The water escape from Mars to space could be in the form of hydrogen and oxygen ions as driven by solar wind–Mars interactions. Although oxygen ion escape has been extensively investigated, the H ^+ escape rate was measured only at solar minimum. To determine the impacts of solar activity on the ionospheric H ^+ escape rate, we report the observational results from the Tianwen-1 spacecraft at solar maximum. The cold dense ionospheric ion outflows through the magnetotail have an equal energy acceleration process, consistent with the characteristics of ambipolar electric field acceleration. The escape rate of planetary cold H ^+ through the magnetotail is estimated to be ∼2 × 10 ^23 s ^−1 , a value substantially lower than the neutral hydrogen escape rate, and the H/O ratio (∼0.3) of the tailward escaping ions (H ^+ , O ^+ and O ${}_{2}^{+}$ ) is below the stoichiometric ratio of water. These results indicate the ionospheric H ^+ outflow plays a minimal role for the water loss on Mars across solar cycles. To assess the contribution of H ^+ escape to total hydrogen loss, future analysis must target the pickup H ^+ escape rate within the magnetosheath.

It is generally accepted that a fraction of H+ pickup ions originating from the Martian hydrogen (H) exosphere can be reflected and energized at the bow shock (BS), but the underlying reflection and acceleration mechanisms have not been explicitly identified. Using in situ observations from the Mars Atmosphere and Volatile EvolutioN ( MAVEN ) spacecraft, we present evidence for both shock surfing acceleration (SSA) and shock drift acceleration (SDA) of exospheric H+ pickup ions at the Martian quasi-perpendicular BS. On 12 August 2016, MAVEN detected a reflected H+ ion beam with energies of similar to 1.3-7.5 keV, propagating nearly along the solar wind convection electric field. The low-energy component is consistent with single reflections via SSA, while the high-energy component exceeds the maximum energy achievable from single reflections, indicating multiple reflections at the BS. These high-energy ions likely experienced either direct SDA or sequential acceleration involving SSA followed by SDA, depending on their incident normal velocities. The middle-energy component can be explained by either single or multiple reflections via SDA alone, or by a combination of SSA and subsequent SDA at the BS.

The Mars Ion and Neutral Particle Analyzer (MINPA), one of the seven scientific payloads aboard the Tianwen-1 orbiter, was specifically designed to investigate the interaction between the solar wind and Mars by measuring ions and energetic neutral atoms (ENAs). This presentation provides a comprehensive overview of MINPA's in-flight operations and its ENA observations from 2021 to 2025. MINPA successfully collected ENA data during observations of the solar wind, magnetosheath, and magnetotail. The in-flight performance was carefully analyzed, including energy and angular response, seasonal variations in the ENA counts, and secondary ENA caused by ion-neutralization on the spacecraft surface. Statistical analysis of solar wind H-ENAs revealed a neutralization rate at the flanks of the Martian magnetosphere, which was used to derive the coincident Jeans escape rate and pick-up ion generation rate. Preliminary results also include the asymmetry of the ENA scattering associated with the crustal magnetic field and the intense enhancement of the ENA signal during CMEs.

When the upstream Alfvén Mach number is low, the magnetic field may play a dominant role in the solar-wind interaction with Mars, yet the resulting magnetospheric dynamics and associated energy conversion remain poorly constrained. Bulk proton acceleration reaching about 150% of the solar-wind speed is detected jointly by MAVEN, Tianwen-1, and MEX missions in the magnetosheath. The acceleration regions exhibit pronounced asymmetry between the two electric-field hemispheres, defined by the solar-wind electric field, while the shape of the adjacent magnetotail shows axial and hemispheric asymmetries. We demonstrate that the large-scale J×B force, with J denoting the electric current density and B the magnetic field, is the primary driver of acceleration and axial asymmetry. Mass loading of planetary ions introduces strong hemispheric asymmetries—features unique to unmagnetized bodies with atmospheres. Here, we reveal a pathway by which magnetic field converges and redistributes solar-wind energy, and infer that plasma acceleration under low upstream Alfvén Mach number operates not only at Earth but also at Mars and other bodies with magnetosheaths. Mars sometimes encounters low-Alfvén-Mach-number solar wind, allowing magnetic fields to control plasma flow. Here, the authors show that this accelerates magnetosheath protons and compresses the Martian magnetotail.

Since November 2021,MINPA has continuously performed ion observations,accumulating a substantial dataset for scientific analysis.Although the instrument's background signals are generally weak,they can still interfere with the identification of ion structures and the estimation of plasma parameters under low-signal conditions.To improve data reliability,this study systematically investigates the statistical characteristics of the background signals.The analysis reveals several distinct features,including a uniform energy distribution,strong dependences on azimuthal angle and mass group,and pronounced temporal variability,with notable differences among detection channels.Based on these insights,a dynamic background removal method was developed by leveraging the statistical properties of the background and validated using representative observational events.The results demonstrate that the proposed method effectively suppresses background interference and enhances the extraction of genuine ion signals,notably improving the accuracy of key parameters such as bulk velocity and temperature during low-signal periods.This work establishes a solid foundation for the high-quality utilization of MINPA data and provides methodological support for future investigations of space plasma environments.

Kinematics of solar eruptive filaments is one of the important diagnostic parameters for predicting whether solar eruptions would induce geomagnetic storms. Particularly, some geomagnetic storms might be induced by solar filament eruptions originating from unexpected surface source regions because of nonradial ejection. The nonradial ejection of filaments has received widespread attention but remains inconclusive. We select two eruptive filaments, both of which are supported by flux ropes, as indicated by the hot channel structures seen in the 94 Å images and the hook-shaped brightenings where the filament material falls back. We measure the three-dimensional ejection trajectory of the eruptive filaments by integrating the simultaneous observations from the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO). Furthermore, we calculate the distribution of the poloidal field along the ejection path and compare it to the ejection acceleration. It is revealed that the reinforcement of the poloidal magnetic field may lead to the suppression of the acceleration, with the acceleration resuming its increase only when the poloidal field diminishes to a certain level. Additionally, we compute the spatial distribution of the poloidal field in various directions and find that the poloidal magnetic field above the filaments is asymmetric. For both investigated events, the filaments appear to eject toward the side where the poloidal magnetic field is weaker, indicating that the eruptive filaments tend to propagate along the side with weaker strapping force. This may provide a new explanation for the inclined ejection of filaments.

Atmospheric escape plays a critical role in shaping the long-term climate evolution of Mars. Among the various escape mechanisms, energetic neutral atoms (ENAs) generated through charge exchange between solar wind ions and exospheric neutrals serve as an important diagnostic for ion-neutral interactions and upper atmospheric loss. This study presents direct observations of hydrogen ENAs (H-ENAs) on the dayside of Mars by using the Mars Ion and Neutral Particle Analyzer (MINPA) onboard China's Tianwen-1 orbiter. By analyzing H-ENA data during a coronal mass ejection and a stream interaction region from December 29, 2021, to January 1, 2022, and comparing these data with MAVEN/SWIA (Mars Atmosphere and Volatile EvolutioN/Solar Wind Ion Analyzer) solar wind measurements, we examine the temporal evolution of H-ENA flux and the associated sputtered escape of atmospheric constituents. The observed H-ENA velocity is consistent with upstream solar wind ions, and the H-ENA-to-ion intensity ratio is used to infer variations in exospheric density, revealing a delayed response to enhanced solar wind activity. Penetrating H-ENA intensities reach up to 5.3 x 10(6) s(-1) cm(-2), with energy fluxes on the order of (0.5-8.1) x 10(-3) mW/m(2). The estimated oxygen sputtered escape rate driven by penetrating H-ENAs ranges from 5.5 x 10(23) s(-1) to 5.2 x 10(24) s(-1), comparable to or exceeding previous estimates based on penetrating ions. The findings highlight the need for low-altitude H-ENA observations to better quantify their atmospheric interactions and refine our understanding of nonthermal escape processes at Mars.

The Light Ion Analyzer (LIA) instrument, part of the Solar-wind-Magnetosphere–Ionosphere-link- Explorer (SMILE) mission, is designed to measure the ion velocity distribution function within an energy range of 5 eV up to 25 keV. LIA provides in-situ measurements of the ion velocity distribution functions of the solar wind and magnetosheath, from which the moments can be derived on the ground, serving as an upstream input for the magnetosphere-ionosphere downstream responses. Two identical 2 π sr field-of-view LIA instruments are mounted on two opposite sides of the spacecraft platform, offering a combined 4 π sr instantaneous field-of-view. Each LIA consists of a top-hat electrostatic analyzer, electrostatic aperture deflectors, and a microchannel plate detector for analyzing the energy, direction, and flux of ions. Depending on the operation mode, the angular resolution ranges from 5.625° to 22.5° in elevation and from 7.5° to 30° in azimuth, and the time resolution spans from 0.25 to 2 seconds. This paper describes the design of the LIA, its performance, ground calibration, operation procedures, and resultant data products.

One of the detection objectives of the Chinese Asteroid Exploration mission is to investigate the space environment near the Main-belt Comet（MBC, Active Asteroid） 311P/PANSTARRS. This paper outlines the scientific objectives, measurement targets, and measurement requirements for the proposed Gas and Ion Analyzer（GIA）. The GIA is designed for in-situ mass spectrometry of neutral gases and low-energy ions, such as hydrogen,carbon, and oxygen, in the vicinity of 311P. Ion sampling techniques are essential for the GIA's Time-of-Flight（TOF） mass analysis capabilities. In this paper, we present an enhanced ion sampling technique through the development of an ion attraction model and an ion source model. The ion attraction model demonstrates that adjusting attraction grid voltage can enhance the detection efficiency of low-energy ions and mitigate the repulsive force of ions during sampling, which is influenced by the satellite's surface positive charging. The ion source model simulates the processes of gas ionization and ion multiplication. Simulation results indicate that the GIA can achieve a lower pressure limit below 10 -13 Pa and possess a dynamic range exceeding 10～9. These performances ensure the generation of ions with stable and consistent current, which is crucial for high-resolution and broad dynamic range mass spectrometer analysis. Preliminary testing experiments have verified GIA's capability to detect gas compositions such as H 2 O and N 2 . In-situ measurements near 311P using GIA are expected to significantly contribute to our understanding of asteroid activity mechanisms, the evolution of the atmospheric and ionized environments of main-belt comets, the interactions with solar wind, and the origin of Earth's water.

The Tianwen-2 mission aims at exploring the near-Earth asteroid 2016HO3 and the main belt comet 311P by means of near-distance measuring and asteroid sampling and return. As one of main payloads of the Tianwen-2 mission, the Charged and Neutral Particle Analyzer (CANPA) will measure in-situ the plasmas and neutral atmosphere around the asteroid and the comet. The CANPA instrument is highly integrated and miniaturized, and composes four independent subsystems: the thermal ion analyzer (TIA), the thermal electron analyzer (TEA), the solar wind ion analyzer (SIA) and the gas and ion analyzer (GIA). The flight model has been calibrated by using the on-ground calibration system. The results show that the TIA can measure thermal ions at the energy range of 2.79 eV-32.03 keV with an energy resolution of 8.79%. The TEA can measure thermal electrons at the energy range of 1.07 eV-20.61 keV with an energy resolution of 14.29%. Both TIA and TEA have the field-of-view of 360 degrees x 90 degrees. The SIA can measure solar wind ions at the energy-per-charge range of 5 eV-5 keV with an energy resolution of 4.23%. The GIA can measure neutral gas and ions of the comet ionosphere at the mass range of 1-350 amu and the mass resolution is about 0.17 amu@1-50 amu, 0.52 amu@51-150 amu, and 1.22 amu@151-350 amu. The CANPA instrument can fulfill the detection requirements for the asteroid and the comet.

The Light Ion Analyzer (LIA) instrument, part of the Solar-wind-Magnetosphere–Ionosphere-link- Explorer (SMILE) mission, is designed to measure the ion velocity distribution function within an energy range of 5 eV up to 25 keV. LIA provides in-situ measurements of the ion velocity distribution functions of the solar-wind and magnetosheath, from which the moments can be derived on ground, serving as an upstream input for the magnetosphere-ionosphere downstream responses. Two identical 2π sr field-of-view LIA instruments are mounted on two opposite sides of the spacecraft platform, offering a combined 4π sr instantaneous field-of-view. Each LIA consists of a top-hat electrostatic analyzer, electrostatic aperture deflectors, and a microchannel plate detector for analyzing the energy, direction, and flux of ions. Depending on operation mode, the angular resolution ranges from 22.5° to 5.625° in elevation and from 30° to 7.5° in azimuth, and the time resolution spans from 0.25 to 2 seconds. This paper describes the design of the LIA, its performance, ground calibration, operation procedures, and resultant data products.

The Martian magnetotail serves as an important channel for the escape of planetary ions, with abundant dynamic processes. After Tianwen-1 successfully entered the scientific orbit around Mars, the sun is becoming increasingly active. With the orbital apoapsis ~10,760 km, Tianwen-1 completed its first magnetotail phase from March to July 2022, providing a good opportunity to investigate the response of the Martian far magnetotail to interplanetary coronal mass ejections (ICMEs). We made a preliminary analysis of the dynamic tail under an ICME impact on 16 May 2022, with Tianwen-1 monitoring magnetotail and Mars Atmosphere and Volatile EvolutioN (MAVEN) providing upstream measurements. Based on MAVEN observations, the arrival of the ICME was determined to be around 05:10 UT on 16 May 2022. Subsequently, a significant increase in the energy levels of H+ and O+ ions was seen when Tianwen-1 entered the magnetotail about one and a half hours later. Tianwen-1 continuously detected a subset of O+ ions with energies exceeding 1 keV. Accordingly, the escape rate of O+ became ~6.2 times greater during this ICME, and the highest O+ enhancement happened between 1 keV and 3 keV. The disturbance lasted 39 hours before returning to a quiet level. Furthermore, we conducted a statistical analysis on the escape rate of O+ in the far magnetotail (attitude higher than 2 Mars radius) during 11 ICME events from March to July 2022. The ion loss rates substantially increased during ICME events, especially for O+ with energy above several keV. This observation suggests the presence of effective acceleration processes in the Martian tail under ICME conditions.

The Mars Ion and Neutral Particle Analyzer (MINPA), one of the seven scientific payloads onboard the Tianwen-1 orbiter, was specifically designed to investigate the interaction between the solar wind and Mars by analyzing ions and energetic neutral atoms (ENAs). Commencing its scientific data collection in November 2021, MINPA successfully completed its first far-magnetotail survey during the summer of 2022. Our presentation will provide a comprehensive overview of MINPA's in-flight operations and its initial scientific findings. Regarding ENA observations, MINPA achieved successful data collection during solar wind, magnetosheath, and nightside observations. An algorithm has been developed to convert ENA count rates into intensity. A statistical analysis of solar wind ENAs revealed a neutralization rate of the solar wind at the flanks of the Mars magnetosphere. We also performed a collaborative analysis using MINPA data and numerical modeling to gain a deeper understanding of the ENA spectrum and its properties. In the ion component, MINPA observed hydrogen and heavy ions across various regions at Mars. With a far apoapsis, MINPA measured heavy ion escape in the far magnetotail, showcasing significant enhancements during periods of coronal mass ejection (CME) impacts. To enhance our understanding of the Martian space environment, an interdisciplinary team, comprising scientists from the Tianwen-1, Emirates Mars Mission (EMM), Mars Atmosphere and Volatile Evolution (MAVEN), and Mars Express missions, has been assembled within the ISSI framework.

Interplanetary coronal mass ejections (ICMEs) are solar transients that have significant effects on the Martian space environment. The simultaneous spacecraft observations from Tianwen-1 and Mars Atmosphere and Volatile Evolution (MAVEN) are used to study the planetary ion escape for a dramatic ICME. MAVEN passes through the upstream solar wind, +E hemisphere, and -E hemisphere in one orbital period at 20:00 UT -24:00 UT on 2022 April 24. During this period, the interplanetary magnetic field (IMF) remained stable and dominated by the +Y component. In addition to the well-known “plume” escape channels located in the +E hemisphere, MAVEN also observed one ion escape channel in each hemisphere. The additional escape channel located in the +E hemisphere was easily identified as ionized atoms originating from the exosphere, which became significant during CME and was first reported. These ions are observed in both the solar wind and the magnetosheath, and the observed flux of these ions is strongest when MAVEN is very close to the upstream of the bow shock. In this event, ion density of this channel is up to 0.03 cm-3, which is 10 % ~ 30 % of the observed plume. The escape channel structure in the -E hemisphere is complex, and MAVEN has insufficient observation of this channel due to its orbital inclination. Tianwen-1 provided a powerful supplement based on the 1.5 hr observation of this structure, revealing many characteristics of this escape channel. The channel in the -E hemisphere also shows a narrow band in the energy spectrum, similar to the plume. Moreover, its density is between the ion densities of the two +E hemispherical channels. Interestingly, it is more likely to be observed near the magnetic pileup boundary rather than the entire -E hemisphere magnetosheath. These new channels reveal more details of Martian ion escape. The solar wind conditions similar to the early solar system during the ICMEs also help to study the early evolution of Mars.

This study delves into a Pick-Up Ion (PUI) event captured by the Mars Ion and Neutral Particle Analyzer aboard Tianwen-1, revealing a faster acceleration than expected within the Martian magnetosheath. This event suggests the presence of a convection electric field considerably stronger than that typically observed in the solar wind. Through Magnetohydrodynamic simulation, we identified two regions of intensified convection electric fields within the inner magnetosheath, prominently manifested at mid to high solar zenith angles (SZA = 40 degrees-70 degrees) in the X-Z plane of the Mars Solar Electric field coordinates. Tianwen-1 observed that the peak of the electric field strength, up to five times of that in the solar wind, is located at the upper edge or within the Magnetic Pileup Boundary. Further study by test particle simulations showed acceleration by the electric field effectively doubles the energy gain of PUIs, in comparison to scenarios absent of this extra acceleration. It is revealed that the presence of such electric field regions within the Martian magnetosheath is a prevailing feature, shaped by the solar wind's interaction with Mars and modulated by the planet's rotating crustal magnetic fields. The interaction between planets and their upstream solar wind holds great significance for the long-time climate evolution of planets. Mars lacks a global dipole magnetic field, which makes it easier for these planetary ions to escape through acceleration by the solar wind convection electric field. The observations of Tianwen-1 and Mars Atmosphere and Volatile Evolution satellites provide a great opportunity to study the acceleration of planetary ions by this electric field. Through a case study involving observation and simulation, we confirm that there are two regions in the Martian magnetosheath, where the convection electric field is stronger than in the solar wind. This electric field may rapidly energize the ions and possibly result in intensified ion escape. In the Martian magnetosheath, joint effects of the plasma flow around Mars and the interplanetary magnetic field pileup result in enhanced convection electric field The strong E field envelops a large part of the Magnetic Pileup Boundary (MPB), with the maximum at the med-high solar zenith angles, at the upper edge or within the MPB The crustal magnetic fields modulate the distribution of the strong E field, leading to hemispheric asymmetry

The stable celestial geological structure,the suitable distance from the Earth to the Moon,and no dense atmosphere and global magnetic field make the Moon a natural and excellent laboratory for the monitoring and research of the Sun-Earth-Moon space weather.This paper reviews the progress of lunar space weather detection and research,and surveys the key scientific problems of lunar space weather and the problems of its prediction application,proposes the concept of the Moon-based space weather monitoring station,set up the specific scientific objectives of the monitoring station,and finally introduces its three major systems and the relationships among them,including the monitoring system,the scientific research system,and the modeling and forecasting system.The establishment of a Moon-based space weather monitoring station is of great scientific significance for studying the mechanism of solar eruptions,the coupling of the Sun to the Earth and the Moon,and the local variations of the Moon's environment.It will also promote the development of lunar space weather modeling and prediction technologies and improve the capability in providing space environmental safeguard services for future lunar explorations.

Since November 2021, the Tianwen-1 mission has activated its scientific instrument, the Mars Ion and Neutral Particle Analyzer (MINPA), to detect particles within Martian space. To evaluate the reliability of the plasma parameters from the MINPA measurements, in this study, we analyze and reduce the background signal (or noise) appearing in the MINPA data and then calculate the plasma moments based on the noise-reduced data. Remarkably, our findings reveal a strong correlation between the velocity measurements from MINPA and those from the Solar Wind Ion Analyzer (SWIA) onboard the MAVEN spacecraft, underscoring MINPA’s accuracy. Similarly, temperature measurements correlate with SWIA data, albeit with a tendency towards underestimation and greater variability. A significant limitation, however, is MINPA’s 2π field of view (FOV), which restricts its ability to observe ions omnidirectionally, leading to a substantial underestimation of number density and thermal pressure compared to SWIA measurements. Addressing this challenge necessitates a sophisticated approach that fully accommodates the FOV constraints to derive accurate values for these parameters. Moreover, our comprehensive investigation into the noise origins traced it back to electronic noise within MINPA’s circuitry. This study confirms MINPA’s operational efficacy and potential to yield dependable plasma parameters with further procedures and contributes valuable insights for the design of future scientific instruments.

The FY-3E satellite plasma analyzer marks China’s first detection of the characteristics, occurrence, and development of the typical plasma environment in the dawn–dusk orbit space. It provides data source support for operational space weather alerts and forecasts, helps ensure the in-orbit safety of the satellite, and accumulates space environment detection data for space environment modeling and space physics research. This paper gives a detailed introduction to the detection technology adopted by the FY-3E satellite plasma analyzer. We calibrated its performance through a calibration experiment and then analyzed and compared it with similar instruments in China. It is indicated that the instrument is capable of measuring an ion energy spectrum of 24 eV~32 keV and an electron energy spectrum of 23.7 eV~31.6 keV, its field of view reaches 180° × 90°, and the inversed measurement range of spacecraft absolute potential is better than −30 kV~+30 kV. All these contribute to a notably improved technology for plasma and satellite potential detection of China’s LEO satellites.