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The morphology of fresh lunar craters contains information about the physical properties of both the impactors and the lunar surface, and is therefore crucial to our knowledge of the impact cratering process. Spectral analysis is a powerful tool to study crater morphology, as it can reveal the topographic variation on different scales. In this study, we calculate the power spectral densities of the radial distance and elevation of the rim crest, floor, and rim flank outlines of fresh lunar craters. The resulting power spectral density can be decomposed into an average component and a natural variability component. For the average component, we derive the classic morphometric parameter‐crater diameter relations that are consistent with previous studies. For the natural variability component, we find that in general the spectral power increases with wavelength, which can be fitted by a piecewise function with four breakpoints. Among the four breakpoints, the power of the third breakpoint (i.e., the degree‐2 power) is of particular interest, as it determines the ellipticity of the outline. The power of the third breakpoint is found to have a diameter dependence with a peak at 20 km, which indicates that transitional craters are more elliptical than simple and complex craters. The diameter dependence of the power spectral density enables us to generate the synthetic outlines of a crater of a particular size, which can be used to develop a preliminary 3‐dimensional shape model for fresh lunar craters that is useful for improving Monte Carlo modeling of cratered surfaces on the Moon. Plain Language Summary: The shape of young impact craters on the Moon can tell us information about the impactor and the lunar surface, which further helps us to better understand how craters are formed on a planetary body. Unlike previous studies that investigated the overall shape of the crater in the spatial domain, in this study we look into more detailed variations of the crater shape in the frequency domain. For our selected young lunar craters, we first extract their rim crest, floor, and rim flank outlines, which are the three key components that make up a lunar crater. For the obtained outlines, we then determine on average how wide and deep they are, and also analyze how variable they are on smaller scales. The correlation between the crater shape and the crater size is investigated next, and we find that the outlines are more elongated for craters with diameters around 20 km. By reconstructing the variability of the outlines, we are able to develop a preliminary, synthetic 3‐dimensional shape model for young lunar craters, which can be used to model the evolution of the lunar surface. Key Points: The rim crest, floor, and rim flank outlines of fresh lunar craters are vectorized in the elevation dataThe radial distance and elevation of the outlines are linked to surface topography via their power spectral densitiesThe degree‐2 power points to the ellipticity of the outline, and transitional craters are more elliptical than simple and complex craters [ABSTRACT FROM AUTHOR]

We investigated the age and origin of 41 light plain deposits around the lunar south pole, using LRO data sets and successfully dated 22 of them using crater size‐frequency distribution measurements. We find that deposits related to Schrödinger basin are ∼3.8 Ga old, including deposits on the Amundsen crater floor, which we interpret as Schrödinger basin ejecta. Six study areas date to ∼3.7 Ga, which reflect an additional large‐scale or basin impact event post‐Schrödinger ‐ possibly Orientale. An additional two areas with younger isolated ages likely represent local impact sources. Finally, smooth, light plains‐like, ejecta deposits around Shackleton crater were found to be Eratosthenian in age. Our findings show that light plain deposits originate from a combination of both basin and local ejecta materials. Thus, samples collected in the region will exhibit a diverse range of basin materials and ages representative of the ejecta from multiple impact events. Plain Language Summary: The southern polar region of the Moon is the focus of future human exploration missions due to the presence of essential resources like water and the possible capability to sustain a prolonged human presence on the Moon. Thus, it is vital to understand the geologic context of the region for a correct interpretation of returned samples. In this paper, we used the Lunar Reconnaissance Orbiter data sets to investigate the age and origin of 41 smooth deposits around the lunar south pole. Of these, 22 could be accurately dated using the size‐frequency distribution of craters, and we found groups of smooth deposits of similar ages that can be related to a one or more source impacts. Some of them are related to the Schrödinger basin impact, while others are likely related to the Orientale basin on the farside of the Moon. We also found two deposits of younger age, likely related to fresh nearby craters, and other ejecta deposits that represent the formation age of the Shackleton crater. Therefore, these deposits appear to have formed from both basin/crater ejecta and local materials. Samples collected in this region will exhibit a diverse range of materials and sources from multiple events. Key Points: Forty‐one light plain deposits in the lunar southern polar region are investigated for origin and absolute model age determinationSchrödinger basin materials date to ∼3.8 Ga, Orientale materials to ∼3.7 Ga and Shackleton impact to ∼2.4 GaMultiple impact events and local sources contributed to light plain deposits across the lunar south pole [ABSTRACT FROM AUTHOR]

Rock abundances on the Moon represent both an opportunity to understand the history of the surface and of the regolith and a hazard to lander missions. While rock erasure by meteoroid bombardment is known to modify rock size˗frequency distributions, the interplay between rock erasure and rock exposure by impact cratering, and the resulting net rock abundance, is not known. Leveraging a coupling between modeling and optical imagery from the lunar orbit, we calculate new rock lifetimes that consider the specific shattering energy and the fragments produced by boulder shattering. We find differences between the estimated and expected specific shattering energy (Qs*), likely suggesting incomplete understanding of the scaling of the shattering energy with velocity and size. We find that the decrease in rock abundances with time on crater ejecta occurs faster than previous estimates based on thermal infrared data. Plain Language Summary: The surface of the Moon is littered with floating rocks ranging in size from centimeters to decameters. These rootless rocks are formed by impact cratering and are reduced to fine grained soil through fragmentation by meteoroid bombardment. Here we combine a model of rock formation and fragmentation with measurements of rock sizes extracted from images obtained from an orbiting spacecraft. We look at the effects of repeated fragmentation events. This gives us a better idea of the energy required for rock erasure as well as the abundance of centimeter‐scale rocks. We obtain an improved estimate of the time it takes for rocks to produce soil around impact craters. Key Points: The specific shattering energy of lunar boulders is estimatedThe decrease in rock abundance with time is modeled around impact cratersThe rock size‐frequency distribution covering the decameter to centimeter scale is modeled [ABSTRACT FROM AUTHOR]

Linear gravity anomalies (LGAs) on the Moon have been interpreted as ancient magmatic intrusions formed during the lunar expansion. The composition of such ancient subsurface intrusions may offer hints for the lunar thermodynamic state in the initial stage of lunar history. To pose a first compositional constraint on magmatism related to lunar expansion, this study analyzed the spectrum and gravity around craters on LGAs, such as Rowland, Roche, and Edison craters. Using reflectance spectra around the craters, we first surveyed non‐mare basaltic exposures. To test the LGA excavation scenario as a possible origin of the discovered exposures, we then compared the Gravity Recovery and Interior Laboratory data and post‐cratering gravity simulation with the iSALE shock physics code. Our spectral analysis reveals no basaltic exposure around the Rowland crater. Further, the observed termination of LGA at the crater rim contradicts the gravity simulation, which assumes that LGA predates the Rowland crater. These results suggest that LGA formation might postdate the Rowland formation and that lunar expansion lasted even after the Nectarian age. On the other hand, we found that both Roche and Edison craters possess basaltic exposures in their peripheries. Because the gravity reduction inside Roche crater can be reproduced in our simulation, the discovered basaltic exposures are possibly LGA materials ejected from these craters. The composition of those exposures shows that the LGA intrusions at the two locations are composed of low‐titanium magma, indicating that ancient magma during the expansion did not contain ilmenite‐rich melt, perhaps resulting from the low‐ilmenite content of the ancient upper mantle. Plain Language Summary: The Moon has positive, narrow, and long gravity anomalies, so‐called linear gravity anomalies (LGAs), which are thought to be magmatic intrusions formed during the ancient lunar expansion. The composition of these intrusions may provide insights into the early lunar thermal state. This study analyzed the reflectance spectra and gravity data around craters located on LGAs, specifically Rowland, Roche, and Edison craters, which are postulated to have ejected the LGA material. By analyzing the reflectance spectra, we first identified non‐mare basaltic exposures that likely originated from these subsurface formations. We next examine if these exposures are composed of the LGA materials by comparing the observed gravity with cratering simulation results. We found no basaltic exposures around Rowland and that gravity inside Rowland is not consistent with the excavation hypothesis, perhaps suggesting that LGA formation and lunar expansion occurred after the Rowland formation. On the other hand, we discovered basaltic exposures around both Roche and Edison craters, which can be interpreted as ejecta from the LGAs consistent with the gravity inside Roche crater. The composition of these exposures indicates that LGAs are composed of low‐titanium magma, which provides a new constraint on the ancient thermal state of the Moon. Key Points: High‐calcium pyroxene exposures and gravity reduction around Roche crater imply an excavation of lunar linear gravity anomaly materialsLunar subsurface dikes formed during the ancient expansion stage are estimated to be composed of low‐titanium magmaA linear gravity anomaly possibly postdates the Rowland crater, suggesting a potential prolongation of lunar expansion beyond the Nectarian age [ABSTRACT FROM AUTHOR]

Impacts into layered targets may generate "concentric craters" where a wider outer crater in the top layer surrounds a smaller, nested crater in the basement, which itself may be complex or simple. The influence of target on cratering depends on the ratio of target strength to lithostatic stress, which, in turn, is affected by gravity, target density, and crater diameter. When this ratio is large, the crater size is primarily determined by target strength, whereas gravitational forces dominate when the ratio is small. In two‐layer targets, strength may dominate in one or both layers, whereby the outer crater develops in the weaker top layer and the nested crater in the stronger substrate. However, large natural craters that should be gravity‐dominated in both cover strata and substrate may be concentric, the reasons for which are not yet fully understood. We performed qualitative impact experiments at 10–502 G and 1.8 km/s with the Boeing Corp. Hypervelocity centrifuge gun, and at 1 G and 0.4 km/s with the CAB CSIC‐INTA gas gun into layered sand targets of different compositions and grain densities but similar granulometry to analyze gravity‐dominated cratering. The results are compared with iSALE‐2D numerical simulations and natural craters on Earth and Mars. We show that target layering also affects the excavation process and concentric crater formation in gravity‐dominated impacts. The most important factors are the density and internal friction of each target layer, respectively. We propose that this is also valid for natural craters of sizes that should make their formation gravity‐dominated. Plain Language Summary: Concentric impact craters show a "soup‐plate" or "inverted sombrero" shape that forms on planetary surfaces with distinct subsurface layers. Generally, a deep inner crater forms in the substrate and a shallower, broader outer crater forms in the upper layer. The shape is obtained either from extensive post‐impact collapse of the upper, often weaker layer, or already during crater excavation, which is the focus of this study. The ratio of outer to inner diameter in the latter craters can be used to probe the depth of the upper layer and the contrast in material properties to the substrate. However, the controls on the relative size of the inner and outer craters are not well understood. While the formation of natural concentric craters is often attributed to a change in cohesive strength between the upper and lower layers, we show through impact experiments and numerical simulations that concentric craters can also form in cohesionless targets with a contrast in both density and friction coefficient between the layers. This provides an additional mechanism for concentric crater formation that may explain the development of some large, gravity‐dominated, naturally occurring concentric craters on Earth, Mars and elsewhere. Key Points: Concentric craters are not only due to strength differences between layers but also observed in cohesionless, gravity‐dominated targetsThis may explain the occurrence of large gravity‐dominated concentric craters on Earth, Mars and elsewhereKey factors affecting the concentric growth in these cases are the density and internal friction of each target layer, respectively [ABSTRACT FROM AUTHOR]

Impact cratering is associated with extreme physical conditions with temperatures and pressures far exceeding conditions otherwise prevailing at the surfaces of terrestrial planets. As a consequence, shock‐metamorphosed rocks contain unique deformation features such as planar deformation features in quartz, high‐pressure mineral polymorphs and melted rock. While the physical conditions of formation for impact‐induced melting following the highest pressure and temperature conditions is relatively well understood, aspects of the formation of melt‐veins in otherwise seemingly relatively low shock material has been the topic of discussion. In a new study, Hamann et al. (2023, https://doi.org/10.1029/2023JE007742) are able to largely reproduce the current classification of progressive shock metamorphism of felsic rocks using a modern experimental set up that eliminates multiple shock wave reflections at sample containers and excavation and ejection of target material. Importantly, however, they find that shear deformation results in the formation of melt veins at pressures as low as 6 GPa. The authors recover stishovite in melt veins formed at low‐moderate (<18 GPa) shock pressure, lower than most previous studies. These results have bearing on our understanding of the conditions of progressive shock metamorphism at terrestrial impact structures. However, since the results are similar to data obtained from experiments on basaltic rocks, the results also have broader implications for understanding the shock histories of meteorite parent bodies. Hamann et al. show the importance of experimental impact cratering for bridging the gap between observations in shocked rocks from terrestrial impact structures, in meteorites, and in returned samples, and their formational conditions. Plain Language Summary: A new publication refines understanding of the conditions and processes required to melt rock during impact cratering. Impact cratering represents one of the most extreme geological processes there is, in terms of pressures and temperatures reached. The process is ubiquitous throughout the Solar System, today and in the past, and therefore understanding of the history of impacts on Earth and in meteorites and returned samples from other planetary bodies is essential in order to interpret Solar System evolution. Hamann et al. (2023, https://doi.org/10.1029/2023JE007742) show that experimental impact cratering is a critical link between observations of shock features and the pressure‐temperature conditions that formed those features. Specifically, Hamann et al. see that low shock pressures (6 GPa) is required for generation of small amounts of localized melt and they recover shock‐formed stishovite, a mineral with the same chemical composition as quartz, but with a different crystal structure, in their experiment at unusually low shock pressures compared to previous studies. Key Points: Intense shear deformation during impact experiments leads to formation of melt veins in granite at pressures as low as 6 GPaMelt veins formed in quartz grains subjected to >10–12 GPa during the experiments contain stishoviteAn update to the classification system of shock metamorphism of felsic rock is proposed by the authors [ABSTRACT FROM AUTHOR]

The volcanic parent rock ("protolith") composing the lunar maria is likely to have developed diverse mechanical properties upon emplacement. The abundance of rocks ejected by impacts may be sensitive to protolith properties. We investigate the relationship between the possible diversity of mare protoliths and the abundance of rocks excavated and emplaced by impacts employing cumulative size‐frequency distributions (SFDs) of rocky craters in the maria. The SFDs of 15 mare units were calculated through varying degrees of Lunar Reconnaissance Orbiter Diviner‐derived rock abundance within crater ejecta blankets. By inspecting the frequency of high rock abundance craters, we find that the age of a surface does not control an impactor's ability to excavate rocks. Through analysis of SFDs, we find that differences in SFD behavior may act as probes for the mechanical strength of the protolith and the thickness of buried lava flows. Generally, regions with SFDs that have shallower slopes with increasing rockiness may be associated with thick, competent flow types, and regions with SFDs that have unchanging slopes with increasing rockiness may be associated with stacked, thin flows that are possibly more friable. The greater frequency of high rock abundance craters and the converging behavior of SFDs at two units within Mare Humorum and Oceanus Procellarum suggest that the surfaces are underlain by thick, competent lava flows. Finally, SFD slope analysis suggests that secondary impact craters are relatively ineffective at excavating rocks and the SFDs of rocky craters may reflect primary cratering populations. Plain Language Summary: When ancient lunar lava flows cooled and hardened into rock, they likely developed different properties depending on the conditions of eruption. The variations in these now‐buried volcanic rocks can be probed using impacts, which break up and eject material from the subsurface. Ejected pieces of lava flow can be measured in terms of their abundance, which we use to infer lava flow properties in this study. By inspecting the populations of craters with a high abundance of rocks in their ejecta, we determine that age does not control the frequency of highly rocky craters. Further, we determine the size‐distribution of craters with rocks in their ejecta and find different relationships between the rock‐free crater populations and the rocky crater populations. We find that changes in the rock‐free and rocky crater populations may represent variations in lava flow properties. Finally, secondary impact craters that are formed from high‐velocity debris made by primary impacts are ordinarily difficult to discern from the primary impact population; however, we determine that by inspecting the slightly rockier crater population, secondaries may be filtered out. Key Points: Rock excavating impact populations are probes of mare protolith propertiesSurface age does not control an impactor's ability to excavate rockThe size‐frequency distributions of rocky crater populations exhibit behaviors reflective of substrate competence [ABSTRACT FROM AUTHOR]

Two impact basins on the Moon—Freundlich‐Sharonov and Hertzsprung—are nearly the same size but exhibit different surface morphologies and subsurface structures. Gravity data reveal a bench‐like transitional structure in the crust‐mantle interface between the outer ring and the inner basin cavity in Hertzsprung, unlike that beneath both Freundlich‐Sharonov and larger multi‐ring basins. We use iSALE‐2D to model the formation of impact basins into a 40‐km thick pre‐impact crust with a range of thermal conditions to understand the divergent development of these basins and gain insight into the factors affecting whether a basin forms with a peak‐ring or multiring basin structure. We find that thermal gradients of at least 30 K/km result in Freundlich‐Sharonov‐type basins, in agreement with previous work. Cooler thermal gradients of approximately 15–20 K/km are needed to develop Hertzsprung‐like multiring basins with observed bench‐like structures in the crust‐mantle topography. We find that for cooler models, the bench structure develops early in the cratering process as a rotated inner normal fault cutting the crust‐mantle interface, whereas models with higher thermal gradients instead develop diffuse deformation zones instead of a discrete inner fault. The peak rings of both basins develop later in the cratering process as the collapsed central uplift. These results highlight the complex interplay between a strong lithosphere needed to develop ring faults and accessible ductile rocks that facilitate multiring basin formation. The varying thermal conditions giving rise to Hertzsprung and Freundlich‐Sharonov impact basins may be a possible constraint on the lunar cooling rate and chronology. Plain Language Summary: Impact cratering is a complex process that depends on several factors describing a planetary body. We studied two large impact craters on the farside of the Moon, Freundlich‐Sharonov and Hertzsprung basins, to understand how the temperatures of the lunar subsurface may have affected their development. We focus on recreating observed crater dimensions and subsurface features to evaluate our models. Specifically, we model the formation of a distinct "bench" feature between the crust and mantle layers that exists beneath Hertzsprung basin but is not present beneath Freundlich‐Sharonov basin. We found that the temperatures at the time of impact play an important role in the nature of the structure that develops after a large impact. We successfully modeled basins that look like Freundlich‐Sharonov using relatively warm temperature conditions and we modeled Hertzsprung‐like basins using cooler temperature conditions. These varying thermal conditions directly relate to the character and location of faulting associated with each basin. These models underscore the effects derived from changing thermal conditions as a planetary surface cools and show that the impact craters that form on a planet or Moon are sensitive to these effects in different ways. Key Points: Highly localized gravity inversions show variability in the subsurface structure of two lunar basins, Hertzsprung and Freundlich‐SharonovDifferences in surface morphology and crust‐mantle structure arise from variation in near‐surface temperatures at the time of each impactRotation during crater collapse is fundamental after large impacts, inverting the orientation of faults formed early in the impact process [ABSTRACT FROM AUTHOR]

Asteroid 4 Vesta has a set of parallel troughs aligned with its equator. Although previous evaluations suggest that it is of shock fracturing tectonic origin, we propose that the equatorial troughs can be created by secondary cratering from the largest impact basin, Rheasilvia. We calculated the trajectories of ejecta particles from Rheasilvia by considering Vesta's rapid rotation. As a result, we found that secondary craters should be parallel to the latitude. In particular, if we assume that ejecta particles are launched at an initial launch velocity of approximately 350–380 m/s and a launch angle of 25°, the parallel equatorial troughs, the Divalia Fossae, can be suitably explained by secondary cratering. This model works well on objects, such as Haumea, Salacia, and Chariklo, but not on Mercury, the Moon, and regular satellites. Plain Language Summary: Asteroid 4 Vesta has a set of parallel troughs aligned with its equator. We propose that the equatorial troughs can be created by secondary cratering from Rheasilvia, the largest impact basin of Vesta. We calculated the trajectories of ejecta particles from Rheasilvia by considering Vesta's rapid rotation. As a result, we found that secondary craters should be parallel to the latitude. In particular, the pattern of troughs indicates that ejecta particles were launched at an initial launch velocity of approximately 350–380 m/s and a launch angle of 25°. Key Points: We propose a new mechanism for the formation of equatorial troughs on VestaWe calculated the distribution of ejecta particles launched from RheasilviaWe found that secondary cratering from Rheasilvia matches with the equatorial troughs [ABSTRACT FROM AUTHOR]

Crater degradation and erosion control the lifetime of craters in the meter‐to‐kilometer diameter range on the lunar surface. A consequence of this crater degradation process is that meter‐scale craters survive for a comparatively short time on the lunar surface in geologic terms. Here, we derive crater lifetimes for craters of <∼200 m in diameter by analyzing existing functional expressions for crater population equilibrium and production. These lifetimes allow us to constrain the topographic degradation needed at different scales to explain when craters become undetectable on equilibrium surfaces. We show how topographic degradation can be treated as a process of anomalous (scale‐dependent) topographic diffusion and find large differences in effective diffusivities at different scales, consistent with a wide range of evidence besides equilibrium behavior. Understanding the range of morphology of meter‐scale craters is particularly relevant for future exploration of the lunar surface with rovers. We illustrate expectations for the d/D distribution of small lunar craters on surfaces with negligible regional‐scale slopes. Our results imply that if volatiles are found in preserved <4 m craters and were delivered after crater formation, the volatiles must have been emplaced in the last ∼50 Ma. Given the rates of surface evolution we infer, the most likely emplacement time for any volatiles discovered at or near the surface in the interior of fresh, small craters may be much younger than this upper limit. Plain Language Summary: Impact craters are the most common landform on the Moon and form across a range of sizes and at vastly different rates. Small, meter‐sized craters form much more frequently than large, kilometer‐sized craters. After crater formation, craters start to widen, fill in, and their topographic relief is reduced due to their exposure to the lunar environment. Eventually, this infilling process is sufficient to render craters unrecognizable on the surface. The time over which this occurs is the crater lifetime, which is a function of crater diameter. This paper quantifies the crater lifetime. As suggested by some earlier workers, we show that, for 10–100 m craters, lifetime increases as a function of diameter to a power p of ∼1.1–1.3. This diverges from what would be expected for one model for how regolith on the Moon is transported ("classical diffusion"), which would have p = 2, and supports a different model ("anomalous diffusion") that implies the rate of infilling depends on the scale being considered. In this study, we also show that this model for surface evolution implies that any volatiles that end up being discovered within small fresh craters on the Moon must have gotten there recently. Key Points: The crater population in equilibrium can be combined with a production model to directly constrain crater lifetime for <∼200‐m diameter cratersWith known initial crater shapes and erasure thresholds, the effective diffusivity compatible with these crater lifetimes can be inferredIf volatiles are found in small (<4‐m) craters and were delivered after crater formation, the volatiles are <∼50 Ma old [ABSTRACT FROM AUTHOR]

We performed cratering experiments on targets composed of glass beads with a power‐law size distribution that simulated the surface of rubble‐pile asteroids, and we improved the previously studied reduction factor on the crater size scaling relationship including the armoring effect using the momentum transfer efficiency. Cratering experiments were conducted using light gas guns at Kobe University and ISAS/JAXA to control the impact velocity, vi ${v}_{\mathrm{i}}$, from 50 to 4,400 m s−1. Two kinds of mixed targets were prepared by mixing glass beads with diameters of 0.1, 1, 3, and 10 mm—one with the smallest diameter beads, and one without. The size ratio of the target bead to the projectile (diameter of 1–3 mm), ϕ $\phi $, changed from 0.03 to 10. The crater size scaling relationships for the mixed targets were found to depend on the first contacted bead size. Notably, first contact with a 10 mm‐sized bead reduced the crater radius by 35% in maximum. The reduction factor due to this armoring effect on the crater size scaling relationship is written as follows: f(ϕ)=1+8.99×10−3vi0.630.34ϕ−0.19 $f(\phi)={\left[1+\left(8.99\times {10}^{-3}\right){v}_{\mathrm{i}}^{0.63}\right]}^{0.34}{\phi }^{-0.19}$; it decreased with the increase of the size ratio of the target bead to the projectile, while it increased with the increase of the impact velocity and approached unity. Our improved crater size scaling relationship that includes the reduction factor could be used to reconstruct the crater size frequency distribution on rubble‐pile asteroids such as Ryugu, and it may lead to a revision of the crater chronology of asteroids. Plain Language Summary: A rubble‐pile asteroid, 162173 Ryugu, was explored by Hayabusa2, and the crater size frequency distribution on the surface was examined. Ryugu's surface age can be estimated from this size distribution using the impact crater chronology, but the size of the asteroids forming the craters is necessary for this estimate. The crater size scaling law is used to estimate the impactor size, but this law was established using homogeneous grains such as granular sand, so it might not be applicable for rubble‐pile asteroids covered with boulders of various sizes. Moreover, because it is well known that cratering efficiency is significantly reduced by an armoring effect when a smaller asteroid collides with a larger boulder, a scaling law that includes the armoring effect is required. In this study, we performed cratering experiments on the surface of simulated rubble‐pile asteroids and examined the armoring effect on the crater size. Based on the results, we improved the previously studied armoring effect and introduced the momentum transfer efficiency, β $\beta $, into the effect, instead of a restitution coefficient, which was assumed to be zero. Using this improved scaling relationship, a more accurate chronology can be established for the asteroid craters. Key Points: We performed cratering experiments on glass bead targets with a power‐law bead size distribution at 50–4,400 m s−1The size of craters formed in the mixed bead target was speculated to be changed with the size of the first contacted beadThe armoring effect is less efficient for granular targets with a size distribution, compared with equal‐sized granular targets [ABSTRACT FROM AUTHOR]

Impact crater records on planetary surfaces are often analyzed for their spatial randomness. Generalized approaches such as the mean second closest neighbor distance (M2CND) and standard deviation of adjacent area (SDAA) are available via a software tool but do not take the influence of the planetary curvature into account in the current implementation. As a result, the measurements are affected by map distortion effects and can lead to wrong interpretations. This is particularly critical for investigations of global data sets as the level of distortion typically increases with increasing distance from the map projection center. Therefore, we present geodesic solutions to the M2CND and SDAA statistics that can be implemented in future software tools. We apply the improved methods to conduct spatial randomness analyses on global crater data sets on Mercury, Venus, and the Moon and compare the results to known crater population variations and surface evolution scenarios. On Mercury, we find that the emplacement of smooth plain deposits strongly contributed to a global clustering of craters and that a random distribution of Mercury's basins is not rejected. On Venus, the randomness analyses show that craters are largely randomly distributed across all sizes but where local nonrandom distributions due to lower crater densities in regions of recent volcanic activity may appear. On the Moon, the global clustering of craters is more pronounced than on Mercury due to mare volcanism and the Orientale impact event. Furthermore, a random distribution of lunar basins is not rejected. Plain Language Summary: The arrangement of craters on a planetary surface can be random or nonrandom. A nonrandom arrangement, such as clustered or ordered, can indicate geologic or cratering‐related processes. There are generalized approaches to quantify the arrangement of craters available via a software tool. The randomness calculations in this tool rely on the spatial relationships between craters and are determined in a two‐dimensional map projection. This is problematic because two‐dimensional representations do not take the influence of a curved planetary surface into account. Thus, measuring the spatial arrangement of craters is prone to errors. We revise the given approaches by implementing improved computations and measure the global spatial arrangement of craters on Mercury, Venus, and the Moon. On Mercury, we observe that the smooth plains' emplacement largely causes global clustering and that the distribution of basins cannot be distinguished from a random population. On Venus, craters across all sizes are largely in a random arrangement. However, nonrandomly distributed populations may occur due to local volcanic activity. On the Moon, we observe that the emplacement of lunar maria and the Orientale impact strongly influenced the global clustering of craters. Furthermore, the arrangement of lunar basins is similar to a random distribution. Key Points: We improve approaches to quantify the spatial randomness of impact craters by applying geodesic methodsWe apply these methods to analyze the global spatial randomness of impact crater populations on Mercury, Venus, and the MoonWe use the results to investigate known crater population variations and surface evolution scenarios on Mercury, Venus, and the Moon [ABSTRACT FROM AUTHOR]

Mercury has one of the best‐preserved impact records in the inner solar system due to the absence of an atmosphere and relatively unmodified ancient surface. However, our knowledge of the early impact record and the nature of the impacting projectiles are far from complete. To get a better understanding of the early impact history, we examined large impact basins (D ≥ 300 km) on Mercury. Here we cataloged 94 basins, 80 of which we classify as certain or probable, 1.7 times more than previously recognized. We re‐evaluate the crater densities of basins using the buffered nonsparseness correction technique, which we successfully applied for the Moon. In contrast with a previous study, we find that basins have a slightly higher N(300) crater density on Mercury than on the Moon, but similar N(500) basin densities. Based on these results and comparison with the Moon, we infer that no more than half of the basin record remains observable and basins older than Borealis have generally been erased from the basin record. Furthermore, we establish the stratigraphic relationships of basins based on N(25) crater frequencies, absolute model ages, and observations of crosscutting relationships. Similarly to our previous study on the Moon, we found no evidence for a change in the size‐frequency distribution of the impacting population; thus, our results are consistent with a single impactor population that bombarded Mercury's surface. Key Points: We cataloged 94 basins on Mercury, 1.7 times more certain and probable basins than in previous worksWe observe roughly half of the basin record, where basins older than Borealis are completely erasedOur results are consistent with a single impactor population that bombarded the surface of Mercury [ABSTRACT FROM AUTHOR]

The chronology of the moons of Saturn, especially Titan, has been limited by a lack of strong constraints on the cratering rate, low number statistics for small‐N counts of large‐diameter craters, and uncertainty about whether impactors are mostly heliocentric impactors orbiting the Sun or planetocentric impactors orbiting Saturn itself. Here, I propose to address these three problems. Instead of looking for an absolute cratering rate, I focus on the relative crater densities, calculating scaling relationships between the moons. I update crater analysis methodology by numerically modeling probability density functions of the uncertainty of crater density, enabling me to accurately assess the error of even single‐crater observations. Using these updated statistics, I show how the heliocentric cratering model leads to a dramatic increase in relative crater density for Mimas, Tethys, Dione, Rhea, and Iapetus with distance from Saturn. Under this model, the surface age of Titan is probably older than the cratered plains of Mimas—implying a very low erosion rate and minimal endogenic resurfacing on Titan. I explore possible explanations, concluding that the likeliest explanation is planetocentric cratering, although saturation effects cannot be ruled out. Under the planetocentric model, the relative crater densities of the cratered plains of Mimas, Tethys, Dione, Rhea, and Iapetus are all very close, with the relative crater density at Titan between 1 and 2 orders of magnitude lower. Under planetocentric cratering, the cratering rate on Titan allows for vigorous erosion and endogenic resurfacing. Plain Language Summary: How old are Saturn's moons? Most studies dating surfaces on the Moon or Mars rely on counting how many impact craters have formed and knowing the cratering rate, but on the moons of Saturn, we do not know the cratering rate. Here, instead of looking for an absolute age, I compare the moons to each other, figuring out which moons are older than others based on which ones have more craters. If most impacts on these moons come from objects orbiting the Sun, the moons Mimas, Tethys, Dione, Rhea, and Iapetus all increase in age with distance from Saturn, and the differences in the numbers of craters on them are enormous. Under this model, the surface of Titan is probably older than the surface of Mimas. I think it makes much more sense for most of the impactors to come from debris orbiting Saturn itself. Under this theory, Mimas, Tethys, Dione, Rhea, and Iapetus are all very close in age, Titan is probably younger than the other moons, and Titan could have very active resurfacing. Key Points: Heliocentric cratering leads to unlikely conclusions about the relative crater densities of the moons of SaturnPlanetocentric cratering leads to more plausible conclusions and high uncertaintyUnder planetocentric cratering, a young, vigorously resurfaced Titan is possible, but not under heliocentric cratering [ABSTRACT FROM AUTHOR]

The National Aeronautics and Space Administration (NASA) Psyche mission will visit the 226‐km diameter main belt asteroid (16) Psyche, our first opportunity to visit a metal‐rich object at close range. The unique and poorly understood nature of Psyche offers a challenge to the mission as we have little understanding of the surface morphology and composition. It is commonly accepted that the main evolutionary process for asteroid surfaces is impact cratering. While a considerable body of literature is available on collisions on rocky/icy objects, less work is available for metallic targets with compositions relevant to Psyche. Here we present a suite of impact experiments performed at the NASA Ames Vertical Gun Range facility on several types of iron meteorites and foundry‐cast ingots that have similar Fe‐Ni compositions as the iron meteorites. Our experiments were designed to better understand crater formation (e.g., size, depth), over a range of impact conditions, including target temperature and composition. We find that the target strength, as inferred from crater sizes, ranges from 700 to 1,300 MPa. Target temperature has measurable effects on strength, with cooled targets typically 10–20% stronger. Crater morphologies are characterized by sharp, raised rims and deep cavities. Further, we derive broad implications for Psyche's collisional evolution, in light of available low resolution shape models. We find that the number of large craters (>50 km) is particularly diagnostic for the overall bulk strength of Psyche. If confirmed, the number of putative large craters may indicate that Psyche's bulk strength is significantly reduced compared to that of intact iron meteorites. Plain Language Summary: Many iron meteorites are thought to be remnants of the cores of melted asteroids. Some cores may have been exposed by collisions during the earliest days of Solar System history, with a few survivors possibly found today in the main asteroid belt. National Aeronautics and Space Administration (NASA) Psyche mission will be the first spacecraft to visit asteroid (16) Psyche, an object thought to be representative of these metallic asteroids. Impacts onto (16) Psyche in the past may therefore be able to tell us about the history and nature of this body. To this end, we performed high‐speed impact experiments into metallic targets in order to understand how crater formation differs from rocky bodies. These experiments revealed that impact craters into metal targets are deeper and have sharper rims than on their rocky counterparts. These results will be crucial for interpreting both the bulk properties of Psyche's interior and the modification of Psyche's surface when the Psyche mission reaches its target. Key Points: We quantify morphological properties of cratering in metallic targets.We derive implications for the Psyche mission. [ABSTRACT FROM AUTHOR]

Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small‐scale petrographic and petrophysical measurements with larger‐scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock‐induced microfracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak ring formation, can accurately predict the distribution and orientation of impact‐induced microfractures in large craters, which plays an important role in the geophysical signature of impact structures. Plain Language Summary: The Chicxulub crater, Mexico, is widely known for its association with the extinction of the nonavian dinosaurs at the end of the Cretaceous period. The crater was first identified due to its gravitational and magnetic anomalies. Potential impact structures are often identified, in part, on the basis of geophysical anomalies, most commonly including a circular gravity low. Gravity is slightly weaker at craters because the impact cratering process removes mass from the impact site. In this study, we examine the cause of the Chicxulub gravity anomaly by combining observations from recent drilling of the crater, geophysical data measured across the crater, and numerical impact simulations. We demonstrate that porosity in rocks beneath the crater floor is primarily accommodated by fracturing during the impact cratering process, that the orientation of those fractures are consistent with predictions from numerical impact simulations, and that impact‐induced porosity is one of the primary causes of gravity anomalies in large impact craters. Key Points: The Chicxulub peak ring is extremely porous and low density due to pervasive shock‐induced microfracturingThe orientation of shock‐induced microfractures are sensitive to the orientation of stress during shockShear‐induced dilatancy is an important cause of gravity anomalies in large complex craters [ABSTRACT FROM AUTHOR]

Several ejecta deposits on Ceres display morphological characteristics not commonly associated with dry ballistic emplacement. We characterized 30 examples of fluidized appearing ejecta (FAE) on Ceres and identified two distinct morphological populations: cuspate/lobate FAE and channelized FAE. The cuspate/lobate FAE typically display one or more of the following characteristics: well‐defined margins, a sheeted or layered appearance, arcuate or cuspate terminal lobes, and occasional mass concentrations at their distal margins. The channelized FAE typically display a morphology dominated by topographically focused channelized flows and arcuate terminal lobes but lack the well‐defined margins common among their cuspate/lobate counterparts. Although Cerean FAE are holistically distinct from rampart/layered ejecta craters on Mars, Ganymede, and other icy solar system objects, many of their aforementioned morphological characteristics are commonly found among these other examples of fluidized ejecta. The formation of Martian and icy satellite fluidized ejecta has been widely attributed to the mobilization of near‐surface volatiles, namely, water ice. The documented Cerean FAE are observed between absolute latitudes of 70°, with a slight enrichment in the midlatitudes of the southern hemisphere. We test the hypothesis that the morphologies and mobilities of Cerean FAE can be explained via impacting into a low‐cohesion ice‐silicate target material, followed by material sliding on a low‐friction partially icy substrate. We do this by comparing the observed Cerean FAE to a kinematic‐dynamic sliding ejecta emplacement model. We find that a mechanically weak, H2O‐rich near‐surface layer is consistent with the range of ejecta mobilities and morphologies observed in this investigation. Plain Language Summary: In March 2015, National Aeronautics and Space Administration's Dawn spacecraft began orbiting the dwarf planet Ceres, the largest object in the main asteroid belt between Mars and Jupiter. Pre‐Dawn research demonstrated that a major volume fraction of Ceres may be composed of water ice, but the amount and distribution of that ice in the upper layer of the dwarf planet is still poorly understood. When Dawn began acquiring data, it observed a small, but significant, number of craters whose ejecta exhibited morphological signs of fluidization, which were similar to fluidized ejecta observed on Mars, Ganymede, Charon, and other icy worlds. We mapped and characterized all the instances of these fluidized appearing ejecta, which are observed between absolute latitudes of 70°, in order to establish any geographical trends and relationships. We then tested the hypothesis that the morphologies and spatial extents of Cerean fluidized appearing ejecta can be explained via impacting into low‐cohesion ice‐rock target materials, followed by material sliding on low‐friction partially icy substrates. We did this by comparing the observed ejecta runout distances to a physics‐based ejecta emplacement model. We found that an ice‐rich near‐surface layer on Ceres is consistent with the range of ejecta runout lengths and morphologies observed. Key Points: We identify 30 examples of fluidized appearing ejecta on CeresCerean fluidized appearing ejecta are divided into two morphological populations: channelized and cuspate/lobateThe mobility of fluidized appearing ejecta on Ceres suggest that it has a weak low‐friction surface consistent with abundant shallow ground ice [ABSTRACT FROM AUTHOR]

The presence of snow and ice at midlatitudes of Mars cannot be explained by current climatic conditions, as surface ice is unstable. However, a large variety of debris‐covered glaciers have been observed at both midlatitudes. Here, we report the presence of local, small‐scale, and debris‐covered stagnant ice deposits on the floor of a valley system in Terra Cimmeria. These deposits, termed valley fill deposits (VFD), have a distribution that is restricted to the host valley floor and to the extent of the ejecta blanket associated with Tarq impact crater. The VFD are characterized by convex‐upward morphology, various crevasses, sublimation pits, an average area of a few square kilometers, and occasional ejecta streaks on their surface. Our model age estimation points to two possible time frames for the Tarq impact event; thus, we suggest two formation scenarios for VFD: (I) distribution of ice due to impact into shallow ice during the Middle Amazonian and (II) post‐impact deposition of VFD due to precipitation. In both scenarios, ice preservation is most likely due to a lag of dust and debris deposited in the valley's topographic lows. Scenario I is more consistent with our geomorphological observation of the VFD being overlain by ejecta streaks. Our results highlight the importance of local geological events and conditions in the distribution and preservation of buried ice deposits on Mars and suggest that more small‐scale and debris‐covered ice deposits may exist in the midlatitudes than previously thought. These deposits are of high importance for future human exploration missions to Mars. Plain Language Summary: In the last two decades with the increase of high‐resolution imagery data, more studies report the presence of ice deposits covered by dust and debris on the Martian surface, in both midlatitudes. These deposits must have been formed under different atmospheric conditions, since water ice is not stable in the current surface environment. One of the generally accepted hypotheses for their formation is precipitation induced by variations of Mars' axial tilt known as obliquity. During high obliquity phases, ice would have sublimated from the poles and redeposited in the midlatitudes. Here, we report the presence of small‐scale ice deposits, located on the floor of a valley system in Terra Cimmeria. Although it is clear that these deposits were formed in different climatic conditions, their formation seems to be related to an impact into a shallow subsurface ice layer, redistributing a mixture of ejected material and ice across the region around the impact site. This study shows the importance of local geological processes, for example, impact cratering, in investigations of water ice distribution on Mars. Near‐surface ice reservoirs are of high importance in the search for life and for future human exploration on Mars. Key Points: Small debris‐covered stagnant ice deposits (termed valley fill deposits or VFD) are located inside a valley system in Terra Cimmeria, MarsMorphological properties (convex upward morphology, crevasses, and sublimation pits) suggest a current degradational stage of VFD evolutionThe location of VFD within the ejecta blanket of Middle Amazonian Tarq crater points to impact into shallow ice as a likely formation process [ABSTRACT FROM AUTHOR]

The diameter range of 15 to 20 km is within the transition from simple to complex impact craters located on the Moon. This range spans roughly a factor of 3 in impact energy for the same impactor speed, composition, and trajectory angle. We analyzed the global population of well‐preserved craters in this size range in order to assess the effects of target and impactor properties on crater shapes and morphologies. We observed that within this narrow diameter range, simple craters are confined to the highlands, and complex craters are more abundant in the mare. We found unusually deep craters around the highlands‐mare boundaries and favor the hypothesis that they form by impact cratering on high‐porosity terrain. We infer that target properties primarily contribute to the observed morphological variations in the craters. Simple crater formation is favored by a terrain that is more homogeneous in strength and topography, while transitional and complex crater formation is aided by heterogeneity in lithology, topography, or strength, or a combination of these parameters. Clearly visible impact melt deposits in a small percentage of simple craters, and two cases of craters differing in morphologies from their nearest neighbors in similar geologic settings, suggest that variation in impactor properties such as impact velocity and impactor size may have some role in causing morphological differences between similar‐sized craters. Plain Language Summary: We investigated the causes of variations in the appearances of impact craters on the Moon whose diameters are similar. The 15–20 km diameter range comprises simple craters (bowl‐shaped depressions), transitional craters (craters in which material slumped down the wall and accumulated locally), and complex craters (in addition to the wall failure, subsurface bedrocks were uplifted to form a central mound at the center of the floor). We noted that simple craters preferentially formed in the highlands, and the complex craters were favored by the mare, while the transitional craters are scattered across the lunar surface. In the mare, weathered material accumulated during the time between lava flows. We hypothesize that this layering reduced target strength and thus caused the cavity formed upon impact to weaken and the material to mobilize and form transitional and complex craters. The highlands are non‐layered and therefore can help stabilize the transient cavity to form simple craters. Transitional craters predominantly occur on highland terrains marked by abrupt increase in slopes. For two cases in which we did not find any differences between properties of the terrains around a simple crater and a transitional crater, we attributed morphological variations to the differences in impactor properties. Key Points: Morphology of similar‐sized lunar craters at the simple‐to‐complex transition is primarily governed by target propertiesIn this size range, simple craters occur on topographically smooth highland surfaces, and complex craters occur on the layered mareThere are unusually deep simple craters in the highlands near the mare margins that indicate a target that is cohesive or of high porosity [ABSTRACT FROM AUTHOR]

Deformation is a ubiquitous process that occurs to rocks during impact cratering; thus, quantifying the deformation of those rocks can provide first‐order constraints on the process of impact cratering. Until now, specific quantification of the conditions of stress and strain within models of impact cratering has not been compared to structural observations. This paper describes a methodology to analyze stress and strain within numerical impact models. This method is then used to predict deformation and its cause during peak‐ring formation: a complex process that is not fully understood, requiring remarkable transient weakening and causing a significant redistribution of crustal rocks. The presented results are timely due to the recent Joint International Ocean Discovery Program and International Continental Scientific Drilling Program drilling of the peak ring within the Chicxulub crater, permitting direct comparison between the deformation history within numerical models and the structural history of rocks from a peak ring. The modeled results are remarkably consistent with observed deformation within the Chicxulub peak ring, constraining the following: (1) the orientation of rocks relative to their preimpact orientation; (2) total strain, strain rates, and the type of shear during each stage of cratering; and (3) the orientation and magnitude of principal stresses during each stage of cratering. The methodology and analysis used to generate these predictions is general and, therefore, allows numerical impact models to be constrained by structural observations of impact craters and for those models to produce quantitative predictions. Plain Language Summary: During impact cratering events, extreme forces act on rocks beneath the crater to produce deformation. Computer simulations of large impact cratering events are particularly important because the conditions of those events can never be simultaneously produced by laboratory experiments. In this study, we describe a method by which the forces and deformations that occur during cratering can be measured in computer simulations of impact cratering events. Combining this analysis with geological observations from impact structures allows us to improve our understanding of impact crater formation. Here, we use this method to study the Chicxulub impact structure, Mexico, to understand the formation of "peak rings," rings of hills found internal to the rim of large impact craters. Our analysis provides estimates of the sequence of forces and deformation during peak‐ring formation. As deformation produces fractures, our analysis has important implications for how fluids flow through rocks in craters. Key Points: Numerical impact simulations are used to track stress and strain during complex crater formationStress and strain predictions allow time, orientation, and magnitude constraints on the deformational history of paraautochthonous rocksPredicted strains are consistent with the deformation observed within rocks of the Chicxulub peak ring [ABSTRACT FROM AUTHOR]

Abstract: We created a global database of Mercurian impact craters with diameters over 5 km, excluding obvious secondary craters. For craters over 10 km in diameter, we assessed basic morphological parameters, including an evaluation of whether significant postimpact filling occurred, the nature of any central structure, a three‐point assessment of degradation state, and a recording of the presence of rays and other atypical features. We used the database to evaluate the spatial patterns of different subsets of the crater population. The distribution of craters with diameters of 5 to 10 km compared to the distribution of larger craters shows many background secondaries associated with primary craters with diameters over 150 km, and their abundance would distort crater counts for surface dating. Counting only unfilled craters gives an estimate of the last possible date of endogenic geologic activity on a surface. Only a third of craters with diameters over 20 km are classified as unfilled, and the highest spatial density of unfilled craters is about half the total population at the same location. Our results support a globally rapid cessation in volcanism, with variations in the volume of late stage volcanism accounting for variations in the number of filled craters. We see regional variations of interior morphology for craters ~100 km in diameter that do not obviously correlate with other patterns derived from surface observations; our observations imply that there are variations in the mechanical properties of the upper several kilometers of crust. [ABSTRACT FROM AUTHOR]

The effects of the coefficient of friction and porosity on impact cratering are not sufficiently considered in scaling laws that predict the crater size from a known impactor size, velocity, and mass. We carried out a systematic numerical study employing more than 1000 two-dimensional models of simple crater formation under lunar conditions in targets with varying properties. A simple numerical setup is used where targets are approximated as granular or brecciated materials, and any compression of porous materials results in permanent compaction. The results are found to be consistent with impact laboratory experiments for water, low-strength and low-porosity materials (e.g., wet sand), and sands. Using this assumption, we found that both the friction coefficient and porosity are important for estimating transient crater diameters as is the strength term in crater scaling laws, i.e., the effective strength. The effects of porosity and friction coefficient on impact cratering were parameterized and incorporated into π group scaling laws, and predict transient crater diameters within an accuracy of ±5% for targets with friction coefficients f ≥ 0.4 and porosities Φ = 0-30%. Moreover, 90 crater scaling relationships are made available and can be used to estimate transient crater diameters on various terrains and geological units with different coefficient of friction, porosity, and cohesion. The derived relationships are most robust for targets with Φ > 10-15%, applicable for a lunar environment, and could therefore yield significant insights into the influence of target properties on cratering statistics. [ABSTRACT FROM AUTHOR]

Both Earth and the Moon share a common history regarding the epoch of large basin formation, though only the lunar geologic record preserves any appreciable record of this Late Heavy Bombardment. The emergence of Earth's first life is approximately contemporaneous with the Late Heavy Bombardment; understanding the latter informs the environmental conditions of the former, which are likely necessary to constrain the mechanisms of abiogenesis. While the relative formation time of most of the Moon's large basins is known, the absolute timing is not. The timing of Crisium Basin's formation is one of many important events that must be constrained and would require identifying and dating impact melt formed in the Crisium event. To inform a future lunar sample dating mission, we thus characterized possible outcrops of impact melt. We determined that several mare lava‐embayed kipukas could contain impact melt, though the rim and central peaks of the partially lava‐flooded Yerkes Crater likely contain the most pure and intact Crisium impact melt. It is here where future robotic and/or human missions could confidently add a key missing piece to the puzzle of the combined issues of early Earth‐Moon bombardment and the emergence of life. Plain Language Summary: How could life get started on Earth nearly four billion years ago if our planet was constantly being impacted by asteroids and comets? While we do not yet know, we are starting to piece together parts of the answer. Earth's largest impact basins are long gone because of our planet's active geology, life, and flowing water. But the Moon's big craters are well preserved. The formation of those large basins melted lots of rocks, which then cooled; by collecting those rocks on future missions and figuring out how old they are, we can determine the timing of when large basins formed on the Moon and, by extension, on Earth. Crisium basin is one of those large basins that we need to get the age for. Most of the rock that was melted from this impact and then cooled is buried by much younger lava flows, but we believe that some of it was brought up when the crater Yerkes formed on top of Crisium. The central mountain of Yerkes Crater is where we believe future robots and/or astronauts should go to collect once‐molten rock and figure out how old it and the basin are. Key Points: Relatively pure impact melt from Crisium Basin is exposed in the central peaks of Yerkes CraterDiluted Crisium impact melt may be exposed in some previously identified kipukas in CrisiumRadiogenic dating of impact melt exposed in Yerkes' central peak during a future mission would yield the age of the Crisium impact event [ABSTRACT FROM AUTHOR]