The radar surface echo can be separated into coherent and incoherent components by statistical approaches, and the coherent component can be described by a backscattering model related to the RMS height. According to backscattering models for fractal surfaces, the coherent power in decibels decreases with RMS height on a scale independent of the wavelength at a rate depending on the Hurst exponent and the roughness scale. We extract the coherent power in four research areas by fitting the amplitude distribution of the Martian surface echoes recorded by the SHARAD radar, and compare the coherent power with the RMS height derived from pulse width of the MOLA laser altimeter. Scatter plots of squared MOLA-derived RMS height-coherent power are drawn to estimate the rates of coherent power fall-off by linear fitting, and the fitting power fall-off rates are compared to the Hurst exponents derived from digital terrain models in those areas. The fitting rates decrease with the Hurst exponent, similar to the theoretical rates. However, the fitting rates decrease with the Hurst exponent more sharply than the theoretical prediction. We explain the mismatch with a linear assumption between different roughness parameters, which helps to estimate the Hurst exponent, and a significant discrepancy between the wavelength and the roughness scale might influence the estimation results due to the scaling dependence of the Hurst exponent. This paper offers an opportunity to learn about the Hurst exponent at a tens-of-meter scale.

China plans to return samples from the near-Earth asteroid (469219) Kamo'oalewa, which we previously identified as an LL-chondrite-compositional, highly space-weathered object with fine-grained regolith. In this study, we developed 10 mL of Kamo'oalewa regolith simulant, designated "IGCAS-AST01", by irradiating LL5/6 chondrite (Kheneg Ljou^ad) powder with a high-energy pulsed laser. We then analyzed the composition, grain size distribution, density, porosity, visible to near-infrared reflectance spectrum, thermal emission spectrum, thermal diffusivity, specific heat capacity, and microstructural features of both the fresh (unirradiated) powder and IGCAS-AST01. IGCAS-AST01 is composed of 57.8 vol.

The Tianwen-2 small bodies exploration mission, as an important part of China’s planetary exploration program, will achieve a sample return of the Earth quasi-satellite 2016 HO3 and a close-proximity exploration of the main-belt comet 311P through a single mission. Here we introduce the targets, engineering goals, scientific goals and payload configuration of the Tianwen-2 mission, as well as the overall flight plan, close-proximity scientific investigation strategy, sampling plan. We also analyze the anticipated scientific data and the scientific goals the mission seeks to address. This mission will establish intelligent and advanced planetary exploration capabilities and is expected to yield groundbreaking scientific discoveries that will enhance our understanding of solar system evolution.

The Tianwen-2 probe carries an asteroid core-scanning radar (ACSR) to study the internal structures of near-Earth asteroid 2016 HO _3 and main-belt comet 311P. Radar signals are often contaminated by surface clutter, which can overlap with weaker subsurface echoes due to propagation attenuation. This paper proposes a surface-clutter separation method based on cross-correlation and moment-matching algorithms. It realizes effective separation by performing joint calibration of the position and amplitude of surface clutter. The simulation results demonstrate that this method can effectively separate surface clutter across various detection scenarios. Ground-test data further validate the method’s capability to separate dominant surface clutter in in situ detections. These results indicate that the approach is effective for investigating the internal structures of asteroids and comets in the Tianwen-2 mission.

This study presents orbital validation of a potential cave candidate (PCC) on the western flank of Elysium Mons, originally cataloged in the Mars Cave Database, and establishes it as a high-priority subsurface exploration target. A multi-sensor investigation integrates morphological, thermal, topographic, and mineralogical datasets to independently confirm the feature as a potential subsurface lava tube skylight. CTX and HiRISE imagery acquired under varied illumination reveal an elliptical opening with persistent shadowing, collapse textures, and a localized aperture consistent with vertical access to a subsurface void, informing robotic ingress strategies. THEMIS nighttime observations show a sustained thermal anomaly indicative of subsurface thermal buffering, while MOLA data constrain elevation, slope, and surface roughness. GRS measurements indicate hydrogen-enriched basalt, and TES mineralogy supports a volcanogenic origin with potential paleoenvironmental preservation. These integrated observations enable preliminary landing site selection and slope-optimized robotic traversal. Building on this validated characterization, we propose a mission-relevant exploration framework using AI-driven legged robotic systems with autonomous mobility, LiDAR-based 3D mapping, and tethered descent capabilities, addressing limitations of wheeled rovers. This work advances operational and scientific readiness for Martian cave exploration and subsurface habitability studies.

In 2026, China's Tianwen-2 mission is scheduled to arrive at the near-Earth asteroid 469219 Kamoʻoalewa (also known as 2016 HO3) to conduct close-range detection and sample return operations. The Tianwen-2 spacecraft carries the Asteroid Core Scan Radar (ACSR), a dual-frequency radar capable of both penetration and imaging. During the hovering phase, the ACSR will utilize Inverse Synthetic Aperture Radar observations to characterize the dielectric properties and internal structure of the asteroid.In contrast to other planetary orbiting radars, such as the MARSIS on Mars, the operational environment of the ACSR differs. Firstly, Kamoʻoalewa features a small radius (~40-100 m) and a short rotation period (~0.467 h) compared to Mars. Thus, unlike an orbital observation of a large-scale target such as Mars, the ACSR continuously illuminates a rotating asteroid, resulting in more complex, time-varying scattering conditions. Secondly, due to the ACSR's close-range observation altitude (~600 m), the spherical nature of the antenna's radiated field cannot be ignored. Finally, given the small size of the target, the strong surface clutter may overlap the weaker subsurface echoes from the asteroid’s subsurface. Therefore, an effective and precise surface clutter suppression is essential for revealing the internal structure of Kamo'oalewa.In this study, we will present the simulation, separation, and analysis based on the working circumstances of the ACSR. To address the complex surface conditions, the proposed surface clutter simulation is based on a physical optics method and considers the curvature of the spherical wavefront. Besides, a joint cross-correlation and moment-matching procedure is deployed to calibrate the potential orbital fluctuations. Our result shows that this approach works well in separating internal signals from radar observations. It will provide essential support for the radar data processing and scientific interpretation of the upcoming Tianwen-2 mission.

The subsurface of the Moon (i.e., shallow crust materials beneath the surface regolith) contains substantial information about regolith formation and crust evolution, but it is beyond the detection range of most lunar remote sensing techniques. Regolith on lunar maria and highlands exhibits systematically different thicknesses, and regolith thicknesses are highly heterogeneous both in a given geological unit and between coeval units, but the potential connection between regolith thickness heterogeneity and subsurface structures remains understudied. Proximal ejecta deposits of impact craters are invaluable probes of rock abundances at depths exceeding the thickness of surface regolith, but relatively fast degradation of boulders exposed on the lunar surface yields additional uncertainties to interpretations. Cold-spot craters are the youngest crater population on the Moon that formed ray patterns with lower night temperatures than mature lunar regolith, and they offer valuable information about rock abundances in the lunar subsurface. We examine the global catalog of cold-spot craters that have diameters of 240-2300 m and investigate rock abundances across their continuous ejecta deposits, deriving rock abundances in the subsurface at depths of approximately 20-200 m. We classify the cold-spot craters according to their background terrane types, i.e., maria, light plains, and highlands. We find that each cold-spot crater exhibits large variations in rock abundance across its continuous ejecta deposits, suggesting that the lunar subsurface materials may contain pervasive heterogeneities in rock abundances at depths of about 20-200 m and lateral distances of less than about 2.3 km. While cold-spot craters formed on the same terrane type exhibit large ranges of rock abundances in their continuous ejecta deposits, those formed on different terranes have systematic differences in mean rock abundances, with the largest in lunar maria and the lowest in highlands. Same-sized cold-spot craters formed on coeval mare units exhibit large variations in rock abundances. Our geological observations support that contemporary volcanic deposits in the lunar maria may contain both pyroclastic deposits and effusive lava flows. On light plains that were formed by the same impact basin, same-sized cold-spot craters also exhibit varying rock abundances in their continuous ejecta deposits, suggesting that cogenetic basin ejecta forming the light plains may contain diverse contents of competent impact melt. We interpret that the pervasive heterogeneities of subsurface rock abundances may be a major reason causing the non-uniform vertical growth rates of surface regolith on the Moon.

The Chang'E-5 samples are the youngest lunar materials collected to date. Determining their dielectric properties is essential for understanding the physical characteristics of lunar regolith and refining its dielectric model. In this study, the real part of permittivity and the loss tangent of the Chang'E-5 samples were systematically measured across a wide frequency range of 0.2-12.2 GHz. The results extend the existing database of lunar regolith dielectric properties and fill a key gap in this frequency band. The measurements show that the real part of permittivity exhibits strong frequency stability and increases exponentially with density. In contrast, the loss tangent decreases with frequency, with a decay rate significantly lower than that of Apollo samples below 0.2 GHz. Moreover, the correlation between loss tangent and density weakens near 10 GHz. This behavior differs from Apollo samples, which exhibit increasing loss tangent with density below 10 GHz. Based on these laboratory measurements, we revised the empirical coefficients for the real part of permittivity and loss tangent previously derived from Apollo data alone. These findings provide new experimental constraints for accurate modeling of lunar dielectric properties and their application in in situ exploration.

Chang'E-4 and its rover Yutu-2 are the first artificial objects that soft-landed on the far side of the Moon. Yutu-2 is also the second planetary rover equipped with a set of ground-penetrating radar (GPR) systems; two with 500 MHz (Channel-2A&2B), and one with 60 MHz (Channel-1) central frequency. GPR is a near surface geophysical technique capable of mapping the subsurface's dielectric properties, which are subsequently used to infer the mechanical and mineralogical properties of the lunar subsurface. The electromagnetic losses of lunar materials are primarily based on oxides of iron and titanium, and in particular on ilmenite. Ilmenite is abundant in Mare soils (%) and basalts (%). It is a unique mineral, being one of the few minerals with frequency dependent dielectric properties. Due to its dispersive nature, ilmenite is acting as a low-pass filter, reducing the central frequency of an incident field. Experimental evidence suggests that the shift of the central frequency is proportional to the ilmenite content of the material. Consequently, frequency attributes of the received radar signal can be used to infer the ilmenite content of different formations. In the current paper, using frequency attributes, we detect a sequence of basaltic layers down to m depth with varying thickness and ilmenite content. Three distinct volcanic phases are observed based on their ilmenite content. These far-side observations point to a volcanic activity with a time-dependent variation in titanium content, consistent with trends documented in other areas of the Moon.

Abstract The Lunar Regolith Penetrating Radar (LRPR) onboard the Chang’E-5 (CE-5) and Chang’E-6 (CE-6) missions represents the first application of an antenna-array ground penetrating radar in lunar exploration. The radar consists of 12 antennas and operates in a multiple-input multiple-output (MIMO) electronic scanning mode, in which one antenna transmits sequentially while the other 11 receive, providing multi-channel observations of the shallow subsurface beneath the landing site. LRPR data are acquired under an array-based multiview/multistatic geometry, causing reflections from the same target to appear as segmented and non-monotonic events in the raw profiles. Therefore, conventional permittivity inversion methods, based on multi-monostatic configurations, developed for rover-borne radar data are inapplicable. To address this problem, we propose a permittivity inversion framework tailored to the LRPR system, in which reflection-curve reconstruction is combined with the joint nonlinear inversion of multichannel traveltimes. This strategy fully exploits the MIMO characteristics of the array radar and enables robust estimation of subsurface permittivity from LRPR observations. The proposed method has been applied to pre-drilling datasets collected at CE-5 and CE-6 landing sites, and provides the permittivity distribution within the upper∼3 m of the subsurface, with average values of 3.13±0.52 for CE-6 and 3.42±0.86 for CE-5.

During the first superior conjunction of the Tianwen-1 Mars probe in October 2021, its downlink signal received by the Wuqing 70-m radio telescope passed within 4.53 solar radii of the Sun. The signal was significantly perturbed by the solar wind, providing a mechanism to probe coronal activity. We analyze the Doppler frequency scintillation spectrum of the solar wind within 10 solar radii to derive a characteristic frequency scintillation parameter. Statistical analysis indicates this parameter increases as the signal path approaches the Sun, with notable anomalies observed on October 5, 13, and 15. Comparisons with SOHO and SDO data reveal strong spatio-temporal correlations between these scintillation anomalies and coronal activity. We demonstrate that this parameter effectively identifies solar phenomena, including coronal streamers, high-speed solar wind, and coronal mass ejections (CMEs). Quantitative analysis confirms a distinct temporal correlation and delay between frequency scintillation and solar wind speed changes, validating the feasibility of spatially localizing solar activity.

Tianwen-2, the China upcoming planetary exploration mission, will conduct close-range investigations of the active asteroid 311P/ PANSTARRS and execute a sample-return operation from the Earth quasi-satellite 2016 HO3, with the aim of advancing our understanding of small-body dynamics and early Solar System evolution. The Dust Multi-properties Analyzer (DMA) onboard Tianwen-2 will investigate the physical properties of particles ejected by 311P. To achieve these scientific goals, a thorough ground validation was performed to evaluate the DMA's detection capability and measurement accuracy. By virtue of the known characteristics of 311P, 226 mineral particles of four compositional types were selected to serve as analogs of 311P's dust. Feasible verification methods and third-party validation tools were employed to conduct an experiment on these micron-scale dust particles. The physical quantities of the particles measured by the DMA, such as particle size, velocity, mass and morphology, were verified in the experiment, and the possible deviations in the results were analyzed. This study provides valuable ground-based data support for future in-orbit dust detection, data retrieval and application during the Tianwen-2 mission. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Lunar volcanic activity and its impact on near-surface material composition are central to lunar geological research. As of March 2024, the Yutu-2 rover has been operational on the Moon for 65 lunar days, covering a total distance of 1617.28 m. Radar data collected by the rover during the 24th to 31st lunar days, spanning approximately 120 m, clear horizontal reflection echoes. These reflections can be exploited for the estimation of the dielectric properties of the stratified structures. In this study, the finite-difference time-domain (FDTD) method is applied to quantitatively assess the positions and the electromagnetic properties of subsurface layers within the shallow subsurface (approximately 40 m in depth) as detected by Yutu-2. Therefore, the article deals with the first quantitative analysis of the positions and dielectric characteristics of four stratified layers beneath the Chang'E-4 (CE-4) landing site. Based on the results, the lunar layered near-surface structure is redefined in terms of a homogeneous regolith layer, an ejecta layer, a basalt layer, and a lightly weathered regolith layer. Furthermore, this study offers a detailed interpretation of the shallow geological structure at the CE-4 landing site, providing potential evidence of recent volcanic activity in the region.

Ground-Penetrating Radar (GPR) has become an essential tool for planetary exploration in China’s deep space exploration missions, enabling subsurface imaging and geological investigations in advancing our understanding of the lunar and Martian evolution. This paper provides an comprehensive overview of the successful application of GPR in China’s deep space exploration missions, including Chang’E-3 (CE-3), Chang’E-4 (CE-4), Chang’E-5 (CE-5), Chang’E-6 (CE-6) and Tianwen-1 missions. The study highlights key technological advancements, scientific discoveries, and the role of GPR in sample retrieval, and subsurface composition analysis. Furthermore, we discuss future prospects of GPR in upcoming lunar and Asteroid missions, emphasizing its continued importance in planetary exploration and resource identification.

The western flank of Elysium Mons, Mars, hosts a potential cave candidate (PCC) associated with a partially collapsed pit chain, previously identified in the Mars Cave Catalog. This study presents the first comprehensive investigation of the PCC, employing high-resolution imagery, thermal observations, topographic, geological, and mineralogical analyses to evaluate its structure and resource potential, and hypothesized to connect to a potential subsurface lava tube cave. High-resolution imagery from CTX and HiRISE on board the Mars Reconnaissance Orbiter (MRO), captured across varying solar angles, reveals an elliptical structure with constant shadowed regions and partial roof collapse, suggesting significant depth and consistency with a Potential Subsurface Lava Tube Skylight. Unlike the adjacent pit chain, which cools rapidly at night due to the lack of subsurface connectivity, the PCC retains heat and shows warmer appearance, indicating connectivity with the subsurface cave environment. Thermal observations from THEMIS on board Mars Odyssey confirm a pronounced night-time thermal anomaly, while topographic data from Mars Orbiter Laser Altimeter on board Mars Global Surveyor (MGS) provide detailed elevation profiles. Mineralogical analysis using Gamma-Ray Spectrometer data from Mars Odyssey identifies geochemical signatures indicative of the presence of olivine and pyroxene, iron oxides, feldspars, and potential volcanic glass. The PCC’s unique morphological, thermal, and mineralogical characteristics, along with cave entrance identification and insights from the conceptual model, highlight a potential environment for astrobiological investigations. These findings, derived from integrated data sets across MRO, Mars Odyssey, and MGS, provide crucial insights into Martian subsurface processes, resource availability, future human/robotic missions, and the planet’s potential to support life.

The Tianwen-2 mission targets the near-Earth asteroid 2016 HO3 and the main-belt comet 311P as its subjects of exploration. It is equipped with 11 payloads to investigate the topography, surface material composition, internal structure, and proximate space environment of these two small celestial bodies. Based on the data characteristics of the Tianwen-2 payloads, we discuss the whole process of data product generation from the data pipeline design to data validation. This paper can provide practical reference for Tianwen-2 data application.