Layered deposits are found on the plateaus surrounding the western portion of Valles Marineris, mantling the chasmata rims. These rim deposits exhibit intricate layering and are described as light-toned layered deposits (LLDs) in previous studies. Light-toned layered deposits are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and later chemically altered. Using Shallow Radar (SHARAD) observations to map radar reflections from what appears to be the base of these deposits, we discovered two additional types of rim deposits that are contiguous with the well-known LLDs; weakly layered deposits (WLDs) that exhibit less obvious stratification and completely unstratified deposits designated as nonlayered deposits (NDs). Complementing the SHARAD data with imagery from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and with narrow-angle imagery from the Mars Global Surveyor Mars Observer Camera (MOC-NA), we mapped the full extent of all rim deposits and present the finished map within this study. We hypothesize that all three deposits originate from pyroclastic ashfall but experienced different degrees of modification due to the variable presence of liquid water. This hypothesis requires a source of volcanic depositional material and past aqueous environments in regions with LLDs and WLDs. We discuss the potential for several large Tharsis volcanoes and a hypothesized degraded volcano within Noctis Labyrinthus as sources of the ash, and we examine the evidence for past aqueous environments.

We present the Infrared spectrometer of SuperCam Instrument Suite that enables the Mars 2020 Perseverance Rover to study remotely the Martian mineralogy within the Jezero crater. The SuperCam IR spectrometer is designed to acquire spectra in the 1.3-2.6 $\mu$m domain at a spectral resolution ranging from 5 to 20~nm. The field-of-view of 1.15 mrad, is coaligned with the boresights of the other remote-sensing techniques provided by SuperCam: laser-induced breakdown spectroscopy, remote time-resolved Raman and luminescence spectroscopies, and visible reflectance spectroscopy, and micro-imaging. The IR spectra can be acquired from the robotic-arm workspace to long-distances, in order to explore the mineralogical diversity of the Jezero crater, guide the Perseverance Rover in its sampling task, and to document the samples' environment. We present the design, the performance, the radiometric calibration, and the anticipated operations at the surface of Mars.

The Perseverance rover has landed in Jezero crater, Mars. Séítah is an exposure of the oldest geologic unit on the Jezero crater floor. This unit contains olivine and hydrated minerals that record volcanism, sedimentation, diagenesis, and aqueous alteration on ancient Mars. Evaluating the depositional origin/timing and diagenesis of this unit will improve our understanding of the geologic evolution and habitability of rocks in the Perseverance field site. Jezero crater was previously a lacustrine environment, and its surrounding region contains a widespread aqueously altered olivine-bearing rock unit that may be an ashfall deposit. Here we use images from SuperCam and Mastcam-Z onboard the Perseverance rover to identify facies in Séítah and constrain its geologic history. Rover observations of Séítah show several distinct facies cropping out within NE-SW-trending, decameter-high ridges. Identified facies include thin (≤ ~1-3 cm) beds with a nodular appearance, erosionally resistant beds of variable (~10-40 cm) thickness, massive rocks, and rocks with large nodules. No definitive clasts or grains have been observed in long-distance images with resolutions of ~2-3 mm/pixel, suggesting subcentimeter grain sizes. An origin as aeolian dune deposits is not favored given the lack of cross-bedding, and fluvial channel geometries have not yet been observed. Planar bedding of variable thickness within the Séítah ridges could be consistent with clastic deposition from suspension coupled with deposition from higher-energy flows in a lacustrine setting. This interpretation would also be consistent with the occurrence of these outcrops within an ancient crater lake basin, basinward of the Jezero delta. However, the potential orbital map correlation of the Séítah outcrop with the regionally widespread olivine-bearing unit outside of Jezero raises the possibility of a subaerial volcaniclastic or airfall origin. Further distinction between subaqueous and subaerial depositional origins for Séítah likely requires fine-scale observations of grain-size, fabric, and textures by the rover’s science instruments upon closer approach. Rocks formed from subaerial and subaqueous deposition have different biosignature preservation potential, making the characterization of depositional environment important.

The main objective of ExoMars 2020 is to search for signs of past and/or present life on Mars. Because these signs may be beneath the inhospitable surface of Mars, the ExoMars Rover has on board a suite of instruments aiming at characterizing the subsurface. In particular, the Rover payload includes WISDOM (Water Ice Subsurface Deposits Observation on Mars), a polarimetric ground penetrating radar designed to investigate the shallow subsurface. WISDOM is able to probe down to a depth of few meters with a resolution of few centimeters; its main objective is to provide insights into the geological context of the investigated Martian sites and to determine the most promising location to collect samples for the ExoMars drill. In this paper, we demonstrate the ability of WISDOM to locate buried rocks and to estimate their size distribution. Indeed, the rock distribution is related to the geological processes at play in the past or currently and thus provides clues to understand the geological context of the investigated site. Rocks also represent a hazard for drilling operations that WISDOM is to guide. We use a 3D FDTD code called TEMSI-FD (which takes into account the radiation pattern of the antenna system) to simulate WISDOM operations on a realistic (both in terms of dielectric properties and structure) ground. More specifically, our geoelectrical models of the Martian subsurface take into account realistic values of the complex permittivity relying on published measurements performed in laboratory on Martian analogues. Further, different distributions of buried rocks are considered based on the size-frequency distribution observed at the Mars Pathfinder landing site and on Oxia Planum, the landing site currently selected for ExoMars 2020. We will describe the algorithm we developed to automatically detect the signature of the buried rocks on radargrams. The radargrams are obtained simulating WISDOM operations along parallel and perpendicular profiles as planned for the ExoMars mission. Our ultimate goal is to show that WISDOM observations can be used to build a 3D map of the subsurface. We will also present experimental data obtained with a prototype of WISDOM to test our method.

This paper presents the abundances and the size-frequency distributions (SFD) of boulders identified on a sector of the prime landing site for the ExoMars 2020 rover, in Oxia Planum region. By means of a HiRISE image, boulders >= 1.75 m across have been identified and subdivided according to the two main Oxia Planum geological units: the Noachian clay-rich formation (Nc), and the Amazonian volcanic deposit (Av). The spatial density of boulders >= 1.75 m over the entire study area is 6.75 x 10(-4)/m(2), with a size frequency that is best fit both with power-law and exponential-law curves with indices of -4.9 + 0.1/-0.2 and -1.29 + 0.04/-0.06 respectively. Significant differences were found by analysing separately the Av and Nc geological units. The data collected in the Av unit are well-fitted with a power-law curve with an index equal to -4.8 +/-0.2 and with an exponential-law curve with an index of -1.24 + 0.05,-0.06, whilst in the Nc unit such indices are -5.5 + 0.3/-0.4 and -1.70 + 0.09/-0.12 (power-law and exponential-law curve, respectively). The spatial density of boulders in the Av unit is 7.0 times larger than in the Nc one. This may be due primarily to the distinct mechanical properties of the two units that may result in a different production rate or preservation of the boulders. Secondly, the Av unit overlies the Nc unit, possibly resulting in more impacts and/or different weathering processes throughout the ages. This study provides a quantitative evaluation of the abundances of boulders >= 1.75 m across on Oxia Planum: it is therefore a reference for the ExoMars 2020 mission, both during the landing phase and the rover traverse to specific areas of interest. The landing ellipse presents much higher abundances of boulders >= 1.75 m than all previous Martian rover landing areas. This is particularly evident when the rougher Av unit is taken into account. Contrarily, the Nc unit shows a much more comparable value, but still slightly higher, to the Mars Pathfinder landing site. We provide illustrative navigating scenarios for both the Nc and the Av units as well. Published by Elsevier Inc.

In response to questions that have been raised about formation and effects of secondary craters on crater chronometry techniques, we studied properties of the secondary crater field around the young Martian primary ray crater Gratteri (diameter 7km). The crater has an estimated age of 1 to 20Myr, based on counts of small craters on flat interior surface, consistent with a likely age for a young crater its size (Hartmann et al., 2010). The following are among our findings: (1) We identify an unusual class of craters we call rampart secondaries which may suggest low-angle impacts. (2) We measure size distributions of secondaries as a function of distance from Gratteri and used these data to reconstruct the mass-velocity distribution of ejecta blasted out of Gratteri. Our data suggest that crater density in rays tends to peak around 120-230km from Gratteri (roughly 20-30D) and reaches roughly 30-70 times the interray crater density. (3) Comparable total numbers of secondaries form inside rays and outside rays, and about half are concentrated in clusters in 2% of the area around Gratteri, with the others scattered over 98% of the area out to 400km away from Gratteri. (4) In the old Noachian plains around Gratteri, secondaries have minimal effect on crater chronometry. These results, along with recently reported direct measurements of the rate of formation of 10m to 20m primaries on Mars (Daubar et al., 2013), tend to negate suggestions that the numbers and/or clustering of secondaries destroy the effectiveness of crater counting as a chronometric tool.

Until recently, Mars was considered a basalt-covered world, but this vision is evolving thanks to new orbital, in situ and meteorite observations, in particular of rocks of the ancient Noachian period. In this contribution we summarise newly recognised compositional and mineralogical differences between older and more recent rocks, and explore the geodynamic implications of these new findings. For example the MSL rover has discovered abundant felsic rocks close to the landing site coming from the wall of Gale crater ranging from alkali basalt to trachyte. In addition, the recently discovered Martian regolith breccia NWA 7034 (and paired samples) contain many coarse-grained noritic-monzonitic clasts demonstrably Noachian in age, and even some clasts that plot in the mugearite field. Olivine is also conspicuously lacking in these ancient samples, in contrast to later Hesperian rocks. The alkali-suite requires low-degree melting of the Martian mantle at low pressure, whereas the later Hesperian magmatism would appear to be produced by higher mantle temperatures. Various scenarios are proposed to explain these observations, including different styles of magmatic activity (i.e. passive upwelling vs. hotspots). A second petrological suite of increasing interest involves quartzo-feldspathic materials that were first inferred from orbit, in local patches in the southern highlands and in the lower units of Valles Marineris. However, identification of felsic rocks from orbit is limited by the low detectability of feldspar in the near infrared. On the other hand, the MSL rover has described the texture, mineralogy and composition of felsic rocks in Gale crater that are granodiorite-like samples akin to terrestrial TTG (Tonalite–Trondhjemite–Granodiorite suites). These observations, and the low average density of the highlands crust, suggest the early formation of ‘continental’ crust on Mars, although the details of the geodynamic scenario and the importance of volatiles in their generation are aspects that require further work.

On 15 February 2013 around 03:20:00 UTC, the largest meteor reported since the 1908 Tunguska event was observed as a fireball traveling through the Earth's atmosphere, exploding in an air burst near the city of Chelyabinsk, Russia. The rarity of such an event provides a unique window on the physics of meteoroid collision. We report the fine seismic detection of Rayleigh waves produced by the coupling of ground motion with the incident shock wave at distances up to 4000 km from the event. Combining information from seismic beam‐forming analysis, reconstructed trajectory from casual video records, and remote sensing, we identify the Rayleigh waves as being initiated by the shock wave produced by the main blast that occasioned damages and injuries in Chelyabinsk. From the Rayleigh wave observations, we report a magnitude Ms∼3.7 seismic source.

Despite recent efforts from space exploration to sound the martian subsurface with RADAR, the structure of the martian subsurface is still unknown. Major geologic contacts or discontinuities inside the martian crust have not been revealed. Another way to analyze the subsurface is to study rocks that have been exhumed from depth by impact processes. The last martian mission, MRO (Mars Reconnaissance Orbiter), put forth a great deal of effort in targeting the central peaks of impact craters with both of its high resolution instruments: CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and HiRISE (High Resolution Science Experiment). We analyzed the composition with CRISM and the physical characteristics on HiRISE of the rocks exhumed from depth from 31 impact craters in the vicinity of Valles Marineris. Our analyses revealed the presence at depth of two kinds of material: massive light-toned rocks and intact layers. Exhumed light-toned massive rocks are enriched in low calcium pyroxenes and olivine. Hydrated phases such as smectites and putative serpentine are present and may provide evidence of hydrothermal processes. Some of the rocks may represent portions of the volatile-rich, pre-Noachian martian primitive crust. In the second class of central peaks, exhumed layers are deformed, folded, and fractured. Visible-near infrared (VNIR) spectra suggest that they are composed of a mixture of olivine and high calcium pyroxene associated with hydrated phases. These layers may represent a Noachian volcanic accumulation of up to 18km due to Tharsis activity. The spatial distribution, as well as the in-depth distribution between the two groups of rocks exhumed, are not random and reveal a major geologic discontinuity below the Tharsis lava plateau. The contact may be vertical over several kilometers depth suggesting the pre-existence of a steep basin (early giant impact or subsidence basin) or sagduction processes.

Thousands of phyllosilicate‐rich outcrops, mainly iron or magnesium‐rich are exposed on Noachian terrains in the Martian southern highlands. We analyzed 90 CRISM observations and more than a hundred HiRISE images located on the plateaus surrounding Valles Marineris. We mapped an extensive Al‐ and Fe/Mg‐phyllosilicate‐rich formation covering at least ∼197,000 km2, for which we introduce the name “Plateau Phyllosilicates.” Tens of meters in thickness, this light‐toned formation crops out at various elevations on top of the Noachian units Npl1 and Npl2, as flat exposures on plateaus and along scarps such as valley walls, chasma walls, pit walls and impact crater rims. The Fe/Mg‐phyllosilicate‐rich lower member of the formation is composed of Fe/Mg‐smectites (nontronite, saponite) and vermiculite. The Al‐phyllosilicate‐rich upper member of the formation contains Al‐smectites (montmorillonite, beidellite) and locally kaolinite and/or halloysite. We suggest that the Plateau Phyllosilicates were mainly formed by pedogenesis related to the weathering of the Noachian bedrock by percolation of meteoric water or melted snow under a temperate and subarid climate during the Noachian Epoch in an alkaline to neutral environment. Kaolinite and/or halloysite may have formed in areas of more intense drainage at the surface under slightly acidic environments during the Noachian and Hesperian Epochs. Fluvial activity and deuteric alteration may have locally contributed to the genesis of phyllosilicates. This study suggests that the alteration of the Noachian basement of the plateaus surrounding Valles Marineris was widespread during the Noachian Epoch, and was still active during the Hesperian Epoch even though the water availability was limited.

Valles Marineris is a unique vertical section through the uppermost kilometers of the martian crust. Its location, east of the Tharsis bulge, and its water-related history, fuel a great diversity of rock types in this area (Carr, M.H., Head, J.W. [2010]. Earth Planet. Sci. Lett. 294.185-203). HiRISE and CRISM data available over the walls of the canyon were analyzed to infer the importance of magmatic and sedimentary processes through time. This contribution provides a complete morphologic and mineralogic characterization of the cross-section of rocks exposed in the canyon walls. Low-calcium pyroxene and olivine are detected in the lower portion of the walls, in association with morphologically distinct outcrops, leading to the idea that pristine Noachian crust might be exposed. Phyllosilicates are also present within the walls, but they appear to correspond to an alteration product. No proper sedimentary layers were observed within the walls of Valles Marineris at the resolution available today. All these detections are limited to the eastern portion of Valles Marineris, especially Juventae, Coprates, Capri, and Ganges chasmata. Preserved Noachian crustal material is rare on the martian surface and is rarely exposed in its pristine geologic context. Such detections lend precious information about early igneous processes. This survey also supports observations from the nearby impact crater central peaks (Quantin, C., Flahaut, J., Allemand, P. [2009]. Lunar Planet. Sci. 10; Quantin, C., Flahaut, J., Clenet, H., Allemand, P., Thomas, P. [2011]. Icarus, submitted for publication) and suggests that the western part of Valles Marineris may be cut into another material, consistent with lavas or volcanic sediments. (C) 2012 Elsevier Inc. All rights reserved.

High albedo features are identified in association with barchan dunes in an equatorial inter-crater dune field on Mars using images from the MRO mission. This paper describes the morphometric properties of these features and their association with the present barchan dune field. We propose that these features are cemented aeolian deposits that form at the foot of the dune avalanche face. A possible terrestrial analog exists at White Sands National Monument, in south-central New Mexico, USA. The presence of these features suggests past episodes of dune migration in inter-crater dunefields and liquid water in the near sub-surface in sufficient quantity to cause the cementation of aeolian dune sediment. (C) 2011 Elsevier Inc. All rights reserved.

Valles Marineris represents the deepest natural incision in the Martian upper crust. Previous studies showed that the upper parts of the walls were made of finely layered probable basalts in most of the chasmata, while the base of the stratigraphy reveals primary Noachian crustal blocks. Exposures of pristine Noachian bedrock are rare on Mars, and mostly observed outside of their geological context. The occurrence of well‐preserved and extended outcrops of pristine material in this giant rift could bring valuable information on the early processes that took place at the surface of Mars. Analyses of high resolution data over the best exposures of lower walls in Coprates Chasma, central Valles Marineris, revealed the presence of multiple magmatic intrusions interpreted as dikes. These dikes intrude an old, massive, fractured bedrock interpreted as being preserved ancient Noachian crust. Their composition, determined using CRISM data, and distribution, limited to this ancient crust at the bottom walls, indicate that they might have formed early in the rift formation, and therefore represent exceptionally well‐preserved outcrops of the early history of Mars.

Dunes have similar morphologies on the Earth and Mars. The main differences between Martian and terrestrial dunes are their size, which is larger on Mars, and their duration of formation, which is longer on Mars. As the characteristic time of Martian dunes is in the same order as that of the Martian climatic oscillations, Martian dunes could be recorders of past winds regimes and past climates. In order to test this hypothesis, we performed a morphological study of 550 dune fields with high resolution images and we inferred the directions of the dune formative winds from the orientation of the dune slip faces. Our study shows that 310 dune fields record one to four distinct wind directions with some geometric patterns that do not exist on the Earth such as barchans built by opposite wind directions coexisting in the same dune field. Our study demonstrates that the inferred formative wind directions are only partially in agreement with the current wind-patterns predicted by General Circulation Models (GCM). Several possible causes for the misalignment between dunes and GCM outputs are discussed: these include the local variation of the global circulation due to local topographic effects or the possibility that these dunes could be in a transient geometry or fossil. Such bedforms are considered indeed to be not in equilibrium with the present-day atmospheric conditions. This latter hypothesis is supported by the presence, in some ergs, of closely spaced dunes showing nearly opposite slip face orientations. Therefore, we propose that Martian dune fields are constituted, in some cases, by active and fossil dunes and therefore have the potential to preserve information on paleoclimates over extensive periods.

Layered deposits have been observed in different locations at the surface of Mars, as crater floors and canyons systems. Their high interest relies in the fact they imply dynamical conditions in their deposition medium. Indeed, in opposition to most of the rocks of the martian surface, which have a volcanic origin, bright layered deposits seems to be sedimentary outcrops.Capri Chasma, a canyon located at the outlet of Valles Marineris, exhibits such deposits called Interior Layered Deposits (ILD). A large array of visible and infrared spacecraft data were used to build a Geographic Information System (GIS). We added HiRiSE images, from the recent MRO mission, which offer a spatial resolution of 25 cm per pixel. It allowed the mapping and the analysis of morphologies in the canyon. We highlighted that the ILD are several kilometers thick and flat-top stratified deposits. They overlap the chaotic floor. They are surrounded and cut by several flow features that imply that liquid water was still acting after the formation of these stratified deposits. The density of crater on the floor of Capri Chasma was quantified. The current topography was aged to 3 Gyr. All these morphological information allow us to suggest a plausible geological history for Capri Chasma. We propose that the Interior Layered Deposits have formed during the Hesperian, during or after the opening of the canyon. Some observations argue that water discharges have happened at several times before and just after the formation of the ILD. Liquid water must have played a major role in the formation of these deposits after 3.5 Gyr, implying that it was present in surface at least locally and temporarily. If this can be applied to ILD in others canyons of Valles Marineris, it would imply that liquid water was stable in surface or sub-surface during the Hesperian. Or in the actual conditions, with a cold and dry martian surface, long-term standing water bodies are not possible. Thus we suggest that either the climate at the Hesperian was cold, but wetter, or as warm as the Noachian climate, what is less likely. Nevertheless, the global climate change which has occurred at the beginning of Mars history may have been later than announced. (C) 2009 Elsevier Inc. All rights reserved.

CRISM is a hyperspectral imager onboard the Mars Reconnaissance Orbiter (MRO; NASA, 2005) which has been acquiring data since November 2006 and has targeted hydrated minerals previously detected by OMEGA (Mars Express; ESA, 2003). The present study focuses on hydrated minerals detected with CRISM at high spatial resolution in the vicinity of Capri Chasma, a canyon of the Valles Marineris system. CRISM data were processed and coupled with MRO and other spacecraft data, in particular HiRiSE (High Resolution Science Experiment, MRO) images. Detections revealed sulfates in abundance in Capri, especially linked to the interior layered deposits (ILD) that lie in the central part of the chasma. Both monohydrated and polyhydrated sulfates are found at different elevations and are associated with different layers. Monohydrated sulfates are widely detected over the massive light-toned cliffs of the ILD, whereas polyhydrated sulfates seem to form a basal and a top layer associated with lower-albedo deposits in flatter areas. Hydrated silicates (phyllosilicates or opaline silica) have also been detected very locally on two mounds about a few hundred meters in diameter at the bottom of the ILD cliffs. We suggest some formation models of these minerals that are consistent with our observations.

McEwen et al. (McEwen, A.S., Preblich, B.S., Turtle, E.P., Artemieva, N.A., Golombek, M.P., Hurst, M., Kirk, R.L., Burr, D.M., Christensen, P. [2005]. Icarus 176, 351–381) developed a useful test for the internal consistency of crater-count chronometry systems. They argued that certain multi-kilometer, fresh-looking martian craters with prominent rays should be the youngest or near-youngest craters in their size range. The “McEwen et al. test” is that the ages determined from crater densities of the smallest superimposed craters (typically diameter D∼5–20m) should thus be comparable to the expected formation intervals of the host primary. McEwen et al. concluded from MOC data that crater chronometry failed this test by factors of 700–2000. We apply HiRISE and other imagery to eight different young craters in order to re-evaluate their arguments. We use existing crater chronology systems as well as the reported observed production rate of 16m craters (Malin, M.C., Edgett, K., Posiolova, L., McColley, S., Noe Dobrea, E. [2006]. Science 314, 1573–1557; Hartmann, W.K., Quantin, C., Mangold, N. [2007]. Icarus 186, 11–23; Kreslavsky [2007]. Seventh International Conference on Mars, 3325). Every case passes the McEwen et al. test. We conclude that the huge inconsistencies suggested by McEwen et al. are spurious. Many of these craters show evidence of impact into ice-rich material, and appear to have ice-flow features and sublimation pits on their floors. As production rate data improve, decameter-scale craters will provide a valuable way of dating these young martian geological formations and the processes that modify them.