Gravity Recovery And Interior Laboratory Research Articles

Boundaries identification of geological structure in lunar Oceanus Procellarum region using full gravity gradient tensor methodology

Boundary recognition visually delineates the horizontal extent of subsurface anomalies, providing a foundational basis for interpreting gravity data. Compared to gravity observations, gravity gradient data offers the benefits of multiple components and the enhancement of shortwave information in graphical representations. In our study, we investigated the delineation of geological structure boundaries in the lunar Oceanus Procellarum region using gravity gradient techniques. First, based on the observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission, we obtained high-precision synthetic full tensor values of the gravity gradient as our primary research data. Moreover, to reduce curvature errors during large-scale terrain forward modeling, we applied the spherical prism of tesseroid to eliminate the effects of near-surface topography. Grounded on the Bouguer anomalies of gravity gradient, four distinct boundary recognition methods have been employed to explore the geological structure of the lunar Oceanus Procellarum region. It includes the Theta map method, the directional Theta map method, the combination of total horizontal derivative and the modulus of full tensor gravity gradient, and the improved edge detection method based on the Theta map method.The common feature of these methods is the utilization of the multi-component data combination from gravity gradient tensors, which can enhance the accuracy of edge detection. From the investigation results presented in the paper, we have found the following: 1) The improved edge detection method, based on the Theta map principle, enables better identification of the center of subsurface anomaly bodies during boundary recognition, utilizing a consistent single color in graphic displays. 2) According to the results of boundary recognition, numerous strip anomalies exist in the Oceanus Procellarum area that show less correlation with topographic relief. One possible explanation for these graphical anomalies of gravity gradient is that they serve as channels for the upwelling of mantle material during lunar evolution.

Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters

AbstractThe present‐day distribution of mare basalts on the Moon is an important constraint on the timing, duration, and flux of volcanism on the Moon. In this work, we find the global distribution of visible mares and cryptomares using the effective density (ρeff) of the Moon, which is sensitive to the vertical density distribution of the crust. We compute ρeff using the Gravity Recovery and Interior Laboratory (GRAIL) data and the Lunar Orbiter Laser Altimeter (LOLA) topography data. We apply this ρeff approach to the search of cryptomare for the first time, and we use a higher resolution grid and larger search area to constrain visible mare thicknesses compared to previous work. We use a Bayesian approach to find the distribution of mare thicknesses and density gradients of the underlying crust that is consistent with the localized ρeff. Assuming a bulk density of the mare basalts of 3,460 kg/m3, we find a mean visible mare thickness of km which is consistent with previous work. We find a candidate cryptomare volume of km3 representing more than half of the total mare volume on Moon. This volume is consistent with the higher end of the previously proposed values. Finally, we search for dark halo craters (DHC) globally to obtain geologic evidence of cryptomares and find 258 craters. Our results are consistent with extensive ancient volcanism, which explains the previously identified discrepancy between the early high volcanic flux predicted by thermal models of the Moon and the dearth of ancient volcanic deposits currently exposed.

Scaliger Crater Region on the Moon: Implications for the Australe North Basin and magmatism in the region

Australe North (35.5°S, 96°E) is a pre-Nectarian impact basin north of Mare Australe, first identified using the GRAIL data. It does not show clear topographic signatures typical of any large impact structure on the Moon. However, results from GRAIL (Gravity Recovery and Interior Laboratory) mission suggested the presence of a ∼ 880 km wide basin whose boundary does not coincide with the earlier identified Australe Basin. In this study, we investigate the Scaliger Crater region to understand the controls that the proposed Australe North Basin played on the local geology in the region. The location of the Scaliger Crater at the intersection of the rims of two pre-Nectarian Basins, Milne and the proposed Australe North provides a unique geological setting to reconstruct the region's geological history. We provide geological evidence substantiating the existence of the rim of the Australe North Basin, as has been proposed using gravity data. Based upon the spectral signatures and morphometry, we suggest the presence of a mafic pluton and/or lower crustal/mantle rocks in the region and provide constraints on its emplacement timescale. For the first time, Late-stage volcanism has been reported inside the Bowditch Crater and Lacus Solitudinis, emplaced at ∼1.7 Ga and ∼ 2.3 Ga, respectively, suggesting prolonged volcanism at the eastern lunar nearside-farside boundary inside an obscured pre-Nectarian basin.

GRAIL gravity gradients evidence for a potential lava tube at Marius Hills on the moon

Lunar lava tubes are underground channels formed by volcanic eruptions and lava flow during the Moon's volcanic period. Intact lunar lava tubes have the potential to serve as secure shelters for humans and facilities, as they provide a safe and pristine environment with a constant temperature. In this study, the lunar gravity field model derived from NASA's GRAIL mission data is analyzed for detecting of an empty lava tube in the Marius Hills region. Compared to the classical Hessian matrix, the gravitational gradient method used in this study is capable of detecting anomaly signals both in the north-south and east-west directions. Using this method, we detect a north-south anomaly signal in the Marius Hills region, located at 57.5°W and 14.3°N, indicating a negative density anomaly near the known lunar sinuous rilles and the Marius Hills Hole skylight. This suggests the presence of a potential lava tube, which is confirmed by the results of the forward method and lunar radar echo data. The extent of the lava tube is estimated with the forward method to be ∼60 km in length, ∼9 km in width, ∼605 m in depth, and ∼55 m in height. Furthermore, the gradient features indicate that the skylight located on the eastern side of the lava tube could serve as an entry to the main part of the lava tube.

Recovering crustal thickness of the Moon from an extended Vening Meinesz-Moritz inversion

Crustal thickness (Moho surface relief) is closely related to geotectonic, which is the predominant research topic in lunar geophysics. For lunar crustal depth inversion, to address the problem of downward continuation in traditional spectral domain methodologies, we adopt a solution from gravity disturbance (geophysical gravity anomaly). It is available to investigate crustal thickness at arbitrary surface outside the geoid. Using gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission and terrain information recovered from the Lunar Orbiter Laser Altimeter (LOLA) mission, global crustal depth of the Moon is recovered by the extended Vening Meinesz-Moritz method. The first application result of this technique on the Moon is validated by four types of released models in the form of spherical harmonic expansion with 310°. Moreover, from the statistics, our lunar Moho solution demonstrates that the average crustal thickness is approximately 41.5 km. The maximum value of 83.1 km and the minimum value of 0.8 km are located in the area of high mountains and Moscoviense mascon, respectively.

Using Lunar Granulites to Constrain Re‐Equilibration Timescales of Contact Thermal Metamorphism on the Moon

AbstractRocks of the lunar granulite suite are the product of high‐temperature metamorphism within the Moon's crust. However, to date, their formation conditions have few constraints. Here, we combine Ti‐in‐pyroxene element diffusion modeling and two‐pyroxene thermometry with thermal modeling of the lunar crust in order to assess potential heat sources that could generate granulite metamorphism within the lunar highland crust. For the samples investigated in this study, the pyroxene crystals experienced peak metamorphic temperatures between ∼1,027 and 1,091°C over timescales ranging from ∼153 years to ∼15.1 Kyrs. To best satisfy these temperature and timescale constraints, hot (∼2,300°C) impact melt sheets with thickness ranging from 350 m to 3.35 km—equating to impact crater diameters between ∼60 and 280 km—have the potential to heat the underlying anorthositic crust. Deep (>20 km) igneous bodies, such as the large (>10 km thick) sills observed by the GRAIL mission near the base of the lunar crust, also have the potential to generate the required peak metamorphic temperatures; however, the thermal equilibration timescales in this scenario are modeled to be much larger (>100 Kyrs) than was witnessed by the granulites investigated. Our modeling highlights that while lunar granulites are only a minor component within the Apollo and meteorite collection, they are likely an important and ubiquitous lithology within the lunar highland crust.

Parameters of the best fitting lunar ellipsoid based on GRAIL’s selenoid model

Since the Moon is less flattened than the Earth, most lunar GIS applications use a spherical datum. However, with the renaissance of lunar missions, it seems worthwhile to define an ellipsoid of revolution that better fits the selenoid. The main long-term benefit of this might be to make the lunar adaptation of methods already implemented in terrestrial GNSS and gravimetry easier and somewhat more accurate. In our work, we used the GRGM 1200A Lunar Geoid (Goossens et al. in A global degree and order 1200 model of the lunar gravity field using GRAIL mission data. In: Lunar and planetary science conference, Houston, TX, #1484, 2016; Lemoine et al. in Geophys Res Lett 41:3382–3389. http://dx.doi.org/10.1002/2014GL060027, 2014), a 660th degree and order potential surface, developed in the frame of the GRAIL project. Samples were taken from the potential surface along a mesh that represents equal area pieces of the surface, using a Fibonacci sphere. We tried Fibonacci spheres with several numbers of points and also separately examined the effect of rotating the network for a given number of points on the estimated parameters. We estimated the best-fitting rotation ellipsoid’s semi-major axis and flatness data by minimizing the selenoid undulation values at the network points, which were obtained for a = 1,737,576.6 m and f = 0.000305. This parameter pair is already obtained for a 10,000 point grid, while the case of reducing the points of the mesh to 3000 does not cause a deviation in the axis data of more than 10 cm. As expected, the absolute value of the selenoid undulations have decreased compared to the values taken with respect to the spherical basal surface, but significant extreme values still remained as well.

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

Precise mapping of the Moon with the Clementine Ultraviolet/Visible Camera

The Ultraviolet/Visible (UVVIS) camera on the Clementine spacecraft provided a global, multispectral view of the Moon. Scientists commonly use individual observations and derived products (optical maturity, mineral abundance, etc.) over 25 years later, addressing questions concerning the composition and relative age of surface features. However, since the mission concluded, our knowledge of lunar topography and the locations of features on the surface have improved with results from the Lunar Reconnaissance Orbiter (LRO) and Gravity Recovery and Interior Laboratory (GRAIL) missions. Before this work, cross-mission comparisons were impaired by spatial offsets between the derived products, which are as large as 2.5 km in some regions. Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) images, acquired under similar lighting conditions, were used as a cartographic reference. We used image-based feature-matching algorithms to automatically derive control points to improve the positional accuracy of each UVVIS observation with the LROC WAC basemap. From ground control points, we calculate a precise camera model (focal length, optical distortion, etc.) for the UVVIS camera and update the pointing for each UVVIS image. Using the updated geometric information and projecting the UVVIS image to the LOLA global shape model, we map the five-band multispectral UVVIS mosaic, the optical maturity map, and FeO and TiO2 abundance maps. We also analyze pitch observations of the polar regions to investigate the influence phase angle has on the derived optical maturity. The new images are registered to the GRAIL-based LRO geodetic framework within a WAC pixel (Ground Sampling Distance ∼75 m; average UVVIS sigma0 = 0.084), creating a foundational geospatial data product that does not require any manual interpretation or nonlinear warping of map products to align with the current lunar reference frame.

Spherical Planting Inversion of GRAIL Data

In large-scale potential field data inversion, constructing the kernel matrix is a time-consuming problem with large memory requirements. Therefore, a spherical planting inversion of Gravity Recovery and Interior Laboratory (GRAIL) data is proposed using the L1-norm in conjunction with tesseroids. Spherical planting inversion, however, is strongly dependent on the correct seeds’ density contrast, location, and number; otherwise, it can cause mutual intrusion of anomalous sources produced by different seeds. Hence, a weighting function was introduced to limit the influence area of the seeds for yielding robust solutions; moreover, it is challenging to set customized parameters for each seed, especially for the large number of seeds used or complex gravity anomalies data. Hence, we employed the “shape-of-anomaly” data-misfit function in conjunction with a new seed weighting function to improve the spherical planting inversion. The proposed seed weighting function is constructed based on the covariance matrix for given gravity data and can avoid manually setting customized parameters for each seed. The results of synthetic tests and field data show that spherical planting inversion requires less computer memory than traditional inversion. Furthermore, the proposed seed weighting function can effectively limit the seed influence area. The result of spherical planting inversion indicates that the crustal thickness of Mare Crisium is about 0 km because the Crisium impact may have removed all crust from parts of the basin.

Constraints on the lunar core viscosity from tidal deformation

We use the tidal deformations of the Moon induced by the Earth and the Sun as a tool for studying the inner structure of our satellite. Based on measurements of the degree-two tidal Love numbers k2 and h2 and dissipation coefficients from the GRAIL mission, Lunar Laser Ranging and Laser Altimetry on board of the LRO spacecraft, we perform Monte Carlo samplings for 120,000 possible combinations of thicknesses and viscosities for two classes of the lunar models. The first one includes a uniform core, a low viscosity zone (LVZ) at the core–mantle boundary, a mantle and a crust. The second one has an additional inner core. All models are consistent with the lunar total mass as well as its moment of inertia. By comparing predicted and observed parameters for the tidal deformations we find that the existence of an inner core cannot be ruled out. Furthermore, by deducing temperature profiles for the LVZ and an Earth-like mantle, we obtain stringent constraints on the radius (500 ± 1) km, viscosity, (4.5±0.8)×1016 Pa s and the density (3400 ± 10) kg/m3 of the LVZ. We also infer the first estimation for the outer core viscosity, (2.07 ± 1.03) × 1017 Pa s, for two different possible structures: a Moon with a 70 km thick outer core and large inner core (290 km radius with a density of 6000 kg/m3), and a Moon with a thicker outer core (169 km thick) but a denser and smaller inner core (219 km radius for 8000 kg/m3).

Lunar ephemeris at sub microarcsecond accuracy (LESMA) leads to sub-millimeter positional accuracy of the moon

The most accurate LLR (lunar laser ranging) initiative, named APOLLO (apache point observatory lunar laser-ranging operation) demonstrated millimeter-range positional accuracy in 2009, thus improving LLR by one order-of-magnitude. Since, LLR is a foundational technique in studying gravity, Murphy (principal investigator of APOLLO) stated in 2009, that with this millimeter-range accuracy, the simulation model has been found to be the limiting-factor in extracting the theoretical science results, and hence, we should: (1) develop the science case and expand our ability to model LLR for a new regime of high precision, (2) develop the theoretical tools for honing the science case for submillimeter LLR, and (3) explore which model/code is worth putting our efforts into. (4) Since millimeter-quality data are a recent development, the model effort lags. (5) Finally, we will code-in new physics so that we may simulate sensitivities. In connection with simulation model/code, Murphy stated in 2013, that among the four available LLR simulation models: JPL (jet propulsion laboratory), CfA (the Harvard-Smithsonian center for astrophysics), LU (leibniz University, Hannover, Germany), and IMCCE (Institut de Mecanique celeste et de calcul des Ephemerides, France), the JPL model currently produces weighted RMS (root-mean-square) residuals at ∼18 mm, which is about half of the other models; so, clearly a gap exists from millimeter ranging-precision of APOLLO. Hence, the CfA, LU, and IMCCE are engaged, since 2013, in a stepwise comparative streamlining effort to identify the model-differences, errors, and shortcomings. All the four available LLR simulation models can be classified as GR (general relativity)-astronomers model; they are basically similar. Professor Douglas Currie of the University of Maryland, College Park, NASA Lunar Science Institute, stated in a Conference presentation, in 2012, that Ground stations, that is, the lunar observatories, have improved by a factor of 200, but the agreement between observations and fitted theory has plateaued at ∼2 cm over the past two decades. However, no substantial progress on improving the fit has been reported in the published literature, till date. Based on about a quarter-century of experience in doing high-precision numerical simulation of celestial orbits, the authors have developed LESMA (lunar Ephemeris at sub Microarcsecond accuracy) utilizing the methodology of evolved general relativity (EGR) that has incorporated the following two concepts: (1) Relativistic time for integration and (2) methodology of conservation of magnitude of the angular momentum, MΦ , for Φ-rotation (in addition to the θ-rotation that leads to the rosetting ellipse) of the orbital plane. Incorporation of the two above-mentioned concepts has led to three orders-of-magnitude accuracy-improvement of the computed (1) precession (compared to JPL's DE405) of Lunar orbit, as verified using three independent methods and (2) radial position (compared to JPL's DE430/431) of the Moon. LESMA will enable scientists to make efficient use of research-funds from NASA, etc., for production of new science results from APOLLO. LESMA will also be useful for getting better science results (than Folkner reported {in 2014} submeter accurate Position of the Moon) from the GRAIL (gravity recovery and Interior laboratory) mission (costing 500 million USD), by spending a little more for revisiting the computations, utilizing LESMA data.

Widespread impact-generated porosity in early planetary crusts

NASA’s Gravity Recovery and Interior Laboratory (GRAIL) spacecraft revealed the crust of the Moon is highly porous, with ~4% porosity at 20 km deep. The deep lying porosity discovered by GRAIL has been difficult to explain, with most current models only able to explain high porosity near the lunar surface (first few kilometers) or inside complex craters. Using hydrocode routines we simulated fracturing and generation of porosity by large impacts in lunar, martian, and Earth crust. Our simulations indicate impacts that produce 100–1000 km scale basins alone are capable of producing all observed porosity within the lunar crust. Simulations under the higher surface gravity of Mars and Earth suggest basin forming impacts can be a primary source of porosity and fracturing of ancient planetary crusts. Thus, we show that impacts could have supported widespread crustal fluid circulation, with important implications for subsurface habitable environments on early Earth and Mars.

Plausible Detection of Feasible Cave Networks Beneath Impact Melt Pits on the Moon Using the Grail Mission

In the future, when humans build their bases on terrestrial planets and their moons, caves will be the safest place for inhabitation. Large holes, believed to be cave entrances, have been discovered on the Moon, along with small features called “impact melt pits.” In the Gravity Recovery and Interior Laboratory (GRAIL) gravity model, which is expressed in spherical harmonics (SH), it is difficult to express the gravity anomaly created by a small empty space below the surface. Nevertheless, we propose that a cave network, akin to an anthill, exists under the impact melt pits discovered on the Moon. This is because we think it is natural to apply a network created by Earth’s small caves to the Moon. We obtained accurate Bouguer gravity measurements by calculating regional crustal density using localized admittance of the study area and detected weak gravity (mass deficit) information. By increasing the degrees and order of SH at regular intervals, we estimated the change in gravity at a specific position at high degrees and order, thereby extracting shallow depth information. To validate our method, we compared our results with those of existing studies that analyzed the previously known Marius Hills Hole (MHH) area. The analysis of seven regions in our study area revealed a mass deficit in some impact melt pits in four lunar regions (Copernicus, King, Stevinus, and Tycho). We propose that there is a cave network in this region, indicated by the gravitation reduction in the impact melt pits region. Our results can be useful for the selection of landing sites for future in situ explorations of lunar caves.

Potential Applications of CE-2 Microwave Radiometer Data in Understanding Basaltic Volcanism in Heavily Ejecta-Contaminated Mare Frigoris

Mare Frigoris is the fifth largest and almost northernmost mare located on the near side of the Moon. Mare Frigoris has an elongated shape, with a length of approximately 1500 km and a width of approximately 200 km, which makes it susceptible to becoming contaminated by the impact ejecta from the nearby highlands. Comparatively speaking, microwave radiometer (MRM) data have good penetration capabilities. Therefore, the MRM data from Chang’e-2 satellite were employed to study the volumetric thermal emission features of basaltic deposits in Mare Frigoris. Combining the MRM data with the basaltic units with FeO and TiO2 abundances identified using the small crater rim and ejecta probing (SCREP) methodology and with the gravity from Gravity Recovery and Interior Laboratory (GRAIL), the four potential conclusions that were obtained are as follows: (1) The MRM data are strongly related to the (FeO + TiO2) abundance of pristine basalts and are less influenced by ejecta contamination; (2) in every quadrant of Mare Frigoris, the (FeO + TiO2) abundance of the basalt decreases with an increase in age; (3) at least in Mare Frigoris, the main influencing factor regarding the brightness temperature remains the (FeO + TiO2) abundance of surface deposits; (4) a warm microwave anomaly was revealed in the western-central and eastern-central areas of Mare Frigoris which has a strong relationship with the positive Bouguer gravity anomaly derived from GRAIL data in terms of spatial distribution. The results are significant in the context of improving our understanding the basaltic igneous rock and thermal evolution of the Moon using MRM data.

Probing the source of ancient linear gravity anomalies on the Moon

A large set of linear to arcuate gravity anomalies which are not associated with any surface expressions was revealed by lunar gravity data from the GRAIL mission. The anomalies can be categorized into two types: a set of large anomalies that border the Procellarum KREEP terrane (PKT) region, and the linear gravity anomalies (LGAs) that are scattered throughout the lunar highlands. In this study, we use band-passed gravity gradient maps and localized power spectral analyses to characterize the nature of and the differences between the two types of anomalies. The results show that the PKT border anomalies are primarily long wavelength features whose power spectra are not clearly distinguishable from the background spectrum of the surrounding region, while the linear gravity anomalies are short wavelength features whose power spectra in at least one case rises significantly above the background spectrum over a wide range of degrees. This difference in gravitational signature suggests a fundamental difference in the nature of the sources of the two types of anomalies. We then used a Markov chain Monte Carlo model to test different interpretations for the most prominent LGA by comparing the observed power spectrum to modeled spectra for elliptical, triangular, and T-shaped intrusive geometries. We find multiple geometries are able to fit the power spectrum of the LGA equally well. Analogs of comparable scale to the LGAs originate from extensional stress regimes, supporting an inferred period of global expansion in the early Moon, though the cause of that expansion remains uncertain. If the depth extent of the intrusions were governed by neutral buoyancy, we find that intrusions on the nearside similar to those on the farside would have been eruptive and may have contributed to the earliest mare volcanism. The total volume of the intrusions is ~20% of the mare volume, revealing a lower magma production rate on the farside than on the nearside.

Combined use of band shape algorithm, linear spectral un-mixing on Clementine & Moon Mineralogy Mapper data for identifying the imprints of magmatic differentiation – A study around Aristarchus Plateau

In this study, we have implemented a band shape algorithm (BSA) to identify the surface distribution of different minerals on parts of the Aristarchus Plateau using selected bands of Clementine and hyperspectral Moon Mineralogy Mapper (M3) data. BSA mineral maps derived using spectral bands of Clementine and M3 sensors could determine broadly similar surface distribution of minerals in the study area. Here we show that M3 based BSA mineral map could detect additional mineralogical details in selected places, especially around Vallis Schroteri, Aristarchus etc. areas. Therefore, we implemented linear spectral un-mixing (LSU) method on hyperspectral bands of M3 data using the reference spectra of Reflectance Experiment Laboratory (RELAB) to estimate the relative abundance of different minerals in above-mentioned areas. Based on the relative abundance of minerals in the LSU map, we could infer the presence of different rocks such as dunite/troctolite, norite, harzburgite, olivine-pyroxenite in those sites of the study area. The relative abundance of each mineral in a particular place was used as the basis for delineating specific rock in that place of the study area. These mineralogically diverse rocks with distinct proportions of mafic mineral and plagioclase content are exposed along a lunar structure that has been delineated using Gravity Recovery and Interior Laboratory (GRAIL) data. We hypothesize that some of these rocks might have formed by a magmatic differentiation process triggered by the structure by separating magma from the crystallized rocks and allowing the magma to compositionally evolve to produce different rocks under the influence of syn-magmatic structural activity.

Point Mascon Global Lunar Gravity Models

Lunar gravitational models are generated using sets of point mass potentials (mascons) fit to the GRGM1200A representation derived from GRAIL mission data. Point mass ensembles allow for simple modeling of a gravity potential and its partial derivatives. The new point mascon models are intended to be low- to medium-resolution replacements for spherical harmonics models in mission planning applications or onboard flight software. The design space of how to parameterize the mascons is explored. The chosen configuration uses equally weighted point mass potentials and requires the successive solutions to thousands of nonlinear optimization problems that adjust the mascon locations. A database of models that vary in resolution is generated and disseminated as supplementary material, with the highest-fidelity model demonstrating equivalent accuracy and memory footprint to a spherical harmonics truncation. Gravitational acceleration and gravity gradient evaluation runtimes are roughly two to eight times faster for the new mascon models when compared with spherical harmonics models with equivalent error, depending on the model fidelity and the computational environment.

Lunar Megaregolith Structure Revealed by GRAIL Gravity Data.

We use gravity data from NASA's GRAIL mission to characterize the porosity structure of the upper lunar crust. We analyze the gravitational anomalies produced by the porosity of craters with diameters D between 10 and 30 km. We find that the gravitational signature of craters changes significantly at D=16.4−0.6+1.4 km, which is related to a discrete change in porosity at a depth ∼3–5 km. We propose that this discrete porosity change reveals the location of the boundary between large‐scale basin ejecta and the deeper less porous portion of the megaregolith, known as the structurally disturbed crust. The ejecta thickness can help constrain models of material transport and mixing on the Moon and, because the ejecta layer acts as an insulating blanket, models of heat flow and magmatism.

Patched Local Lunar Gravity Solutions Using GRAIL Data.

We present a method to determine local gravity fields for the Moon using Gravity Recovery and Interior Laboratory (GRAIL) data. We express gravity as gridded gravity anomalies on a sphere, and we estimate adjustments to a background global start model expressed in spherical harmonics. We processed GRAIL Ka‐band range‐rate data with a short‐arc approach, using only data over the area of interest. We determine our gravity solutions using neighbor smoothing constraints. We divided the entire Moon into 12 regions and 2 polar caps, with a resolution of 0.15°×0.15° (which is equivalent to degree and order 1199 in spherical harmonics), and determined the optimal smoothing parameter for each area by comparing localized correlations between gravity and topography for each solution set. Our selected areas share nodes with surrounding areas and they are overlapping. To mitigate boundary effects, we patch the solutions together by symmetrically omitting the boundary parts of overlapping solutions. Our new solution has been iterated, and it has improved correlations with topography when compared to a fully iterated global model. Our method requires fewer resources, and can easily handle regionally varying resolution or constraints. The smooth model describes small‐scale features clearly, and can be used in local studies of the structure of the lunar crust.