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.

The dielectric properties of lunar regolith are critical in constraining radar wave propagation and guiding geological interpretation in planetary subsurface exploration. While previous assessments at the Chang'E-5 (CE-5) landing site relied on orbital remote sensing, this study introduces a novel in situ permittivity inversion framework tailored for the lunar regolith penetrating radar (LRPR) system, providing the point-scale measurements that complement previous orbital assessments. This approach overcomes the limitations of conventional hyperbolic diffraction analysis commonly applied to the Chang'E-3/4 (CE-3/CE-4) radar data. By integrating the LRPR's geometric configuration with electromagnetic wave propagation theory, we developed a depth-resolved inversion methodology based on iterative coherence optimization of radar echoes. The retrieved results indicate an average relative permittivity of 4.04 +/- 1.51 (1 sigma) within the upper 2.5 m of the regolith. This methodology enhances in situ dielectric characterization for future lunar missions and reveals stratified permittivity zones and an immature regolith structure, providing direct evidence for the Eratosthenian-aged geological context of the CE-5 sampling site.

As humanity’s first sample return mission from the lunar farside, China’s Chang’E-6 mission provides a unique window into understanding the dichotomy in lunar nearside-farside evolution. Chang’E-6 landed in the southwestern Apollo basin (~2.79 Ga) within the South Pole–Aitken basin, providing a valuable record of early solar system impacts. Equipped with a Multi-Input-Multi-Output Lunar Regolith Penetrating Radar, the mission enabled the first detailed investigation of the shallow subsurface structure at the farside. By employing a tailored data processing approach, we obtained high-resolution subsurface images and revealed a distinct two-layer structure to a depth of 3 m. The upper layer (~1.7 m thick) consists of fine-grained, highly weathered regolith, while the lower layer (extending to 3 m) contains coarse, unweathered ejecta. Furthermore, by integrating data from Apollo and Chang’E missions, we identified a potential relationship between the lunar surface geological age and the shallow regolith’s electromagnetic losses. Specifically, geologically older regions exhibit lower electromagnetic attenuation, suggesting a possible link between regolith maturity and electromagnetic properties. These findings provide critical insights into the geological evolution of the Moon, and also offer unprecedented opportunities for correlating in-situ radar measurements with laboratory analyses of the farside samples, fundamentally advancing our understanding of lunar exploration. An analysis of subsoil structure using lunar regolith penetrating radar at the Chang’E-6 landing site indicates a distinct 2-layer structure, and when compared with Apollo mission data, suggests a link between regolith maturity and electromagnetic properties.

This work presents the results achieved by applying a microwave tomographic approach to the data collected by the Lunar Penetrating Radar onboard Yutu-2 rover in the frame of the Chang’e 4 mission. The adopted signal processing pipeline comprises two steps: the first one is a pre-processing stage involving time-domain procedures required to filter the clutter and noise on raw data; the second step regards the exploitation of a microwave tomographic approach designed to tackle the computational issue imposed by the large (in terms of probing wavelength) domain investigated by the rover. Two tomographic approaches, different for modeling the signal propagation through the air-soil interface, are considered and compared. The results are provided as tomographic images along the route of 1340 m; the tomographic images confirm the presence of interesting subsurface geometrical features, whose geological interpretation agrees with the studies presented in previous papers.

The Rover-mounted Subsurface Penetrating Radar (RoSPR) is one of the scientific payloads onboard China’s first independent Mars exploration mission, Tianwen-1. The radar aims to characterize the thickness of the upper Martian soil and investigate the subsurface stratigraphy by collecting and processing the data. This article is mainly divided into two parts, the introduction of data pre-processing and analysis of pre-processed radar signals, aiming at helping scientists make more effective use of radar data. The first part describes the operating principle of the RoSPR and the procedure of radar data pre-processing at all levels. Data pre-processing is mainly designed to transfer the raw data format to a common PDS (Planetary Data System) and eliminate the influence of the instrument. In the signal analysis part, the performances of both self-check signals and echo signals of low- and high-frequency channels are analyzed, which indicate a stable radar system and are useful for background removal. Phase and time calibration is of great importance for improving data quality and making the radar data more accurate. Moreover, further processing is required to obtain clear radar images, such as filtering, background removal and gain setting.

Mars Orbiter Subsurface Investigation Radar (MOSIR) is carried by China's first Mars probe, Tianwen-1 orbiter, investigating the Martian subsurface stratification. Surface clutter from topography off-nadir will overlap with the subsurface echoes, which affects the recognition of Martian subsurface reflections. Surface clutter simulation can effectively distinguish the nadir and off-nadir radar echoes. In this paper, we choose the facet method to model the Mars surface topography and combine the roughness parameter with the radar backscatter function. We also provide an analytic expression of the echo phase considering the distance variation in the whole facet. The Chinese first Mars landing site is on Utopia Planitia, which is also one of the key investigating regions of MOSIR. Therefore, we also carried on surface clutter simulation of this region and generated simulation radargram with the Chirp Scaling algorithm. Furthermore, we use the contrast method to compensate for ionospheric error introduced by the NeMars Mars ionosphere model. Our surface clutter simulation program will significantly support MOSIR subsurface investigation, and provide a chance to verify the related data processing.

The MOSIR (Mars Orbiter Subsurface Investigation Radar) is one of the scientific payloads carried by the Tianwen-1 orbiter. MOSIR conducted a ground experiment in the desert near Dengkou County, northern China, before the launch of the Tianwen-1 satellite. The MOSIR prototype was suspended from a hot air balloon and flew over a flat region at an altitude of 2500–3300 m. This experiment aimed to verify the system performance and data processing. The data collected in subsurface sounding mode is performed range compression, and the altitude measurement data removes invalid data. After processing, the altitude measurement results of two operating modes are analyzed and compared with that of the Global Position System (GPS), which verifies the accuracy of the altitude measurement.

Low surface brightness galaxies (LSBGs) are defined as galaxies that are fainter than dark night sky and are important for studying our universe. Particularly, edge-on galaxies are useful for the study of rotational velocity and dynamical properties of galaxies. Hence here we focus on searching for edge-on LSBGs. In order to find these edge-on dim galaxies, a series of effects caused by inclination, including the surface brightness profile, internal extinction, and scale length, have been corrected. In this work, we present a catalog of 281 edge-on LSBG candidates, which are selected from the crossmatch between Sloan Digital Sky Survey Data Release 7 and the 40% ALFALFA catalog. We also present the properties of these edge-on LSBG candidates including the absolute magnitude, central surface brightness, B − V color, scale length, and relative thickness. Our result suggests that the correction of inclination effects is very important for obtaining a complete sample of LSBGs.

Wei Du , Gong-Bo Zhao , Zuhui Fan, Yiping Shu , Ran Li, and Shude Mao 1 National Astronomical Observatories, Chinese Academy of Science, Beijing, 100101, People’s Republic of China; duwei@bao.ac.cn, gbzhao@nao.cas.cn 2 School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China 3 South-Western Institute for Astronomy Research, Yunnan University, Kunming, 650500, People’s Republic of China 4 Department of Astronomy, Peking University, Beijing, 100871, People’s Republic of China 5 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK 6 Department of Astronomy, Tsinghua University, Beijing, 100084, People’s Republic of China Received 2020 April 9; published 2020 May 18

In the standard cosmological model, dark matter drives the structure formation and constructs potential wells within which galaxies may form. The baryon fraction in dark halos can reach the universal value (15.7%) in massive clusters and decreases rapidly as the mass of the system decreases. The formation of dwarf galaxies is sensitive both to baryonic processes and the properties of dark matter owing to the shallow potential wells in which they form. In dwarf galaxies in the Local Group, dark matter dominates the mass content even within their optical-light half-radii (r_e ~ 1 kpc). However, recently it has been argued that not all dwarf galaxies are dominated by dark matter. Here we report 19 dwarf galaxies that could consist mainly of baryons up to radii well beyond r_e, at which point they are expected to be dominated by dark matter. Of these, 14 are isolated dwarf galaxies, free from the influence of nearby bright galaxies and high dense environments. This result provides observational evidence that could challenge the formation theory of low-mass galaxies within the framework of standard cosmology. Further observations, in particular deep imaging and spatially-resolved kinematics, are needed to constrain the baryon fraction better in such galaxies.

To study the disc central surface brightness (N) distribution in optical and near-infrared bands, we select 708 disc-dominated galaxies within a fixed distance of 57 Mpc from SDSS DR7 and UKIDSS DR10. Then we fit mu(0) distribution by using single and double Gaussian profiles with an optimal bin size for the final sample of 538 galaxies in optical griz bands and near-infrared YJHK bands. Among the eight bands, we find that mu(0) distribution in optical bands cannot be much better fitted with double Gaussian profiles. However, for all the near-infrared bands, the evidence of being better fitted by using double Gaussian profiles is positive. Especially for K band, the evidence of a double Gaussian profile being better than a single Gaussian profile for mu(0) distribution is very strong, the reliability of which can be approved by 1000 times test for our sample. No dust extinction correction is applied. The difference of mu(0) distribution between optical and near-infrared bands could be caused by the effect of dust extinction in optical bands. Due to the sample selection criteria, our sample is not absolutely complete. However, the sample incompleteness does not change the double Gaussian distribution of mu(0) in K band. Furthermore, we discuss some possible reasons for the fitting results of mu(0) distribution in K band. Conclusively, the double Gaussian distribution of mu(0) in K band for our sample may depend on bulge-to-disc ratio, colour and disc scale length, rather than the inclination of sample galaxies, bin size, and statistical fluctuations.

The light absorption enhancement (E-abs) of black carbon (BC) caused by non-BC materials is an important source of uncertainty in radiative forcing estimate, yet remains poorly understood in relatively polluted environment such as the megacity Beijing. Here BC absorption enhancement at 630 nm was in-situ measured using a ther-modenuder coupled with a soot particle aerosol mass spectrometer and a single scattering albedo monitor in Beijing in summer. The project average (+/- 1 sigma) E-abs was 1.59 ( +/- 0.26), suggesting a significant amplification of BC absorption due to coating materials. E-abs presented a clear daytime increase due to enhanced photochemical processing, and a strong dependence on the mass ratios of non-BC coatings to BC (R-BC). Our results showed that the increase in E(abs )as a function of R-BC was mainly caused by the increased contributions of secondary aerosol. Further analysis showed that the BC absorption enhancement in summer in Beijing was mainly associated with secondary formation of nitrate, sulfate and highly oxidized secondary organic aerosol (SOA), while the formation of freshly and less oxidized SOA appeared not to play an important role.

In the standard cosmological model, dark matter drives the structure formation and constructs potential wells within which galaxies could form. The baryon fraction in dark halos could reach the universal value in rich clusters and drops fast towards low mass systems. The formation of dwarf galaxies is sensitive both to baryonic processes and the properties of dark matter due to their shallow potential well. In dwarf galaxies in the Local Group, dark matter dominates the mass content even within their half optical light radii (r_e ~ 1 kpc). However, statistical studies beyond the Local Group were hampered by the extreme faintness of such systems in the past. Here we report 19 dwarf galaxies that could mainly consist of baryons up to radii well beyond r_e, where they are expected to be dominated by dark matter. 14 of them are isolated dwarf galaxies, free from the influence of nearby bright galaxies/AGNs and high dense environments. This result provides observational evidence that could challenge the formation theory of low-mass galaxies in the framework of standard cosmology.

The tunneling contribution of evanescent waves carrying high density of state of photons can substantially strengthen the near-field Planckian thermal radiation with efficiency far beyond the classic blackbody limit. In this aspect, the monolayer graphene (Gr) has the special potential due to its strong surface plasmonic response in the thermal infrared window. In this work, we manage to characterize the near-field heat transfer between two macroscopic Gr-sheets seated on different silicon substrates at nanoscale gaps and unambiguously verify the role of Gr-plasmons in enhancing the thermal radiation. This effect is firstly demonstrated using an intrinsic silicon (i-Si) substrate without doping so that the plasmonic contribution of graphene is solely inspected. A large super-Planckian heat transfer efficiency 8 times larger than the blackbody limit is obtained at a gap size of 435 nm at a temperature difference of 35 K. Highly doped silicon (d-Si) substrate with plasmonic response in the long wavelength range is then used, which alone can give rise to a large near-field heat flux. When covered with a Gr-sheet, the electromagnetic (EM) coupling between the two alien plasmonic materials can further enhance the Gr-Si radiation efficiency with an increment about 11%. The underlying charging doping arising from the Gr-Si heterojunction and their electromagnetic influence are investigated. The experimental results are in good agreement with the analytical calculations incorporating the measurement uncertainties, which in turn validates the classic fluctuating electrodynamics theory used in describing the graphene-involved near-field heat transfer system.

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147 000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically averaged clustering in both configuration and Fourier space. Our observational data set and the 1400 simulated realizations of the data set allow us to detect a preference for BAO that is greater than 2.8 sigma. We determine the spherically averaged BAO distance to z = 1.52 to 3.8 per cent precision: D-V (z = 1.52) = 3843 +/- 147 (r(d)/r(d, fid)) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat Lambda CDMbest-fitting cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find Omega(Lambda) > 0 at 6.6 sigma significance when testing a Lambda CDM model with free curvature.

The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) has a significant impact on both nocturnal particulate nitrate formation and photochemistry on the following day through the photolysis of nitryl chloride (ClNO2), yet these processes in highly polluted urban areas remain poorly understood. Here we present measurements of gas-phase N2O5 and ClNO2 by high-resolution time-of-flight chemical ionization mass spectrometer (ToF-CIMS) during summer in urban Beijing, China as part of the Air Pollution and Human Health (APHH) campaign. N2O5 and ClNO2 show large day-to-day variations with average (±1σ) mixing ratios of 79.2±157.1 and 174.3±262.0 pptv, respectively. High reactivity of N2O5, with τ (N2O5)−1 ranging from 0.20 × 10−2 to 1.46 × 10−2 s−1, suggests active nocturnal chemistry and a large nocturnal nitrate formation potential via N2O5 heterogeneous uptake. The lifetime of N2O5, τ (N2O5), decreases rapidly with the increase in aerosol surface area, yet it varies differently as a function of relative humidity with the highest value peaking at ∼ 40 %. The N2O5 uptake coefficients estimated from the product formation rates of ClNO2 and particulate nitrate are in the range of 0.017–0.19, corresponding to direct N2O5 loss rates of 0.00044–0.0034 s−1. Further analysis indicates that the fast N2O5 loss in the nocturnal boundary layer in urban Beijing is mainly attributed to its indirect loss via NO3, for example through the reactions with volatile organic compounds and NO, while the contribution of the heterogeneous uptake of N2O5 is comparably small (7–33 %). High ClNO2 yields ranging from 0.10 to 0.35 were also observed, which might have important implications for air quality by affecting nitrate and ozone formation.

We present long-slit optical spectra of 12 edge-on low surface brightness galaxies (LSBGs) positioned along their major axes. After performing reddening corrections for the emission-line fluxes measured from the extracted integrated spectra, we measured the gas-phase metallicities of our LSBG sample using both the [N II]/ Ha and the R-23 diagnostics. Both sets of oxygen abundances show good agreement with each other, giving a median value of 12. +. log(O/H). =. 8.26 dex. In the luminosity-metallicity plot, our LSBG sample is consistent with the behavior of normal galaxies. In the mass-metallicity diagram, our LSBG sample has lower metallicities for lower stellar mass, similar to normal galaxies. The stellar masses estimated from z-band luminosities are comparable to those of prominent spirals. In a plot of the gas mass fraction versus metallicity, our LSBG sample generally agrees with other samples in the high gas mass fraction space. Additionally, we have studied stellar populations of three LSBGs, which have relatively reliable spectral continua and high signal-to-noise ratios, and qualitatively conclude that they have a potential dearth of stars with ages < 1 Gyr instead of being dominated by stellar populations with ages > 1 Gyr. Regarding the chemical evolution of our sample, the LSBG data appear to allow for up to 30% metal loss, but we cannot completely rule out the closed-box model. Additionally, we find evidence that our galaxies retain up to about three times as much of their metals compared with dwarfs, consistent with metal retention being related to galaxy mass. In conclusion, our data support the view that LSBGs are probably just normal disk galaxies continuously extending to the low end of surface brightness.

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5σ. We determine the spherically averaged BAO distance to z = 1.52 to 4.4 per cent precision: DV (z = 1.52) = 3855 ± 170 (rd/rd,fid) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat ΛCDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find ΩΛ > 0 at 6.5σ significance when testing a ΛCDM model with free curvature.

Despite extensive efforts to characterize organic nitrogen (ON) in atmospheric aerosols, knowledge of the sources and processes of ON in the megacity of Beijing is still limited, mainly due to the complexity of ON species and the absence of highly time-resolved measurements. Here we demonstrate the applications of Aerodyne high-resolution time of-flight aerosol mass spectrometer combined with positive matrix factorization in characterization of ON in submicron aerosols. Our results show that the average nitrogen-to-carbon ratios (N/C) vary from 0.021 to 0.028, and the average ON concentrations range from 0.26 to 0.59 mu g m(-3) during four seasons in Beijing. ON accounts for 7-10% of the total nitrogen (TN) on average, yet the sources vary differently across different seasons. We found that 56-65% of ON was secondary during three seasons except winter when 59-67% was related to primary emissions. Particularly, more oxidized secondary organic aerosol contributes the dominant fraction of ON (39-44%) in spring, summer and autumn, while biomass burning is a more important source of ON in winter (23-44%). These results are consistent with the better positive correlations between N/C and oxygen-to-carbon ratio, a surrogate of organic aerosol aging, during these three seasons than that in winter. N/C also shows a clear increase as a function of relative humidity during all seasons, suggesting that aqueous-phase processing likely played an important role in formation of nitrogen-containing compounds. In addition, the uncertainties and limitations in quantification of ON with aerosol mass spectrometry are illustrated, particularly, ON could be underestimated by similar to 20-42% by ignoring the fragment contributions in NHx+ and NOx+.

In this Letter, we report the observational constraints on the Hu-Sawicki f(R) theory derived from weak lensing peak abundances, which are closely related to the mass function of massive halos. In comparison with studies using optical or x-ray clusters of galaxies, weak lensing peak analyses have the advantages of not relying on mass-baryonic observable calibrations. With observations from the Canada-France-Hawaii-Telescope Lensing Survey, our peak analyses give rise to a tight constraint on the model parameter |f_{R0}| for n=1. The 95% C.L. is log_{10}|f_{R0}|<-4.82 given WMAP9 priors on (Ω_{m}, A_{s}). With Planck15 priors, the corresponding result is log_{10}|f_{R0}|<-5.16.