Using the Van Allen Probes data, we conduct a statistical investigation into the effects of different solar wind and geomagnetic conditions on the relativistic electron (E-k > 1 MeV) accelerations in the Earth's outer radiation belt. Key findings include: (a) The peak flux locations for 1.0 and 3.4 MeV electrons (L*(max1) and L*(max2)) during the storm recovery phase exhibit strong negative correlations with storm intensity (|CC| >= 0.76). Continuous substorms in the early recovery phase may facilitate relativistic electron acceleration at L* < similar to 3.6. (b) Both intense and moderate geomagnetic storms (SYM-H-min < -50 nT) contribute to relativistic electron acceleration (CC >= 0.50). The peak fluxes for 1.0 and 3.4 MeV electrons (F-max1 and F-max2) during the recovery phase are strongly correlated with substorm intensity (CC >= 0.67). Persistent and intense substorms during the storm recovery phase are conducive to reaching the acceleration upper limit. During this process, chorus-driven local acceleration may be the main mechanism. (c) Long-duration high-speed flows with higher speeds are associated with flux enhancements in relativistic electrons occurring at lower L* shells. During the acceleration process, ULF wave-driven inward radial diffusion may play a dominant role. (d) Acceleration timescales of relativistic electrons are strongly influenced by solar wind speed and substorm activity during the recovery phase, not just electron energy. Our results underscore the importance of storm intensity, solar wind speed, and substorm activity in governing relativistic electron accelerations (specifically their peak fluxes, locations, and acceleration timescales) in the outer radiation belt.

Abstract Plasmaspheric plume hiss plays a crucial role in shaping Earth's electron radiation belts and influencing magnetosphere–ionosphere energy coupling. However, its generation mechanism remains contested between cyclic‐linear and localized‐nonlinear models. By analyzing over 64,000 high‐resolution plume hiss wave segments from the Van Allen Probes (1 January 2013–31 July 2019), we identify a distinct frequency dependence in their latitudinal distributions of directionality and amplitude. For high‐frequency hiss, bidirectional propagation is sharply confined near the magnetic equator, beyond which poleward‐propagating waves overwhelmingly dominate, and the wave amplitude increases obviously with latitude. These signatures are consistent with a rapid, single‐pass, equatorially confined, nonlinear amplification process. In contrast, low‐frequency hiss exhibits a high prevalence and wide latitudinal extension of bidirectional propagation, with relatively smooth amplitude variations. This pattern supports a generation scenario involving slower growth, potentially linear or nonlinear, that is coupled with wave bounce motion along magnetic field lines.

Why is Earth, among the eight planets in our solar system, the only habitable one? Over the 4.6-billion-year evolution of the solar system, why did Mars and Venus evolve so differently? Where did life originate, and how will Earth evolve in the future? These questions are not only central to planetary science in the 21st century but are also deeply connected to humanity’s fundamental understanding of its own existence and planetary habitability. Addressing these grand scientific challenges demands a systematic, multidimensional research approach. In the temporal dimension, we need to trace the early formation and evolution of terrestrial planets; in the spatial dimension, we need to analyze the layered structure of planets and the coupling between these layers; from a comparative perspective, we also need to explore the atmospheric characteristics of exoplanets and the influence of their host stars on habitability. Supported by the Chinese Academy of Sciences’ Strategic Priority Research Program on “Formation, Evolution, and Habitability of Terrestrial Planets,” we have taken planetary habitability as the main research theme and conducted systematic, in-depth studies on terrestrial planets by integrating multiple approaches, including extraterrestrial sample analysis, deep-space exploration data processing, and numerical and experimental simulation. This paper comprehensively summarizes the significant advancements made by the project over the past five years. It covers topics ranging from the early processes and environmental evolution of terrestrial planets to open planetary systems linked to the external space environment, and from Earth’s Moon to exoplanets. Key achievements include the first confirmation of a solid inner core on Mars, revealing its core-mantle differentiation under high-pressure and high-temperature conditions, and the discovery that the youngest lunar basalts originated from a non-KREEP, volatile-poor mantle source region, challenging the long-held traditional hypothesis that “volatile-rich material drives late-stage volcanism”—a textbook-level achievement. While summarizing the latest research advances, this paper also looks toward future directions. Significantly improving the capability for multi-layered, multi-parameter detection of planets, especially global planetary survey capabilities, and vigorously developing related techniques and research methods, particularly the application of cutting-edge technologies such as quantum technology and artificial intelligence, will be the key to achieving further major breakthroughs in planetary science. By sharing these research findings and insights, we aim to inspire more young people to pursue careers in planetary science—a field full of opportunities and challenges—thereby promoting the sustainable development of planetary science in China and over the world.

Abstract Interactions between the ionospheres of unmagnetized bodies and ambient plasma flows form induced magnetospheres. The induced magnetosphere is generally affected by external magnetic fields. Observations of response processes of the induced magnetosphere to external magnetic fields are important for understanding global dynamical processes in unmagnetized planets. Here, using simultaneous observations of Tianwen-1 and Mars Atmosphere and Volatile EvolutioN missions, we show the response of Mars’ induced magnetosphere to interplanetary magnetic field (IMF) rotation. The magnetic field in Mars’ induced magnetosphere rotated within at least 165 seconds following the sudden IMF clock-angle change and gradually stabilized. The convective electric field rotated accordingly, bringing the pickup oxygen-ion plume into the spacecraft’s field of view within 3 minutes. These short timescales demonstrate that Mars’ induced magnetosphere is highly dynamic and sensitive to external magnetic-field variations. IMF changes should therefore be regarded as a common form of Mars’ space weather, highlighting the importance of upstream IMF monitoring and short-term forecasting.

In the induced magnetotail of Mars, the neutral sheet is an important channel for atmospheric ion escape, yet the role of heavy planetary pickup ions in shaping its geometry has been unclear. Using three-dimensional hybrid simulations, we demonstrate that these ions induce a global neutral sheet asymmetry via mass loading. Ambient plasma flow deceleration bends draped interplanetary magnetic field (IMF) lines, extending the sheet along the direction at large IMF Parker spiral angles and tilting its -hemisphere segment toward the plane in the Mars-Solar-Electric coordinate system at small angles. The asymmetry's magnitude is modulated by both the planetary ion production rate and solar wind dynamic pressure. These results show that Mars' magnetotail is not solely governed by IMF draping and crustal fields, but also dynamically reshaped by pickup ions.

The Martian magnetotail current sheet shares characteristics with its terrestrial counterpart and serves as a critical pathway for the escape of ionospheric ions. Understanding this process is vital for reconstructing the historical evolution of Mars' atmosphere. In this study, we report on an unique Martian current sheet where the thermal pressure of electrons, rather than ions, counterbalances the ambient magnetic pressure. Our numerical analysis indicates that electron heating within the current sheet is predominantly driven by magnetosonic waves via Landau resonance. These waves are likely generated in the upstream magnetosheath region. Our results highlight the crucial role of wave-particle interactions in shaping the plasma environment around Mars.

The Martian magnetotail current sheet serves as a critical pathway for ionospheric ion escape. Contrary to the conventional view that external magnetic pressure is balanced mainly by internal ion thermal pressure, we present novel observations from the Mars Atmosphere and Volatile Evolution spacecraft of an electron‐dominated pressure balance configuration. The current sheet electrons exhibit two distinct populations: a thermal core of ionospheric origin and a suprathermal shell of magnetosheath origin. Their bulk temperature reaches up to three times higher than that outside the current sheet. Based on linear instability analysis, we propose two candidate heating mechanisms: (a) Landau resonant or transit‐time heating by magnetosonic waves likely originating from the magnetosheath, and (b) Landau or cyclotron resonant heating by whistler and electron cyclotron harmonic waves generated spontaneously from the shell‐like electron velocity distribution. These results highlight the potentially significant role of plasma waves in sustaining the Martian atmospheric escape channels.

We statistically analyze the power spectral density (PSD) of magnetic field turbulence in the upstream solar wind of the Martian bow shock by investigating the data from Tianwen-1 and Mars Atmosphere and Volatile Evolution (MAVEN) during 2021 November 13 and December 31. The spectral indices and break frequencies of these PSDs are automatically identified. According to the profiles of the PSDs, we find that they could be classified into three types: A, B, and C. Only less than a quarter of the events exhibit characteristics similar to the 1 au PSDs (Type A). We observe the energy injection in more than one-third of the events (Type B), and the injected energy usually results in the steeper spectral indices of the dissipation ranges. We find the absence of the dissipation range in over one third of the PSDs (Type C), which is likely due to the dissipation occurring at higher frequencies rather than proton cyclotron resonant frequencies. We also find that the two spacecraft observed different types of PSDs in more than half of the investigated episodes, indicating significant variability upstream of the Martian bow shock. For example, the Type-B PSDs are more often seen by Tianwen-1, which was near the flank of the bow shock, than by MAVEN near the nose. This statistical study demonstrates the complicated turbulent environment of the solar wind upstream of the Martian bow shock.

Inward radial diffusion driven by ultra-low-frequency (ULF) waves is one of the dominant acceleration mechanisms of relativistic (>1.0 MeV) electrons in the Earth’s outer radiation belt. However, the role of interplanetary (IP) shocks in the ULF-wave-driven acceleration remains inadequately understood. Here we report the rapid acceleration events caused by IP shocks on 2013 January 17 and 18. Based on simultaneous observations, we propose a three-step physical process for the acceleration of relativistic electrons. Our results indicate that IP shocks not only excite ULF waves and provide source populations for the ULF-wave-driven acceleration, but also contribute to establishing a significant phase-space density radial gradient of relativistic electrons in the outer boundary. These can lead to rapid enhancements of relativistic electrons in the outer radiation belt.

Plasma waves can initiate, regulate, or reflect magnetic reconnection efficiently converting magnetic energy into plasma energy. While waves ranging from below the ion cyclotron frequency to above the electron plasma frequency are commonly observed near reconnection sites, electromagnetic ion cyclotron (EMIC) waves-frequent in other plasma environments-have been rarely observed in the reconnection region. Here, we report the first detection of EMIC waves in a magnetic reconnection exhaust at Earth's magnetopause. The free energy required for EMIC wave growth was supplied by the strong perpendicular-to-parallel temperature anisotropy of hot proton beams. This proton temperature anisotropy was generated by magnetopause reconnection, rather than inherited from the magnetosheath. Our findings differ from previous reports of parallel-preferential proton heating during magnetopause reconnection, calling for revised theoretical frameworks to reconcile observed perpendicular-preferential heating with established reconnection paradigms.

The Fokker‐Planck diffusion equation is widely used for simulating the evolution of Earth's radiation belt electrons, which pose significant hazards to space‐borne systems. To preserve the positivity of the numerical solution of the electron phase space density (PSD), several finely designed finite difference, Monte Carlo, spatiotemporal interpolation, and finite volume schemes have been developed. However, these schemes often suffer from either high implementation complexity or low execution efficiency. Here we propose an efficient, easy‐to‐implement, and positivity‐preserving finite difference scheme, named the Semi‐Implicit Logarithmic Linearization (SILL) scheme. The basic principle is to linearize the nonlinear equation of the natural logarithmic PSD. This scheme ensures accuracy and stability, even with large time steps, up to hundreds of seconds for typical radiation belt electron diffusion processes. Nonetheless, it exhibits oversensitivity to near‐vanishing phase space densities, which necessitates reduced time steps when handling extremely large variations in orders of magnitude between neighboring grid points. We have publicly released the protype code of the SILL scheme, which could be useful for the radiation belt modeling community.

Cold oxygen ions escaping from the ionosphere and temporarily trapped near the plasmapause form the oxygen torus. Mass‐loading by these oxygen ions significantly affects magnetospheric plasma processes. However, due to the technical challenges in measuring cold oxygen ions and the limited spatial and temporal coverage of space missions within the magnetosphere‐ionosphere coupling system, the generation mechanism of oxygen torus remains unclear. Here, we propose a novel approach to determine the ion abundances from the observable polarization and propagation characteristics of electromagnetic ion cyclotron (EMIC) waves and identify a narrow oxygen torus near the noonside plasmapause during a geomagnetically quiet period. Our data and theoretical calculations suggest that the formation of this oxygen torus involved excitation of EMIC waves by ring current protons, wave‐driven Landau heating of plasmaspheric electrons, heat conduction from the magnetosphere to the ionosphere, and upwelling of ionospheric oxygen ions into the magnetosphere.

Plasma waves around terrestrial planets mediate energy transfer between electromagnetic fields and charged particles, significantly influencing the dynamics of their space plasma environments. While such interactions are well documented at Earth and Mars, their role at Venus remains uncertain due to sparse in situ measurements. Here we analyze a recently reported magnetosonic wave event at Venus detected by the Pioneer Venus Orbiter, characterized by large-amplitude (∼10 nT), quasi-perpendicular fluctuations that coincide with enhanced electron temperatures in the topside ionosphere. These waves, generated in the upstream, propagate through the low-density magnetosheath with negligible damping before impinging on the topside ionosphere. Numerical modeling shows that these waves can Landau resonate efficiently with ionospheric thermal electrons in the 0.01–0.1 eV range, increasing the local electron temperature by nearly a factor of 2 on a timescale of ∼10 minutes. Such heating may intensify the ambipolar electric field, consequently facilitating the escape of light ions.

Using the data from the Van Allen Probes, we statistically studied 2.1 MeV electron flux oscillation events in the Earth's outer radiation belt during non-storm activities. Based on the different magnetic local times (MLT), the oscillation events are divided into "dayside events" (DE, 6 <= MLT <= 18) and "nightside events" (NE, 18 < MLT < 6). These NEs are divided into "weak substorm events" (WSE, AE < 200 nT) and "strong substorm events" (SSE, AE > 200 nT). The SSE is further divided into "strong substorm with low solar wind dynamic pressure change (Delta P-sw) events" (SSLP, AE > 200 nT, Delta P-sw < 5 nPa) and "strong substorm with high Delta P-sw events" (SSHP, AE > 200 nT, Delta P-sw > 5 nPa). Our statistical results show that: (a) For DE, WSE, and SSHP, Delta P-sw and solar wind speed (V-sw) are the main factors affecting the oscillation location, while Delta P-sw is the dominant factor affecting the oscillation amplitude. The interplanetary magnetic field B-z component has no significant effects on the oscillations of DE. These results support the idea that these oscillations are mainly caused by ultralow frequency (ULF) waves excited by Delta P-sw; (b) For SSLP, substorm activity and V-sw do not affect the oscillation location. However, the intense substorm activity and Delta P-sw can cause a large oscillation amplitude. This shows the idea that these oscillations are mainly caused by a combination of ULF waves excited by Delta P-sw and substorm activity. These can help us further understand the ULF waves and relativistic electron dynamics of the Earth's outer radiation belt.

Atmospheric escape processes are crucial for shaping the long-term surface habitability of terrestrial planets. A key question is how planetary magnetic fields influence atmospheric escape. On present-day Mars, there are crustal magnetic anomalies predominantly in the southern hemisphere, whose impact on the escape of ionospheric heavy ions remains under debate. Based on MAVEN observations, we propose a new candidate mechanism to explain how ionospheric heavy ions can escape from regions with strong crustal magnetic anomalies. This mechanism is triggered by reconnection between draped interplanetary and crustal magnetic fields, forming magnetic cusps with open field lines and generating plasma jets that impact the crustal anomalies. Within these anomalies, ions and electrons exhibit distinct spatial and temporal behaviors, leading to charge separation and the formation of an electrostatic potential. This potential lifts cold, heavy ions from the ionosphere along open field lines to escape altitudes. The process occurs within minutes, producing localized escape fluxes up to two orders of magnitude higher than background levels. This explosive leakage pattern may hold significance for other unmagnetized or weakly magnetized planets where magnetospheric and ionospheric boundaries converge.

Martian water loss to space is commonly attributed to the thermal escape of atomic hydrogen. However, when projecting the currently recognized escape rates over Mars' 4.5-billion-year history, it only accounts for less than one-tenth of the loss amount inferred from analyses of geological remnants and water isotopes. This significant gap indicates that the entire spectrum of potential escape rates remains unidentified due to limitations in datasets or methodology. Here, by analyzing the large-amplitude proton cyclotron waves during a fortuitous alignment of the Tianwen-1 and MAVEN missions, we identify an extreme escape of atomic hydrogen. The instantaneous escape rate was at least 1028 hydrogen atoms per second, nearly one order of magnitude higher than previous estimations. This extreme escape was probably driven by a fast solar wind stream, within the context of seasonally enhanced atmospheric water vapor transport when Mars approached its perihelion. These results demonstrate that, in the history of Mars, under the external influence of a younger, more active Sun and with stronger internal transport of water vapor, the atomic hydrogen escape rate could have been much higher than it is today.

Abstract Surface charging is one of the most common causes of spacecraft anomalies. When and to what potential the spacecraft is charged are two important questions in space weather. Here, for a Chinese geosynchronous navigation satellite, we infer the extreme negative surface charging potentials from the ion differential fluxes measured by a low‐energy ion spectrometer. Without the solar eclipse effect away from the midnight, the charging potentials are found to have a negative limit which is determined by the maximum SuperMAG electrojet index in the preceding 2 hr. Such an empirical relation can be reasonably explained by the dependence of 1–50 keV electron fluxes on substorm strength. Similar relations may also exist for other inner magnetospheric spacecraft in the non‐eclipse region, which would be useful for spacecraft engineering and space weather alerts.

Abstract Martian mini‐magnetospheres contain whistler‐mode chorus waves potentially contributing to atmospheric escape, analogous to the Earth's inner magnetosphere. At Earth, the chorus waves have been found to originate from the near‐equatorial region spanning approximately 2% of the entire magnetic field line length. However, because of the lack of wave Poynting flux measurements, the Martian chorus source region remains unclear. By comparing the frequency dependence between observed wave power and modeled linear growth rates, we present the first attempt to explore the chorus wave source distribution along the Martian mini‐magnetospheric field lines. Our data‐to‐model comparisons support that these waves are not generated by a single source tightly confined near the magnetic strength minimal location but by intermittent or continuous sources spanning up to 40% of the entire field line length. These results imply that the Martian mini‐magnetospheres could have more active energy transfer processes mediated by whistler‐mode chorus waves than the expectation.

Abstract Plasmaspheric hiss waves are important to shape the Earth’s electron radiation belt. These waves are commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. However, this hypothesis has not been experimentally confirmed yet, because of the challenging observational requirements in terms of location and timing. With wave and particle measurements from five magnetospheric satellites and detailed modeling, we present the first report of long lifetime (∼42 s) hiss rays in the substorm‐disturbed plasmasphere. The low‐frequency hiss waves are found to originate from the middle piece of the plasmaspheric plume, bounce between two hemispheres, and eventually drift into the plasmaspheric core. These hiss rays can travel through ∼3 hr magnetic local time and ∼4 magnetic shell. Such a long‐time and large‐scale permeation of hiss rays could benefit from the ducting process by plasmaspheric field‐aligned density irregularities.

Electron cyclotron harmonic (ECH) waves are electrostatic emissions frequently observed in the Earth’s magnetosphere. By precipitating magnetospheric hot electrons into the ionosphere, ECH waves play a critical role in the formation of diffuse aurora. Previous research has extensively investigated the strong dependence of ECH waves on the geomagnetic activities. In this study, we present the first report of the prompt response of ECH waves to an interplanetary shock on the basis of WIND and Van Allen Probes observations. Our observations and analyses demonstrate that the interplanetary shock compression can increase >0.1 keV hot electron fluxes in the dayside inner magnetosphere, consequently leading to the prompt intensification of ECH waves by promoting the wave instability. These findings expand our comprehension of the impacts of solar wind disturbances on magnetospheric plasma waves and offer fresh insights into solar wind-magnetosphere-ionosphere coupling.