetry of the current sheet itself. The apparent asymmetry was suggested to primarily originate from local current sheet flapping, which carries current sheet with parameters different from those carried by the global current sheet flapping. The compressional bursts may also contribute to the apparent asymmetry. These two sources were both attributed to interactions with solar wind, indicating the potential mechanisms for external processes to affect Jupiter's magnetospheric dynamics.

Saturn's magnetosphere, shaped by solar wind interaction with its dipole field, differs from Earth's due to faster rotation and Enceladus's internal plasma sources. An ongoing focus of investigation is how the internal plasma sources and rapid rotation result in a different global magnetospheric picture. The magnetospheric cusp, a crucial interaction region between solar wind and planetary magnetic field, serves as an indicator of global magnetic configuration. Here we utilize Cassini observations from 2004 to 2010 to study dawn-dusk asymmetry in Saturn's cusp distribution with peak occurrence in the post-noon sector and signatures extending to post-dusk, resembling recent observations of Jupiter's post-dusk cusp. We further examine magnetic topology using high-resolution magnetohydrodynamic simulations to visualize the cusp asymmetry, providing a global view of Saturn’s magnetic topology near the magnetopause. This asymmetry of cusp distribution demonstrates how rapid rotation and internal plasma sources fundamentally alter magnetospheric configuration, offering insights for understanding other rotating planetary systems within and beyond the solar system.

Discrete features in Jupiter’s ultraviolet aurora have been interpreted as signatures of plasma injections in the middle magnetosphere. There exists some ambiguity as to whether magnetodisc scattering or high-latitude Alfvénic acceleration best describes the observed properties of these injection signatures, and also the extent to which extent arcs in the outer emission are related to injections. Many injection signatures are the result of the evolution of dawn storms; however, there is limited evidence that non-dawn-storm injection signatures are sometimes present in the aurora. We use automatic detection of these discrete features, alongside data from Juno-UVS and in situ measurements by other Juno instruments, to show that scattering likely accounts for most of the electron precipitation associated with injection signatures. Additionally, there is evidence that injection signatures can be classified into two types: dawnstorm and non-dawn-storm. Arc-like features in the outer emission show very similar properties to traditional blob-like injection signatures and may consist of sequences of injection signatures that have broadened into an arc via energy-dependent electron drift.