geothermal heat flow (HF) is critical to understanding the interior composition, structure, and thermal evolution of the Moon. Microwave radiometer (MRM) data are susceptible to the temperature and compositions of the substrate, making them suitable for retrieving HF information. However, existing HF retrieval methods are limited by retrieval uncertainty and calibration issues in MRM data. To address these issues, a novel HF retrieval model was constructed with the brightness temperature (TB) simulation model by constraining thermophysical parameters using Apollo in-suit HF experiments and Lunar Reconnaissance Orbiter (LRO) Camera Diviner data, and a normalized TB (nTB) mapping scheme to avoid the calibration issue of the MRM data. Utilizing identified optimal TB data derived from Chang'e-2 MRM observations, the HF on a global scale was retrieved utilizing the location-specific HF retrieval models. The main results are as follows: 1) the HF values range from 0 to 66.7 mW & centerdot;m-2, with an average of 18.1 mW & centerdot;m(-2); 2) four HF distribution patterns were proposed, indicating that the distribution of radiogenic heat-producing elements derived from the Lunar Prospector Gamma-Ray Spectrometer (LP-GRS) data cannot represent the vertical distribution throughout the entire crust; and 3) there probably exists the localized enrichment of heat-producing elements below the lunar crust, which shows a strong correlation with the basins with diameter ranging from 244 to 380 km. This study is helpful to improve our understanding of the thermal evolution and interior dynamics of the Moon.

Chang'E-4 (CE4), the first mission to soft-land on the lunar farside, provides a unique opportunity for astronomical observations from an environment shielded from terrestrial radio interference, and thus serves as pathfinder for lunar farside radio search for extraterrestrial intelligence (SETI) studies. We present a search for periodic technosignatures using low-frequency radio observations from the CE-4 mission, the first radio SETI study based on data from on the observation in lunar farside. We analyze the CE4 dynamic spectra with a component-level framework that combines principal component analysis (PCA), cross-antenna basis alignment, as well as temporal periodicity and frequency comb structure diagnostics. No final periodic candidate signal is found after the selection procedure, and we therefore find no evidence in the present CE4 sample for a credible periodic artificial signal. This study serves as a pathfinder and provides a practical framework for lunar radio SETI analysis. As more future lunar missions begin to incorporate radio instrumentation, lunar farside may become a promising site for expanding radio SETI research.

Each solar-system observable is characterised by celestial reference system (CRS) coordinate time, proper time on its world line, and the transformation between them. Ephemerides and Deep Space Network (DSN) tracking use the International Astronomical Union (IAU) barycentric and body-centric hierarchy, now extended to cislunar and Mars work. The IERS Conventions, Moyer radiometric models, and recent lunar-time papers distribute metric, scale, and tracking formulae across separate manuals. Merged Chang'e- or Tianwen-class data can acquire microsecond-level range and Doppler biases unless proper time τ is mapped consistently to barycentric and body-centric coordinate times. We present a unified 1PN documentation chain: tabulated harmonic Christoffel symbols through 𝒪(c^-4), the barycentric-geocentric-terrestrial coordinate-time sequence, Fermi normal coordinates, null-geodesic observables, and a 1PN two-way range-rate expansion, applied in parallel to Mars (MCRS/MCG) and lunar (LCRS/TCL) body-centric systems. The chain yields a Mars areoid-geoid metric clock-rate difference of ∼48 μs day^-1 and lunar selenoid-geoid rates of ∼57.4-58.7 μs day^-1 consistent with published nested coefficients. Mars-range Shapiro-rate terms reach 10^-12-10^-13. Multi-CRS consistency relies on documented transformation chains rather than a single master clock.

How to unify time outside the earth, from the point of view of relative time, using the two concepts of proper time and coordinate time in relativity, to combine time and space. The physical significance of the simultaneity compensation term in the resolution formula of the International Astronomical Union is analyzed, and the projection relationship of the meridian equivalent simultaneous plane contained in the compensation term is illustrated. There are three different forms of the moon's center of mass coordinate system, which have different axes orient and different rotational motions. Only in the Frenet coordinate system are there symmetrical and conserved laws of physics, and simple conversion coefficients that relate the proper time to the coordinate time. We define lunar standard time at the origin of the Frenet coordinate system, not on a equipotential surface, and only the coordinate time at the origin are recognized and unique. Let multiple timekeeping devices measure their respective local proper times. Converter this proper time to coordinate time like as the origin, and compare the origin coordinate time pairwise. Save the two-dimensional data table of the clock difference, and check out one which the rate of change in clock difference is the largest, to adjust its conversion coefficients of coordinate time. Select the timekeeping device with the largest deviation from the average value,to adjust its ephemeris. When the clock difference converges within a specified range, the coordinate origin can be agreed upon, achieving uniformity in coordinate time. There are three basic principles: 1) traceability; 2) four-dimensional space-time simultaneity; 3) conventionality.

The dielectric properties of the regolith are critical for the design and data interpretation of microwave systems and surface electromagnetic experiments of the Moon. In this study, an equivalent dielectric constant retrieval model was developed by formulating a brightness temperature (TB) simulation model for an equivalent regolith layer under constrained temperature conditions. Then, using TB maps at 19.35 and 37 GHz derived from Chang’e-2 microwave radiometer data, the real and imaginary parts of the equivalent dielectric constants and the corresponding loss tangent of the regolith were retrieved. The results agree well with the mare and highland dichotomy of the Moon, and the accuracy is about 82.13% compared with the measurements of the Surveyor, Apollo, and Chang’e missions. Finally, using empirical relationships among density, (FeO + TiO2) abundance, and the dielectric properties of the regolith, the equivalent density and (FeO + TiO2) abundance were further derived from the retrieved dielectric parameters, with overall accuracies of approximately 81.37% and 76.54%, respectively. The work is of great significance to further understanding the surface properties and even the magmatic evolution of the Moon.

Brightness temperature difference (TBD) derived from microwave radiometers (MRMs) onboard the Chang'e (CE)-1/2 satellites has been widely used to characterize basaltic flows on the lunar surface. However, the physical attributes of TBD and their geological correlations are not yet fully constrained. Based on the radiative transfer equation and the heat equation, a new TB model of the regolith is produced by considering parameters such as location, regolith composition, slope, and lunation hour. Subsequently, a TBD model is constructed from the difference in simulated TB at two different lunation hours. The simulation results show that regolith composition controls the TBD, with contributions also from latitude or surface temperature variations. To mitigate the variations with latitude or surface temperature, the TBD supplement (supTBD) model is proposed to generate the effective TBD (TBD eff ) by calculating the difference in simulated TB between the target location and its equivalent value at the equator. The results show that: 1) the TBDeff effectively weakens the influence of latitude change; 2) TBDeff better distinguishes variations in subsurface deposits, particularly concerning TiO2 abundance and the mare basaltic units; and 3) in lunar highlands, TBDeff demonstrates a positive correlation between microwave propagation and rocks, presenting an inhomogeneous distribution in both lateral and vertical directions. These findings are instrumental for evaluating subsurface deposits and the evolution of impact craters on the Moon from a new perspective.

Research on lunar oxides abundance has been spotlighted for its great significance in reconstructing the evolutionary history of the moon. In recent years, artificial intelligence technologies have been introduced to map oxides abundance on the lunar surface for their reliability and robustness. However, there are still some shortcomings in existing studies. First, the majority of these studies rely on spectral data and used in situ (drilled) ground truth samples collected by satellite missions. The detection depth of spectral sensors and the drilled depths of the returned samples are not consistent, lowering the reliability of the results. Moreover, existing machine/deep learning models may not be suitable for processing the data acquired in lunar exploration. In this article, we propose a novel deep learning model named multifrequency brightness temperature feature fusion network (MFBTFF-Net) for processing Chang'e-2 lunar microwave sounder (CELMS) data and it exploits the thermal radiation features related to various drilling depths to acquire the global lunar oxide abundance maps. The experimental results demonstrated that the proposed MFBTFF-Net model can significantly improve the estimation precision of most lunar oxides. The proposed method achieved root-mean-square error indices of 1.4449, 1.4826, and 0.9824 (wt.%) on estimating Al2O3, FeO, and TiO2, which outperformed the state-of-the-art models by at least 0.0674, 0.6217, and 0.0578, respectively. Furthermore, based on the proposed model, we generated a new set of lunar oxide abundance maps. Compared with the abundance maps derived from spectral data, some discoveries can be obtained due to the unique penetration depth-related information provided by Chang'e-2 CELMS data. This study demonstrates the large potential of Chang'e-2 CELMS as a powerful new tool to understand the vertical structures of the moon under the regolith.

Research on lunar oxides abundance has been spotlighted for its great significance in reconstructing the evolutionary history of the moon. In recent years, artificial intelligence (AI) technologies have been introduced to map oxides abundance on the lunar surface for their reliability and robustness. However, there are still some shortcomings in existing studies. Firstly, the majority of these studies rely on spectral data and used in-situ (drilled) ground truth samples collected by satellite missions. The detection depth of spectral sensors and the drilled depths of the returned samples are not consistent, lowering the reliability of the results. Moreover, existing machine/deep learning models may not be suitable for processing the data acquired in lunar exploration. In this paper, we propose a novel deep learning model named Multi-Frequency Brightness Temperature Feature Fusion Network (MFBTFF-Net) for processing Chang'e-2 Lunar Microwave Sounder (CELMS) data and it exploits the thermal radiation features related to various drilling depths to acquire the global lunar oxides abundance maps. The experimental results demonstrated that the proposed MFBTFF-Net model can significantly improve the estimation precision of most lunar oxides. The proposed method achieved root mean square error (RMSE) indices of 1.4449, 1.4826, and 0.9824 (wt.%) on estimating Al2O3, FeO and TiO2, which outperformed the state-of-the-art models by at least 0.0674, 0.6217, and 0.0578 respectively. Furthermore, based on the proposed model, we generated a new set of lunar oxides abundance maps. Compared with the abundance maps derived from spectral data, some discoveries can be obtained due to the unique penetration depth-related information provided by Chang'e-2 CELMS data. This study demonstrates the large potential of Chang'e-2 CELMS as a powerful new tool to understand the vertical structures of the moon under the regolith. The source code related to the experiments of this paper is publicly available at: https://github.com/liyuatbjut/MFBTFF-Net.

The Changu2019e-6 (CE-6) lander-ascender combination softly touched down at the designated landing site in the Apollo basin within the South Poleu2013Aitken (SPA) basin on 2024 June 2. As one of the 4 international payloads onboard CE-6, the INstrument for landing-Roving laser Retroreflector Investigations (INRRI) was installed on the top panel of the lander. Developed by the Italian National Institute for Nuclear Physicsu2013Frascati National Laboratory (INFN-LNF), with support from ASI (Italian Space Agency), this Italian instrument had already been deployed on Mars surface missions: ExoMars (ESA-ASI), InSight (NASA), and Perseverance (NASA). The piggybacking of this instrument came through the collaboration between Italian and Chinese scientists in response to an international Announcement of Opportunity issued by the China National Space Administration in 2018. To optimize its mounting on the CE-6 lander, adaptive design and environmental qualification tests were conducted to meet the requirements of surviving on the far side lunar surface environment. The INRRI retroreflector can be observed using the laser altimeter onboard the Lunar Reconnaissance Orbiter (LRO) and future lunar orbiter missions (e.g., Changu2019e-7). The successful landing of CE-6 establishes the first permanent location marker on the Moonu2019s far side, and it will serve as an absolute control point to support lunar surface positioning and mapping, and orbit determination and navigation of future lunar orbiters with laser ranging instruments.

The Lunar Laser Ranging (LLR) technology has been used to determine the Earth Rotation Parameters (ERP) since the 1970s.Conventional determination methods incorporate state-of-the-art models and LLR data spread over decades.The up-to-date studies achieve an accuracy of tens of microseconds for UT1 and several milliarcseconds (mas) for polar motion coordinates (PMC). This paper determines the instant PMC using the lunar laser ranging common view method (LLRCV). Through quantitative analysis of derivatives of lunar range residual to ERP variation, we formulated a linear equation to solve for the instant PMC with simultaneous range measurements. The precision of the solution were evaluated from the precision of the measurement through the analysis of the linear equation. We found 184 LLRCV events in the LLR data during 2012-2022 to solve for PMC. To form the solution errors, the results of our method are compared to the IERS C04 data.The results showed that 29.3% of the solution errors were less than 150 mas, and 21.7% of the solutions were more accurate than the prediction data. This method has the potential to address short-term and transient geophysical changes.  Nonetheless, its dependence on long-term geodetic data means it is not a substitute for conventional techniques.

Extensive radio frequency interference (RFI) monitoring is essential in the site selection process before constructing radio astronomy observatories, followed by mitigation strategies to minimize its adverse effects. Malaysia has an enormous prospect for radio astronomy due to its prominent location in the centre of Southeast Asia, but is challenged by its relatively high population density. In this research article, we perform high-cadence, low-frequency RFI monitoring at two sites, each representing an urban and a rural environment. Using modified generalized spectral kurtosis (GSK) as an RFI detection method, we ascertain the suitability of Glami Lemi, a rural area in the centre of Peninsular Malaysia previously assigned as a candidate radio notification zone (RNZ), as a potential site for radio astronomy observations due to its lower RFI contamination in our high-cadence monitoring, especially when compared with urban areas. We identified a number of persistent and transient RFI in our dataset, associate each of them with their potential origins and, if present, characterize their temporal evolution. A few types of RFI mitigation strategies were also tested and discussed. This study lays the groundwork for Malaysia's endeavours in establishing its first research-grade radio telescope, emphasizing the importance of robust RFI detection and mitigation strategies in optimizing observational outcomes.

The Chang’e-6 (CE-6) lander-ascender combination softly touched down at the designated landing site in the Apollo basin within the South Pole–Aitken (SPA) basin on 2024 June 2. As one of the 4 international payloads onboard CE-6, the INstrument for landing-Roving laser Retroreflector Investigations (INRRI) was installed on the top panel of the lander. Developed by the Italian National Institute for Nuclear Physics–Frascati National Laboratory (INFN-LNF), with support from ASI (Italian Space Agency), this Italian instrument had already been deployed on Mars surface missions: ExoMars (ESA-ASI), InSight (NASA), and Perseverance (NASA). The piggybacking of this instrument came through the collaboration between Italian and Chinese scientists in response to an international Announcement of Opportunity issued by the China National Space Administration in 2018. To optimize its mounting on the CE-6 lander, adaptive design and environmental qualification tests were conducted to meet the requirements of surviving on the far side lunar surface environment. The INRRI retroreflector can be observed using the laser altimeter onboard the Lunar Reconnaissance Orbiter (LRO) and future lunar orbiter missions (e.g., Chang’e-7). The successful landing of CE-6 establishes the first permanent location marker on the Moon’s far side, and it will serve as an absolute control point to support lunar surface positioning and mapping, and orbit determination and navigation of future lunar orbiters with laser ranging instruments.

The Apollo basin, situated on the northeastern edge of the South Pole-Aitken (SPA) basin, is the sampling area for the Chang'e -6 (CE-6) mission. In this study, we investigated the microwave thermophysical properties of surface deposits in the region by comparing brightness temperature (TB) and TB difference (dTB) maps derived from CE2 Microwave Radiometer data combined with topography, chemical elements, and Moon Mineralogy Mapper products. The main results are as follows. (1) High dTB anomaly: A significant high dTB anomaly is identified near the CE-6 landing region, characterized by the highest FeO and TiO2 contents estimated from the small-fresh craters; (2) Basaltic Volcanism: High dTB anomaly is proposed as a new basaltic unit in late stage of mare infill, and, by combining derived ages and geomorphology, we provide a new perspective on the basaltic volcanism with four episodes of magma infill in the CE-6 landing region; (3) Thermophysical Parameters: The high dTB anomaly indicates the potential importance of analyzing the returned CE-6 samples to enhance our understanding of the Moon's surface deposits using the passive microwave remote sensing data.

Due to the tidal locking, the far side of the Moon is permanently turned away from the Earth. Its polarization characteristics are still poorly understood, limiting our knowledge of material composition and evolution. Previous studies have indicated a correlation between the distributions of degree of polarization (DOP) and the iron oxide (FeO) abundance on the Moon, suggesting a new approach to infer the polarization characteristics of the lunar far side from FeO abundance distribution. Three critical issues have been analyzed: (1) A linear regression model between DOP and FeO abundance is proposed based on control points from ground-based near side polarization images. (2) The DOP distribution of the lunar far side is estimated, based on the established model, revealing significant hemispheric differences in polarization characteristics. (3) The relationship between DOP and lunar phase angle is examined, with the fitted values demonstrating strong agreement with the observations in both magnitude and variation trend. These insights offer valuable guidance for comprehensive polarimetric studies of the Moon.

The Chang’e-6 (CE-6) mission, part of China's lunar exploration program, marked a significant milestone as the first mission to return samples from the far side of the Moon. One of the highlights of CE-6 mission is that it piggybacked four international payloads, including the INstrument for landing-Roving Laser Retroreflector Investigations (INRRI), developed through a collaboration between the Italian National Institute for Nuclear Physics — Frascati National Labs (INFN-LNF) and the Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS).INRRI is a lightweight, passive optical instrument composed of eight cube corner retroreflectors made from fused silica, offering a wide 120° field of view. This robust and miniaturized design has a high level of maturity and inheritance from previous missions such as NASA’s Mars InSight and Perseverance, where similar retroreflectors had been successfully deployed. For CE-6 mission particularly, INRRI was mounted on a specialized bracket to minimize interference from ascender plume effects during liftoff. CE-6 INRRI underwent rigorous qualification tests, including mechanical (acceleration, shock, sinusoidal and random vibrations) and thermal vacuum tests, to validate its structural integrity. After integrated with the lander, CE-6 INRRI underwent the whole spacecraft random and sinusoidal vibration tests and successfully passed all evaluations.The CE-6 INRRI serves as a high-precision absolute control point, crucial for improving lunar surface mapping especially for the lunar far side. Initial validation of INRRI’s operational status has been achieved through observations by the Lunar Orbiter Laser Altimeter (LOLA) onboard NASA’s Lunar Reconnaissance Orbiter (LRO). Future observations by laser ranging from lunar orbiters will refine its position, and will contribute to improving the accuracy of orbit determination for lunar orbiters, advancing studies of lunar geodesy, Earth-Moon dynamics and lunar physics.Building on this success, the Italian-Chinese collaboration team are working on the piggybacking of Chang’e-7 LAser Retroreflector Arrays (CLARA), including MoonLIGHT (Moon Laser Instrumentation for Geodesy, Geophysics and General relativity High accuracy Tests) and INRRI. Currently INRRI for CE-7 has just completed its mechanical tests and is in the process of arranging the subsequent experiments.

Brightness temperature (TB) derived from the Chang'e-2 microwave radiometer (MRM) data has provided a useful way to study the thermal and dielectric properties of the subsurface deposits on the Moon. However, the obvious TB change with the latitude, named latitude effect, has highly limited the application of the MRM data. To solve this problem, a new TB mapping method, named normalized TB (nTB) mapping method, is developed, which is defined as the ratio between the TB and the standard TB at the same point. Based on the newly derived global nTB maps, we identified and classified four types of subsurface deposits with distinct dielectric properties, two of which indicate the abnormally high heat flux or the existence of the granitic systems and the existence of the surface rocks, respectively. Moreover, the nTB at the daytime demonstrates a strong correlation with both the TiO2 and FeO abundances of subsurface deposits, the latter of which has been severely underestimated by the previous studies directly using MRM data. This work is significant to improve the understanding of the basaltic volcanism and thermal evolution of the Moon.

In view of the requirements of Tianwen-1 missions on precision orbit determination and scientific application, this paper proposes a high-precision open-loop velocity measurement method based on ground-based radio. At first, relying on space–ground TT&C resources of the Tianwen-1 probe, the paper designs an open-loop velocity measurement strategy based on China’s deep-space network. Then, it proposes a core algorithm of open-loop velocity measurement based on local cross-correlation reconstruction to obtain instantaneous Doppler frequency observables. This algorithm is characterized by a high ability to avoid phase lock loss, convenient and efficient implementation, and flexible parameter configuration and is suitable for high-precision velocity measurement in the case of high dynamics and low signal-to-noise ratios. On this basis, the similarity and difference of velocity observables between open-loop and baseband velocity measurements are analyzed comparatively. Finally, on the basis of the open-loop velocity measurement method, the paper carries out tests on high precision orbit determination with independent support of velocity measurement, as well as on Mars radio occultation. According to the research results, the accuracy of open-loop velocity measurement can reach 0.05 mm/s (in 1-s integration time), which is 2 to 3 times better than that of baseband velocity measurement. Open-loop velocity measurement can independently support orbit determination accuracy of 50 m of the Tianwen-1 probe and effectively support autonomous retrieval of Martian ionospheric electron density profiles. Thus, this method can be effectively applied to future missions of deep-space exploration and research of planetary radio science.

Lunar optical polarization is a fascinating phenomenon that occurs when sunlight reflects off the surface of the Moon and becomes polarized. This study employs a novel split-focus plane polarimetric camera to conduct the initial white light polarimetric observations on the near side of the Moon. We obtained the linear degree of polarization (DOP) parameters of white light by observation from the eastern and western hemispheres of the Moon. The findings indicate that the white light polarization is lower in the lunar highland than in the lunar maria overall. Combining the analysis of lunar soil samples, we noticed and determined that the DOP parameters of white light demonstrate high consistency with iron oxide on the Moon. This study may serve as a new diagnostic tool for the Moon.