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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.

The formation and differentiation of the crust of Mars in the first tens of millions of years after its accretion can only be deciphered from incredibly limited records. The martian breccia NWA 7034 and its paired stones is one of them. This meteorite contains the oldest martian igneous material ever dated: ~4.5 Ga old. However, its source and geological context have so far remained unknown. Here, we show that the meteorite was ejected 5–10 Ma ago from the north-east of the Terra Cimmeria—Sirenum province, in the southern hemisphere of Mars. More specifically, the breccia belongs to the ejecta deposits of the Khujirt crater formed 1.5 Ga ago, and it was ejected as a result of the formation of the Karratha crater 5–10 Ma ago. Our findings demonstrate that the Terra Cimmeria—Sirenum province is a relic of the differentiated primordial martian crust, formed shortly after the accretion of the planet, and that it constitutes a unique record of early crustal processes. This province is an ideal landing site for future missions aiming to unravel the first tens of millions of years of the history of Mars and, by extension, of all terrestrial planets, including the Earth. A new study pinpoints the ejection site of the 4.5-Ga-old Martian breccia NWA 7034 and paired stones to an area northeast of the Terra 679 Cimmeria–Sirenium province.

Lacking plate tectonics and crustal recycling, the long-term evolution of the crust-mantle system of Mars is driven by mantle convection, partial melting, and silicate differentiation. Volcanic landforms such as lava flows, shield volcanoes, volcanic cones, pyroclastic deposits, and dikes are observed on the martian surface, and while activity was widespread during the late Noachian and Hesperian, volcanism became more and more restricted to the Tharsis and Elysium provinces in the Amazonian period. Martian igneous rocks are predominantly basaltic in composition, and remote sensing data, in-situ data, and analysis of the SNC meteorites indicate that magma source regions were located at depths between 80 and 150 km, with degrees of partial melting ranging from 5 to 15 %. Furthermore, magma storage at depth appears to be of limited importance, and secular cooling rates of 30 to 40 K Gyr −1 were derived from surface chemistry for the Hesperian and Amazonian periods. These estimates are in general agreement with numerical models of the thermo-chemical evolution of Mars, which predict source region depths of 100 to 200 km, degrees of partial melting between 5 and 20 %, and secular cooling rates of 40 to 50 K Gyr −1 . In addition, these model predictions largely agree with elastic lithosphere thickness estimates derived from gravity and topography data. Major unknowns related to the evolution of the crust-mantle system are the age of the shergottites, the planet’s initial bulk mantle water content, and its average crustal thickness. Analysis of the SNC meteorites, estimates of the elastic lithosphere thickness, as well as the fact that tidal dissipation takes place in the martian mantle indicate that rheologically significant amounts of water of a few tens of ppm are still present in the interior. However, the exact amount is controversial and estimates range from only a few to more than 200 ppm. Owing to the uncertain formation age of the shergottites it is unclear whether these water contents correspond to the ancient or present mantle. It therefore remains to be investigated whether petrologically significant amounts of water of more than 100 ppm are or have been present in the deep interior. Although models suggest that about 50 % of the incompatible species (H 2 O, K, Th, U) have been removed from the mantle, the amount of mantle differentiation remains uncertain because the average crustal thickness is merely constrained to within a factor of two.

ChemCam is a remote sensing instrument suite on board the “Curiosity” rover (NASA) that uses Laser-Induced Breakdown Spectroscopy (LIBS) to provide the elemental composition of soils and rocks at the surface of Mars from a distance of 1.3 to 7 m, and a telescopic imager to return high resolution context and micro-images at distances greater than 1.16 m. We describe five analytical capabilities: rock classification, quantitative composition, depth profiling, context imaging, and passive spectroscopy. They serve as a toolbox to address most of the science questions at Gale crater. ChemCam consists of a Mast-Unit (laser, telescope, camera, and electronics) and a Body-Unit (spectrometers, digital processing unit, and optical demultiplexer), which are connected by an optical fiber and an electrical interface. We then report on the development, integration, and testing of the Mast-Unit, and summarize some key characteristics of ChemCam. This confirmed that nominal or better than nominal performances were achieved for critical parameters, in particular power density (>1 GW/cm 2 ). The analysis spot diameter varies from 350 μm at 2 m to 550 μm at 7 m distance. For remote imaging, the camera field of view is 20 mrad for 1024×1024 pixels. Field tests demonstrated that the resolution (∼90 μrad) made it possible to identify laser shots on a wide variety of images. This is sufficient for visualizing laser shot pits and textures of rocks and soils. An auto-exposure capability optimizes the dynamical range of the images. Dedicated hardware and software focus the telescope, with precision that is appropriate for the LIBS and imaging depths-of-field. The light emitted by the plasma is collected and sent to the Body-Unit via a 6 m optical fiber. The companion to this paper (Wiens et al. this issue ) reports on the development of the Body-Unit, on the analysis of the emitted light, and on the good match between instrument performance and science specifications.

Recent gullies on Mars are suspected to be the result of liquid‐water‐bearing flows. A formation from wet flows has been challenged by studies invoking granular (dry) flows. Our study focuses on the sinuous shapes observed for some of the recent Martian gullies. Sinuous gullies are found in locations and slopes (of 10°–15°) similar to straight gullies, and they are therefore related to the same formation processes. Numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles, roughness, or slope changes that could possibly generate flow sinuosity. None of these simulations was able to reproduce sinuous shapes on a slope lower than 18° with friction angles typical of dry granular material. The only way to simulate sinuous shapes is to create small‐amplitude periodic variations of the topography of the deposit, an origin not supported by current Martian imagery. Given the presence of sinuosity in natural terrestrial debris flows, we have concluded that sinuous Martian gullies are better reproduced by liquid‐water‐bearing debris flows. Sinuous shapes in leveed flows are used to derive mechanical parameters from several Martian gullies using photoclinometry. Values in yield strength of 100–2200 Pa, velocities of 1.1–3.3 m s−1, and viscosities from 40 to 1040 Pa s are found, which are all within the range of values for terrestrial debris flows with various proportions of liquid water (20%–40%).

Small‐scale artisanal mining is a vital sector of the economy of Burkina Faso. This activity, correctly regulated, remains essential for the population despite security issues since 2015. Exploration of new areas for gold mining in this condition is difficult but essential to continue extractive activities. It is, therefore, important to define viable corridors, with science‐based evidence for the good prospects, to support artisanal miners’ activities in a way that minimizes the environmental impact. We describe a remote sensing approach to study the structural control of expanding small‐scale artisanal gold activity at the Bouda site and define future mining corridors. This remote sensing approach can also mitigate and remedy environmental impacts. The Minimum Noise Fraction (MNF) is applied to Landsat images (7‐ETM+, 5‐TM, and 8‐OLI, respectively, for 2000, 2011, and 2022) to detect extraction sites and perform a spatiotemporal analysis of the expansion of areas affected by gold extraction. The near‐infrared and mid‐infrared bands of Landsat images significantly contribute to detecting extraction areas. A morphological study of the site over time and Principal Component Analysis (PCA) on Landsat 8‐OLI enable us to perform a lineament analysis. The expansion of mining activity is structurally controlled, as revealed by the correlation between gold occurrences and high lineament densities, especially in the dominant NE‐SW direction. These analyses suggest five potential prospecting corridors in the Bouda site. Key Points Bouda is an artisanal and small‐scale mining district in Burkina Faso Remote sensing using Landsat images allowed us to study the structural control of the expansion of the Bouda site Remote sensing using Landsat images allowed to define future exploitation corridors of the Bouda site

The severe drought of 1983–1984 in the Sahel region, and its socio‐economic impacts for people relying on farming had for consequence the first major gold rush at Koma Bangou in the southwestern part of Niger. Initiated in 1984, the gold panning activities were interrupted from 1989 to 1999 with exploration permits assigned to the mining industry. The site was reclassified at the year‐end 1999 as a gold panning site and artisanal mining resumed until present‐day. Gold panning activities such as ore extraction and cyanide processing produced mining waste including rocks, mine tailings, and treatment residues. Mining waste is a serious environmental, health and safety problem. Multispectral Landsat images (TM4‐5, ETM7+, OLI/TIRS) acquired between 1984 and 2020 were used to map the spatial evolution of waste generated by gold panning activities at Koma Bangou. Different processing methods were tested, including Minimum Noise Fraction (MNF) transform, Band Ratio (BR), and Feature Oriented Principal Component Selection (FPCS). The FPCS applied to hydroxyl‐bearing minerals appears to be most efficient to map gold extraction and cyanidation waste areas. The waste surface associated with ore extraction has increased from 9.43 ha in 1984 to 234.20 ha in 2020, with continuous expansion during the period of clandestine activity (1989–1999). The waste surface associated with cyanidation has increased from 5.56 ha in 2009 (the year of cyanide treatment introduction) to 99.53 ha in 2020. Landsat multispectral imagery proved a suitable data source for monitoring the evolution of gold mining waste and consequences of public policies at Koma Bangou. Plain Language Summary Artisanal gold mining in Niger is an alternative income‐generating activity for farmers. The first gold rush took place in Koma Bangou, in 1984, following the drought of 1983–1984 in order to cope with famine. The gold panning started in 1984, was interrupted during 1989–1999, and then resumed until present day. This work is based on multispectral analysis of almost 40 years of Landsat data to evaluate the evolution of the surface areas associated with gold extraction and cyanidation (cyanidation is a hydrometallurgical technique for extracting gold from ore by converting the gold to a water‐soluble coordination complex). Several image processing methods were tested for the purpose of mapping the extension of waste surfaces from 1984 onwards and the area of cyanidation waste from the year of introduction of this technique in 2009. Using the most efficient method, we report that the waste surface associated with gold extraction has increased from 9.43 ha in 1984 to 234.20 ha in 2020 with continuous expansion during the period of clandestine activity (1989–1999). The cyanidation areas have increased from 5.56 ha in 2009 to 99.53 ha in 2020. Key Points Koma Bangou is the major artisanal gold mining site in Niger and one of the major sites of artisanal gold mining in the Sahel Gold panning in Koma Bangou produces waste that degrades and pollutes the environment The use of Landsat satellite sensors allows to monitor the evolution of mining activities during four decades (1984–2020)

Mars is characterized by geological landforms familiar to terrestrial geologists. It has a tenuous atmosphere that evolved differently from that of Earth and Venus and a differentiated inner structure. Our knowledge of the structure and evolution of Mars has strongly improved thanks to a huge amount of data of various types (visible and infrared imagery, altimetry, radar, chemistry, etc) acquired by a dozen of missions over the last two decades. In situ data have provided ground truth for remote-sensing data and have opened a new era in the study of Mars geology. While large sections of Mars science have made progress and new topics have emerged, a major question in Mars exploration—the possibility of past or present life—is still unsolved. Without entering into the debate around the presence of life traces, our review develops various topics of Mars science to help the search of life on Mars, building on the most recent discoveries, going from the exosphere to the interior structure, from the magmatic evolution to the currently active processes, including the fate of volatiles and especially liquid water.

Artisanal and small‐scale gold mining (ASGM) represents a significant economic activity for communities in developing countries. In southeastern Senegal, this activity has increased in recent years and has become the main source of income for the local population. However, it is also associated with negative environmental, social, and health impacts. Considering the recent development of ASGM in Senegal and the difficulties of the government in monitoring and regulating this activity, this article proposes a method for detecting and mapping ASGM sites in Senegal using Sentinel 2 data and the Google Earth Engine. Two artisanal mining sites in Senegal are selected to test this approach. Detection and mapping are achieved following a processing pipeline. Principal component analysis (PCA) is applied to determine the optimal period of the year for mapping. Separability and threshold (SEaTH) is used to determine the optimal bands or spectral indices to discriminate ASGM from other land use. Finally, automatic classification and mapping of the scenes are achieved with support vector machine (SVM) classifier. The results are then validated based on field observations. The PCA and examination of spectral signatures as a function of time indicate that the best period for discriminate ASGM sites against other types of land use is the end of dry season, when vegetation is minimal. The classification results are presented as a map with different categories of land use. This method could be applied to future Sentinel scenes to monitor the evolution of mining sites and may also be extrapolated to other relevant areas in the Sahel. Plain Language Summary In recent years, artisanal and small‐scale gold mining (ASGM) has become a significant source of income for communities in southeastern Senegal. However, this activity is also associated with negative environmental and social impacts. The lack of information regarding the constantly evolving geographical distribution and extent of the mining sites is an obstacle for the regulations of this activity by the government. To fill this gap, we have elaborated and tested a method using publicly available multispectral remote sensing data (Sentinel 2) and a cloud computing service (Google Earth Engine). The objective maps of environmental impacts produced by this method shall lead to a better knowledge of the areas affected by artisanal mining activities in the Sahelian region. This low‐cost approach, using public data and computing resources, is designed to become a decision support tool for governments of developing countries. Key Points artisanal and small‐scale gold mining Sentinel 2 Google Earth Engine

The univariate statistics of Potassium (K), thorium (Th), and uranium (U) concentrations, in the Earth’s oceanic and continental crust are examined by different techniques. The frequency distributions of the concentrations of these elements in the oceanic crust are derived from a global catalog of mid‐ocean ridge basalts. Their frequency distributions of concentrations in the continental crust are illustrated by the North Pilbara Craton, and the West Africa Craton. For these two cratons, the distributions of K, Th, and U derived from geochemical analyses of several thousand whole rock samples differ significantly from those derived from airborne radiometric surveys. The distributions from airborne surveys tends to be more symmetric with smaller standard deviations than the right‐skewed distributions inferred from whole rock geochemical analyses. Hypothetic causes of these differences include (a) bias in rock sampling or in airborne surveys, (b) the differences between the chemistry of superficial material and rocks, and (c) the differences in scales of measurements. The scale factor, viewed as consequence of the central limit theorem applied to K, Th, and U concentrations, appears to account for most of the observed differences in the distributions of K, Th, and U. It suggests that the three scales of auto‐correlation of K, Th, and U concentrations are of the same order of magnitude as the resolution of the airborne radiometric surveys (50–200 m). Concentrations of K, Th, and U are therefore generally heterogenous at smaller scales. Plain Language Summary Potassium (K), thorium (Th), and uranium (U), termed together heat‐producing elements (HPE) are commonly analyzed in Earth sciences, owing to their faculty to trace various geological processes. The concentrations of these elements may be analyzed in rock samples, or mapped by airborne radiometric surveys (mapping of gamma ray emitted by 40K, 232Th, and 238U), which are very different techniques. Here, we reveal that frequency distributions of HPE concentrations estimated from data sets build from these different techniques are different. The possible causes of these differences, including possible biases in the data, and the large differences between measurement scales are investigated. We conclude the scale factor and the heterogeneity of HPE at scales that are typically lower than the footprint of airborne radiometric surveys is the main factor controlling the shapes of the frequency distributions. The evolution of asymmetric (right‐skewed) frequency distributions toward normal distributions as a function of the sample size is a natural consequence of the Central Limit Theorem. Key Points Frequency distributions of Potassium (K), thorium (Th), and uranium (U) concentrations from airborne radiometric surveys and geochemical databases are compared Frequency distributions of K, Th, and U concentrations are scale‐dependent Concentrations of K, Th, and U are heterogeneous at the sub‐pixel scale of gridded airborne radiometric maps