Rapid Single Image-Based DTM Estimation from ExoMars TGO CaSSIS Images Using Generative Adversarial U-Nets

The lack of adequate stereo coverage and where available, lengthy processing time, various artefacts, and unsatisfactory quality and complexity of automating the selection of the best set of processing parameters, have long been big barriers for large-area planetary 3D mapping. In this paper, we propose a deep learning-based solution, called MADNet (Multi-scale generative Adversarial u-net with Dense convolutional and up-projection blocks), that avoids or resolves all of the above issues. We demonstrate the wide applicability of this technique with the ExoMars Trace Gas Orbiter Colour and Stereo Surface Imaging System (CaSSIS) 4.6 m/pixel images on Mars. Only a single input image and a coarse global 3D reference are required, without knowing any camera models or imaging parameters, to produce high-quality and high-resolution full-strip Digital Terrain Models (DTMs) in a few seconds. In this paper, we discuss technical details of the MADNet system and provide detailed comparisons and assessments of the results. The resultant MADNet 8 m/pixel CaSSIS DTMs are qualitatively very similar to the 1 m/pixel HiRISE DTMs. The resultant MADNet CaSSIS DTMs display excellent agreement with nested Mars Reconnaissance Orbiter Context Camera (CTX), Mars Express’s High-Resolution Stereo Camera (HRSC), and Mars Orbiter Laser Altimeter (MOLA) DTMs at large-scale, and meanwhile, show fairly good correlation with the High-Resolution Imaging Science Experiment (HiRISE) DTMs for fine-scale details. In addition, we show how MADNet outperforms traditional photogrammetric methods, both on speed and quality, for other datasets like HRSC, CTX, and HiRISE, without any parameter tuning or re-training of the model. We demonstrate the results for Oxia Planum (the landing site of the European Space Agency’s Rosalind Franklin ExoMars rover 2023) and a couple of sites of high scientific interest

The geomorphology of gravity instabilities on Mars using data from the CaSSIS imager on the ExoMars orbital probe

Depuis leur mise en orbite autour de Mars, les sondes spatiales ont permis de mettre en lumière la richesse géologique de la planète, dont la présence de glissements de terrain. Plus de 3000 glissements ont été recensés à sa surface mais leur mécanisme de formation ainsi que leur dynamique d’écoulement sont encore, à l’heure actuelle, très mal compris. Dans le but de mieux cerner leur dynamique, cette thèse se focalisera sur l’étude de glissements martiens dont la taille permet des comparaisons morphologiques avec des analogues terrestres. Pour cela des méthodes de reconstruction topographique ont été développées, et l’analyse morphologique des glissements a été effectuée à l’aide de différents imageurs présents en orbite autour de Mars (CTX, CaSSIS, HiRISE). Ces analyses morphologiques ont notamment permis d’arriver aux conclusions suivantes : i) l’identification de glissements récents à l’échelle géologique de la planète. ii) l’importance des morphologies dans la compréhension des dynamiques d’écoulements. iii) la présence de glissements de formes atypiques impliquant très probablement des volatiles (ex : eau) dans leur dynamique d’écoulement. Cette thèse, via l’étude de glissements de terrain récents, s’inscrit dans l’optique d’une meilleure compréhension de l’histoire hydrologique de la planète. L’implication de volatile dans la formation de ces glissements permettrait en effet de nuancer l’idée d’une planète complètement froide et sèche au cours des derniers millions d’années.Since their orbit around Mars, space probes have highlighted the planet's geological diversity, including the presence of landslides. More than 3000 landslides have been recorded on its surface, but their formation mechanism and flow dynamics are still poorly understood. In order to better understand their dynamics, this thesis will focus on the study of martian landslides whose size allows morphological comparisons with terrestrial analogues. For this purpose, topographic reconstruction methods have been developed, and morphological analysis of the landslides has been carried out using different imagers in orbit around Mars (CTX, CaSSIS, HiRISE). These morphological analyses have led to the following conclusions: i) the identification of recent landslides on the geological scale of the planet. ii) the importance of morphologies in the understanding of flow dynamics. iii) the presence of atypical landslides that most probably involve volatiles (e.g. water) in their flow dynamics. This work, through the study of recent landslides, is part of a better understanding of the hydrological history of the planet. The involvement of volatiles in the formation of these landslides would indeed allow us to nuance the idea of a completely cold and dry planet over the last few million years

The geomorphology of gravity instabilities on Mars using data from the CaSSIS imager on the ExoMars orbital probe

Depuis leur mise en orbite autour de Mars, les sondes spatiales ont permis de mettre en lumière la richesse géologique de la planète, dont la présence de glissements de terrain. Plus de 3000 glissements ont été recensés à sa surface mais leur mécanisme de formation ainsi que leur dynamique d’écoulement sont encore, à l’heure actuelle, très mal compris. Dans le but de mieux cerner leur dynamique, cette thèse se focalisera sur l’étude de glissements martiens dont la taille permet des comparaisons morphologiques avec des analogues terrestres. Pour cela des méthodes de reconstruction topographique ont été développées, et l’analyse morphologique des glissements a été effectuée à l’aide de différents imageurs présents en orbite autour de Mars (CTX, CaSSIS, HiRISE). Ces analyses morphologiques ont notamment permis d’arriver aux conclusions suivantes : i) l’identification de glissements récents à l’échelle géologique de la planète. ii) l’importance des morphologies dans la compréhension des dynamiques d’écoulements. iii) la présence de glissements de formes atypiques impliquant très probablement des volatiles (ex : eau) dans leur dynamique d’écoulement. Cette thèse, via l’étude de glissements de terrain récents, s’inscrit dans l’optique d’une meilleure compréhension de l’histoire hydrologique de la planète. L’implication de volatile dans la formation de ces glissements permettrait en effet de nuancer l’idée d’une planète complètement froide et sèche au cours des derniers millions d’années.Since their orbit around Mars, space probes have highlighted the planet's geological diversity, including the presence of landslides. More than 3000 landslides have been recorded on its surface, but their formation mechanism and flow dynamics are still poorly understood. In order to better understand their dynamics, this thesis will focus on the study of martian landslides whose size allows morphological comparisons with terrestrial analogues. For this purpose, topographic reconstruction methods have been developed, and morphological analysis of the landslides has been carried out using different imagers in orbit around Mars (CTX, CaSSIS, HiRISE). These morphological analyses have led to the following conclusions: i) the identification of recent landslides on the geological scale of the planet. ii) the importance of morphologies in the understanding of flow dynamics. iii) the presence of atypical landslides that most probably involve volatiles (e.g. water) in their flow dynamics. This work, through the study of recent landslides, is part of a better understanding of the hydrological history of the planet. The involvement of volatiles in the formation of these landslides would indeed allow us to nuance the idea of a completely cold and dry planet over the last few million years

Relationship between subsurface ice reservoirs and Amazonian landslides in the Nilosyrtis Mensae region of Mars

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Atypical landslides in the Nilosyrtis region of Mars

International audienceThis study focuses on four unusual landslides located inside a 25 km diameter impact crater located in Nilosyrtis Mensae (Fig.1). Our initial study revealed that one of these landslides bears close similarity to a mudslide on Earth [1]. We performed a detailed morphological analysis and a comparison with terrestrial analogues to better understand their formation mechanism. We also consider the possible role of volatiles in their formation

Geologically Recent Earthflow-Like Landslides on Mars

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High resolution topographic analysis and numerical simulations of landslides on Mars

International audienceLandslides on Mars have been studied since the Mariner missions in the 1970s. These landslides were found to be exceptionally large by terrestrial standards and were also found to be abnormally mobile. Here we study three martian landslides that have a more terrestrial scale (1.1-3.2 km long) with the aim of discovering if these smaller landslides obey the same rules as their larger cousins. By virtue of their size and through the size-frequency of superposed impact craters we know that these three landslides must be younger than the larger landslides included in previous studies. Hence, this gives us a vision as to whether conditions for landsliding (possibly related to activity of water in the crust, through alteration or the hydrosphere) have changed over Mars' history. Because of their more manageable size we are able to take advantage of stereo images taken by NASA's High Resolution Imaging Science Experiment (HiRISE) to reconstruct their topography at 2 m/pix horizontal resolution, with a vertical accuracy of ∼0.5 cm. This enables us to accurately reconstruct their volumes, which range between 4.5 x 106 and 9.5 x 108 m3, but also enables us to simulate their dynamics. We do this by making a best-guess estimation of the initial topography and the release area and then run the model SHALTOP. This model can simulate gravity-driven dry granular flow using different friction laws. We vary the density, the friction coefficient and the friction law calculation (Coulomb or Pouliquen) in the model and "good" solutions are those where the spatial distribution of deposition thickness and deposit morphology most closely match those measured from our elevation data. Our preliminary results suggest that these three martian landslides do not have the same friction coefficient. Morphological similarity with mudflows in one case suggests fluid may have been involved in its formation

Unknown population of binary asteroids

International audienceIntroductionPlanetary 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

Evidence for widely-separated binary asteroids recorded by craters on Mars

International audienceOver the last decades, a significant number of small asteroids (diameter <10 km) having a satellite in orbit around them have been discovered. This population of binary asteroids has very specific properties (secondary-to-primary diameter ratio of about 0.3, semi-major axis to primary diameter ratio around 2 and an obliquity of the system close to either 0∘ or 180∘) pointing at formation by YORP-induced spin-up and rotational fission. When impacting the surface of terrestrial bodies, those exotic objects lead to the formation of binary craters, exhibiting various morphologies depending on the configuration of the system at the moment of the impact. Planetary surfaces constitutes therefore the best (if not the only one) record of binary asteroid population through time. In contrast to the Moon or Mercury, a large fraction of impact craters on Mars exhibits thick ejecta layers due to the presence of volatile material at the moment of the impact (e.g., water ice). The martian surface represents thus the ideal case to survey for the existence of binary craters, as the ejecta morphology can attest of a synchronous impact. From a survey of 87% of Mars surface, we identify 150 binary craters (0.5% of the total), likely formed by the impact of binary asteroids. The properties of these craters contrast with those of the population of binary asteroids: size ratio close to unity, large separation, and isotropic orientation on the surface. We run numerical simulations of impacts to test whether tidal effects on the impact trajectory can explain these discrepancies. Our results suggest that a population of similarly-sized and well-separated binary asteroids with non-zero obliquity remains to be observed