Hairong Lai

Whistler-mode waves are a common class of electromagnetic emissions in Jupiter’s magnetosphere and play an important role in regulating radiation belt dynamics by accelerating and precipitating energetic electrons. These waves span a broad frequency range from f _cp to f _ce , where f _cp and f _ce denote the equatorial proton and electron cyclotron frequencies, respectively. Using measurements from the Juno spacecraft, we report frequency-dependent responses of whistler-mode waves to an electron injection event in the Jovian middle magnetosphere. Near the premidnight equator at M ∼ 11, Juno observed an electron injection lasting ∼ 30 minutes, characterized by significant flux enhancements from 0.1 to 30 keV. In response, the preexisting whistler-mode waves below 0.25 f _ce nearly vanished, whereas both lower- and upper-band chorus emissions emerged at higher frequencies. We further evaluate the influence of electron injection on whistler-mode waves within the framework of linear theory. The results indicate that electron injection can facilitate the local generation of whistler-mode waves above 0.25 f _ce , while simultaneously suppressing lower-frequency waves through enhanced Landau damping.

Large magnetic flux ropes mediate plasma transport, particle acceleration, and energy dissipation in planetary magnetospheres. While well studied in the solar wind–driven terrestrial magnetosphere, their evolution at Saturn, where strong internal driving combines with intermittent solar-wind forcing under variable upstream conditions, remains less well characterized. We present a systematic survey of seven years of Cassini magnetometer and plasma data, focusing on the low-latitude region outside Saturn’s magnetodisc where the magnetopause and magnetosheath respond directly to the solar wind. Using stringent selection criteria, we identify 67 large-scale flux rope candidates. Minimum variance analysis constrains axial orientations for all events, and for 9 events with high-quality plasma measurements we apply three-dimensional Grad-Shafranov reconstructions to resolve magnetic structure and flux content. The resulting ropes span diameters of 0.7-13.2 Saturn radii andmagnetic fluxes of 6 × 10 ⁶ to 8.7 × 10 ⁸ Wb, generally exceeding the size range of previously reported flux transfer events at Saturn. We find a pronounced dawn-dusk asymmetry: flux ropes occur more often near dawn but are typically larger near dusk, consistent with Kelvin-Helmholtz instability (KHI) formation. A substantial subset shows north-south axes, also consistent with KHI. Individual events can transport up to ∼ 10% of the open magnetic flux exchanged during a Dungey cycle, indicating that these flux ropes can move substantial magnetic flux across Saturn’s magnetopause and contribute meaningfully to magnetospheric circulation.

The 2029 close encounter of near-Earth asteroid (99942) Apophis, at approximately 38,000 km from Earth center, offers a unique opportunity to advance planetary science, defense, and public engagement. This rare event enables real-time observations of tidal effects, surface displacement, spin changes, and dust ejection, deepening our understanding of rubble-pile asteroids and improving models of their evolution. Detailed data will refine predictions of the Yarkovsky and YORP effects, enhancing asteroid dynamics research. From a planetary defense perspective, Apophis provides a critical test case for impact risk assessment and mitigation strategies, informing rapid-response reconnaissance missions. Public outreach during the event will raise awareness of asteroid science and planetary safety, fostering interest in space exploration. International collaborations, including NASA’s OSIRIS-APEX and ESA’s RAMSES missions, along with the potential contributions from China, aim to maximize scientific returns, making the 2029 Apophis flyby a milestone in global planetary exploration and defense efforts.

High solar wind dynamic pressure, particularly during stream interaction regions (SIRs), can strongly compress the Earth's magnetosphere, posing a risk to space‐based technologies critical to modern society. This study investigates the response of the low‐latitude magnetopause to an extreme SIR on 14 March 2016, using in situ observations. The magnetopause was compressed inward to near geosynchronous orbit and remained compressed for several hours after the SIR's passage, revealing an unusually prolonged recovery phase. We present three lines of analyses: (a) multi‐spacecraft observations of magnetopause crossings; (b) magnetic pressure measurements inside the magnetopause; and (c) ground‐based records of low‐latitude geomagnetic field perturbations. The extended recovery challenges the conventional view that the magnetosphere rebounds within minutes after solar wind compression. These findings highlight the complexity of magnetospheric dynamics under extreme conditions and the need for further investigation into these regions, in order to improve space weather forecasts and protect critical technologies.

Magnetic flux ropes are an important area of research in space physics. Among the various magnetic field enhancement events in the solar wind, some remain puzzling due to their multiple possible origins, with interlinked flux ropes being a key candidate. In this study, we analyzed two distinct events to develop a classification framework. Using high-resolution Hall MHD models of interlinked flux ropes, we reproduced the observed magnetic field and velocity components. Our findings show that one event involved flux ropes with a chirality combination that favors magnetic reconnection, while the other had a configuration that suppressed reconnection, consistent with observations. By applying standard data analysis methods, we identified chirality combinations consistent with our models. This study provides direct evidence of 3D flux rope interactions and offers data products to facilitate future event classification.

Submicron debris released in interplanetary collisions gets charged in the solar wind and generates disturbances to the magnetic field environment. The unique magnetic field disturbances, named interplanetary field enhancements (IFEs) are recorded by many spacecraft. In this study, we have developed a novel model to trace the IFEs to their origins. By employing this model, we can pinout regions with highly collision frequencies, thereby identifying regions of intense collisional activity. We can also determine the long-term variation of these highly collisional regions with interplanetary magnetic field observations over decades. The model can help constrain interplanetary magnetic disturbances and our results can be used to guide part of the interplanetary-object survey.

Magnetic flux ropes are a fundamental component in both space and laboratory plasmas. We present a Hall-MHD simulation exploring the interaction between two isolated magnetic flux ropes under mesoscale solar wind conditions. The interaction interface is resolved with a resolution approaching the kinetic scale, to reveal unprecedented details of this process. As we replicate previous findings that such interactions can lead to the formation of two new ropes, we also find that magnetic reconnection occurs in multiple locations inside the central current sheet, leading to transient small flux ropes, which is qualitatively consistent with previous magnetospheric multiscale observations. Consequently, each field line undergoes multiple reconnections that alter its connectivity before it exits the current sheet. Later, each flux rope divides into two branches: the reconnected flux moving away from the current sheet to form the transition regions of the new ropes and the remnant flux sustaining the current sheet. For each magnetic flux rope (MFR), the core field reconnects after most surface fields are reconnected so that the reconnecting MFRs maintain a relatively symmetric shape. These results in unprecedented detail highlight the complex internal dynamics and call for further observational and theoretical studies.

The levitation of charged dust, which may cause serious hazards to astronauts and lunar rovers, has been one of the most significant challenges in lunar exploration. Here we simulate lunar sheath potentials in different solar wind conditions and solar zenith angles (SZAs) on the lunar surface by the particle-in-cell method. The simulated potentials exhibit two types of distributions as a function of height, depending on the SZAs. For SZA ∼ 0°–70°, the nonmonotonic distribution with positive surface potential dominates in the photoelectron sheath. For SZA >∼81°, the monotonic distribution with negative surface potential is observed in the plasma sheath. With the calculated potentials and the assumption that the dust radius distribution exponentially decreases, we further investigate spatial distributions of the dust levitated above the surface. It is found that number density of the levitating lunar dust is enhanced at the terminator (SZA ∼ 81°) in the plasma sheath. In the photoelectron sheath it gradually decreases as the SZA increases from 0° to 70°. Further calculations of the potential and the derived electrostatic field suggest that the dust spatial distributions can be influenced by the bulk velocity, number density, and temperature of the solar wind. Those findings deepen our understanding of lunar surface charging and the mechanism of lunar dust levitation, which can provide technical support for lunar explorations.

Within the solar wind throughout the inner heliosphere, observations reveal the presence of magnetic field enhancements accompanied by thin current sheets at varying distances from the sun and across different longitudes and latitudes. Two primary explanations have been proposed to elucidate these phenomena: Solar wind‐dust interaction and interlacing flux ropes. In this study, we employ multi‐fluid Magnetohydrodynamics (MHD) and Hall MHD models to simulate these hypotheses, respectively. Our findings indicate a concurrence between both models and the observed phenomena, suggesting that both processes may result in the same kind of enhancement. Furthermore, both models make predictions pointing to additional types of observational data, occurring at distinct spatial or temporal stages of the interaction. This convergence of model predictions with empirical data underscores the need for further observational and modeling studies to comprehensively test these models. This research enhances our knowledge of the inner heliosphere's dynamics and the influence of the solar wind on the Earth's magnetosphere, thereby shedding light on critical aspects of space weather and its potential impact on our planet.

A document by Yingdong Jia. Click on the document to view its contents.