Fresh Craters Research Articles

An Investigation on the Morphological and Mineralogical Characteristics of Posidonius Floor Fractured Lunar Impact Crater Using Lunar Remote Sensing Data

Lunar floor-fractured craters (FFCs) are a distinguished type of crater found on the surface of the Moon with radial, concentric, and/or polygonal fractures. In the present study, we selected the Posidonius FCC to explore the mineralogy, morphology and tectonic characteristics using remote sensing datasets. The Posidonius crater is vested with a wide moat of lava separating the crater rim inner wall terraces from the fractured central floor. Lunar Reconnaissance Orbiter’s (LRO) images and Digital Elevation Model (DEM) data were used to map the tectonics and morphology of the present study. The Moon Mineralogy Mapper (M3) data of Chandrayaan-1 were used to investigate the mineralogy of the region through specified techniques such as integrated band depth, band composite and spectral characterization. The detailed mineralogical analysis indicates the noritic-rich materials in one massif among four central peak rings and confirm intrusion (mafic pluton). Spectral analysis from the fresh crater of the Posidonius moat mare unit indicates clinopyroxene pigeonite in nature. Integrated studies of the mineralogy, morphology and tectonics revealed that the study region belongs to the Class-III category of FFCs. The lithospheric loading by adjacent volcanic load (Serenitatis basin) generates a stress state and distribution of the fracture system.

Size–frequency measurements of meter-sized craters and boulders in the lunar polar regions for landing-site selections of future lunar polar missions

The concentrations of volatiles, especially hydrogen (or water), at the lunar poles have been reported from remote sensing data in previous studies. Many future missions are targeting to investigate the permanently shadowed regions inside polar craters, where water ice can exist because the temperature is extremely low. Accordingly, landing sites are being planned around polar craters. We conducted a geomorphological analysis of the ejecta blankets of Shackleton Crater at the South Pole (89.63°S, 130.0°E) and Whipple Crater at the North Pole (89.14 N°, 119.5°E). Size–frequency measurements of the craters and boulders were derived from high resolution (~1 m/pix) image data obtained by the Narrow Angle Camera onboard the Lunar Reconnaissance Orbiter. The number of identified craters (diameter > 10 m) and boulders (diameter > 3 m) were 35,799 and 1273, respectively, around Shackleton and 17,074 and 3092, respectively, around Whipple. The number densities of boulders around fresh craters on Shackleton and Whipple rim are lower than at the Apollo and Luna landing sites, suggesting a low production rate of boulders in these regions. The number density of small craters is lower than expected from the formation ages of Shackleton and Whipple and is strongly correlated with regional topographic slopes, implying that small craters were eliminated by resurfacing with mass wasting from the continuous ejecta of Shackleton and Whipple. Ejecta blankets from small craters may cover and preserve past subsurface accumulations of water molecules. Based on the crater counting data, we propose feasible landing sites around Shackleton Crater and scenarios for exploring local subsurface water using excavators in future missions.

A 2-year locomotive exploration and scientific investigation of the lunar farside by the Yutu-2 rover.

The lunar nearside has been investigated by many uncrewed and crewed missions, but the farside of the Moon remains poorly known. Lunar farside exploration is challenging because maneuvering rovers with efficient locomotion in harsh extraterrestrial environment is necessary to explore geological characteristics of scientific interest. Chang’E-4 mission successfully targeted the Moon’s farside and deployed a teleoperated rover (Yutu-2) to explore inside the Von Kármán crater, conveying rich information regarding regolith, craters, and rocks. Here, we report mobile exploration on the lunar farside with Yutu-2 over the initial 2 years. During its journey, Yutu-2 has experienced varying degrees of mild slip and skid, indicating that the terrain is relatively flat at large scales but scattered with local gentle slopes. Cloddy soil sticking on its wheels implies a greater cohesion of the lunar soil than encountered at other lunar landing sites. Further identification results indicate that the regolith resembles dry sand and sandy loam on Earth in bearing properties, demonstrating greater bearing strength than that identified during the Apollo missions. In sharp contrast to the sparsity of rocks along the traverse route, small fresh craters with unilateral moldable ejecta are abundant, and some of them contain high-reflectance materials at the bottom, suggestive of secondary impact events. These findings hint at notable differences in the surface geology between the lunar farside and nearside. Experience gained with Yutu-2 improves the understanding of the farside of the Moon, which, in return, may lead to locomotion with improved efficiency and larger range.

Determining the age of Vaughan, a potential source crater for lunar meteorites, using boulder size-frequency distributions

We use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images to analyze the boulder distribution around Vaughan crater, a small, fresh crater on the far side of the Moon. Using six similar lunar impact craters of known age for comparison, we determine the approximate age of the crater. Vaughan crater lies in a part of the South Pole-Aitken basin that is compositionally similar to lunar meteorite Dhofar 961, on the basis of Lunar Prospector Gamma Ray Spectrometer data, making Vaughan crater a potential candidate for the source of this meteorite and possibly others paired with it. Boulder distributions reveal that as impact craters age, the boulder population density in their ejecta decreases. This understanding allows us to use size-frequency distributions to compare crater ages on the basis of their boulder population density. We find that Vaughan crater is very young (<25 Ma) owing to its placement within the boulder size-frequency comparison plot and its population of large (>10 m diameter) boulders. Additionally, we compare LROC NAC distributions to thermophysically derived values for rock abundance from the Diviner Lunar Radiometer. We find that our LROC NAC count is consistent with Diviner rock abundance values, which further supports the inference that Vaughan is a very young impact crater and could plausibly be a source of lunar meteorite Dhofar 961.

Effect of Topographic Degradation on Small Lunar Craters: Implications for Regolith Thickness Estimation

AbstractSmall crater morphology method has been used extensively in lunar regolith thickness estimation. However, topographic degradation can change crater morphology and thus bias regolith thickness estimation. In this study, we first developed a shape model for small fresh craters with normal, central mound, flat‐bottomed, and concentric geometry. We then simulated their degradation processes by using a topographic diffusion model. Simulation results show that as a small crater degrades, its morphology changes from concentric/central mound to flat‐bottomed, from flat‐bottomed to normal, and from normal to invisible, depending on its initial morphology. Upon the time a crater becomes invisible, its diameter can be enlarged by a factor of ∼70%. We proposed a revised small crater morphology method and applied it to the Apollo 11 and 14 landing sites. Our revised method permits a more accurate estimate of regolith thickness, and our results are helpful in understanding the evolution of the Moon's surface.

Investigation of the source region of the lunar-meteorite group with the remote sensing datasets: Implication for the origin of mare volcanism in Mare Imbrium

Lunar meteorites provide information about areas of the Moon not sampled by the Apollo and Luna missions, so they can be used as more-representative geochemical datasets for evaluating global lunar evolution. However, the launching craters remain unknown for many lunar meteorites. This paper, therefore, aims to identify the launching sites of lunar meteorites with remote-sensing datasets. This work focuses on one lunar-meteorite group, the Northwest Africa 773 (NWA 773) clan, which has the very-low-Ti basaltic composition and one of the youngest crystallization ages (~3 Ga) among the lunar basaltic meteorites. We investigated the source of the NWA 773 clan by comparing their geochemical compositions and geochronological information with the following remote-sensing datasets: 1) the Lunar Prospector gamma-ray elemental maps (FeO, TiO2, Th) and the SELENE gamma-ray elemental maps (CaO), 2) the surface ages determined from imaging data by using the crater-counting method, and 3) high-spatial-resolution maps of the FeO and TiO2 and spectral-ratio images made from the SELENE multi-band imager data. From these comparisons, the NWA 773 clan is most likely to have originated from the north part of Mare Imbrium inside the Procellarum KREEP Terrane (PKT). Furthermore, the eruption age of surface basalt surrounding the Le Verrier D crater in the north part of Mare Imbrium between 3.0 and 3.3 Ga, and the formation of the Le Verrier D crater, are consistent with the duration of igneous activity and timing of meteoroid impact of the NWA 773 clan. There is a fresh crater with bright ejecta on the edge of the Le Verrier D crater, and it is possibly the young launch crater of this meteorite group.

Regolith Properties in the Chang'E‐5 Landing Region of the Moon: Results From Multi‐Source Remote Sensing Observations

AbstractIn December 2020, China's Chang'E‐5 (CE‐5) spacecraft successfully collected 1.731 kg samples from Oceanus Procellarum on the Moon's nearside, becoming the first lunar sample return mission since Luna 24 in 1976. These samples, collected from one of the youngest mare basalt units within the Procellarum KREEP Terrain, are critical to deciphering several fundamental questions of the Moon. In order to provide geologic context for interpreting the returned samples, we conducted a comprehensive analysis of regolith properties in the landing region using optical, topographic, multispectral, thermal, and radar observations. The CE‐5 landing site is within a flat, young mare basalt unit with intermediate titanium. A ballistic sedimentation model suggests that ∼98% of the surface regolith are local materials. The dielectric permittivity of the regolith is estimated to be 2.96 + i0.03 based on its composition and porosity. Morphologies of small fresh craters identified in high‐resolution optical images show that regolith thickness varies from ∼1.5 to ∼8 m with a median value of ∼5 m, implying a large mean regolith growth rate over the landing region. A comparison between radar image and Lunar Reconnaissance Orbiter Diviner surface rock abundance (RA) map indicates that subsurface rocks play a significant role in producing the observed radar backscatter. Further analysis of the radar echo suggests that subsurface RA is ∼0.47%–0.88% if the effective size is 3 cm, which can explain the shallow sampling depth of the CE‐5 drilling device. All these results provide valuable information for understanding the geological context and properties of the returned regolith samples.

Discrete Element Modelling of Pit Crater Formation on Mars

Pit craters are now recognised as being an important part of the surface morphology and structure of many planetary bodies, and are particularly remarkable on Mars. They are thought to arise from the drainage or collapse of a relatively weak surficial material into an open (or widening) void in a much stronger material below. These craters have a very distinctive expression, often presenting funnel-, cone-, or bowl-shaped geometries. Analogue models of pit crater formation produce pits that typically have steep, nearly conical cross sections, but only show the surface expression of their initiation and evolution. Numerical modelling studies of pit crater formation are limited and have produced some interesting, but nonetheless puzzling, results. Presented here is a high-resolution, 2D discrete element model of weak cover (regolith) collapse into either a static or a widening underlying void. Frictional and frictional-cohesive discrete elements are used to represent a range of probable cover rheologies. Under Martian gravitational conditions, frictional-cohesive and frictional materials both produce cone- and bowl-shaped pit craters. For a given cover thickness, the specific crater shape depends on the amount of underlying void space created for drainage. When the void space is small relative to the cover thickness, craters have bowl-shaped geometries. In contrast, when the void space is large relative to the cover thickness, craters have cone-shaped geometries with essentially planar (nearing the angle of repose) slope profiles. Frictional-cohesive materials exhibit more distinct rims than simple frictional materials and, thus, may reveal some stratigraphic layering on the pit crater walls. In an extreme case, when drainage from the overlying cover is insufficient to fill an underlying void, skylights into the deeper structure are created. This study demonstrated that pit crater walls can exhibit both angle of repose slopes and stable, gentler, collapse slopes. In addition, the simulations highlighted that pit crater depth only provides a very approximate estimate of regolith thickness. Cone-shaped pit craters gave a reasonable estimate (proxy) of regolith thickness, whereas bowl-shaped pit craters provided only a minimum estimate. Finally, it appears that fresh craters with distinct, sharp rims like those seen on Mars are only formed when the regolith had some cohesive strength. Such a weakly cohesive regolith also produced open fissures, cliffs, and faults, and exposed regolith “stratigraphy” in the uppermost part of the crater walls.

Maria Basalts Chronology of the Chang’E-5 Sampling Site

Chang’E-5 is the first lunar sample return mission of China. The spacecraft was landed in the northwest of the Procellarum KREEP Terrane (43.0576°N, 308.0839°E) on 1 December 2020 and returned 1731 g samples from a previously unvisited region. The landing area has been proposed as one of the youngest mare basalt units of the Moon and holds important information of lunar thermal evolution and chronology. However, the absolute model ages estimated in previous studies are quite different, ranging from 2.07 Ga to 1.21 Ga. Such significant difference may be caused by (1) different crater counting areas, (2) different crater diameter ranges, (3) effects of secondary craters, and (4) biases in crater identification. Moreover, the accurate landing site was unknown and the ages were estimated over the Eratosthenian-aged mare unit (Em4) instead. In light of the above unsatisfactory conditions, this study seeks to establish a standard crater size-frequency distribution of the CE-5 landing site. We derived the concentrations of FeO and TiO2 to map out the pure basaltic areas where external ejecta deposits are negligible and thus secondary craters are rare. Based on the geochemistry of basaltic ejecta excavated by fresh craters in the mare unit, the FeO concentration threshold for mapping pure basaltic areas is 17.2 wt.%. The morphologically flat subunits in the pure basaltic areas were selected for crater identification and age dating to exclude the contamination of external ejecta to the best as we could. In the Chang’E-5 sampling site subunit, we detected 313 craters with a diameter greater than 100 m and derived the absolute model age as 1.49−0.084+0.084 Ga. The craters identified in all pure basaltic subunits of Em4 gave the model age of 1.41−0.028+0.027 Ga. As least affected by secondary craters, the crater size-frequency distribution of the sample-collected pure basaltic subunit can provide important constraints for lunar cratering chronology function in combination with isotopic age of returned samples.

Dwarf planet (1) Ceres surface bluing due to high porosity resulting from sublimation

The Dawn mission found that the dominant colour variation on the surface of dwarf planet Ceres is a change of the visible spectral slope, where fresh impact craters are surrounded by blue (negative spectral-sloped) ejecta. The origin of this colour variation is still a mystery. Here we investigate a scenario in which an impact mixes the phyllosilicates present on the surface of Ceres with the water ice just below. In our experiment, Ceres analogue material is suspended in liquid water to create intimately mixed ice particles, which are sublimated under conditions approximating those on Ceres. The sublimation residue has a highly porous, foam-like structure made of phyllosilicates that scattered light in similar blue fashion as the Ceres surface. Our experiment provides a mechanism for the blue colour of fresh craters that can naturally emerge from the Ceres environment.

Thickness of orthopyroxene-rich materials of ejecta deposits from the south pole-Aitken basin

The South Pole-Aitken (SPA) basin is the largest impact structure on the Moon and is believed to have excavated the orthopyroxene (Opx)-rich lower crust and/or upper mantle materials. For the complex craters outside of the SPA transient cavity, the origin of the Opx-rich central peaks is possibly from either the Opx-rich materials of the SPA ejecta deposits or the unexcavated lower crust and/or upper mantle. To estimate the thickness of the Opx-rich materials of the SPA ejecta deposits, this study investigated large complex craters (dozens of kilometers) that have penetrated the Opx-rich materials and exposed deeper mafic-poor crustal material based on spectra extracted from small fresh craters (sub-kilometer scale). The amount of foreign material introduced to these large complex craters by other lunar impact events was estimated to guarantee the least influence on the compositional analysis. The study results suggest that a 56 km-diameter crater at ~640 km northwest of the SPA center is large enough to penetrate the Opx-rich materials of the SPA ejecta deposits, which are thinner than ~4.7 km at this location. This result also indicates that the intense bombardment history of the large craters and basins outside of the SPA transient cavity excavated and redistributed a large amount of crustal material across the basin, possibly resulting in the heterogeneous distribution of mafic-rich and mafic-poor materials on the SPA surface.

Thickness of Lava Flows Within the Northern Smooth Plains on Mercury as Estimated by Partially Buried Craters

AbstractPartially and completely buried impact craters are widely distributed over the northern smooth plains of Mercury. Using imagery data acquired from the MESSENGER mission, we compiled a database of 257 partially buried and 765 completely buried craters on Mercury. The elevation profiles of fresh craters were constructed, and by inputting these into a topographic degradation model, we estimated the lava flow thicknesses around partially buried craters. Along the edges of the northern smooth plains, lava flow thicknesses were inverted to be 23–536 m with a median of 228 m. Lava flow thicknesses on Mercury are twice that on the Moon, possibly due to a denser crust on Mercury that favors the ascent of magmas or to higher production rates of magmas. The topographic diffusivity used for crater degradation on Mercury is 3 times that for lunar craters, which is likely a result of a higher cratering rate on Mercury.

Photometric modelling and VIS-IR albedo maps of Rhea from Cassini-VIMS

ABSTRACT Photometric correction based on the Shkuratov method is applied to derive visible and infrared albedo maps of Rhea from disc-resolved Cassini VIMS data. Differently from I/F images, albedo maps offer an optimal disentanglement of composition and physical properties of the surface from illumination-viewing effects and to study spectral variations occurring at hemispherical and local scales. A similar methodology has been already applied to Dione’s and Tethys’s data sets returned by VIMS. Following the same scheme also for Rhea, spectral albedo is derived at 59 wavelengths between 0.35 and 5.047 µm. Equigonal albedo maps are rendered in cylindrical projection with a 0.5$^\circ \, \times$ 0.5° angular resolution in latitude and longitude, corresponding to a maximum spatial resolution of 6.7 km bin−1. Apart from albedo, 0.35–0.55 and 0.55–0.95 µm spectral slopes and the water ice 1.5–2.0 µm band depth maps are computed from photometric-corrected data with the specific scope to investigate the leading-trailing hemisphere colour-albedo dichotomy and to constrain spectral properties above different morphological units including fresh craters (Inktomi) and bright tectonics features (Wakonda-Avaiki Chasmata).

The Oldest Highlands of Mars May Be Massive Dust Fallout Deposits

The oldest terrains of Mars are cratered landscapes, in which extensive valleys and basins are covered by ubiquitous fluvial plains. One current paradigm maintains that an impact-generated megaregolith underlies these sediments. This megaregolith was likely largely generated during the Early Noachian (~4.1 to ~3.94 Ga) when most Martian impact basins formed. We examined the geologic records of NW Hellas and NW Isidis, which include this epoch’s most extensive circum-basin outcrops. Here, we show that these regions include widespread, wind-eroded landscapes, crater rims eroded down by several hundred meters, pitted plains, and inverted fluvial and crater landforms. These surfaces exhibit few fresh craters, indicating geologically recent wind erosion. The deep erosion, topographic inversions, and an absence of dunes on or near talus across these regions suggest that sediments finer than sand compose most of these highland materials. We propose that basin-impact-generated hurricane-force winds created sediment-laden atmospheric conditions, and that muddy rains rapidly settled suspended sediments to construct extensive Early Noachian highlands. The implied high abundance of fine-grained sediments before these impacts suggests large-scale glacial silt production and supports the previously proposed Noachian “icy highlands” hypothesis. We suggest that subglacial meltwater interactions with the sedimentary highlands could have promoted habitability, particularly in clay strata.

Compositional mapping and the evolutionary history of Mare Tranquillitatis

This study signifies the compositional variability of Mare Tranquillitatis basalt and the Irregular Mare patches (IMPs) – the youngest volcanic feature on the Moon, using hyperspectral data from Moon Mineralogy Mapper (M3) for the first time. Along with composition, the topographic and morphological mapping has been done to understand the possible evolutionary history of this mare. Total 22 spectral units has been identified based on Integrated Band Depth (IBD) parameter technique. Number of reflectance spectra were collected from the fresh craters of each spectral unit and quantitative mineralogical abundances estimated using band parameters like band centre, band strength and band area. The result shows abundances of olivine and pyroxene mixture bearing material in the mare basalt. The compositional map shows smaller spectral units in the western-low lying half and larger spatial distribution of spectral unit in the eastern half depicts probable large-scale volcanic eruption in the eastern part that may have flowed to longer distances from the Cauchy shield to the central mare. This study marks 61 new domes in the Cauchy shield area and also depicts possible formation and evolutionary history of the Mare Tranquillitatis.

The Tsiolkovskiy crater landslide, the moon: An LROC view

Evidence suggests that the lobate flow feature that extends ~72 km outward from the western rim of Tsiolkovskiy crater is a long runout landslide. This landslide exhibits three (possibly four) morphologically different parts, likely caused by local conditions. All of these, plus the ejecta of Tsiolkovskiy crater, and its mare fill are approximately of the same crater model age, i.e., ~3.55 ± 0.1 Ga. The enormous size of this landslide is unique on the Moon and is a result of a combination of several geometric factors (e.g., its location relative to Fermi crater), and that Tsiolkovskiy crater was an oblique impact that produced an ejecta forbidden zone on its western side (Schultz, 1976). The landslide formed in this ejecta free zone as the rim of Tsiolkovskiy collapsed and its debris flowed across the relatively smooth, flat floor of Fermi crater. In this location, it could be easily identified as a landslide and not ejecta. Its mobility and coefficient of friction are similar to landslides in Valles Marineris on Mars, but less than wet or even dry terrestrial natural flows. This suggests that the Mars landslides may have been emplaced dry. The high density of small craters on the landslide is likely an illusion caused by the effects of age related differences in regolith thickness on crater morphology, and the presence of the abundant young, circular secondary craters produce by debris ejected from distant fresh craters.

Global mapping of lunar refractory elements: multivariate regression vs. machine learning

Context.The quantitative estimation of elemental concentrations at the spatial resolution of hyperspectral near-infrared (NIR) images of the lunar surface is an important tool for understanding the processes relevant for the origin and evolution of the Moon.Aims.We aim to map the abundances of the elements Fe, Ca, and Mg at a typical accuracy of about 1 wt.% at the spatial resolution of the Moon Mineralogy Mapper (M3) instrument on-board Chandrayaan-1 lunar mission.Methods.The NIR reflectance of the lunar regolith is an integrated response to the presence of refractory elements and soil alteration processes. Our approach was to define a combination of spectral parameters that are robust with respect to the effects of soil maturity. We calibrated the spectral parameters with respect to elemental abundances measured by the Lunar Prospector Gamma Ray Spectrometer (LP GRS) and the Kaguya GRS (KGRS). For this purpose, we compared a classical multivariate linear regression (MLR) approach and the machine learning based support vector regression (SVR) technique applied to M3global observations.Results.The M3-based global elemental maps are consistent in distribution and range with the LP GRS and KGRS elemental maps and do not show artifacts in immature areas such as small fresh craters. The results derived using MLR and SVR are compared to sample-based ground truth data of the Apollo and Luna sample-return sites, where the root-mean-square deviations obtained by the two regression models are similar.Conclusions.The main advantage of the proposed new algorithm is its ability to minimize artifacts due to space-weathering effects. The elemental maps of Mg and Ca provide additional information and reveal structures not always visible in the Fe map. The global elemental abundance maps derived for the fully calibrated M3observations might thus serve as important tools to investigate the lunar geology and evolution.

Reflectance spectra of seven lunar swirls examined by statistical methods: A space weathering study

Higher magnetic field in lunar swirls is believed to deflect majority of incoming charged particles away from the lunar-swirl surfaces. As a result, space weathering inside and outside swirls should be different. We wanted to evaluate these differences, therefore we have examined seven swirl areas on the Moon (four mare and three highland swirls). We applied the Modified Gaussian Model to statistical sets of the Moon Mineralogy Mapper spectra. Using Principal Component Analysis (PCA), we were able to distinguish the old (weathered) material from both the fresh crater and swirl materials. The swirls did not follow the same behavior as the fresh material, nor were they fully separable. Additionally, we could distinguish between the mare and highland swirls (mare/highland dichotomy) based on the PCA and histogram plots of the albedo and strength of the 1000-nm absorption band. The mare/highland dichotomy can partially be caused by different FeO content in maria and highlands, which points to the existence of a threshold value that changes the spectral evolution due to space weathering. Slope behavior seemed to be dependent on whether the swirl was on the near- or far-side of the Moon, likely due to shielding of lunar nearside by Earth's magnetotail. Our results thus favor the solar wind stand-off hypothesis in combination with the fine dust transport hypothesis and point to the fact that micrometeoroid impacts generally do not reproduce the same weathering trends as all the space weathering effects together.

A New Method for Simulation of Lunar Microwave Brightness Temperatures and Evaluation of Chang'E‐2 MRM Data Using Thermal Constraints From Diviner

AbstractWe used the bolometric brightness temperatures (TBol) derived from the Lunar Reconnaissance Orbiters Diviner Lunar Radiometer (Diviner) as an upper boundary condition in our thermal model. We then calculated temperature profiles at any local time based on our improved thermal model at low to middle latitudes (70° N/S). Based on the temperature profiles, we modeled the midnight brightness temperature at 19.35 (TB19) and 37 GHz (TB37). Comparing to the Chang'E‐1 and Chang'E‐2 (CE‐1/2) observations, we found that CE‐1 showed a better data quality than that of CE‐2, especially for the TB37 data. Assuming that the issue with the CE‐2 data is caused by heat contamination of the cold‐reference antennas, we performed an empirical normalization of the CE‐2 microwave radiometer data near midnight following the approach of Hu et al. (2017). The results show that TB difference (modeled values minus modified TB) for 19.35 GHz is less than 3.40 K for ∼80% of the pixels. At 37 GHz, ∼67% of the pixels have TB difference less than 2.88 K. Additionally, we identified some areas of low microwave temperature in our modified TB maps. These low‐TB features can be characterized by two types: (1) low TB spots at fresh craters with high rock abundance and bright rays and (2) high‐Ti lunar mare surfaces with a low content of rock fragments. Investigating these low‐TB regions with the modified TB data can reveal more information about subsurface thermal regime and properties and help us better understand the evolution of regolith on the Moon.

Mineralogy of northern nearside mare basalts

The mineralogy of mare basalts reflects the chemical composition of the magma source, as well as the physical and chemical environment of the rocks’ formation. This is significant for understanding the thermal evolution of the Moon. In this study, the spatial distribution of mineralogy on the lunar northern nearside basalts was mapped using the Moon Mineralogy Mapper (M3) data. The study area, which is an elongated mare, Mare Frigoris and northern Mare Imbrium, was mapped and characterized into 27 units based on multi-source data, including spectrum, terrain and element abundance. We extracted 177 M3 spectra from fresh craters. Spectral parameters such as absorption center and band area ratio (BAR) were obtained through data processing. The variation of mafic minerals in this region was acquired by analyzing these parameters. The basaltic units in eastern Mare Frigoris, which are older, have been found to be dominated by clinopyroxene with lower CaO compared to the returned lunar samples; this is similar to older basaltic units in Mare Imbrium. The basaltic units of western Mare Frigoris and Sinus Roris which are younger have been found to be rich in olivine. The late-stage basalts in Oceanus Procellarum and Mare Imbrium show the same feature. These widespread olivine-rich basalts suggest uniqueness in the evolution of the Moon. Geographically speaking, Mare Frigoris is an individual mare, but the magma source region has connections with surrounding maria in consideration of mineral differences between western and eastern Frigoris, as well as mineral similarities with maria at the same location.