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The Afar depression at the northern end of the East African Rift system is the only analog on earth where magmatic continental rifting and associated ongoing break-up processes are exposed onshore. This unique active system presents the key advantage to expose extensional structures related to ocean-continent transition, with magmatic rift segments characterized by contrasted morphologies, and magmato-tectonic styles. The main goal of this study is to identify the location and investigate the functioning and persistence of magma reservoirs at the active magmatic segments in the central Afar depression (Manda Hararo, northern Tendaho grabben), in order to (i) highlight their relationships and potential control with the first- and second-order local segmentation, and (ii) understand the interplay between magmatic and tectonic processes during the generation of such magmatic crust. We combine remote sensing, field investigations, precise and comprehensive mapping of volcanic and tectonic structures, cosmogenic (36Cl) exposure dating of lava surfaces, and geochemical analysis to constrain the temporal frame and the dynamics of magmatic and tectonic processes. The first result of remote sensing analysis allows us to identify two active and self-consistent axial rift subsegments within this extensional system, map detailed lava flow fields which form these segment surfaces and investigate their relationships with caldera formation and focussed fissural activity. Geochemical analysis and dating of lava flows from this Manda Hararo rift system will be conducted to test the integrity of this model of contiguous subsegments.

1. Introduction Plagioclase feldspar (Plg) is a common mineral in terrestrial rocks. It is a solid solution between a Ca-rich (anorthite) and a Na-rich (albite) endmember, and it is most commonly classified based on its anorthite (An) content. Powders of anorthite-rich Plg were previously studied using reflectance spectroscopy in the visible near-infrared (VNIR) range [1]. They showed that Plg display a band centered around 1.3µm due to Fe2+ substitutions, and that the position of this absorption band is a function of the An content. Other studies have investigated mixture of binary powders and showed that the Plg spectral signature is no longer visible when 10%, or more, of mafic minerals are added [2, 3]. According to these studies, a minimum of 90% of Plg are necessary in the rock composition for its spectral signature to be visible on the average spectrum of the rock. A more recent study, mixing large Plg and pyroxene grains [4], showed that at least 50% of mafic minerals are needed to mask the Plg spectral signature. Therefore, in addition to the An content, the size of the grains and the associated minerals influence the spectral signature of Plg. Thus, the analysis of whole rocks, and not powders, appears to be more relevant as a comparison with remote sensing analysis of planetary surfaces. The present study seeks to understand when Plg signatures are detectable, and how the Plg absorption band is affected by the nature of the host rock. In other words, does the spectral signature of Plg differ from one rock type to another, and if so, can a reflectance spectrum in VNIR be associated with a specific feldspathic rock type? 2. Method We combined petrological and spectral laboratory analyses of five terrestrial rock samples that contain Plg: an anorthosite (NM6), a granite (NJ11), two porphyritic basalts (NR1 and NR2) and a dacite (NJ2) (Figure 1). Firstly, reflectance spectroscopy measurements were carried out on the macroscopic samples using an ASD Fieldspec 4 point-spectrometer. The instrument operates in three different wavelength ranges: VNIR (0.35 – 1 µm), SWIR 1 (1.001 – 1.801 µm), and SWIR 2 (1.801 – 2.5 µm), with a spectral resolution between 3 and 8 nm. All resulting spectra (Figure 2) have an absorption band centered around 1.3µm with broad shoulders located around 0.8µm and 1.7µm. In order to accurately determine if this band is related to Plg in the rocks, additional analyses were performed. A petrographic study of each sample mineralogy (Figure 1) was carried out using an optical microscope as shown for sample NR1 in Figure 3. The use of hyperspectral cameras made it possible to further determine the spectral signature of each grain contained in these rocks (Figure 1). Hyperspectral cubes were acquired with the HySpex VNIR-3000-N and SWIR-640 cameras that acquire high-resolution data respectively from 0.4µm to 1µm, and from 0.96µm to 2.5µm, at a distance of 30cm from the sample. The resulting pixel size is about 29 µm in the VNIR, and 130 µm in the SWIR. The hyperspectral cubes are converted to reflectance using a reference target, and then analyzed with the ENVI software to classify the image pixels according to their spectral signature. Therefore, the different minerals in the rocks, which are often on a millimeter scale, are grouped into different classes. The statistics give the mean spectrum of each class, and therefore each mineral group (Figure 4). 3. Results and Discussion For each sample, the mineralogical composition (Figure 3) and spectral signature of each mineral (Figure 4) are determined. We observe that only Plg has an absorption band centered at 1.3µm with broad shoulders at 0.8 and 1.7µm. In conclusion, this same absorption band, that we see on the average spectrum of the rock (Figure 2), is the spectral signature of Plg. However, it should also be noted that in the matrix of Figure 4, composed of Plg and iddingsitized olivine, this band is no longer visible. This is also the case for the other samples: some minerals can mask the spectral signature of Plg by overlaying or attenuating its absorption band. Looking at the reflectance spectra (Figure 2), the position of the band seems to vary. It is centered around 1.2µm for dacite (NJ2) and granite (NJ11), around 1.25µm for basalts (NR1 and NR2), and 1.3µm for anorthosite (NM6). However, one must be careful with the interpretation: this shape might be related to the Plg chemical composition, but also the grain size, and the presence of other minerals contributing to the average rock spectra. Our study, therefore, shows that it is indeed possible to detect the presence of Plg in a whole feldspathic rock, even though it does not contain 90% of feldspar, and regardless of its nature (e.g., sample NR1 shown in Figure 4 contains ~66% of Plg). These results can be applied to the study of feldspathic rocks at the surface of rocky planets and more precisely of Mars. Indeed, recent detections of Plg [5, 6, 7] were made using the CRISM instrument (MRO) at the surface of Mars. The interpretation of these signatures, in terms of lithologies, is still under discussion given the variety of feldspathic rocks containing plagioclase [4, 5, 6, 7, 8] that exhibit the typical Plg absorption band. The construction of a reference library acquired on macroscopic rock fragments that we undertook should lead to a more accurate interpretation of Martian detections. 4. References [1] J.B. Adams an L.H. Goullaud (1978). LPSC Conference, 9th, 3, 2901-2909 (A79-39253 16-91). [2] D.A. Crown and C.M Pieter (1987). Icarus, 72(3), 492-506. [3] L.C. Cheek et al. (2014). American Mineralogist, 99(10), 1871-1892. [4] A.D. Rogers et H. Nekvasil (2015). Geophy.Res.Lett., 42, 2619-2626. [5] J.J. Wray et al. (2013). Nature Geoscience, 6, 1013-1017. [6] J. Carter et Poulet (2013). Nature Geoscience, 6, 1008–1012. [7] J. Flahaut et al. (2020). EGU General Assembly (EGU2020-13377). [8] A.D. Rogers et W.H. Farrand (2022). Icarus, 376, 114883.

1. Introduction The dynamic of lava flows as inferred from rheological models is characterized by physical parameters, such as viscosity and yield strength (assuming the flow is a Non-Newtonian fluid). Historically, the rheological behavior of lava flows is controlled, and determined (when samples are available), from intrinsic parameters, e.g chemical composition of the melt, crystal fraction rates, outgassing. Rheology is also reflected in outer characteristics such as the 3D morphology [1], whose analysis is the most common approach in planetary science. To study extraplanetary volcanic features, terrestrial analogue sites are useful. The Altiplano Puna Volcanic Complex (APVC), a volcano-tectonic province located at the Central Andes, has been suggested as an excellent site for the combined use of satellite imagery and ground truthing studies, being extraordinarily well-exposed and preserved due to the aridity of the Atacama Desert [2]. Its volcanic units vary in composition and geomorphology [3], representing potential analogs to a range of Mars volcanic features [4]. In this work, we focus on Andean volcanic geoforms from the APVC and apply two main approaches: chemical and morphological, to constrain the rheological behavior and viscosity estimates by testing several existing models [e.g., 1] in the Atacama Desert site, as an analog for Mars lava flows. 2. Methods About 30 terrestrial lava flows of age < 1 Ma from stratovolcanoes and monogenetic centres from the APVC (21°S 69°W to 24°S 67°W) have been study from orbit and field (Table 1). The composition of these lava samples ranges from basaltic-andesite (53.07 wt.% SiO2) to dacite (64.62 wt.% SiO2) [5,6,7]. 2.1 Rheological models Lava flow viscosities are estimated using two different, but complementary approaches. First, the melt viscosity (ηG) is calculated using the geochemical composition of the lava samples [8]. Then, the lava flow geometry is used as an input in existing models [9,10,11] to determine the apparent viscosity (ηA) from orbit. Morphological dimensions of the lava flows are measured using topographic data to determine the flow length, height, width, and slope angle from a 12.5 m/pixel Alos Palsar digital elevation model. The ratio of the apparent viscosity to the melt viscosity (relative viscosity ηR) is known to increase with the presence of crystals. Existing models rely on the Rosco-Einstein equation to quantify the crystal effects on viscosity, assuming a theoretical maximum packing fraction (φ) at which magmas essentially become solid [10]. We further evaluate the amount and shape of phenocrysts in the lava flows through petrographic analyses. 3. Results Results for a first selection of lava flows are presented in Table 1. Calculated melt viscosities (ηG) for basaltic andesites and dacites range from 5.8E+04 to 3.58E+08 Pa.s, which is in agreement with the theoretical viscosity values of intermediate silicic flows. However, apparent viscosities (ηA) estimated from orbit show values ranging from 8.0E+07 to 2.30E+13 Pa s (Table 1). This subset of lava flows returns high relative viscosity (ηR) values in the order of 10E+03 to 10E+07, implying packing fractions close to the theoretical maximum. Petrological analyses confirm that all these samples contain phenocrysts with abundances comprised between 7.09 and 19.67%, as obtained using the modal counting method. 4. Discussion and perspectives Different approaches have been used to estimate lava viscosities, with large gaps observed between remote sensing estimates and actual melt viscosities. With a complete range of geochemical compositions and crystal abundances, our catalog should help to note some limitations of existing rheological models. An inherent limitation is the use of single values for viscosity and yield strength for each lava flow because these parameters may indeed vary within the lava flow, both parallel to the flow direction, and vertically. Some authors agree that crystallinity is likely to play a more important role in viscosity changes in less evolved lavas [1]. On the contrary, for more evolved compositions, the crystallization sequence might not be the principal or decisive factor affecting the viscosity, compared to degassing and glass content [12]. Combining different rheological models for a wider compositional (i.e., SiO2 content) and textural (i.e., more aphanitic) range may allow us to better understand complex rheological scenarios of extra-terrestrial lava flows. On Mars, previous estimates of lava viscosities seem to be more consistent with basaltic to andesitic compositions [1], however, more evolved rocks (e.g., trachyandesite and trachyte) have been described recently based on orbital, in situ and meteorite data [13], and could be identified with our approach. Volcano TAS composition L (m) H (m) W (m) Apparent viscosity (ηA) Meltviscosity (ηG) Relativeviscosity(ηR) Packing fraction (φ) El Negrillar Basaltic andesite [12] 1809 53 827 3.10E+11 3.58E+08 4.5E+05 0.74 La Poruña Basaltic andesite 7670 59 1778 8E+07 5.8E+04 1.5E+03 0.70 Azufre Andesite 6740 336 3227 2.29E+13 1.3E+06 2.8E+07 0.73 Paniri Trachyte 8140 199 2013 1.02E+12 1.34E+06 7.6E+05 0.73 San Pedro Dacite 11800 153 2526 3.15E+11 1.12E+06 2.8E+05 0.73 El Negrillar Dacite[12] 1679 54 509 2.30E+13 2.00E+06 4.6E+03 0.72 Table 1. Summary of rheological parameters calculated for selected lava flows in study. η is in Pa.s. 5. Acknowledgements This work is funded by ANID - Fondecyt de Iniciación N° 11200293 and N° 11200013, Otelo JCJC and the ANR Mars-Spec grants. 6. References [1]Chevrel et al., 2013. EPSL 384, 109-120.[2]Flahaut et al., 2017. Icarus, 282, 152-173.[3]Wörner et al., 2018. Elements 14 (4), 237-244.[4]De Silva et al., 2013. Analog Sites for Mars Missions II.[5]González-Maurel et al., 2019. Lithos 346-347.[6]Godoy, B. 2019. JSAES 95 102295.[7]Parra-Encalada et al., 2022. J. Volcanol. Geotherm. Res, 426, 107541.[8]Giordano et al., 2008. EPSL 271, 123-134[9]Hulme, G, 1974. Geophys. J. R. Astron. Soc. 39, 361-383.[10]Warner and Gregg, 2003. J. Geophys. Res. 108, No. E10, 5112[11]Pinkerton and Wilson, 1994. Bull. Volcanol, 56, 108-120.[12] Hess and Dingwell, 1996.Minerals, 81 1297- 1300.[13]Sautter et al., 2016. Lithos, 254-255, 36–52.

International audience; Lunar mare basalts represent flood volcanism between ~4.0 and 1.2 Ga, therefore providing insights into the thermal and volcanic history of the Moon. The present study investigates the spectral and chemical characteristics as well as ages of the nearside mare basaltic units from the Grimaldi basin, namely Mare Grimaldi and Mare Riccioli, using a wealth of orbital remote sensing data. This study delineated distinct basaltic units of varying albedo, mineralogy, and titanium contents in both Mare Grimaldi and Mare Riccioli. The Crater sizefrequency Distribution technique revealed that at least two phases of basaltic magmatism have occurred in the Grimaldi basin spanning ~3.5 Ga to 1.5 Ga (Late Imbrian-Eratosthenian). High-Ti olivine basalts dated at 2.05 Ga are found to be surrounded by Late Imbrian (~3.47 Ga) low to intermediate-Ti basalts in Mare Grimaldi. Low to intermediate-Ti basalts observed in Mare Riccioli date back to two different volcanic events at ~3.5 Ga and ~3.2 billion years, while patches of basalts having remarkably higher titanium content within the Mare Riccioli record the youngest age of ~1.5 Ga. The chemical trend of the pyroxenes from distinct basaltic units also revealed that multiple events of volcanism have occurred in the Grimaldi basin. The high-Ti basalts in the Mare Grimaldi crystallized from a Fe-enriched late-stage magma while the low-Ti basalts crystallized from an Mg and Ca-rich initial magma that experienced an ultra-late stage quenching. The low to intermediate-Ti basaltic magma erupted in both the units was derived by partial melting of early cumulate materials from the hybrid source region in the post-overturn upper mantle and made its way to the surface through dikes that propagated by excess pressures accumulated in the diapirs stalled at the base of the crust due to buoyancy trap. The intermediate to high-Ti magma erupted in the Mare Grimaldi was generated by a hot plume ascended from deeper clinopyroxene-ilmenite rich cumulate layer near the core-mantle boundary. Whereas, the Eratosthenian (~1.5 Ga) intermediate-Ti volcanic activity in the Mare Riccioli rather sourced from the ilmenite-clinopyroxene cumulate materials remained in the upper mantle after mantle overturn. The new results suggest that volcanism had not ceased in the Grimaldi basin at 3.27 Ga, rather it was active and fed by different mantle sources until 1.5 Ga for a period spanning ~2 billion years.

The search for exploitable deposits of water and other volatiles at the Moon’s poles has intensified considerably in recent years, due to the renewed strong interest in lunar exploration. With the return of humans to the lunar surface on the horizon, the use of locally available resources to support long-term and sustainable exploration programs, encompassing both robotic and crewed elements, has moved into focus of public and private actors alike. Our current knowledge about the distribution and concentration of water and other volatiles in the lunar rocks and regolith is, however, too limited to assess the feasibility and economic viability of resource-extraction efforts. On a more fundamental level, we currently lack sufficiently detailed data to fully understand the origins of lunar water and its migration to the polar regions. In this paper, we present LUVMI-X, a mission concept intended to address the shortage of in situ data on volatiles on the Moon that results from a recently concluded design study. Its central element is a compact rover equipped with complementary instrumentation capable of investigating both the surface and shallow subsurface of illuminated and shadowed areas at the lunar south pole. We describe the rover and instrument design, the mission’s operational concept, and a preliminary landing-site analysis. We also discuss how LUVMI-X fits into the diverse landscape of lunar missions under development.

The first definitive evidence for continental vents on Mars is the in situ detection of amorphous silica-rich outcrops by the Mars Exploration Rover Spirit. These outcrops have been tentatively interpreted as the result of either acid sulfate leaching in fumarolic environments or direct precipitation from hot springs. Such environments represent prime targets for upcoming astrobiology missions but remain difficult to identify with certainty, especially from orbit. To contribute to the identification of fumaroles and hot spring deposits on Mars, we surveyed their characteristics at the analog site of the Solfatara volcanic crater in central Italy. Several techniques of mineral identification (VNIR spectroscopy, Raman spectroscopy, XRD) were used both in the field and in the laboratory on selected samples. The faulted crater walls showed evidence of acid leaching and alteration into the advanced argillic-alunitic facies, with colorful deposits containing alunite, jarosite, and/or hematite. Sublimates containing various Al and Fe hydroxyl-sulfates were observed around the active fumarole vents at 90 °C. One vent at 160 °C was characterized by different sublimates enriched in As and Hb sulfide species. Amorphous silica and alunite assemblages that are diagnostic of silicic alteration were also observed at the Fangaia mud pots inside the crater. A wide range of minerals was identified at the 665 m diameter Solfatara crater that is diagnostic of acid-steam heated alteration of a trachytic, porous bedrock. Importantly, this mineral diversity was captured at each site investigated with at least one of the techniques used, which lends confidence for the recognition of similar environments with the next-generation Mars rovers.

The Yilgarn Craton in Australia has a large number of naturally occurring shallow ephemeral lakes underlain by a dendritic system of paleodrainage channels. Processes like evaporation, flooding, erosion, as well as inflow of saline, often acidic and ion-rich groundwater contribute to the (dynamic) nature of the lakes and the composition of the sediments. The region has previously been described as an analog environment for early Mars due to its geological and geophysical similarities. Here, we investigated sediment samples of four lake environments aimed at getting a fundamental understanding of the native microbial communities and the mineralogical and (bio)chemical composition of the sediments they are associated with. The dominant mineral phases in the sediments were quartz, feldspars and amphiboles, while halite and gypsum were the only evaporites detected. Element analysis revealed a rich and complex image, in which silicon, iron, and aluminum were the dominant ions, but relative high concentrations of trace elements such as strontium, chromium, zirconium, and barium were also found. The concentrations of organic carbon, nitrogen, and phosphorus were generally low. 16S amplicon sequencing on the Illumina platform showed the presence of diverse microbial communities in all four lake environments. We found that most of the communities were dominated by extremely halophilic Archaea of the Halobacteriaceae family. The dynamic nature of these lakes appears to influence the biological, biochemical, and geological components of the ecosystem to a large effect. Inter-and intra-lake variations in the distributions of microbial communities were significant, and could only to a minor degree be explained by underlying environmental conditions. The communities are likely significantly influenced by small scale local effects caused by variations in geological settings and dynamic interactions caused by aeolian transport and flooding and evaporation events.

International audience

The Andean volcanoes in the Atacama Desert offer a unique environment to perform remote sensing investigations as these bare surfaces are well exposed and well preserved due to their relatively young (quaternary) ages, and to hyper-arid environmental conditions. The Atacama Desert is, in fact, the driest non-polar desert on Earth, and for this reason, it has already been previously studied as a Moon and Mars analog environment (e.g., Flahaut et al., 2017). In the present study, we compare dacitic domes from the Altiplano-Puna Volcanic Complex (APVC) of the Atacama desert with volcanic edifices which have been previously reported as possible silicic domes on the Moon.Five Atacama domes were studied from orbit, and three of them were sampled to obtain ground truth. These features formed by monogenetic eruptions and comprise high-K dacitic to rhyodacitic compositions with SiO2 contents ranging from 66 to 68 wt%. The dome dimensions measured from ASTER DEM indicate diameters between 1.5 to 6.2 km and heights between 250 and 700 m. Similar measurements were performed on various lunar domes with the LOLA DEM and show diameters ranging from a few km to 30 km, with slopes up to 9°. To the first order, dome eruptions can be considered as the extrusion of a Bingham fluid (the cooling magma) characterized by a yield strength τ and a plastic viscosity η (e.g., Hulme, 1974). Using the dome 3D dimensions as inputs into a rheological model, we estimate apparent viscosity to be in the order of 109-1011 Pa.s for both the Atacama domes and the lunar silicic domes.In parallel, the non-Arrhenian Newton silicate melt viscosity is calculated using the Atacama dome bulk composition and the model of Giordano et al. (2008). Resulting liquid viscosities range from 4.5 to 8 x 106 Pa.s. The difference between the apparent and actual liquid viscosity was further used to calculate the packing fraction with the Einstein-Roscoe equation, which was found to be around 0.70-0.73 for all domes.Dacitic domes in the APVC have aspect ratios, yield strengths and apparent viscosities similar to the Gruithuisen and Mairan lunar edifices, where elevated silica contents were previously reported (Glotch et al., 2011). We thus argue that the studied domes may be good analogs for these lunar domes, which are likely made of felsic rocks. However, when comparing viscosity estimates obtained from remote sensing data (apparent viscosity) and sample analyses (liquid viscosity) for the domes, we found that they differ by several orders of magnitude. Plausible explanations, which include a high amount of crystals in the mush (suggested by the high packing fraction values) will be discussed at the conference time.References: Flahaut J. et al. (2017), Icarus, 282, 152-173; Giordano D. et al. (2008), EPSL 271,123–134; Glotch, T. D. et al. (2011), GRL, 38, L21204; Hulme G. (1974), Geophys. Journal International, 39 (2), 361–383.

The far side of the Moon, which has generally been less frequently targeted by robotic and human missions in the past, has become more available for compositional analyses with measurements made by the Chang’E-4 mission that landed in South Pole-Aitken Basin in 2019. The rover of the mission, Yutu-2, has traversed over 500 m now and acquired more than 100 measurements of visible and near-infrared (VNIR) reflectance spectra. In this study, we analyze the full set of VNIR reflectance spectra collected so far in order to better understand the geology of the Von Karman mare. We compute spectral parameters to quantize major features of spectra and infer mineralogy, e.g., pyroxene composition analysis using the relationship between spectral band depths at 1 µm and 2 µm. Many of Chang’E-4 spectra do not have a detectable spectral band at 2 µm in which case we use spectral parameters for the band at 1 µm to make classifications and infer the presence of other minerals. Pyroxene composition inferred from Chang’E-4 spectra are midway between orthopyroxene and clinopyroxene, showing noticeably unique grouping when compared with 1 µm and 2 µm band depth data available from past studies. For spectra without detectable band at 2 µm, initial classification efforts based solely on spectral parameters of the 1 µm band seem to indicate that at least two distinct groups exist. We are further investigating these preliminary findings, such as through comparisons to data from Moon Mineralogy Mapper, to better understand the mineralogy of the measured materials and the geology of the region explored by Yutu-2 rover.

Lunar volatiles, such as water, are a crucial resource for future exploration, and their exploitation should enable the use of the Moon as a platform for even more remote destinations. As water is most likely to be found in the form of ice at the lunar poles (where surface temperatures can be as low as 40K, i.e. below the H2O temperature of sublimation in vacuum, 110K), multiple upcoming missions target the south pole (SP) cold traps. PSRs (Permanently Shadowed Regions) are especially cold enough to capture and retain volatiles but present challenging access conditions (rough topography, low illumination, low temperatures, limited Earth visibility).Funded by the EU program Horizon 2020, Space Applications Services developed the LUVMI-X rover (LUnar Volatiles Mobile Instrument eXtended), aimed at sampling and analysing lunar volatiles in the polar regions, including within a PSR. The LUVMI-X nominal payload includes an instrumented drill, the Volatiles Sampler (VS), along with a mass spectrometer, the Volatiles Analyser (VA), for surface and subsurface volatile detection and characterisation. A LIBS and a radiation detector are also included. Deployable and propellable surface science payloads are in development for inaccessible sites (e.g., some of the PSRs). This solar-powered rover has an autonomy of one or two Earth nights and can drill down to 20cm in the lunar regolith. The goal of this paper is to find suitable landing sites & traverses’ paths for this rover project, that are both scientifically interesting and technically reachable.Available remote sensing imagery for the lunar SP was downloaded from the PDS or corresponding instruments’ websites and added into a Geographic Information System (GIS). LUVMI-X scientific objectives and technical specifications were then translated into a list of criteria and computed in our GIS using reclassifications, buffers, and intersections. Using our GIS, reclassified data were overlaid with different weights to define and rank areas meeting the compulsory criteria. A global analysis was led to select the landing sites, followed by a local analysis (based on higher resolution data) for the establishment of traverses.The global GIS analysis allowed us to identify six regions of interest (ROI), which were compared with previous SP ROI from the literature (Lemelin, 2014; Flahaut, 2020). The identified ROI were further ranked based on areas and statistics on Sun and Earth visibilities, Diviner average surface temperatures, and H/water ice signatures (LPNS, LEND, M3).A prime ROI located between Shackleton and the Shoemaker/Faustini ridge was selected for traverse analysis. Four landing ellipses of 2x2km were located and ranked inside the ROI. Way Points (WP) were then identified to include the following scientific interests in each traverse: a boulder casting shadows, a PSR to throw a propellable payload in, an accessible PSR to go into, etc. As several WP are possible, Earth visibility was used to select the best ones. WP were then connected by using slope maps (LOLA DEM at 5m/px: avoid slopes over 20°), Earth & Sun visibilities (avoid no-go zones) and the LROC NAC mosaics at 1m/px (avoid boulders and craters), constituting a tentative traverse.

Impact craters are often used to date planetary surfaces, the density of crater increasing with the exposure age of the surface. However, some geologic event, such as lava flows, do not totally “reset” the crater clock. Indeed, larger craters, rather than being totally recovered by the lava flow will be only partially filled.In that case, the crater size frequency distribution differs from cratering models. In order to better describe crater populations, additional parameters can be included. To this purpose we build crater size and depth frequency distributions that offers a snapshot of the current degradation state of the population.We used cratering models to interpret crater size and depth frequency distributions in terms of crater infilling rates. Using both global crater database and more local high resolution crater maps, we estimated crater obliteration rates on various Martian volcanic provinces.Our method proven efficient to track activity of the main Martian volcanic provinces. Resurfacing rates reach several thousands of m/Gy. Pic activity differs from provinces. Syrtis and Hesperia are the oldest with the highest and oldest observed rates around 3.7 Gy. The activity of those provinces quickly decreases reaching few hundreds of m/Gy around 3.4 Gy. During Hesperian, Tharsis is the most active surface of Mars with high resurfacing until 3.3 Gy. Finally, our result shows an increase of resurfacing, reaching few hundreds of m/Gy in Amazonis planitia from 2 Gy to present.

1. Introduction Lunar volatiles, such as water, are considered to be a crucial resource for In Situ Resource Utilization (ISRU) in using the Moon as an enabling platform for future space exploration. As water is most likely to be found in the form of ice at the lunar poles (temperature of stability in vacuum: 110K [1]), multiple missions target the South Pole cold traps [2]. With challenging conditions (rough topography, low illumination, low temperatures, and limited Earth visibility; [3] and references within), the South Pole comprises numerous PSR (Permanently Shadowed Regions) which are cold enough to capture and retain volatiles such as water ice (annual average temperatures of 40K [2]). Funded by the EU program Horizon 2020, Space Applications Services coordinates the LUVMI-X (LUnar Volatiles Mobile Instrument) project, where the company develops a robotic platform and international partners develop a dedicated payload suite [4], aimed at sampling and analyzing lunar volatiles in these polar regions. LUVMI-X is a commercial rover with modular interfaces to facilitate the integration of payloads from the community. The goal of this paper is to find suitable landing sites and study areas for this rover, that are both scientifically interesting and technically reachable [2,3]. 2. Selection of criteria and data Available remote sensing imagery for the lunar South Pole (Table 1) was downloaded from the PDS or corresponding instruments ’websites and added into a Geographic Information System (GIS). LUVMI-X scientific objectives and technical specifications were then translated into a list of criteria and computed in our GIS [3,4]. Using ArcGIS, reclassified data were overlaid with different weights to define and rank compliant areas which respect the established constraints (Table 1). Regions Of Interest (ROI) were finally identified by mapping out compliant areas > 80 km2 (i.e., areas allegedly large enough to hold a 10km-diameter landing ellipse. This arbitrary ellipse size is based on the technical abilities of current commercial landers). 3. Landing sites ranking and selection Results of the GIS analysis (Figure 1) show six identified ROI (red) for the LUVMI-X mission, which are compared with previous ROI from the literature (Lemelin et al, 2014, stars [6]; Flahaut et al, 2019, pink [2]). First, none of the LUVMI-X ROI intersects with Lemelin’s landing sites because the latter are only in PSR; Lemelin's sites do not meet the technical specifications of the LUVMI-X rover (areas without illumination are not accessible for a solar-powered rover). However, parts of Flahaut’s ROI overlap with the LUVMI-X sites of this study. Flahaut’s largest ROI (Amundsen, Ibn Bajja) do not or only partially overlay with LUVMI-X ROI as Flahaut’s study only considers surface water ice (with a temperature of 110K maximum). This study is intended for rovers unable to drill, which is not the case for LUVMI-X (drilling is possible down to 20cm). The identified ROI are further ranked based on areas and statistics on Sun and Earth visibilities, temperatures, and H signatures. ROI 1 has the best mean Sun and Earth visibilities, but its amount of non-compliant pixels and the temperature are too high. Furthermore, its area is too restricted to hold a perfectly circular ellipse of 10 km, which is also true for ROI 6. ROI 2 and 3 are discarded as they contain high percentages of non-compliant pixels. H signatures from Lunar Exploration Neutron Detector (LEND) and water ice signatures from Moon Mineralogy Mapper (M3) [7] of ROI 4 and 5 were then compared. ROI 4 seems to present more evidence of surface water ice, which is a strategic asset in case LUVMI-X encounters drilling issues. This ROI presents the highest score in H signatures (LPNS, LEND) and the lowest temperatures while comprising the best site selected by Flahaut et al [2]. 4. Perspectives for LUVMI-X The requirements from some CLPS landers include slopes < 10°, which is larger than used in our initial study [8]. Future work includes revision of our ROI with an eventually relaxed set of parameters, and selection of 1-3 test sites for establishing traverses based on the mission’s initial scenario. Traverses will be established by listing different specifications based on LUVMI-X concept of operations and scientific objectives, in order to identify “waypoints” (stops along the traverse). High resolution mosaics from the LROC’s Narrow Angle Camera (resolution of 1m/px) and LOLA 20m/px DEM will be used to map potential hazards and check PSR accessibility. The established waypoints should then be linked either by minimizing the used energy or maximizing Sun and/or Earth visibilities and will be used as an input to parametric and thermal models of the rover. 5. References [1] Paige D. et al. (2010). Science, 330, 479-480. [2] Crawford J. et al. (2020). Lunar Resources. [3] Flahaut J. et al. (2020). Planetary and Space Science, 104750. [4] Gancet J. et al. (2019). LUVMI and LUXMI-X Concept and extension. In the proc. of ESA ASTRA Symposium. [5] Mazarico E. et al. (2011). Icarus, 211. [6] Lemelin et al. (2014). Planetary and Space Science, 101. [7] Li S. et al. (2018). Proc. Natl. Acad. Sci. 115 (36). [8] Astrobotic. (2020). Peregrine Lunar Lander, Payload User’s Guide.

1. Introduction Located in northern Chile's central Andean region, the Altiplano-Puna volcanic complex is a province characterized by stratovolcanoes, ignimbrites, domes, and other volcanic features with composition ranging from basaltic andesite to dacite [1]. This region, along with its vicinity, possesses unique environments comparable to some planetary bodies due to its arid climate, volcanic terrain, and hydrothermal activities, and it has particularly been used as analog sites to study the geology and mineralogy of Mars [2]. We carry out geological and mineralogical mapping of the Altiplano-Puna volcanic complex and its vicinity using Hyperion hyperspectral imager onboard the Earth Observing One (EO-1) satellite. This is done in order to accomplish three goals: 1) Understand the regional context of the samples collected from this area in previous field expeditions; 2) Improve interpretations of similar datasets of Mars; and 3) Utilize the advantage of remote sensing to better understand the geology and mineralogy of Altiplano-Puna volcanic province. In this work, we present our first attempts at characterizing potential feldspar spectral signatures to give insights into recent feldspar detections on Mars [3]. 2. EO-1 Hyperion EO-1 Hyperion is NASA's spaceborne hyperspectral imaging instrument that operated from 2000 to 2017. It contained 220 spectral bands in the 0.4 to 2.5 µm wavelength range. Two separate detectors, visible-near infrared (VNIR) and shortwave infrared (SWIR) detectors, operated in the 0.4–1.0 µm and 0.9–2.5 µm ranges, respectively, with 30 m/pixel spatial resolution. Hyperion acquired data in push-broom method, and its products are usually long, narrow strips of hyperspectral cube with 7.7 km swath width. 3. Methods Hyperion L1T GeoTiff radiance products were downloaded from US Geological Survey Earth Explorer data portal and converted to reflectance using ENVI FLAASH atmospheric correction tool. Reflectance image cubes, which contained noticeable amounts of noise and occasional unrealistically large/small values, were first despiked and then smoothed with a sliding median method using a custom made program for processing spectral data known as Mineral Recognizer [3]. Using the processed data, we computed band depth index at 1.3 µm (BD1300) in a similar manner as those done for Mars hyperspectral data [4] in order to infer the presence of feldspar. As Hyperion spectral bands are not exactly the same as those in Mars hyperspectral data, i.e., Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we have used slightly different, but overall consistent, wavelengths in computing band depth indices. In parallel, spectra of samples of ignimbrites, domes, and lava flows collected during previous field campaigns were measured in the laboratory using a portable point spectrometer. The Fieldspec 4 allowed measurements of reflectance spectra from 0.35 to 2.5 µm with three detectors and a minimum spectral resolution of 3 to 8 nm. Finally, the BD1300 spectral index was also computed for collected sample spectra. 4. Results Identified pixels (BD1300 > 0) (Figure 1) generally corresponded with volcanic domes and pyroclastic flow deposits based on a comparison with a geological map of the Altiplano-Puna volcanic complex [5] and a subset of available samples collected during field campaigns. Band depth indices of identified pixels (0.016-0.039 interquartile range) were generally consistent with those from select samples of volcanic domes and ignimbrites (0.02-0.06). Microscope observation of samples of volcanic domes and ignimbrites indicated that they can contain 0.1–1 mm sized plagioclase feldspar grains in roughly 20-40% abundance. Band depths of the weathered surfaces of the samples were considerably shallower. Likely for this reason, identified pixels were spatially sparse with overall lower magnitudes of 1.3 µm band depth index than those of the samples, indicating detections mainly on relatively fresh surfaces. 5. Summary and Conclusions Using Hyperion hyperspectral imagery, we computed 1.3 µm band depth index in the Altiplano-Puna volcanic complex. This index is usually known to capture feldspar signatures, although other minerals could induce positive values (e.g. olivine, glass, micas). These minerals are not necessarily present in the analyzed samples, but further work is needed to exclude them from the candidate mineral list. Both volcanic domes and pyroclastic flow deposits with potentially less than 50% plagioclase feldspar abundance were highlighted with the BD1300 index. Our next step is to refine the index computation to more precisely capture the feldspar spectral signature and measure more spectra of samples. Dataset and the processing procedure used in this study are analogous to those for Mars, and our work will likely be useful for solving problems existing in Mars geology, e.g., detection of feldspathic and felsic rocks and interpretation of feldspar spectral signatures using CRISM [2]. Acknowledgements This work was funded by CNRS Momentum and LUE future leader programs. References [1] de Silva, S. L.: Altiplano-Puna volcanic complex of the central Andes, Geology, Vol. 17, pp. 1102-1106, 1989. [2] Flahaut, J., Martinot, M., Bishop, J. L., Davies, G. R. and Potts, N. J.: Remote sensing and in situ mineralogic survey of the Chilean salars: An analog to Mars evaporate deposits? Icarus, Vol. 282, pp. 152-173, 2017. [3] Flahaut, J., Barthez, M., Payet, V., Fueten, F., Guitreau, M., Ito, G., Allemand, P., Quantin-Nataf, C.: Identification and characterization of new feldspar-bearing rocks in the walls of Valles Marineris, Mars, European Geophysical Union General Assembly, 4–8 May 2020, Online, 2020. [4] Viviano-Beck, C. E., Seelos, F. P., Murchie, S. L., Kahn, E. G., Seelos, K. D., Taylor, H. W., Taylor, K., Ehlmann, B. L., Wiseman, S. M., Mustard, J. F. and Morgan M. F.: Revised CRISM spectral parameters and summary products based on the currently detected mineral diversity on Mars. Journal of Geophysical Research: Planets, Vol. 119, pp. 1403-1431, 2014. [5] Sélles, M. D. and Gardeweg, M. P.: Geología del Área Ascotán-Cerro Inacaliri Región de Antofagasta, Carta Geológica de Chile, Serie Geología Básica, No 190, 2017.

1. IntroductionNew feldspar detections made by visible-near infrared spectroscopy this year on Mars [1], raise questions on the nature of the rocks involved and the magmatic processes responsible for their formation. Based on lunar studies, the presence of a 1.3 µm absorption band has been so far interpreted, as diagnosis of anorthosites containing more than 90% plagioclase [2]. However, these studies are based on VNIR spectra acquired in the laboratory, on binary mixtures of powders, containing Ca-plagioclase feldspar mixed with a mafic mineral such as olivine or pyroxene [3]. This paper presents our laboratory results regarding VNIR spectra measurements of several (uncrushed) terrestrial rocks containing feldspars of various compositions, in various amounts, and with different grain sizes as we expected all these factors to influence the spectral response. Our results allow us to survey in which cases the 1.3 µm band can be reproduced, and which are therefore possible analogue rock candidates. Finally, the sparse detections that have been recently made in the Valles Marineris region of Mars are compared with our library results.2. MethodThe objective of our study is to use VNIR reflectance spectroscopy to create a new reference spectral library containing reflectance spectra acquired on uncrushed terrestrial feldspathic rocks. Over 40 terrestrial feldspathic rocks of various types (volcanic, plutonic and metamorphic, Figure 1) were analyzed in this study.Reflectance spectra of this wide range of rocks was measured with an ASD Fieldspec4 spectrometer in our laboratory. This instrument operates in three different wavelength ranges: VNIR (0.35 – 1 µm), SWIR 1 (1.001 – 1.801 µm), and SWIR 2 (1.801 – 2.5 µm), with a spectral resolution between 3 and 8 nm. Spectra were collected with the instrument bare fiber, contact probe, or Muglight. The distance of the fiber using accessories was ~ 15 mm from the rock, with a phase angle of ~45° and using an artificial light source. Approximately five different spectra were measured on each rock sample. Selected spectra are presented in Figure 2.In parallel, Mars VNIR hyperspectral remote sensing data from the CRISM instrument (Compact Reconnaissance Imaging Spectrometer for Mars) onboard MRO (Mars Reconnaissance Orbiter) where feldspar signatures were recently reported [1] were analyzed. Raw data were downloaded from the PDS, corrected with the ENVI CAT (CRISM Analysis Toolkit) following the method described in [4] and then denoised using a custom-made routine [1].Spectral criteria [5] are then computed to investigate whether or not an absorption band for a given wavelength was present. The BD1300 criteria was used in this study to highlight pixels which might contain a feldspar absorption band at 1.3 µm.3. ResultsOut of 42 measured analogue rocks, 18 rocks display absorption features around 1.3 µm. The rocks with positive 1.3 µm signatures include dacites, basalts, granodiorites, granites and diabase. Several spectra were measured on these rocks resulting in 82 positive spectra in our new spectral library (Table 1). The feldspar-bearing have absorption band centers varying from 1.15 to 1.4 µm.A similar absorption is observed on eight analyzed CRISM cubes (Figure 2). The position of the center of the absorption band in the CRISM data is around 1.25 µm. If we compare the CRISM data to the spectra of our library, the right and left shoulders of the absorption band are very often equidistant from the center of the band, although the CRISM spectra here are limited at wavelengths >1 µm, making the left shoulder difficult to examine.4. Discussion and PerspectivesSpectra collected on entire terrestrial feldspathic whole rocks show diagnosis plagioclase signatures which are similar to the ~1.3 µm absorption feature observed on Mars. Other candidate minerals, however, could show broad absorption bands centered between 1.1 and 1.3 µm, such as garnet, micas or volcanic glass. Still, spectral characteristics of both our library spectra and Mars CRISM spectra are more consistent with plagioclases.Future work includes a detailed petrographic characterization of the analyzed samples. It is already shown, however, that some of our samples do not contain more than 40% plagioclase crystals and still display absorption band centered at 1.3 µm on the reflectance spectrum. These results are in contradiction with previous analysis of powder mixtures [6] which determined that the presence of 90% of calcic plagioclase is necessary in a rock for its band to be observable in a reflectance spectrum [3]. We argue that presence of an absorption band can also be influenced by the grain size which is an important factor to take into account: the larger the grain size, the deeper the absorption band, and most of our studied rocks do contain feldspar phenocrysts.We conclude, from the comparison of our library spectra with the Mars CRISM spectra, that a range of effusive and cumulate rocks could correspond to the observed signatures. Previous studies suggested that these spectral signatures correspond to anorthositic primary crust [2], or felsic tertiary crust [7]. Although these hypotheses are plausible, our results suggest that it is virtually impossible to use feldspar detections to infer the presence of a primary or tertiary crust until we further constrain the true nature of the rocks and the exact geological context of these peculiar signatures.5. References[1] J. Flahaut et al. (2019). Goldschmidt Abstracts, 2019, 1010 (and article in prep.).[2] J. Carter et al. (2013). Nature Geoscience, 6, 1008–1012.[3] L.C. Cheek et al. (2014). American Mineralogist, 99(10), 1871-1892.[4] S. Murchie et al. (2007). J. Geophy. Res, 112, E5.[5] C.E. Viviano-Beck et al. (2014). Journal of Geophysical Research: Planets, 119, 1403–1431.[6] D.A. Crown and C.M Pieter (1987). Icarus, 72(3), 492-506.[7] V. Sautter et al. (2016). Lithos, 254-255, p.36-52.

1. IntroductionOne of the Moon’s most surprising characteristics is its crustal asymmetry; the farside hemisphere, dominated by ancient highlands and covered with a few mare deposits, has a different volcanic history than the (sampled) nearside [1]. Surface dating of the lunar mare basalts revealed that the volcanism on the Moon lasted between ~3.9-4.0 and ~1.2 Ga, with a peak in the volcanic activity ~3.6-3.8 Ga ago [2]. A recent study further demonstrated that the mineralogy of the nearside mare basalts reveals a late stage volcanism with high titanium and olivine contents [3]. More recent spectroscopic analyses focused on the farside’s crustal rocks composition (e.g. [4] for South Pole-Aitken [SPA] basin), but no comprehensive study of the farside mare compositions has been conducted up to now.2. Data and methodsIn this work, we used spectroscopic data of the Moon Mineralogy Mapper (M3) onboard Chandrayaan-1 to survey the mineralogy of all mare deposits in the VNIR domain (0.4-3 μm). Each mare unit was mosaicked separately and processed using the method of [5]: an IDL routine automatically computes and removes the continuum of each spectrum, and determines its spectral parameters (e.g. band centers, band areas, band depths, spectral slope). To compare with the mineralogy of the nearside [3], we also mosaicked three selected mare regions, each representative of one spectral unit. Finally, we applied statistics on spectral parameters of interest to survey the variation in mineral signatures and compositions of farside maria.3. Preliminary resultsWe found that spectra of mare basalts are dominated by pyroxene signatures (Figure 1).However, some mare units (e.g. Apollo, see Figure 2) showed considerable differences in band characteristics in which cases we computed statistics on each mare subunits.Major differences were also observed in SPA mare units when they were compared to Mare Australe deposits and other maria outside of the SPA basin (Figure 3).This suggests different pyroxene compositions within SPA. Moreover, the nearside mare units we defined based on [3] are clearly distinct from all farside mare deposits since they are the richest in clinopyroxenes (Figure 3).4. Conclusion and perspectivesThe results we have so far indicate slightly different mineralogies of mare basalts between the nearside and the farside of the Moon and, if confirmed by looking at the other spectral parameters, could mirror its crustal dichotomy. We plan to investigate possible evidence of olivine and possible correlations with age and location, as well as intra-SPA diversity with our spectral parameters set.AcknowledgementsThe authors want to thank Jan Hendrik Pasckert and Harald Hiesinger for having kindly shared with us their shapefiles of SPA mare deposits [8]. Fundings from the CNRS Momentum, LUE Future Leader and CNES APR are much appreciated.References[1] Head III, J. W., and Wilson, L.: Lunar mare volcanism: Stratigraphy, eruption conditions, and the evolution of secondary crusts, Geochimica et Cosmochimica Acta, Vol. 56, 1992.[2] Hiesinger, H., et al.: Ages of mare basalts on the lunar nearside, Journal of Geophysical Research, Vol. 105, 2000.[3] Staid, M. I., et al.: The mineralogy of late stage lunar volcanism as observed by the Moon Mineralogy Mapper on Chandrayaan-1, Journal of Geophysical Research, Vol. 116, 2011.[4] Moriarty, D. P., and Pieters, C. M.: The Character of South Pole-Aitken Basin: Patterns of Surface and Subsurface Composition, Journal of Geophysical Research, Vol. 123, 2018.[5] Martinot, M., et al.: Mineralogical Diversity and Geology of Humboldt Crater Derived Using Moon Mineralogy Mapper Data, Journal of Geophysical Research, Vol. 123, 2018.[6] Klima, R. L., et al.: Spectroscopy of synthetic Mg-Fe pyroxenes I: Spin-allowed and spin-forbidden crystal field bands in the visible and near-infrared, Meteoritics & Planetary Science, Vol. 42, 2007.[7] Adams, J. B.: Visible and near-infrared diffuse reflectance spectra of pyroxenes as applied to remote sensing of solid objects in the solar system, Journal of Geophysical Research, Vol. 79, 1974.[8] Pasckert, J. H., Hiesinger, H., Van der Bogert, C. H.: Lunar farside volcanism in and around the South Pole-Aitken basin, Icarus, Vol. 299, 2018.

1. IntroductionVolcanic activity on Earth and elsewhere is expressed through a variety of features including volcanic edifices (strato-volcanoes, shields, cones, domes, craters…), lava flows, intrusive features (dikes, laccoliths…), among others. The shape of surface features is known to result from complex, interrelated parameters such as the magma properties, eruption style, but also the planetary variables (e.g., gravity, presence of an atmosphere…) (e.g., [1]). On the Moon, large plains of basaltic composition referred to as lunar maria are most representative of surface eruptions, and volcanic edifices are rarer (e.g., [2]). Still, a range of volcanic constructs such as pyroclastic deposits, cones and domes are observed at various locations. The focus of this study are lunar domes which show various geometries, with diameters typically ranging from a few km to 30 km and slopes up to 9° [3,4]. Previous studies have used the dome geometries as an input for rheological models, in order to estimate the magma apparent viscosity [3-6]. In the present paper, we apply (and discuss) similar models to terrestrial analog domes from the Atacama Desert in northern Chile, for which we obtained ground truth through field sampling and analyses.2. Geological contextThe Andean volcanoes in the Atacama Desert offer an unique environment to test and improve existing mineral mapping techniques and rheology equations, as they are well preserved due to their relatively young (quaternary) ages, and to the Atacama desert hyperarid environment (e.g., [7]). Indeed, the Atacama Desert is the driest non-polar desert on Earth, and for this reason, it has already been previously studied as a Moon and Mars analog environment (e.g., [8]). Five Atacama domes were studied from orbit, and three of them were sampled on the field. Dome dimensions as measured on ASTER DEM are presented in Table 1. Previous studies suggest these features were emplaced by monogenetic eruptions and comprise high K dacitic and rhyodacitic rocks [9, 10]. Collected samples are dominated by glass (~60 vol%), and phenocrysts of plagioclase (~20 vol%), hornblende (~7 vol%), biotite (~4 vol%), alkali feldspar (~3 vol%), orthopyroxenes (~1 vol%) and quartz. Dome bulk rock compositions were further determined by ICP-MS/ICP-OES analyzed at the SARM facility in Nancy, France. The bulk compositions of the domes are very similar to each other with SiO2 contents ranging from 66 to 68 wt%.3. Dome rheologyRheology, which refers to the flow properties of the lavas, is controlled by magma properties and especially viscosity. Viscosity is a function of multiple parameters such as the temperature, composition, gas content and degree of crystallization. Fluid dynamics laws have been utilized to develop first-order mathematical equations that tie magma viscosity to the geometry of a flow or edifice (e.g., [11]).To the first order, dome eruptions can be considered as the extrusion of a Bingham fluid (the cooling magma) characterized by a yield strength τ and a plastic viscosity η. By applying similar rheologic equations to the ones in [2-6], the yield strength and apparent plastic viscosity of the Atacama domes has been estimated (Table 1).In parallel, the non-Arrhenian Newton silicate melt viscosity is calculated using the dome bulk composition as an input in the models of [12] (Table 1). The difference between apparent and liquid viscosity was further used to calculate the packing fraction with the Einstein-Roscoe equation, as in [13] (Table 1).4. Discussion and PerspectivesWe compare viscosity estimates obtained from remote sensing data (apparent viscosity) and sample analyses (liquid viscosity) for the domes and found that they differ by several orders of magnitude (Table 1).A plausible explanation is that magma viscosity depends on several parameters (see above). The presence of crystals likely played a role in the elevated apparent viscosity values that we obtained, as suggested by the high packing fraction of ~0.7 (very close to the theoretical maximum packing fraction of 0.74), calculated for all domes.Dacitic domes in the Atacama Desert have aspect ratios, yield strengths and apparent viscosities similar to the G class of lunar domes as reported by [4] (also referred to as highland domes). This class of domes include the Gruithuisen and Mairan edifices where elevated silica contents were previously reported (e.g., [5-14]. We thus argue that the Atacama domes may be a good analog for these lunar domes, which are likely made of felsic rocks, and could represent the source of the lunar granites/rhyolites and zircons found in the Apollo samples.5. AcknowledgmentsSupport to JF from the CNES Luna APR, the LUE future leader and the CNRS Momentum program is much appreciated. This work has been also funded by the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT-FONDAP 15090013/Centro de Excelencia en Geotermia de los Andes-Universidad de Chile). OGM and JF are grateful for support from the Claude Gay program of the French embassy in Chile.6. References[1] Whitford-Stark J.L. and J.W. Head (1982), Lunar and Planetary Science Conference, 8th, 2705-2724.[2] Head III J.W., & L. Wilson (1992), Geochimica et Cosmochimica Acta, 56(6), 2,155-2,175.[3] Wöhler C. et al. (2007), Icarus, 189(2), 279-307.[4] Lena, R. et al. (2013), Springer Praxis Books.[5] Wilson L. and J.W. Head (2003), JGR, 108, 5012.[6] Schnuriger N. et al. (2020), PSS, 185, 104901.[7] Ito G. et al., (2020), this meeting.[8] Flahaut J. et al. (2017), Icarus, 282, 152-173.[9] de Silva S.L. et al. (1994), JGR, 99, B9, 17,805-17,825.[10] Taussi M. et al. (2019), JVGR, 373, 179-198.[11] Hulme G. (1974), Geophys. Journal International, 39 (2), 361–383.[12] Giordano D. et al. (2008), EPSL 271,123–134.[13] Chevrel M.O. et al. (2013), EPSL, 394, 109-120.[14] Glotch, T. D. et al. (2011), GRL, 38, L21204.

This study exploits recent advances in image calibration and feature extraction techniques for analysis of hyperspectral images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to characterize subtle geologic outcrops at the border of phyllosilicate-bearing and sulfate-bearing regions of Mars. Specifically, a unique spectral “doublet” feature at 2.21-2.23 and 2.26-2.28 μm is isolated to characterize salty regions that may represent a changing climate on Mars. The martian locations exhibiting these spectral features are identified and compared with terrestrial settings with similar geologic compositions.

International audience; Spectroscopic data from the Moon Mineralogy Mapper (M 3) instrument are used to study the mineralogy of the central peak or peak ring of 75 craters located in the lunar anorthositic Feldspathic Highlands Terrane (FHT-a), as defined by Jolliff et al. (2000). The thickness of South-Pole Aitken (SPA) ejecta at the location of the selected craters is estimated. Crustal thickness models are used with empirical cratering equations to estimate the depth of origin of the material excavated in the studied central peaks, and its distance to the crust-mantle interface. The goal of this survey is to study the composition of the FHT-a crust, and the extent of its potential lateral and vertical heterogeneities. High-Calcium Pyroxene (HCP) and featureless spectra are mostly detected throughout the entire FHT-a, whereas the number of pure plagioclase detections is small. No relationship between the central peak composition and the distance to SPA or the depth within the SPA ejecta is observed. The SPA ejecta material cannot be spectrally distinguished from crustal material. We interpret the paucity of plagioclase spectra in the FHT-a, which contrasts with more frequent plagioclase detections in the central peaks of craters sampling the crust in younger lunar terranes using identical spectroscopic techniques Martinot et al. (2018b), as a possible effect of terrane maturation, or of mixing with mafic components that mask their signature in the visible near-infrared. Overall, the FHT-a appears homogeneous laterally. However, data hint at a pyroxene compositional change with increasing depth, from high-calcium content in the upper crust towards less calcic compositions with increasing depth, which is consistent with prior studies of the architecture of the lunar crust.

The Martian Valles Marineris, located on the eastern flank of the Tharsis region, is a 4000 km long linked system of troughs. The formation of the up-to-11 km deep chasmata of Valles Marineris is thought to have taken place during a two-stage process in which ancestral basins collapsed and were later linked by tectonism. Located within most chasmata are enigmatic layered deposits, referred to as interior layered deposits (ILDs), whose origin and mechanism of formation are uncertain. It has been estimated that ILDs cover 17% of the total area, representing 60% by volume of all deposits within Valles Marineris with several deposits nearly reaching the height of the surrounding plateau.Here we present the results of a detailed study of the ILD mounds located within three of the presumed ancestral basins in the center of Valles Marineris. In this study HiRISE and CTX images were used to measure layer attitudes of ILDs within East and West Candor and Ophir chasmata. Because only CTX images cover the entire chasms, the ILDs were grouped into distinct varities of bedding based on their appearance in CTX imagery. In both East and West Candor and Ophir, the stratigraphically lowest unit is a massive unit which displays no layering in any available imagery. Layered units with dips between 10° and 20° are deposited on top of this massive unit. The lowest layered units in all three chasms appear to show multiple prominent benches, indicative of significant competency contrasts. These units can be shown in multiple places to be unconformably overlain by thinner layered units. It is not possible to correlate or determine the number of thinner layered units because the unconformable contacts cannot be correlated. The general similarities of types of units and unit relationships between the ILDs in these three chasms suggests that they share a similar depositional history. We believe that the ILD morphology is most compatible with an environmental setting in which the ancestral basins were lakes which may have been periodically frozen. We suggest that the unconformities are the result of multiple erosional events indicating that ILD deposition was not continuous. A general trend of massive units overlain by thinner layered units may reflect a change in the environment and sediment supply. Associated with this change is a general observation that polyhydrated sulfate is most commonly found on top of the monohydrated material. Work to correlate more closely units within these chasms, including their mineralogy, is currently ongoing.

VNIR spectroscopy has previously led to many discoveries pertaining to Mars geologic history (e.g., the discovery of hydrated minerals associated to ancient terrains with OMEGA, Bibring et al., 2006). Plagioclase feldspar minerals can also be identified with spectroscopic techniques thanks to a 1.3 microns absorption in the VNIR domain (e.g., Adams and Goullaud, 1978). Previous lunar analog studies show however that when mixing powders of Ca plagioclase and a mafic component (olivine or pyroxene), the feldspars absorption band is quickly masked (e.g., Cheek and Pieters, 2014). This study further demonstrates that the 1.3 micron feature is only detectable if the plagioclase abundance is > 90 %. Based on this observation, previous feldspar absorptions on Mars have been interpreted as evidence for nearly pure anorthositic rocks (e.g., Carter and Poulet, 2013). A recent study by Rogers and Nekvasil (2015) however suggests that phenocryst basalts with less than 90% plagioclase could reproduce the 1.3 micron feature if large crystals are involved, although no whole rock measurements were made.In the present study, we describe new feldspar signatures detected with the CRISM VNIR spectral-imager in the walls of the Valles Marineris grand canyon, on Mars. The associated rock textures and elevations were assessed from CTX and HiRISE images and DTMs. In parallel, we are collecting VNIR spectra of various (uncrushed) terrestrial rocks containing a large range of feldspar abundances and grain sizes. Analyses are carried out between 0.35 and 2.5 microns with an ASD Fieldspec at CRPG Nancy, France, and will be presented at the conference time. By combining laboratory measurements of a range of possible terrestrial analog rocks with the study of Mars feldspar-bearing outcrops, we should bring more clues on the nature and origin of these feldspathic rocks.

International audience; The detection of biosignatures on Mars is of outstanding interest in the current field of Astrobiology and drives various fields of research, ranging from new sample collection strategies to the development of more sensitive detection techniques. Detailed analysis of the organic content in Mars analog materials collected from extreme environments on Earth improves the current understanding of biosignature preservation and detection under conditions similar to those of Mars. In this article, we examined the biological fingerprint of several locations in the Atacama Desert (Chile), which include different wet and dry, and intermediate to high elevation salt flats (also named salars). Liquid Chromatography and Multidimensional Gas Chromatography Mass Spectrometry measurement techniques were used for the detection and analysis of amino acids extracted from the salt crusts and sediments by using sophisticated extraction procedures. Illumina 16S amplicon sequencing was used for the identification of microbial communities associated with the different sample locations. Although amino acid load and organic carbon and nitrogen quantities were generally low, it was found that most of the samples harbored complex and versatile microbial communities, which were dominated by (extremely) halophilic microorganisms (most notably by species of the Archaeal family Halobacteriaceae). The dominance of salts (i.e., halites and sulfates) in the investigated samples leaves its mark on the composition of the microbial communities but does not appear to hinder the potential of life to flourish since it can clearly adapt to the higher concentrations. Although the Atacama Desert is one of the driest and harshest environments on Earth, it is shown that there are still sub-locations where life is able to maintain a foothold, and, as such, salt flats could be considered as interesting targets for future life exploration missions on Mars.

The last decades have been marked by increasing evidence for the presence of near-surface volatiles at the lunar poles. Enhancement in hydrogen near both poles, UV and VNIR albedo anomalies, high CPR in remotely sensed radar data have all been tentatively interpreted as evidence for surface and/or subsurface water ice. Lunar water ice and other potential cold-trapped volatiles are targets of interest both as scientific repositories for understanding the evolution of the Solar System and for exploration purposes. Determining the exact nature, extent and origin of the volatile species at or near the surface in the lunar polar regions however requires in situ measurements via lander or rover missions. A number of upcoming missions will address these issues by obtaining in situ data or by returning samples from the lunar surface or shallow subsurface. These all rely on the selection of optimal landing sites. The present paper discusses potential regions of interest (ROI) for combined volatile and geologic investigations in the vicinity of the lunar South Pole. We identified eleven regions of interest (including a broad area of interest (>200 km × 200 km) at the South Pole, together with smaller regions located near Cabeus, Amundsen, Ibn Bajja, Wiechert J and Idel'son craters), with enhanced near-surface hydrogen concentration (H > 100 ppm by weight) and where water ice is expected to be stable at the surface, considering the present-day surface thermal regime. Identifying more specific landing sites for individual missions is critically dependent on the mission's goals and capabilities. We present detailed case studies of landing site analyses based on the mission scenario and requirements of the upcoming Luna-25 and Luna-27 landers and Lunar Prospecting Rover case study. Suitable sites with promising science outcomes were found for both lander and rover scenarios. However, the rough topography and limited illumination conditions near the South Pole reduce the number of possible landing sites, especially for solar-powered missions. It is therefore expected that limited Sun and Earth visibility at latitudes >80° will impose very stringent constraints on the design and duration of future polar missions.

International audience; Mare Tranquillitatis corresponds to the deposit of successive Early to Late Imbrian basaltic units filling the Tranquillitatis basin on the Moon. The present study focuses on the western half of the mare, in the vicinity of the Arago crater (6.16°N, 21.42°E). High resolution datasets from recent remote sensing missions were used to reconstruct the geologic history of the area, which includes a variety of geological features such as: 8 extrusive domes, numerous wrinkle ridges, a sinuous rille and 37 Irregular Mare Patches (IMPs). We performed crater counting to date the domes emplacement and estimated the domes lava rheologic properties (plastic viscosities, lava effusion rates, and durations of effusion) using their geometric characteristics. As a result we classify the Arago domes into three groups: E1-type domes (Arago 1 and 8), H1-type domes (Arago 4 to 7), and B-type domes (Arago 2 and 3) respectively emplaced ​~ ​3.7 ​Ga, ~3.4 ​Ga, and ~2.8 ​Ga ago. IMPs are observed in the younger mare unit and on the top of the Arago 6 dome; they likely correspond to a late stage of waning mare volcanism in the area. Both IMPs and domes have a composition similar to the surrounding mare in the VNIR spectral domain, consistent with mafic materials. The exceptionally long-lived volcanism and its diversity recorded in the Arago region may be related to both a Th-rich anomaly reported nearby and to the large-scale magma center responsible for the Lamont positive Bouguer anomaly. In addition, volcanic features of the Arago region are superimposed on a Ti-rich mare unit visited by the Apollo 11 crew 175 ​km to the south at Tranquility Base. The geological and historical richness of this region makes it a compelling site for future science and/or In Situ Resources Utilization (ISRU) driven missions to the Moon.

Full list of authors: Cremonese, G.; Capaccioni, F.; Capria, M. T.; Doressoundiram, A.; Palumbo, P.; Vincendon, M.; Massironi, M.; Debei, S.; Zusi, M.; Altieri, F.; Amoroso, M.; Aroldi, G.; Baroni, M.; Barucci, A.; Bellucci, G.; Benkhoff, J.; Besse, S.; Bettanini, C.; Blecka, M.; Borrelli, D.; Brucato, J. R.; Carli, C.; Carlier, V.; Cerroni, P.; Cicchetti, A.; Colangeli, L.; Dami, M.; Da Deppo, V.; Della Corte, V.; De Sanctis, M. C.; Erard, S.; Esposito, F.; Fantinel, D.; Ferranti, L.; Ferri, F.; Ficai Veltroni, I.; Filacchione, G.; Flamini, E.; Forlani, G.; Fornasier, S.; Forni, O.; Fulchignoni, M.; Galluzzi, V.; Gwinner, K.; Ip, W.; Jorda, L.; Langevin, Y.; Lara, L.; Leblanc, F.; Leyrat, C.; Li, Y.; Marchi, S.; Marinangeli, L.; Marzari, F.; Mazzotta Epifani, E.; Mendillo, M.; Mennella, V.; Mugnuolo, R.; Muinonen, K.; Naletto, G.; Noschese, R.; Palomba, E.; Paolinetti, R.; Perna, D.; Piccioni, G.; Politi, R.; Poulet, F.; Ragazzoni, R.; Re, C.; Rossi, M.; Rotundi, A.; Salemi, G.; Sgavetti, M.; Simioni, E.; Thomas, N.; Tommasi, L.; Turella, A.; Van Hoolst, T.; Wilson, L.; Zambon, F.; Aboudan, A.; Barraud, O.; Bott, N.; Borin, P.; Colombatti, G.; El Yazidi, M.; Ferrari, S.; Flahaut, J.; Giacomini, L.; Guzzetta, L.; Lucchetti, A.; Martellato, E.; Pajola, M.; Slemer, A.; Tognon, G.; Turrini, D. -- This is an open access article, The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the BepiColombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will provide high-resolution images of about 20% of the surface, and the Visible and near-Infrared Hyperspectral Imaging channel (VIHI), with high spectral resolution (6 nm at finest) in the 400-2000 nm range and spatial resolution reaching 120 m/px, it will provide global coverage at 480 m/px with the spectral information, assuming the first orbit around Mercury with periherm at 480 km from the surface. SIMBIO-SYS will provide high-resolution images, the Digital Terrain Model of the entire surface, and the surface composition using a wide spectral range, as for instance detecting sulphides or material derived by sulphur and carbon oxidation, at resolutions and coverage higher than the MESSENGER mission with a full co-alignment of the three channels. All the data that will be acquired will allow to cover a wide range of scientific objectives, from the surface processes and cartography up to the internal structure, contributing to the libration experiment, and the surface-exosphere interaction. The global 3D and spectral mapping will allow to study the morphology and the composition of any surface feature. In this work, we describe the on-ground calibrations and the results obtained, providing an important overview of the instrument performances. The calibrations have been performed at channel and at system levels, utilizing specific setup in most of the cases realized for SIMBIO-SYS. In the case of the stereo camera (STC), it has been necessary to have a validation of the new stereo concept adopted, based on the push-frame. This work describes also the results of the Near-Earth Commissioning Phase performed few weeks after the Launch (20 October 2018). According to the calibration results and the first commissioning the three channels are working very well. © 2020, The Author(s)., We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0. The SIMBIO-SYS instrument has been developed by Leonardo under ASI contract I/054/10/0.

The Rümker region (41–45°N, 49–69°W) is located in northern Oceanus Procellarum of the Moon. Mons Rümker is the most distinctive geological feature in the area. The region is characterized by prolonged lunar volcanism (Late Imbrian Period to Eratosthenian Period), forming multiple geologic units in the area, including very low-Ti to low-Ti mare basalts, high-Ti mare basalts, and volcanic complexes. Each geologic unit has distinct element composition and mineral assemblages. The Rümker region, overlying the Procellarum KREEP Terrain, was selected as the landing region for China's Chang'E-5 lunar sample return mission. Prelanding analyses of the geologic context and scientific potential are reported in this contribution. We conducted detailed geological mapping using image, spectral, and altimetry data. Fourteen geological units were defined, a geologic map was constructed, and the geologic history was outlined. The western mare units (Im1, Im2, and Im3) are Imbrian-aged (~3.4–3.5 Ga) representing the major stage of lunar mare eruptive volcanism. The eastern young mare units (Em3 and Em4

Moon Mineralogy Mapper (M3) spectroscopic data and high-resolution imagery data sets were used to study the mineralogy and geology of the 207 km diameter Humboldt crater. Analyses of M3 data, using a custom-made method for M3 spectra continuum removal and spectral parameters calculation, reveal multiple pure crystalline plagioclase detections within the Humboldt crater central peak complex, hinting at its crustal origin. However, olivine, spinel, and glass are observed in the crater walls and rims, suggesting these minerals derive from shallower levels than the plagioclase of the central peak complex. High-calcium pyroxenes are detected in association with volcanic deposits emplaced on the crater's floor. Geologic mapping was performed, and the age of Humboldt crater's units was estimated from crater counts. Results suggest that volcanic activity within this floor-fractured crater spanned over a billion years. The felsic mineralogy of the central peak complex region, which presumably excavated deeper material, and the shallow mafic minerals (olivine and spinel) detected in Humboldt crater walls and rim are not in accordance with the general view of the structure of the lunar crust. Our observations can be explained by the presence of a mafic pluton emplaced in the anorthositic crust prior to the Humboldt-forming impact event. Alternatively, the excavation of Australe basin ejecta could explain the observed mineralogical detections. This highlights the importance of detailed combined mineralogical and geological remote sensing studies to assess the heterogeneity of the lunar crust.

The lack of open-source tools for hyperspectral data visualization and analysis creates a demand for new tools. In this paper we present the new PlanetServer, a set of tools comprising a web Geographic Information System (GIS) and a recently developed Python Application Programming Interface (API) capable of visualizing and analyzing a wide variety of hyperspectral data from different planetary bodies. Current WebGIS open-source tools are evaluated in order to give an overview and contextualize how PlanetServer can help in this matters. The web client is thoroughly described as well as the datasets available in PlanetServer. Also, the Python API is described and exposed the reason of its development. Two different examples of mineral characterization of different hydrosilicates such as chlorites, prehnites and kaolinites in the Nili Fossae area on Mars are presented. As the obtained results show positive outcome in hyperspectral analysis and visualization compared to previous literature, we suggest using the PlanetServer approach for such investigations.

Juventae Chasma is an isolated chasm located north of the interconnected chasms within Valles Marineris. It contains four separate interior layered deposit (ILD) mounds. We have combined layer measurements, as well as mineralogical data of the mounds with topographic data of the remaining chasm and the surrounding plateau. Our observations indicate that the chasm underwent a complex geological history. We suggest that individual ILD mounds are not contemporaneous with each other and a series of progressive collapses enlarged an initially smaller chasm to its current shape. ILDs were deposited in a lacustrine setting, and the time of ILD deposition was limited. Basin collapse and chasm enlargement continued beyond the time of ILD deposition and thus were not driven by sediment load. Glacial processes appear to have played a role in the late, postlacustrine history of the chasm. We present a simplified model that highlights some of the complexity of the chasm evolution, but acknowledge that the true history is undoubtedly more complicated.

Magmatic dikes have been proposed to have weakened and fractured the crust, allowing the formation of Valles Marineris. Hence, dikes were studied in the region of eastern Coprates Chasma in an area that includes a major transition between Hesperian-aged volcanic deposits in the western walls and pristine Noachian crust in the eastern walls. Over a hundred dikes were identified. Dike widths are 13 m on average. Estimation of magma eruption rates are comparable with previous estimates for Hesperian lava flows on Mars (105 to 106 m3 s-1). Dikes dips range from 55° to 90°, orientations record two distinct main tectonic stress fields (90° and 70°) different from the Chasmata. Dikes striking 90° are only observed at elevations below 1500 m. Dikes striking 70° are observed at elevation below 0 m and are therefore considered older. However, linear features are also observed on the late Noachian/early Hesperian surrounding plateaus and could be related to the 70° dike group. In the western part of our study area, dikes (~10 % of the total amount of dikes mapped) strike 110, sub-parallel to Valles Marineris and suggests a relationship between dike emplacement and graben formation. The presence of pre-existing faults in the two directions (90° and 70°) could explain the shape of eastern Valles Marineris and chaotic terrains, which have a different general orientation than the Valles Marineris main rift. Our results suggest a complex relationship between dike emplacement and the formation of Valles Marineris.

Planetary surface compositions are fundamental to an understanding of both the interior activity through differentiation processes and volcanic activity and the external evolution through alteration processes and accumulations of volatiles. While the Moon has been studied since early on using ground-based instruments and returned samples, observing the surface composition of the terrestrial planets did not become practical until after the development of orbital and in situ missions with instruments tracking mineralogical and elemental variations. The poorly evolved, atmosphere-free bodies like the Moon and Mercury enable the study of the formation of the most primitive crusts, through processes such as the crystallization of a magma ocean, and their volcanic evolution. Nevertheless, recent studies have shown more diversity than initially expected, including the presence of ice in high latitude regions. Because of its heavy atmosphere, Venus remains the most difficult planetary body to study and the most poorly known in regards to its composition, triggering some interest for future missions. In contrast, Mars exploration has generated a huge amount of data in the last two decades, revealing a planet with a mineralogical diversity close to that of the Earth. While Mars crust is dominated by basaltic material, recent studies concluded for significant contributions of more felsic and alkali-rich igneous material, especially in the ancient highlands. These ancient terrains also display widespread outcrops of hydrous minerals, especially phyllosilicates, which are key in the understanding of past climate conditions and suggest a volatile-rich early evolution with implications for exobiology. Recent terrains exhibit a cryosphere with ice-rich landforms at, or close to the surface, of mid- and high latitudes, generating a strong interest for recent climatic variability and resources for future manned missions. While Mars is certainly the planetary body the most similar to Earth, the observation of specific processes such as those linked to interactions with solar wind on atmosphere-free bodies, or with a thick acidic atmosphere on Venus, improve our understanding of the differences in evolution of terrestrial bodies. Future exploration is still necessary to increase humankind’s knowledge and further build a global picture of the formation and evolution of planetary surfaces.

Moon Mineralogy Mapper spectroscopic data were used to investigate the mineralogy of a selection of impact craters' central peaks or peak rings, in order to characterize the lunar crust‐mantle interface, and assess its lateral and vertical heterogeneity. The depth of origin of the craters' central peaks or peak rings was calculated using empirical equations, and compared to Gravity Recovery and Interior Laboratory crustal thickness models to select craters tapping within +10/−20 km of the crust‐mantle interface. Our results show that plagioclase is widely detected, including in craters allegedly sampling lower crustal to mantle material, except in central peaks where Low‐Calcium Pyroxene was detected. Olivine detections are scarce, and identified in material assumed to be derived from both above and below the crust‐mantle interface. Mineralogical detections in central peaks show that there is an evolution of the pyroxene composition with depth, that may correspond to the transition from the crust to the mantle. The correlation between High‐Calcium Pyroxene and some pyroxene‐dominated mixture spectra with the location of maria and cryptomaria hints at the existence of lateral heterogeneities as deep as the crust‐mantle interface., Key Points Plagioclase is widely detected in the central peaks of craters allegedly sampling the lower crust or mantle, except where LCP is observedLateral heterogeneities at the crust‐mantle interface and a pyroxene compositional evolution with depth (from HCP to LCP) were observedThis study's mineralogical observations support the GRAIL crustal thickness model 1 better than the model 3

Pedogenesis has been previously proposed on the plateaus around Coprates Chasma, Valles Marineris to explain the presence of widespread clay sequences with Al-clays and possible hydrated silica over Fe/Mg-clays on the surface of the plateaus (Le Deit et al., 2012; Carter et al., 2015). We use previous observations together with new MRO targeted observations and DEMs to constrain the extent and thickness of the plateau clay unit: the Al-clay unit is less than 3 m thick, likely ∼1 m, while the Fe/Mg-clays underneath are few tens of meters thick. We also refine the age of alteration by retrieving crater retention ages of the altered plateau and of later deposits: the observed clay sequence was created by surface pedogenesis between model ages of 4.1 Ga and 3.75 Ga. Using a leaching model from Zolotov and Mironenko (2016), we estimate the quantity of atmospheric precipitations needed to create such a clay sequence, that strongly depends on the chemistry of the precipitating fluid. A few hundreds of meters of cumulated precipitations of highly acidic fluids could explain the observed clay sequence, consistent with estimates based on late Noachian valley erosion for example (Rosenberg and Head, 2015). We show finally that the maximum quantity of sulfates potentially formed during this surface weathering event can only contribute minimally to the volume of sulfates deposited in Valles Marineris.

ISEM (Infrared Spectrometer for ExoMars) is a pencil-beam infrared spectrometer that will measure reflected solar radiation in the near infrared range for context assessment of the surface mineralogy in the vicinity of the ExoMars rover. The instrument will be accommodated on the mast of the rover and will be operated together with the panoramic camera (PanCam), high-resolution camera (HRC). ISEM will study the mineralogical and petrographic composition of the martian surface in the vicinity of the rover, and in combination with the other remote sensing instruments, it will aid in the selection of potential targets for close-up investigations and drilling sites. Of particular scientific interest are water-bearing minerals, such as phyllosilicates, sulfates, carbonates, and minerals indicative of astrobiological potential, such as borates, nitrates, and ammonium-bearing minerals. The instrument has an ∼1° field of view and covers the spectral range between 1.15 and 3.30 μm with a spectral resolution varying from 3.3 nm at 1.15 μm to 28 nm at 3.30 μm. The ISEM optical head is mounted on the mast, and its electronics box is located inside the rover's body. The spectrometer uses an acousto-optic tunable filter and a Peltier-cooled InAs detector. The mass of ISEM is 1.74 kg, including the electronics and harness. The science objectives of the experiment, the instrument design, and operational scenarios are described. Key Words: ExoMars-ISEM-Mars-Surface-Mineralogy-Spectroscopy-AOTF-Infrared. Astrobiology 17, 542-564.