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The Lunar CRater Observations and Sensing Satellite (LCROSS) impacted a Centaur rocket stage into a permanently shadowed region (PSR) in Cabeus crater, excavating water ice and other volatiles. We used the Miniature Radio Frequency (Mini‐RF) instrument on the Lunar Reconnaissance Orbiter and the ShadowCam instrument on the Korean Pathfinder Lunar Orbiter to detect the probable 22‐m diameter crater that resulted from the LCROSS impact. The crater formed superposed upon a dense small crater population along a crater ray from a larger pre‐existing crater. From its geologic context, the ice and regolith excavated by LCROSS were likely modified within the last 0.1–0.5 Gyr. An upper limit for the excavated volatiles is ~0.9 Gyr, as the location was not a PSR prior to that time. A young age for the LCROSS‐detected volatiles supports the idea that they were mostly emplaced by an exogenic mechanism, such as from comets or the solar wind. Plain Language Summary: The LCROSS experiment formed an impact crater in an area of permanent shadow on the Moon, striking the surface at 2.5 km/s with a 2,300 kg spent rocket body on 9 October 2009. The impact ejecta from this cratering event included detectable amounts of water and other volatiles, which is perhaps the most direct evidence for significant water deposits on the Moon. However, since the impact location is in permanent shadow (no direct solar illumination), it proved hard to observe definitively the crater that LCROSS formed. Here, we use data from Mini‐RF, which illuminated the surface with S‐band radar, combined with ShadowCam, which acquires images within permanent shadows, to find the probable LCROSS impact crater. The impact crater is 22‐m in diameter, a bit smaller than was inferred indirectly after LCROSS. We also present new evidence that the volatiles in the ejecta likely got there in the last 20% of lunar history, which is important for understanding their origin and evolution. Key Points: We used Mini‐RF and ShadowCam to locate the 22‐m crater formed by LCROSS within a permanently shadowed region near the Moon's south poleGiven the crater's size, the regolith that was excavated, including volatiles, likely came from approximately the upper 2 mThe geologic context of the LCROSS crater suggests that the volatiles it excavated were relatively young, from the Copernican epoch [ABSTRACT FROM AUTHOR]

The Mars Reconnaissance Orbiter and its Context Camera (CTX) have acquired more than 100,000 separate panchromatic images that capture nearly the entire surface of Mars at ∼5–6 m/pixel. This paper describes a data processing workflow used to generate the first contiguous global mosaic of CTX data, which represents a large improvement in spatial resolution over existing 100 m/pixel contiguous global mosaics. We describe the overarching strategy for the mosaic's construction, which was to maximize the scientific utility of a continuous mosaic that is 5.7 trillion pixels in size. The pipeline used for data processing prioritized traceability and reproducibility of the final mosaic, such that the provenance of all pixels is reported, equipping scientists with information to differentiate mosaic artifacts from surface landforms and to incorporate critical image metadata into their analyses. The CTX data set synthesized into a global CTX mosaic facilitates ready analysis and provides a new capability in transitioning global studies of Mars from high‐resolution investigations of individual images to systematic studies of the entire Martian surface at outcrop‐resolving quality without regard to image boundaries. Plain Language Summary: We generated a global mosaic of Mars using Context Camera satellite imagery at 5.0 m/pixel, a substantial improvement in spatial resolution over the previous global mosaic at 100 m/pixel. This paper describes a new technique for merging overlapping images together in a way that preserves all information from each component image and produces a map of all image boundaries that is included with the mosaic. This makes scientific analyses that are facilitated by the mosaic fully traceable and reproducible. With this mosaic, scientists can now readily analyze landforms without the overhead of downloading individual images and perform complete global analyses of Mars at a resolution capable of seeing rock outcrops on the surface. Key Points: A global mosaic of Mars at 5.0 m/pixel has been created from 86,571 Context Camera images that are co‐registered to each other and seam‐correctedNon‐destructive image processing was used to preserve all image metadata and map seamsThe new mosaic will facilitate systematic studies of Mars at 5.0 m/pixel spatial resolution [ABSTRACT FROM AUTHOR]

The ancient surface of Mars is dominated by degraded impact craters with reduced or eliminated rim relief. Some degraded craters have an inlet valley, while many remain fluvially isolated. Despite controlling Martian fluvial connectivity, few constraints exist on why some—but not all—degraded craters possess inlets. We compared a suite of properties around degraded Martian craters with and without inlets to ascertain what topographic and hydrologic factors influenced inlet formation. Slope and surface roughness are similar, but topographic inset within the catchment, drainage density, and potential contributing areas diverge for breached and non‐breached craters. We suggest that the importance of basin hydrology‐related factors over topographic factors is the result of the former less frequently surpassing inlet incision thresholds than the latter. We conclude that greater topographic inset (i.e., craters deeper within regional depressions) promoted higher discharge, and that inlet valley formation was ultimately controlled by Mars' crater‐dominated topography. Plain Language Summary: The ancient surface of Mars is dominated by impact craters that have been modified by mass wasting, aeolian infilling, water activity, and subsequent impact cratering. Erosion has lowered or eliminated the relief of many craters' rims, resulting in "degraded" craters. On early Mars, water activity also led to the formation of branching valley networks, which flow into some Martian impact craters. However, many degraded craters remain without an inlet valley. Inlet formation reveals that water activity could overcome the disruption of topography caused by impact crater formation. Yet, little is known about factors that would promote or limit inlet valley formation and it is unclear why some—but not all—degraded craters were breached by inlet valleys on Mars. We compared a suite of properties around degraded Martian craters with and without inlets to find out what topographic (e.g., slope) and hydrologic factors (e.g., the number of valleys per area) affected inlet formation. We find that hydrology‐related factors are very different between craters with and without inlets, while topographic factors are similar. Our results suggest that inlet valley formation was ultimately controlled by hydrologic routing on Mars' crater‐dominated surface. Key Points: We compared slope, roughness, drainage density, and catchment geometry around degraded Martian craters with and without an inlet valleyOnly relative topographic inset, drainage density, and potential contributing area differ between the breached and non‐breached subsetWe conclude that more inset craters (i.e., deeper or more central in a basin) received greater discharge which promoted inlet breaching [ABSTRACT FROM AUTHOR]

Boulder‐sized clasts are common on the surface of Mars, and many are sufficiently large to be resolved by the high resolution imaging science experiment (HiRISE) camera aboard the Mars reconnaissance orbiter. The size, number, and location of boulders on the surface and their spatial distribution can reveal the processes that have operated on the surface, including boulder erosion, burial, impact excavation, and other mechanisms of boulder transport and generation. However, quantitative analysis of statistically significant boulder populations, which could inform these processes, entails prohibitively laborious manual segmentation, granulometry, and morphometry measurements over large areas. Here, we develop, describe, and validate an automated tool to locate and measure boulders on the Martian surface: the Martian Boulder Automatic Recognition System (MBARS). Our open‐source Python‐based toolkit automatically measures boulder diameter and height in HiRISE images enabling rapid and accurate assessments of boulder populations. We compare our algorithm with existing boulder‐counting methods, manual analyses, and objects of known size to verify accuracy and precision. Additionally, we test how MBARS quantitatively characterizes boulders around an impact crater in the Martian northern lowlands. We compare this to previous work on rock excavation during impact cratering using manually counted boulders around lunar craters. Plain Language Summary: Large boulders (>1 m diameter) are widely distributed on the Martian surface. They are easily observed from orbit, making them visible with high‐resolution imaging. Mapping the location, number, and size of boulders is helpful for understanding which geological processes bring boulders to the surface, move them around, and fragment them into smaller rocks and soil. Here, we describe and validate the Martian Boulder Automatic Recognition System (MBARS), a set of tools that automatically locates and measures boulders in high‐resolution images of the Martian surface. We compare results generated by MBARS with results from other automated boulder‐measuring tools as well as with results from manual boulder measurements to ensure accuracy. We also use MBARS to map boulders around an impact crater on Mars and compare the boulder distribution to a similar‐sized crater on the Moon. Key Points: The Martian Boulder Automatic Recognition System (MBARS) is a new tool to detect and measure boulders on the Martian surfaceMBARS is comparably or more accurate than prior published algorithms that measure bouldersMBARS readily reproduces manually measured results [ABSTRACT FROM AUTHOR]

Lunar water is redistributed by various processes. Topographic diffusion affects the transport of water and contributes to its preservation in subsurface layers. Here, we analyze 16 complex craters (∼3.2 – ∼4.2 Ga) larger than 20 km in diameter near the lunar south pole to quantify their degradation states. The results show that the diffusive rates of late Imbrian craters are similar to those of similarly aged simple craters, while Nectarian and pre‐Nectarian craters are degraded less efficiently. Within a complex crater, the mass accumulation by topographic diffusion and ejecta blankets from other complex craters preserves water, ranging up to 1 wt% on average. However, impact mixing and internal heat further limit the stability of ancient water to subsurface regions with ages younger than 3.9 Ga and at depth from a few meters to 10s of meters. Plain Language Summary: Water in lunar shadowed regions is redistributed by various processes. When small craters form on a large crater's wall, its topography gradually erodes. Surface materials and deposited water move downhill, leading to a mixture of these materials and accumulations on the complex crater's floor. Here, we analyze 16 complex craters older than 3.2 Ga and larger than 20 km in diameter near the lunar south pole to investigate how fast these complex craters are topographically eroded. The results show that the speeds of topographic degradation of craters with an age of ∼3.2 Ga are comparable to those of similarly aged simple craters, while older craters experience significant degradation but are diffused inefficiently. On a complex crater, water may be stored in accumulated mass by topographic diffusion and large ejecta blankets for a long time. Such accumulated regions may host water, ranging up to 1 wt%. However, impact mixing and internal heat compete against the water supply and storage, limiting the water existence in subsurface layers at 10s of meters but a few meters below the surface and younger than 3.9 Ga. Key Points: Topographic degradation of 16 complex craters near the lunar south pole significantly varies with surface age and crater sizeMass wasting by topographic diffusion and ejecta blanketing mixes water with regolith, giving a water mass fraction of up to 1 wt%Impact mixing and internal heat limit the existence of unaffected ancient water at 10s of meters in depth and younger than 3.9 Ga [ABSTRACT FROM AUTHOR]

Abstract: Impact cratering is likely a primary agent of regolith generation on airless bodies. Regolith production via impact cratering has long been a key topic of study since the Apollo era. The evolution of regolith due to impact cratering, however, is not well understood. A better formulation is needed to help quantify the formation mechanism and timescale of regolith evolution. Here we propose an analytically derived stochastic model that describes the evolution of regolith generated by small, simple craters. We account for ejecta blanketing as well as regolith infilling of the transient crater cavity. Our results show that the regolith infilling plays a key role in producing regolith. Our model demonstrates that because of the stochastic nature of impact cratering, the regolith thickness varies laterally, which is consistent with earlier work. We apply this analytical model to the regolith evolution at the Apollo 15 site. The regolith thickness is computed considering the observed crater size‐frequency distribution of small, simple lunar craters (< 381 m in radius for ejecta blanketing and <100 m in radius for the regolith infilling). Allowing for some amount of regolith coming from the outside of the area, our result is consistent with an empirical result from the Apollo 15 seismic experiment. Finally, we find that the timescale of regolith growth is longer than that of crater equilibrium, implying that even if crater equilibrium is observed on a cratered surface, it is likely that the regolith thickness is still evolving due to additional impact craters. [ABSTRACT FROM AUTHOR]

Abstract: Boulder halos are circular arrangements of clasts present at Martian middle to high latitudes. Boulder halos are thought to result from impacts into a boulder‐poor surficial unit that is rich in ground ice and/or sediments and that is underlain by a competent substrate. In this model, boulders are excavated by impacts and remain at the surface as the crater degrades. To determine the distribution of boulder halos and to evaluate mechanisms for their formation, we searched for boulder halos over 4,188 High Resolution Imaging Science Experiment images located between ~50–80° north and 50–80° south latitude. We evaluate geological and climatological parameters at halo sites. Boulder halos are about three times more common in the northern hemisphere than in the southern hemisphere (19% versus 6% of images) and have size‐frequency distributions suggesting recent Amazonian formation (tens to hundreds of millions of years). In the north, boulder halo sites are characterized by abundant shallow subsurface ice and high thermal inertia. Spatial patterns of halo distribution indicate that excavation of boulders from beneath nonboulder‐bearing substrates is necessary for the formation of boulder halos, but that alone is not sufficient. Rather, surface processes either promote boulder halo preservation in the north or destroy boulder halos in the south. Notably, boulder halos predate the most recent period of near‐surface ice emplacement on Mars and persist at the surface atop mobile regolith. The lifetime of observed boulders at the Martian surface is greater than the lifetime of the craters that excavated them. Finally, larger minimum boulder halo sizes in the north indicate thicker icy soil layers on average throughout climate variations driven by spin/orbit changes during the last tens to hundreds of millions of years. [ABSTRACT FROM AUTHOR]