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Seismic activity generated by impacts depends on impact conditions and properties of the impact site. Here, we combined mapping of the regolith thickness with numerical impact simulations to better estimate the seismic efficiency and seismic moment generated in small impact events in the uppermost crust on Mars. We used mapping of crater morphology to determine the regolith thickness that craters formed in. We found that local regolith thickness in the late Amazonian units is between 4 and 9 m. Combined with previous estimates for the NASA InSight landing site, we composed a more realistic uppermost crust analog and implemented it in numerical impact simulations. We estimated the seismic efficiency and seismic moment for small craters on Mars impacting a non-porous or fractured bedrock overlaid by 5, 10, or 15 m thick regolith. Seismic energy showed more dependence on target properties. Three orders of magnitude more energy were produced in stronger targets. The seismic moment does not depend on target properties, and we confirm that seismic moment is almost proportional to impact momentum. The resulting seismic moment is in agreement up to a factor of 4 between different target types. We improved the scaling relationships developed from numerical simulations used in seismic moment approximations by constraining its dependence on more realistic target properties. more...

The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts. The locations and geological contexts of the launch sites are currently unknown. Determining the impact locations is essential to unravel the relations between the evolution of the martian interior and its surface. Here we adapt a Crater Detection Algorithm that compile a database of 90 million impact craters, allowing to determine the potential launch position of these meteorites through the observation of secondary crater fields. We show that Tooting and 09-000015 craters, both located in the Tharsis volcanic province, are the most likely source of the depleted shergottites ejected 1.1 million year ago. This implies that a major thermal anomaly deeply rooted in the mantle under Tharsis was active over most of the geological history of the planet, and has sampled a depleted mantle, that has retained until recently geochemical signatures of Mars’ early history., The ejection sites of the martian meteorites are still unknown. Here, the authors build a database of 90 million craters and show that Tharsis region is the most likely source of depleted shergottites ejected 1.1 Ma ago, thus confirming that some portions of the mantle were recently anomalously hot. more...

Le nom d’André Antoine reste attaché avant tout à l’histoire du théâtre ; même pour ceux qui en connaissent l’existence, sa carrière cinématographique est largement ignorée. Le créateur du Théâtre-Libre a, en effet, révolutionnée en France au tournant du xxe siècle. Promoteur d’un réalisme scénique, reconstituant sur scène les lieux de la vie quotidienne et faisant du rideau un quatrième mur, il a ainsi coupé l’action du public et l’a donnée à voir comme une tranche de vie. Considéré comme le... more...

The supporting material for'Automatic Mapping of Small Lunar Impact Craters Using LROC NAC'. This File contains: Supporting Material(.pdf); List of True Positive detections (.csv); List of all ground truth and CDA detections (.csv); Folder (.zip) with images of the evaluation sites (.pdf); and Folder (.zip) with training image tiles (.png and .txt). Refer toSupporting Material(.pdf) for file name and header information. more...

After formation of a primordial crust, early impacts influenced when habitable conditions may have occurred on Mars. Martian meteorite Northwest Africa (NWA) 7034 is a regolith breccia that contains remnants of the earliest Martian crust. The paucity of shock deformation in NWA 7034 was previously cited as recording a decline in giant impacts by 4.48 billion years and evidence for habitable Mars by 4.2 billion years ago. We present new evidence of high-pressure shock effects in a 4.45–billion year–old zircon from the matrix of NWA 7034. The zircon contains {112} shock twins formed in the central uplift of a complex impact structure after 4.45 billion years and records impact pressures of 20 to 30 gigapascals. The zircon represents the highest shock level reported in NWA 7034 and paired rocks and provides direct physical evidence of large impacts, some potentially life-affecting, that persisted on Mars after 4.48 billion years. more...

Context. Until recently, camera networks designed for monitoring fireballs worldwide were not fully automated, implying that in case of a meteorite fall, the recovery campaign was rarely immediate. This was an important limiting factor as the most fragile - hence precious - meteorites must be recovered rapidly to avoid their alteration. Aims. The Fireball Recovery and InterPlanetary Observation Network (FRIPON) scientific project was designed to overcome this limitation. This network comprises a fully automated camera and radio network deployed over a significant fraction of western Europe and a small fraction of Canada. As of today, it consists of 150 cameras and 25 European radio receivers and covers an area of about 1.5 × 10km. Methods. The FRIPON network, fully operational since 2018, has been monitoring meteoroid entries since 2016, thereby allowing the characterization of their dynamical and physical properties. In addition, the level of automation of the network makes it possible to trigger a meteorite recovery campaign only a few hours after it reaches the surface of the Earth. Recovery campaigns are only organized for meteorites with final masses estimated of at least 500 g, which is about one event per year in France. No recovery campaign is organized in the case of smaller final masses on the order of 50 to 100 g, which happens about three times a year; instead, the information is delivered to the local media so that it can reach the inhabitants living in the vicinity of the fall. Results. Nearly 4000 meteoroids have been detected so far and characterized by FRIPON. The distribution of their orbits appears to be bimodal, with a cometary population and a main belt population. Sporadic meteors amount to about 55% of all meteors. A first estimate of the absolute meteoroid flux (mag < -5; meteoroid size ≥∼1 cm) amounts to 1250/yr/10km. This value is compatible with previous estimates. Finally, the first meteorite was recovered in Italy (Cavezzo, January 2020) thanks to the PRISMA network, a component of the FRIPON science project., FRIPON was initiated by funding from ANR (grant N.13- BS05-0009-03), carried by the Paris Observatory, Muséum National d’Histoire Naturelle, Paris-Saclay University and Institut Pythéas (LAM-CEREGE). VigieCiel was part of the 65 Millions d’Observateurs project, carried by the Muséum National d’Histoire Naturelle and funded by the French Investissements d’Avenir program. FRIPON data are hosted and processed at Institut Pythéas SIP (Service Informatique Pythéas), and a mirror is hosted at IMCCE (Institut de Mécanique Céleste et de Calcul des Éphémérides / Paris Observatory) with the help of IDOC (https://idoc.ias.u-psud.fr) (Integrated Data and Operation Center), supported by CNRS and CNES. PRISMA is the Italian Network for Systematic surveillance of Meteors and Atmosphere. It is a collaboration initiated and coordinated by the Italian National Institute for Astrophysics (INAF) that counts members among research institutes, associations and schools (http://www.prisma.inaf.it). PRISMA was partially funded by 2016 and 2020 Research and Education grants from Fondazione Cassa di Risparmio di Torino and by a 2016 grant from Fondazione Agostino De Mari (Savona). FRIPON-Bilbao is supported by a grant from Diputacion Foral Bizkaia (DFB/BFA). FRIPONMOROI was supported by a grant of the Romanian Ministery of Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDI2017-0226/16PCCDI/2018 , within PNCDI III. Rio de Janeiro camera is hosted and partially maintained by MAST (Museum of Astronomy and Related Sciences)/MCTIC. The Meteorix project acknowledges supports from labex ESEP (Exploration Spatiale des Environnements Planétaires), DIM-ACAV+ Région Île-de-France, Janus CNES, IDEX Sorbonne Universités and Sorbonne Université. more...

The impact flux over the last 3 Ga in the inner Solar System is commonly assumed to be constant through time. However, asteroid break-up events in the main belt may have been responsible for cratering spikes over the last ~2 Ga on the Earth-Moon system. We investigate here the possible variations of the size frequency distributions of impactors from the record of small craters of 521 martian impact craters larger than 20 km in diameter. We show that 49 craters (out of the 521) correspond to the complete crater population of this size formed over the last 600 Ma. Our results on Mars show that the flux of both small (> 5 m) and large asteroids (> 1 km) are coupled, does not vary between each other over the last 600 Ma. Existing data sets for large craters on the Earth and the Moon are analyzed and compared to our results on Mars. On Earth, we infer the formation location of a set of impact craters thanks to plate tectonic reconstruction and show that a cluster of craters formed during the Ordovician period, about 470 Ma ago, appears to be a preservation bias. On the Moon, the late increase seen in the crater age signal can be due to the uncertain calibration method used to date those impacts (i.e. rock abundance in lunar impact ejecta), and other calibrations are consistent with a constant crater production rate. We conclude to a coupling of the crater production rate between kilometer-size craters and down to ~100 m in diameter in the inner Solar System. This is consistent with the traditional model for delivering asteroids to planet-crossing orbits: the Yarkovsky effect slowly pushes the large debris from asteroid break-ups towards orbital resonances while smaller debris are grinded through collisional cascades. This suggests that the influence of past asteroid break-ups in the cratering rate for D > 100 m is limited or inexistent., 45 pages, 8 figures, accepted in Earth and Planetary Science Letters, 28/12/2021 more...

International audience; Recent research suggests that major meteorite impact events into a Late Hesperian/Early Amazonian ocean likely produced a mega‐tsunami that would have resurfaced coastal areas in northwestern Arabia Terra. The orientations of the associated lobate deposits, a conspicuous type of landforms called Thumbprint Terrain, suggests that if an impact event triggered the mega‐tsunami, the most likely location of the source crater is within the northern plains regions situated north of Arabia Terra. This study focuses on the identification of impact craters that impacted into the ocean and are likely to have produced the tsunami. We selected 10 complex impact craters, based on their diameters, location, and geomorphic characteristics. Of those, the Late Hesperian ~120‐km‐diameter Lomonosov crater exhibits a unique topographic plan view asymmetry (compared to other similar‐sized and similar‐aged craters in the northern plains such as Micoud, Korolev, and Milankovic). We attribute its broad and shallow rim, in part, to an impact into a shallow ocean as well as its subsequent erosion from the collapsing transient water cavity. The likely marine formation of the Lomonosov crater, and the apparent agreement in its age with that of the Thumbprint Terrain unit (~3 Ga), strongly suggests that it was the source crater of the tsunami. These results have implications for the stability of a late northern ocean on Mars. more...

Introduction: Martian meteorites are the only samples from the Red Planet available for in-depth laboratory analyses. More than 280 pieces of 152 unique samples, originating from at least 11 source craters, are curated in the world’s collections [1]. Ejection ages, based on cosmic ray exposure (CRE), vary from 0.7 to 20 Myr [2-4]. The ejection sites are still unknown, despite several previous propositions [5-7], motivated by the significance of establishing a link between the crystallization ages, and the chemical and mineralogical properties of these samples with surface geology.Secondary impact craters, the key to identify the meteorites ejection sites: The formation of an impact crater generates debris ejected with speeds above and below the escape velocity on Mars (5 km/s). The fraction of ejecta material with a velocity higher than the escape velocity may get through the Martian atmosphere and into the interplanetary space. Numerical simulations suggest that impact events capable of producing such fragments would form craters larger than ~3 km in diameter on the Martian surface [8-9]. Material with a velocity lower than 5 km/s falls back to the surface in a radial pattern or rays around the primary source crater and forms secondary craters with a maximum size of about 2 to 5% of the primary crater diameter [10-12]. These secondaries are shallower than those formed by primary impacts and are rapidly eroded. Typically, a secondary crater of 100 m in diameter would be completely erased in about 50 Myr. Therefore, the occurrence of radial patterns of small secondaries is a diagnostic feature of young primary craters [6,13-14]. The use of high-resolution imagery would allow the identification of such small craters, but manual mapping of the tens of millions of secondary impact craters constellating the surface of Mars is not feasible.Machine learning approach to identify small craters on high-resolution images: We adapted an automated Crater Detection Algorithm (CDA) [15] to identify craters smaller than 1 km in diameter across the entire surface of Mars. The algorithm was trained using High-Resolution Imagery System Experiment (HiRISE) images (25 cm/pixel) and applied on the global Context Camera (CTX) mosaic [16] (6 m/pixel), thus generating a database of more than 90 million detections (Figure 1).Figure 1: Crater Size-Frequency Distribution of the automatic crater database (in red) compared to the manual catalogue (in blue) from [11-12].We evaluated the performance of our model against ~1000 impact craters >60 m (10 pixels in diameter on CTX imagery) manually mapped on 6 different geological units, thus constituting the ground truth (GT). For craters > 100 m in diameter, it results in an average true positive detection rate (or recall) of more than 80% and an average precision of 96%. The diameter estimation derived from our model is within 25% of uncertainty compared to our ground truth (Figure 2), which is within the expected human performance [17].Figure 2: Comparison between the difference in the diameter of craters estimated by the CDA and the ground truth (black crosses). The kernel density estimator shows that detections larger than 100m are estimated within 25% of uncertainties compared to manually identified impact craters.The ejection site of a group of Martian meteorites: We analyzed the spatial and size distribution of craters smaller than 300 m by computing a crater density map from this dataset. The figure 3 presents the results obtained by combining three density maps with red, green, and blue channels corresponding to local crater density (in a 0.05° grid) for three diameter size ranges, in order of decreasing range of diameter, respectively 150 < D < 300 m, 75 < D < 150 m and < 75 m. Using this map, we identified 19 secondary ray systems associated with large and recent primary craters (Figure 3).Figure 3: Density map of craters < 300 m in diameter (89,054,458 entries). Colors indicate crater densities of specific diameter ranges (see text for details).Using crater counts on the ejecta blanket of each of those 19 impact craters and their surrounding terrains, we derived respectively the model age of those impacts and the age of the impacted material. Those results are compared with the ejection age of Martian meteorites as well as their crystallization ages. We found that two craters, both located in the Tharsis volcanic province, are the most likely source of depleted Shergottites launched ~1 Myr ago [3]. Considering the magmatic ages and the petrogenesis of these samples, this implies that a major thermal anomaly deeply rooted in the mantle under Tharsis was active over most of the geological history of the planet, and has sampled a depleted mantle that has retained geochemical signatures of Mars’ early history.References: [1] https://www.lpi.usra.edu/meteor/metbull.php. [2] Herzog, G.F., & Caffee, M.W. Treatise on Geochemistry, 1, 419-454 (2014). [3] Lapen, T.J., et al. Sci. Adv., 3(2), e1600922 (2017). [4] Udry, A., et al. J. Geophys. Res., 25, e2020JE006523 (2020). [5] Werner, S. C., et al., Science, 343, 1343–1346 (2014). [6] McEwen, A.S., et al. Icarus, 176, pp. 351-381 (2005). [7] Mouginis-Mark, P.J. & Boyce, J.M. Chemie der Erde - Geochemistry, 72, 1-23 (2012). [8] Artemieva, N., & Ivanov, B.A. Icarus, 1, 84-101 (2004). [9] Head, J.N., et al., Science, 298, 1752-1756 (2002). [10] Lagain, A., et al., in Reimold, W.U., and Koeberl, C., eds., Large Meteorite Impacts and Planetary Evolution VI, 550, p. 1-16 (2021). [11] Robbins, S.J., & Hynek, B.M. J. Geophys. Res., 117, E05004, (2012). [12] Robbins, S.J. & Hynek, B.M. J. Geophys. Res., 116, E10003 (2011). [13] Hartmann, W.K., et al., Icarus, 208, 621-635 (2010). [14] Tornabene, L.L., et al. J. Geophys. Res., 111, 1-25 (2006). [15] Benedix, G.K., et al. Earth. Sp. Sci., 7, e2019EA001005 (2020). [16] Dickson, J.L., et al., 49th Lunar and Plan. Sci. Conf. (2019). [17] Robbins, S.J., et al. Icarus, 234, 109–131 (2014). more...

Introduction Planetary surfaces not protected by dense atmospheres suffered by many impacts by asteroids and comets, leaving craters as a reminders of it. Among all craters observed on surfaces of Earth, Mars, Moon, and Venus, about 3-4% are binary craters. It is believed they formed by the simultaneous impacts of the two components of binary asteroid systems.Binary asteroids represent 15% of near-Earth asteroids, apparently at odd with the rate of binary craters on planetary surfaces. Miljkovic et al. showed with 3-D hydrocode simulations that only a fraction of impacts by binary asteroids create distinguishable binary craters, solving the apparent discrepancy with the fraction of binary craters of 3-4%. However, the few binary crater examples in have striking properties: nearly similar size and North-South orientation, unexpected from a population of binary asteroids displaying a typical size ratio of 0.3 and with a mutual orbit closely aligned with the ecliptic. Survey and simulationsA large fraction of impact craters on Mars exhibits thick and continuous ejecta blanket emplaced in a pyroclastic flow-like regime due to the presence of volatile material at the moment of the impact. This facilitates the recognition of synchronous impact events, making the surface of Mars an ideal case to survey for the existence of binary craters and infer the binary asteroids properties.Our study focuses on craters more than 4km in diameter located between latitudes 50°N and 50°S compiled in the database and recently revised by A. Lagain in 2021. We chose this minimum diameter to remove potential bias that could be caused by isolated secondary impacts and this range of latitude to avoid high-latitudes resurfacing processes. Binary craters are recognized based on the morphology of their cavity or their ejecta blanket.The presence of a septum (i.e. a linear contact perpendicular to the direction of both crater centers on their shared rim or ejecta blanket), is one of the main morphological characteristics allowing to identify them, as illustrated on Fig.1. We classify candidates binary craters following Miljkovic scheme: Elliptical, Peanut, Doublet, Tear drop, Overlapping and Circular. We will not analyze the last category as it represents craters whose a binary asteroid impact origin is more uncertain. In parallel, we conduct three-body dynamical simulations to predict the orientation or binary craters on Mars surface as inferred from the known population of binary asteroids, extending the previous work by Melosh and Stansberry. Results and ConclusionsOut of the 31,778 craters we inspected, we identify 28 doublet, 44 peanut, 17 overlapping, 23 tear, and 13 elliptical craters. Using crater scaling laws adapted for Mars impact condition, the size of impactors having formed those craters range between approximately 100 m and 5 km. 28 doublet craters indicate on largely separated binary asteroids with more than 10 diameters of the primary asteroid size.The observed distribution of orientation angle θ of doublet craters as well as the simulated one are presented in Fig.2. It is clearly seen that the distributions are different. We also performed a Kolmogorov-Smirnov test on the two distributions and we can reject with a 99.99% confidence that the two distributions are similar.Our numerical simulations show that neither the separation nor the orientation of the binary asteroid components is affected by tidal forces of Mars. It means that there is an unobserved population of widely separated binaries, whose mutual orbits is not coplanar with their heliocentric orbits. These binary systems are very difficult to be detected by typical lightcurve programs but our results reveal the existence of these systems. more...

This volume represents the proceedings of the homonymous international conference on all aspects of impact cratering and planetary science, which was held in October 2019 in Brasília, Brazil. The volume contains a sizable suite of contributions dealing with regional impact records (Australia, Sweden), impact craters and impactites, early Archean impacts and geophysical characteristics of impact structures, shock metamorphic investigations, post-impact hydrothermalism, and structural geology and morphometry of impact structures—on Earth and Mars. Many contributions report results from state-of-the-art investigations, for example, several that are based on electron backscatter diffraction studies, and deal with new potential chronometers and shock barometers (e.g., apatite). Established impact cratering workers and newcomers to the field will appreciate this multifaceted, multidisciplinary collection of impact cratering studies. more...

Introduction: The Moon’s bombarded surface acts as a 4 Ga cratering record due to the lack of any significant crustal renewal or erosional processes. This extensive record is analysed by studying the spatial densities of craters on the Moon’s surface across different geological landscapes. These differences in relative cratering densities are quantified and linked to radiometrically dated samples collected during the Apollo and Luna missions. Through all this, one can derive a model age of a cratered surface [1]. This technique is referred to as crater counting. Over the years, this technique has grown to be utilised in dating the surfaces of rocky bodies throughout the solar system [1]. The accuracy of this technique still lies in the ability to detect and measure impact craters. The availability of the Lunar Reconnaissance Orbiter (LRO) Narrow-Angle Camera (NAC) images, with a 0.5-2m/px resolution [2], allows us to see craters at the metre-scale. The leading lunar crater database, consisting of ~1.3 million manually counted craters, is complete down to 1km [3]. To utilise the high-resolution NAC imagery, we need to count ever-smaller craters. The number of smaller craters scale as a power law, meaning there are tens of millions of craters Our team has developed a Crater Counting Algorithm (CDA), based on a Convolutional Neural Network (CNN), that specialises in impact crater detection. Initially developed for Martian crater counting [4,5], the algorithm has now been adapted to analyse the Moon. The Crater Counting Algorithm: The CDA is a CNN developed using You Only Look Once version 3 (YOLOv3), a pattern recognition algorithm, as its architecture. YOLO specialises in real-time single-pass object detection over an image, making it perfect for crater detection [6]. The CDA is run using a trained lunar detection model consisting of 25,973 manually marked craters across 188 tiled NAC images (416x416 pixel). These NAC images have incidence angles ranging from 65°-75° (afternoon/morning lighting), producing favourable shadows when identifying craters. The algorithm is run on a directory of input NAC images where it generates a detection output consisting of crater Long/Lat locations and a diameter. NAC Image Preparation: The NAC images are downloaded in their raw IMG format, where they are georeferenced (a process of linking an images internal coordinate system to a geographical coordinate system) using the USGS’s Integrated Software for Imagers and Spectrometers (ISIS) [7]. ISIS ensures the NAC images have their correct lunar geometry. The images are then exported as GeoTiff files using GDAL, which are used as inputs for the CDA. Model Evaluation: To evaluate the CDA’s ability in accurate small crater detection (D≤100m), the CDA analysed two ideal NAC images (one of each lunar terrain: highland and mare). Altogether, 4874 Craters within 750m2 subsections of each image, Mare Serenitatis (NAC: M1320016983LE) and Terra Sanitatis (NAC: M1338833866LE), were manually counted to validate against 3852 craters detected by the CDA (Fig. 1). The manual counting included all levels of crater degradation states with a ~5m cut off point. Most size categories boast high True Positive (TP) detection rates (>80%) (Tab. 1). True crater diameters across both terrains were mostly overestimated by the CDA (Tab. 1) but are still within the error margins (±20%) of human manual detections [8]. 18 ‘fresh craters’ (craters with clear and easily identifiable rims), with D≥25m, were chosen across both images (Tab. 1*). The CDA has excellent TP detection rates (100%) and diameter estimations (~±10%) for the fresh craters (Tab. 1*). Prospects of the Lunar CDA: With further analysis and evaluation of the lunar CDA across broader lunar terrains, we want to create an accurate small crater lunar dataset. This dataset will fill the gap for craters Figure 1: Visual comparison between CDA and manual detection over two 750m2 NAC subsections, manual detections are in red and CDA detections are in blue. Counting was completed across all levels of degradation. A) Highland terrain, Terra Sanitatis (NAC image M1338833866L at 1m/px resolution), counted crater diameter range: 5m-125m; B) Mare terrain, Mare Serenitatis (NAC image M1320016983L at 1m/px resolution), counted crater diameter range: 5m-137m. Table 1: Confusion matrix of the manual (N=4874) and CDA (N=3852) detections over a 750m2 subsection. A) Highland terrain, Terra Sanitatis (NAC image M1338833866L at 1m/px resolution), counted crater diameter range: 5m-125m; B) Mare terrain, Mare Serenitatis (NAC image M1320016983L at 1m/px resolution), counted crater diameter range: 5m-137m. Note: ‘+’ average diameters indicated the CDA overestimated the true crater diameter, ‘-’ are underestimations. References: [1] Neukum G., Ivanov B. and Hartmann, W.K. (2001). Chronology and Evolution of Mars, Kluwer. 96, 55–86. https://doi.org/10.1023/A:1011989004263. [2] Robinson, M.S., et al. (2010). Sp. Sci. Rev. 150, 81-124.[3] Robbins, S. J. (2019). Journal of Geophysical Research: Planets. 124, 871– 892. https://doi.org/10.1029/2018JE005592. [4] Lagain, A., et al. (2021). Earth and Space Science. https://doi.org/10.1029/2020EA001598. [5] Benedix, G.K., et al. (2020). Earth and Space Science. https://doi.org/10.1029/2019EA001005. [6] Redmon, J., Farhadi, A. (2018). arXiv :1804.02767. [7] https://isis.astrogeology.usgs.gov/. [8] Robbins, S.J., et al. (2014). Icarus. 234, 109–131. https://doi.org/10.1016/j.icarus.2014.02.022 . more...