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.

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.

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.

As a natural satellite of the Earth, the moon is a prime target for planetary remote sensing exploration. However, lunar polarization studies are not popular in the planetary science community. Polarimetry of the lunar surface had not been carried out from a spacecraft until the Korean lunar exploration program was initiated. In previous polarization observations of the moon, images of different polarization states were obtained by a rotating linear polarizer. This method is not well suited for future polarization observations from space-based spacecraft. To this end, we present a new kind of polarized observation of the moon using a division of a focal-plane polarization camera and propose a pipeline on the processing method of the polarization observation of the moon. We obtain a map of the degree of white-light polarization on the nearside of the moon through polarization observation, data processing, and correction. The observation and data processing methods presented in this study have the potential to serve as a reference for analyzing polarization observation data from future orbiting spacecraft. These are expected to lead to new discoveries in the fields of astronomy and planetary science.

The Netherlands-China Low-Frequency Explorer (NCLE) (Boonstra et al., 2017, https://www.ursi.org/proceedings/procGA17/papers/Paper_J19-2(1603).pdf; Chen et al., 2020, https://ui.adsabs.harvard.edu/abs/2020AAS & mldr;23610203C/abstract) is a radio instrument for astrophysical studies in the low-frequency range (80 kHz-80 MHz). As a technology demonstrator, NCLE shall inform the design of future radio receivers that aim at low-frequency radio astronomy. NCLE can make observations at very high spectral resolution (<1 kHz) and generate radio sky maps at an angular resolution of approximate to 1.5 radians. NCLE uses three monopole antennas, each 5 m long, and three identical analog signal chains to process the signal from each antenna. A single digital receiver samples the signal and calculates the auto-correlated and cross-correlated spectra. The instrument's analog and digital signal chains are extensively configurable. They can be fine-tuned to produce broadband spectra covering the instrument's complete operating frequency range or sub-bands. NCLE was developed within a veryshort timescale of 2 years, and currently, it is on board Queqiao, the relay spacecraft of the Chang'e- 4 mission, in a halo orbit around the Earth-Moon L2 point. This paper outlines the science cases, instrument architecture with focus on the signal chain, and discusses the laboratory measurements during the pre-launch phase.

Type Ⅱ radio bursts are the best tracers of Coronal Mass Ejections（CME）. The coronal or interplanetary shocks are generated along with a dramatic effect on the Earth′s magnetosphere, when CME exceed the local Alfin velocity. The detection of type Ⅱ radio bursts in the radio band manifests the generation of coronal shock waves. The prediction of the arrival time of shock waves to the Earth is essential to the space weather prediction. Type Ⅱ radio burst was detected for the first time by Qitai low frequency（Qitai LFRA） at around 06: 20 UT on September 28, 2021, with a frequency coverage of 18-50 MHz and a duration of more than 10 minutes. Since virtually no observation with effective spatial resolution have been made at extremely low frequency（＜40 MHz） band, there is a great possibility to discover unknown phenomena at this band in future. Our observation shows that Qitai LFRA has good performance（Typical gain: 6 dBi） and high sensitivity（-78 dBm/125 kHz, DR: 72 dB）, and can play a unique role in the 25 th annual solar activity peak.

嫦娥四号着陆器搭载的低频射电频谱仪已成功开展观测，每月把观测数据回传到地面，并且把经过一定的预处理后的2C级别的频谱数据释放给了科学团队。本文旨在评估该级别数据是否满足探测宇宙黑暗时代21cm整体谱的要求。我们对生成的2C级别数据进行了长时间积分，并对银河系前景射电辐射被着陆器接收进行了模拟仿真。通过对两套数据进行比对分析，发现2C 数据被减弱40-50 dB，几乎不包含银河系前景的远场辐射信号，这种大幅度的减弱进而影响到了该载荷对宇宙黑暗时代的探测能力。

嫦娥四号着陆器搭载的低频射电频谱仪(Low Frequency Radio Spectrometer,LFRS)已成功开展观测,每月把观测数据传回地面,并且把经过一定预处理后的2C级别的频谱数据释放给科学团队.旨在评估该级别数据是否满足探测宇宙黑暗时代21 cm整体谱的要求,对生成的2C级别数据进行了长时间积分,并模拟仿真银河系前景射电辐射.通过对两套数据进行对比分析发现,2C数据减弱40～50 dB,几乎不包含银河系前景的远场辐射信号,这种大幅度的减弱进而影响了该载荷对宇宙黑暗时代的探测能力.

At low frequency electron-magnetic wave band, planetary bodies not only emit thermal radiation, but also emit non-thermal radiation burst. The typical emission is planetary auroral radio burst consists of planetary kilometric wave burst, Jovian radiation at hectometer and decameter wavelengths. This kind of burst has been observed on the ground and in the space for dozens of years. The developed method can also be used as remote sensing tool to detect the inner structure of Jovian magnetosphere. However, the characteristics and mechanism have not been fully understood for the solar system planetary radio burst, there are still quite a lot of open questions left. Similar radio burst may also be observed from the exoplanetary systems. Following the development of space technology, radio astronomical observation has extended to kilometer wave. In the future the large radio array at low frequency can play key role to uncover the mechanism for the planetary radio burst, and also can be used to detect the exoplanets. The Chang’e-4 lunar mission with its low frequency payloads is working as pathfinder for the Earth Auroral Kilometer Radiation (AKR) and Jovian bursts,

After more than fifty years lunar exploration, our understanding of the lunar space environment is still superficial. The lunar dusty exosphere research was based on ARTEMIS mission and the lunar atmosphere and dust environment detector which were developed by NASA. Based on the radio experiments of several lunar missions, the existence of lunar ionosphere is determined. The current status and observation of lunar exosphere and ionosphere are introduced in this paper. With the help of the low frequency radio astronomical payloads carried by Chang'E-4 relay satellite and the lander, more of lunar space environment will be uncovered.

Due to the almost hemispheric observational scope of the Moon-based Earth observations, the effects of sampling time interval on the image offsets of the observed points are fundamentally different from the cases of traditional satellite-based platforms. Sampling time intervals will affect the offsets in the full-disc image, while the magnitude of the image offsets is dependent on the spatial resolution. Hence, their relationships merit further investigation. To this end, a novel method to determine the image coordinates based on radius-angle pair expression is proposed. The offsets of the observed points between two adjacent samplings can be calculated and the effects of the sampling time interval on the offsets can be analysed. We found that the magnitude of the image offsets in the x-axis direction is approximately two times larger than that in y-axis direction under the same sampling time interval and the effects of the sampling time interval is related to the observed point's latitude. Further, based on the fact that the maximum offsets occur at the Earth's equator, the detailed calculation of the shortest sampling time interval taken to exceed 1-pixel offset corresponding to different spatial resolutions is carried out. The results described herein can provide guidance for designing sensors for Moon-based Earth observations.

After more than fifty years lunar exploration, our understanding of the lunar space environment is still short. The information of lunar dusty exosphere was given by ARTEMIS mission and the lunar atmosphere and dust environment detector which were developed by NASA. Based on the radio experiments of several lunar missions, the existence of lunar ionosphere is proofed. The current status and observation of lunar exosphere and ionosphere are introduced in this paper. With the help of the low frequency radio astronomical payloads carried by chang'e-4 relay satellite and the lander, more information of lunar space environment will be detected.

The goal of Project GAUSS (Genesis of Asteroids and evolUtion of the Solar System) is to return samples from the dwarf planet Ceres. Ceres is the most accessible candidate of ocean worlds and the largest reservoir of water in the inner Solar System. It shows active volcanism and hydrothermal activities in recent history. Recent evidence for the existence of a subsurface ocean on Ceres and the complex geochemistry suggest past habitability and even the potential for ongoing habitability. GAUSS will return samples from Ceres with the aim of answering the following top-level scientific questions: What is the origin of Ceres and what does this imply for the origin of water and other volatiles in the inner Solar System?What are the physical properties and internal structure of Ceres? What do they tell us about the evolutionary and aqueous alteration history of dwarf planets?What are the astrobiological implications of Ceres? Is it still habitable today?What are the mineralogical connections between Ceres and our current collections of carbonaceous meteorites?

When the Cassini spacecraft finally plunged into the Saturnian atmosphere on 2017 September 15, China’s deep space telescope pointed to Saturn to observe Cassini and study the Saturnian upper neutral atmosphere. In this first Chinese Saturnian radio science experiment, X band Doppler velocity radio science data between the deep space telescope and the Cassini spacecraft were obtained. After removing Saturnian and solar gravity effects, Earth rotation effect, the remaining Saturnian atmosphere drag information was retrieved in the Cassini final plunge progress. Saturn’s upper neutral atmosphere mass density profile is approximately estimated based on atmosphere mass density derived principally by real orbit measurement data. Saturn’s upper neutral atmospheremass density from76 000 km to 1400 km is estimated fromthe orbit measurement data, the mass density results are about from 1.4 × 10−15 kg cm−3 to 2.5 × 10−14 kg cm−3.

The goal of Project GAUSS is to return samples from the dwarf planet Ceres. Ceres is the most accessible ocean world candidate and the largest reservoir of water in the inner solar system. It shows active cryovolcanism and hydrothermal activities in recent history that resulted in minerals not found in any other planets to date except for Earth's upper crust. The possible occurrence of recent subsurface ocean on Ceres and the complex geochemistry suggest possible past habitability and even the potential for ongoing habitability. Aiming to answer a broad spectrum of questions about the origin and evolution of Ceres and its potential habitability, GAUSS will return samples from this possible ocean world for the first time. The project will address the following top-level scientific questions: 1) What is the origin of Ceres and the origin and transfer of water and other volatiles in the inner solar system? 2) What are the physical properties and internal structure of Ceres? What do they tell us about the evolutionary and aqueous alteration history of icy dwarf planets? 3) What are the astrobiological implications of Ceres? Was it habitable in the past and is it still today? 4) What are the mineralogical connections between Ceres and our current collections of primitive meteorites? GAUSS will first perform a high-resolution global remote sensing investigation, characterizing the geophysical and geochemical properties of Ceres. Candidate sampling sites will then be identified, and observation campaigns will be run for an in-depth assessment of the candidate sites. Once the sampling site is selected, a lander will be deployed on the surface to collect samples and return them to Earth in cryogenic conditions that preserves the volatile and organic composition as well as the original physical status as much as possible.

Lunar surface temperature is one of the fundamental thermophysical parameters of the lunar regolith, which is of great significance to the interpretation of remote-sensing thermal data. In this study, a daytime surface temperature model is established focusing on the lunar superficial layer with high spatial-temporal resolution. The physical parameters at the time of interest are adopted, including effective solar irradiance, lunar libration, large-scale topographic shading, and surrounding diffuse reflection. Thereafter, the 1/64° temperature distributions at five local times are quantitatively generated and analyzed in Sinus Iridum. Also, combined with Chang’E-2 microwave radiometer (CELMS) data and Diviner thermal infrared (TIR) data, the spectral emissivity distributions are estimated as a potential geological application of the simulated surface temperature. The results are as follows: (1) daytime surface temperature in Sinus Iridum is significantly affected by the local topography and observation time, and the influence of diffuse reflection energy is obvious; (2) the emissivity distributions provide a new way to understand the thermophysical properties difference of lunar regolith at different depths; (3) the influence of lunar orbiting revolution and precession on surface temperature should be analyzed carefully, which shows the importance of using the parameters at the time of interest.