Binary craters on Ceres and Vesta and implications for binary asteroids

Planetary surfaces present binary craters that can be associated with the synchronous impact of binary asteroids. In this work, we identify binary craters on asteroids (1) Ceres and (4) Vesta, and aim to characterize the properties (size ratio and orbital plane) of the binary asteroids that might have formed them. We used global crater databases developed in previous studies and mosaics of images from the NASA DAWN mission. We established selection criteria to identify craters that were most likely a product of the impact of a binary asteroid. We find geomorphological evidence of synchronous impacts on the surfaces of Ceres and Vesta. The associated binary asteroids are widely separated and similar in diameter in contrast to the current census of binary asteroids. The distributions of the orientation of these binary craters on both bodies are statistically different from numerical impact simulations that assume binary asteroids with coplanar mutual and heliocentric orbits. These findings agree with a population of well-separated and similarly sized binary asteroids with non-zero obliquity that remains to be observed

Lunar Surface Model Age Derivation: Comparisons Between Automatic and Human Crater Counting Using LRO‐NAC and Kaguya TC Images

Abstract Dating young lunar surfaces, such as impact ejecta blankets and terrains associated with recent volcanic activities, provides critical information on the recent events that shaped the surface of the Moon. Model age derivation of young or small areas using a crater chronology is typically achieved through manual counting, which requires a lot of small impact craters to be tediously mapped. In this study, we present the use of a Crater Detection Algorithm (CDA) to extract crater populations on Lunar Reconnaissance Orbiter—Narrow Angle Camera (LRO‐NAC) and Kaguya Terrain Camera images. We applied our algorithm to images covering the ejecta blankets of four Copernican impact craters and across four young mare terrains, where manually derived model ages were already published. Across the eight areas, 10 model ages were derived. We assessed the reproducibility of our model using two populations for each site: (a) an unprocessed population and (b) a population adjusted to remove contaminations of secondary and buried craters. The results showed that unprocessed detections led to overestimating crater densities by 12%–48%, but “adjusted” populations produced consistent results within <20% of published values in 80% of cases. Regarding the discrepancies observed, we found no significant error in our detections that could explain the differences with crater densities manually measured. With careful processing, we conclude that a CDA can be used to determine model ages and crater densities for the Moon. We also emphasize that automated crater datasets need to be processed, interpreted and used carefully, in unity with geologic reasoning. The presented approach can offer a consistent and reproducible way to derive model ages

Automatic Mapping of Small Lunar Impact Craters Using LRO‐NAC Images

Abstract Impact craters are the most common feature on the Moon’s surface. Crater size–frequency distributions provide critical insight into the timing of geological events, surface erosion rates, and impact fluxes. The impact crater size–frequency follows a power law (meter‐sized craters are a few orders of magnitude more numerous than kilometric ones), making it tedious to manually measure all the craters within an area to the smallest sizes. We can bridge this gap by using a machine learning algorithm. We adapted a Crater Detection Algorithm to work on the highest resolution lunar image data set (Lunar Reconnaissance Orbiter‐Narrow‐Angle Camera [NAC] images). We describe the retraining and application of the detection model to preprocessed NAC images and discussed the accuracy of the resulting crater detections. We evaluated the model by assessing the results across six NAC images, each covering a different lunar area at differing lighting conditions. We present the model’s average true positive rate for small impact craters (down to 20 m in diameter) is 93%. The model does display a 15% overestimation in calculated crater diameters. The presented crater detection model shows acceptable performance on NAC images with incidence angles ranging between ∼50° and ∼70° and can be applied to many lunar sites independent to morphology

Recent aqueous alteration associated to sedimentary volcanism on Mars

International audienceSedimentary volcanism, whereby material is brought to the surface by fluid overpressure, has been proposed to explain some of the periglacial landforms, including pitted cones, in the Northern Plains of Mars. However, in the absence of convincing mineralogical evidence, the origin for these deposits has never been conclusively determined. Here we conduct a remote sensing-based mineralogical survey to identify hydrated minerals within the Thumbprint Terrains and neighbouring Vastitas Borealis Formation. We detect several occurrences of hydrated silica along with sulfate salts in candidate mud volcano-like morphologies which likely formed during the Early Amazonian period, supporting the sedimentary volcanism origin. Buoyancy-driven analytical modelling suggests the hydrated silica and sulfate salts are sourced from reservoirs at depths of several 10 s and 100 s of metres, respectively below the Thumbprint Terrains and Vastitas Borealis Formation. The exposed sulfates may have been derived from ancient buried evaporite deposits suggesting, at least locally, a salt-rich aqueous origin for the Vastitas Borealis Formation, and would be consistent with the presence of a past northern ocean on Mars.</div