The Planetary Terrestrial Analogues Library (PTAL) – An exclusive lithological selection of possible martian earth analogues

Dypvik et al. (Planetary and Space Science, 2021)

The Planetary Terrestrial Analogues Library (PTAL) is a dedicated lithological collection that currently consists of 102 terrestrial rock samples selected to be possible Mars analogues. The ultimate goal is improving future remote mineralogical and petrological analysis on Mars and other planetary bodies based on selected analysis such as Near- Infrared Reflectance Spectroscopy (NIR), Raman spectroscopy, Laser Induced Breakdown Spectroscopy (LIBS) and X-ray diffraction (XRD).
Most international standards applied in the remote martian mineralogical and petrological analysis have so far been based on single, pure mineral analysis, with minimal interferences from other naturally occurring minerals. Here we present detailed lithological sample evaluations based on field appearance along with optical and XRD analysis of key terrestrial rock types. The detailed mineralogical and petrological descriptions give good basis for more complete lithological understanding. In combination with NIR, LIBS and Raman analysis of the very same samples PTAL aims at improving mineralogical and petrographical information from future rovers on Mars e.g. NASA's Mars2020-Perseverance and ESA and Roscosmos's ExoMars - Rosalind Franklin.
The PTAL sample collection covers exclusively collected volcanic, magmatic and various sedimentary rocks and regoliths from well-known locations all over the world. These samples have a general composition comparable to what is currently known from Mars. The strength of this sample collection is its origin as common whole rock samples, in which minerals occur in their natural settings. It thereby allows studying possible detection interferences and a comparison of the sensitivity of the different techniques. The collection, in addition, forms the base for various alteration studies to better understand and explain alteration and weathering conditions on Mars.
The complete results and sample preparations will be available to all scientists interested.


Mineralogical and Spectral (Near-Infrared) Characterization of Fe-Rich Vermiculite-Bearing Terrestrial Deposits and Constraints for Mineralogy of Oxia Planum, ExoMars 2022 Landing Site

Krzesińska et al. (Astrobiology, 2021)

Oxia Planum is a Noachian plain on Mars. It was chosen as the final landing site for in situ studies by ExoMars 2022 rover. The main scientific objectives of the mission are to understand the mineralogy and aqueous evolution of ancient Mars with relevance to habitability. Oxia is covered by vast deposits of Fe,Mg-phyllosilicates, but the exact nature of these deposits is not yet fully understood. We performed a survey of potential terrestrial analog rocks, and here we show combined mineralogical characterization of these rocks with their near-infrared spectral analysis. Samples from two terrestrial sites were studied: (1) vermiculitized chlorite-schists from Otago, New Zealand, which underwent an alteration process without significant oxidation; and (2) basaltic tuffs from Granby, Massachusetts, USA, with Fe-rich clays filling amygdales of supposedly hydrothermal origin. Both analogues are incorporated into the newly built Planetary Terrestrial Analogue Library (PTAL) collection. Oxia bedrock clay-rich deposits are spectrally matched best by a well-crystallized trioctahedral vermiculite/saponite mixture from the basaltic tuff, although the contribution of saponite must be minor. Otago vermiculite is a good analogue to Oxia vermiculite in terms of overall mineralogy and Fe content. However, spectral inconsistencies related to the Al content in the Otago clays indicate that illitization of vermiculite, which results from postalteration oxidation, did not occur at Oxia. This implies limited water/rock interactions and reducing conditions during deposition of sediments now constituting the bedrock at Oxia. Whereas the spectral match does not conclusively imply the mineralogy, trioctahedral vermiculite should be considered a likely mineral component of the bedrock unit at Oxia Planum. Vermiculite has great potential to store organic matter, and the postdeposition geological context of Oxia Planum derived from understanding of environmental conditions in analog sites is promising for organic matter preservation.


Raman semi-quantification on Mars: ExoMars RLS system as a tool to better comprehend the geological evolution of martian crust

Veneranda et al. (Icarus, 2021)

This work presents the latest chemometric tools developed by the RLS science team to optimize the scientific outcome of the Raman system onboard the ExoMars 2022 rover. Feldspar, pyroxene and olivine samples were first analyzed through the RLS ExoMars Simulator to determine the spectroscopic indicators to be used for a proper discrimination of mineral phases on Mars. Being the main components of Martian basaltic rocks, lepidocrocite, augite and forsterite were then used as mineral proxies to prepare binary mixtures. By emulating the operational constraints of the RLS, Raman datasets gathered from laboratory mixtures were used to build external calibration curves. Providing excellent coefficients of determination (R² 0.9942÷0.9997), binary curves were finally used to semi-quantify ternary mixtures of feldspar, pyroxene and olivine minerals. As Raman results are in good agreement with real concentration values, this work suggests the RLS could be effectively used to perform semi-quantitative mineralogical studies of the basaltic geological units found at Oxia Planum. As such, crucial information about the geological evolution of Martian Crust could be extrapolated. In light of the outstanding scientific impact this analytical method could have for the ExoMars mission, further methodological improvements to be discussed in a dedicated work are finally proposed.


Spectroscopic study of terrestrial analogues to support rover missions to Mars e A Raman-centred review

Rull et al. (Analytica Chimica Acta, 2021)

The 2020s could be called, with little doubt, the “Mars decade”. No other period in space exploration history has experienced such interest in placing orbiters, rovers and landers on the Red Planet. In 2021 alone, the Emirates' first Mars Mission (the Hope orbiter), the Chinese Tianwen-1 mission (orbiter, lander and rover), and NASA's Mars 2020 Perseverance rover reached Mars. The ExoMars mission Rosalind Franklin rover is scheduled for launch in 2022. Beyond that, several other missions are proposed or under development. Among these, MMX to Phobos and the very important Mars Sample Return can be cited. One of the key mission objectives of the Mars 2020 and ExoMars 2022 missions is the detection of traces of potential past or present life. This detection relies to a great extent on the analytical results provided by complementary spectroscopic techniques. The development of these novel instruments has been carried out in step with the analytical study of terrestrial analogue sites and materials, which serve to test the scientific capabilities of spectroscopic prototypes while providing crucial information to better understand the geological processes that could have occurred on Mars. Being directly involved in the development of three of the first Raman spectrometers to be validated for space exploration missions (Mars 2020/SuperCam, ExoMars/RLS and RAX/MMX), the present review summarizes some of the most relevant spectroscopy-based analyses of terrestrial analogues carried out over the past two decades. Therefore, the present work describes the analytical results gathered from the study of some of the most  distinctive terrestrial analogues of Martian geological contexts, as well as the lessons learned mainly from ExoMars mission simulations conducted at representative analogue sites. Learning from the experience gained in the described studies, a general overview of the scientific outcome expected from the spectroscopic system developed for current and forthcoming planetary missions is provided.


Analytical database of Martian minerals (ADaMM): Project synopsis and Raman data overview

Veneranda et al. (Journal of Raman Spectroscopy, 2021)

The Mars2020/Perseverance and ExoMars/Rosalind Franklin rovers are both slated to return the first Raman spectra ever collected from another planetary surface, Mars. In order to optimize the rovers scientific outcome, the scientific community needs to be provided with tailored tools for data treatment and interpretation. Responding to this need, the purpose of the Analytical Database of Martian Minerals (ADaMM) project is to build an extended multianalytical database of mineral phases that have been detected on Mars or are expected to be found at the landing sites where the two rovers will operate. Besides the use of conventional spectrometers, the main objective of the ADaMM database is to provide access to data collected by means of laboratory prototypes simulating the analytical performances of the spectroscopic systems onboard the Mars 2020 and ExoMars rovers. Planned to be released to the public in 2022, ADaMM will also provide access to data treatment and visualization tools developed in the framework of the mentioned space exploration missions. As such, the present work seeks to provide an overview of the ADaMM online platform, spectral tools, and mineral collection. In addition to that, the manuscript describes the Raman spectrometers used to analyze the mineral collection and presents a representative example of the analytical performance ensured by the Raman prototypes assembled to simulate the Raman Laser Spectrometer (RLS) and SuperCam systems.


ExoMars Raman Laser Spectrometer: A Tool to Semiquantify the Serpentinization Degree of Olivine-Rich Rocks on Mars

Veneranda et al. (Astrobiology, 2021)

We evaluated the effectiveness of the ExoMars Raman laser spectrometer (RLS) to determine the degree of serpentinization of olivine-rich units on Mars. We selected terrestrial analogs of martian ultramafic rocks from the Leka Ophiolite Complex (LOC) and analyzed them with both laboratory and flight-like analytical instruments. We first studied the mineralogical composition of the samples (mostly olivine and serpentine) with state-of-the-art diffractometric (X-ray diffractometry [XRD]) and spectroscopic (Raman, near-infrared spectroscopy [NIR]) laboratory systems. We compared these results with those obtained using our RLS ExoMars Simulator. Our work shows that the RLS ExoMars Simulator successfully identified all major phases. Moreover, when emulating the automatic operating mode of the flight instrument, the RLS ExoMars Simulator also detected several minor compounds (pyroxene and brucite), some of which were not observed by NIR and XRD (e.g., calcite). Thereafter, we produced RLS-dedicated calibration curves (R2 between 0.9993 and 0.9995 with an uncertainty between ±3.0% and ±5.2% with a confidence interval of 95%) to estimate the relative content of olivine and serpentine in the samples. Our results show that RLS can be very effective in identifying serpentine, a scientific target of primary importance for the potential detection of biosignatures on Mars—the main objective of the ExoMars rover mission.


ExoFiT trial at the Atacama Desert (Chile): Raman detection of biomarkers by representative prototypes of the ExoMars/Raman Laser Spectrometer

Veneranda et al. (Nature Scientific Reports, 2021)

In this work, the analytical research performed by the Raman Laser Spectrometer (RLS) team during the ExoFiT trial is presented. During this test, an emulator of the Rosalind Franklin rover was remotely operated at the Atacama Desert in a Mars-like sequence of scientific operations that ended with the collection and the analysis of two drilled cores. The in-situ Raman characterization of the samples was performed through a portable technology demonstrator of RLS (RAD1 system). The results were later complemented in the laboratory using a bench top RLS operation simulator and a X-Ray diffractometer (XRD). By simulating the operational and analytical constraints of the ExoMars mission, the two RLS representative instruments effectively disclosed the mineralogical composition of the drilled cores (k-feldspar, plagioclase, quartz, muscovite and rutile as main components), reaching the detection of minor phases (e.g., additional phyllosilicate and calcite) whose concentration was below the detection limit of XRD. Furthermore, Raman systems detected many organic functional groups (–C≡N, –NH2 and C–(NO2)), suggesting the presence of nitrogen-fixing microorganisms in the samples. The Raman detection of organic material in the subsurface of a Martian analogue site presenting representative environmental conditions (high UV radiation, extreme aridity), supports the idea that the RLS could play a key role in the fulfilment of the ExoMars main mission objective: to search for signs of life on Mars.


Raman spectroscopy and planetary exploration: Testing the ExoMars/RLS system at the Tabernas Desert (Spain)

Veneranda et al. (Microchemical Journal, 2021)

ExoFit trials are field campaigns financed by ESA to test the Rosalind Franklin rover and to enhance collaboration practices between ExoMars working groups. During the first trial, a replicate of the ExoMars rover was remotely operated from Oxfordshire (United Kingdom) to perform a complex sequence of scientific operation at the Tabernas Desert (Spain). By following the ExoMars Reference Surface Mission (RSM), the rover investigated the Badlands subsoil and collected drill cores, whose analytical study was entrusted to the RLS (Raman Laser Spectrometer) team. The preliminary characterization of core samples was performed in situ through the RLS Engineering and Qualification Model (EQM-2) and the Raman Demonstrator (RAD1), being this a new, portable emulator of the RLS. In situ results where then complemented by laboratory analysis using the RLS ExoMars simulator and the commercial version of the Curiosity/CheMin XRD system. Raman data, obtained by closely simulating the operational constraints of the mission, successfully disclosed the mineralogical composition of the samples, reaching the detection of minor/trace phases that were not detected by XRD. More importantly, Raman analysis detected many vibrational peaks potentially emitted by organic functional groups, thus suggesting the presence of microorganisms in the arid sub-surface of the Tabernas Desert. In light of the forthcoming ExoMars mission, the results here presented proves that RLS could play a critical role in the characterization of Martian sub-surface environments and in the analytical detection of potential traces of live.


ExoMars Raman Laser Spectrometer: A Tool for the Potential Recognition of Wet-Target Craters on Mars

Veneranda et al. (Astrobiology, 2020)

In the present work, near-infrared, laser-induced breakdown spectroscopy, Raman, and X-ray diffractometer techniques have been complementarily used to carry out a comprehensive characterization of a terrestrial analogue selected from the Chesapeake Bay impact structure (CBIS). The obtained data clearly highlight the key role of Raman spectroscopy in the detection of minor and trace compounds, through which inferences about geological processes occurred in the CBIS can be extrapolated. Beside the use of commercial systems, further Raman analyses were performed by the Raman laser spectrometer (RLS) ExoMars Simulator. This instrument represents the most reliable tool to effectively predict the scientific capabilities of the ExoMars/Raman system that will be deployed on Mars in 2021. By emulating the analytical procedures and operational restrictions established by the ExoMars mission rover design, it was proved that the RLS ExoMars Simulator can detect the amorphization of quartz, which constitutes an analytical clue of the impact origin of craters. Beside amorphized minerals, the detection of barite and siderite, compounds crystallizing under hydrothermal conditions, helps indirectly to confirm the presence of water in impact targets. Furthermore, the RLS ExoMars Simulator capability of performing smart molecular mappings was successfully evaluated.


ExoMars Raman Laser Spectrometer (RLS): development of chemometric tools to classify ultramafc igneous rocks on Mars

Veneranda et al. (2020)

This work aims to evaluate whether the multi-point analysis the ExoMars Raman Laser Spectrometer (RLS) will perform on powdered samples could serve to classify ultramafic rocks on Mars. To do so, the RLS ExoMars Simulator was used to study terrestrial analogues of Martian peridotites and pyroxenites by applying the operational constraints of the Raman spectrometer onboard the Rosalind Franklin rover. Besides qualitative analysis, RLS-dedicated calibration curves have been built to estimate the relative content of olivine and pyroxenes in the samples. These semi-quantitative results, combined with a rough estimate of the concentration ratio between clino- and ortho-pyroxene mineral phases, were used to classify the terrestrial analogues. XRD data were finally employed as reference to validate Raman results. As this preliminary work suggests, ultramafic rocks on Mars could be effectively classified through the chemometric analysis of RLS data sets. After optimization, the proposed chemometric tools could be applied to the study of the volcanic geological areas detected at the ExoMars landing site (Oxia Planum), whose mineralogical composition and geological evolution have not been fully understood.


Planetary Terrestrial Analogues Library project: 2. building a laboratory facility for MicrOmega characterization

Loizeau et al. (2020)

Multiple spectroscopic techniques have been selected on previous, present and forthcoming missions to explore planetary surfaces in the Solar System. In particular, forthcoming ESA/Roscosmos and NASA missions to the surface of Mars will bring instruments capable of near-infrared (NIR), Raman and Laser Induced Breakdown Spectroscopies to analyze the mineralogy and chemistry of rocks. The PTAL (Planetary Terrestrial Analogues Library) project aims at building a multi-instrument spectral database of a large variety of natural Earth rock samples, including Mars analogues. The NIR hyperspectral microscope MicrOmega was selected to characterize the mineralogy of these analogues within the PTAL project. The instrument model used for the PTAL project is a spare flight model that requires specific care. For the safety of the instrument, and because of the large number of samples in the PTAL library and the requirement to optimize the observational conditions, a dedicated and semi-automated setup was built for the use of the MicrOmega instrument for this project. This paper presents the requirements specified for this setup, the technical solutions that have been selected, their implementation and the performances of the set-up. Sample preparation and operations during sample observations are explained, and a characterization example is presented to briefly illustrate the capabilities of MicrOmega in this set-up. The complete results from the MicrOmega characterizations of the PTAL rock analogues will be presented in a forthcoming paper (Loizeau et al. in prep).


Planetary Terrestrial Analogues Library project: 1. characterization of samples by near-infrared point spectrometer

Lantz et al. (2020)

The PTAL project aims at building and exploiting a database involving several analytical techniques, the Planetary Terrestrial Analogues Library, to help characterizing the mineralogical evolution of terrestrial bodies, starting with Mars. A total of 94 natural Earth rocks have been collected from selected locations around the world to get a selection of analogues for Martian geology. The PTAL library gathers a variety of igneous rocks from different plutonic and volcanic origins and compositions, associated to different environments and levels of aqueous alteration. Samples of impact craters and sedimentary units are also present.The full set of samples will be characterized with optical thin section analysis and XRD (Oslo University, Norway), NIR spectroscopy (Paris-Saclay University, France), Raman spectroscopy (Valladolid University, Spain) and LIBS (Paul Sabatier University, France). The multianalytical study used within the PTAL project provides an unique opportunity to coordinate minerals/elements detection by different techniques that are similar to the instruments onboard current and forthcoming Martian missions. Such combined analysis should give the opportunity to prepare and improve ExoMars/ESA-Roscosmos and Mars2020/NASA observations. This paper focuses only on the NIR measurements and interpretations.
The diversity of the PTAL samples is well revealed by the diversity of spectra from the NIR observations. The detected minerals are representative of various formation, alteration and geochemical environments. The major diagnostic features observed are those of primary Fe2+ bearing silicates like olivine or pyroxene with low and/or high calcium content; altered silicates detected with vibrational features associated to OH and/or H2O and/or metal-OH features; oxides; zeolites; and carbonates.
This collection brings together a set of rocks and minerals that have been reported elsewhere in the Solar System and particularly on Mars.


Mawrth Vallis, Mars: A Fascinating Place for Future In Situ Exploration

Poulet et al. (2020)

After the successful landing of the Mars Science Laboratory rover, both NASA and ESA initiated a selection process for potential landing sites for the Mars2020 and ExoMars missions, respectively. Two ellipses located in the Mawrth Vallis region were proposed and evaluated during a series of meetings (three for Mars2020 mission and five for ExoMars). We describe here the regional context of the two proposed ellipses as well as the framework of the objectives of these two missions. Key science targets of the ellipses and their astrobiological interests are reported. This work confirms that the proposed ellipses contain multiple past martian wet environments of a subaerial, subsurface, and/or subaqueous character, in which to probe the past climate of Mars; build a broad picture of possible past habitable environments; evaluate their exobiological potentials; and search for biosignatures in well-preserved rocks. A mission scenario covering several key investigations during the nominal mission of each rover is also presented, as well as descriptions of how the site fulfills the science requirements and expectations of in situ martian exploration. These serve as a basis for potential future exploration of the Mawrth Vallis region with new missions and describe opportunities for human exploration of Mars in terms of resources and science discoveries.


The M3 project: 2 - Global distributions of mafic mineral abundances on Mars

Riu et al. (2019)

A radiative transfer model was used to reproduce several millions of OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) spectra representative of igneous terrains of Mars. This task provided the modal composition and grain sizes at a planetary scale. The lithology can be summarized in five mineral maps at km-scale. We found that the low albedo equatorial regions of the Martian surface (from 60°S to 30°N) are globally dominated by plagioclase with average abundance ~50 vol% and pyroxenes with total averaged abundance close to 40 vol%. An evolution of the LCP/(LCP + HCP) ratio is observed with time at the global scale, suggesting an evolution of the degree of partial melting throughout the Martian eras. Olivine and Martian dust are minor components of the modelled terrains. The olivine distribution is quite different from the other minerals because it is found on localized areas with abundance reaching 20 vol%. A statistical approach, to classify the pixels of the abundances maps, using k-means clustering, highlighted seven distinct mineral assemblages on the surface. This classification illustrates that diverse mineralogical units are found in the Noachian and Hesperian terrains, which suggests the presence of various and complex magmatic processes at a global scale during the two oldest eras. The chemical composition was derived from the modal composition maps. The OMEGA-derived chemical composition is quite consistent with several distinctive geochemical characteristics previously considered as fingerprints of the Martian surface. A major discrepancy is in regards to the Fe content that is significantly smaller than soil and rock analyses from GRS and in situ measurements. The discrepancy could be partly explained by the assumptions used for the spectral modelling or could also indicate surface alteration rinds.


The M3 project: 1- A global hyperspectral image-cube of the Martian surface

Riu et al. (2019)

This paper is the first paper of a series that will present the derivation of the modal mineralogy of Mars (M3 project) at a global scale from the near-infrared dataset acquired by the imaging spectrometer OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) on board ESA/Mars Express. The objective is to create and provide a global 3-D image-cube of Mars at 32 px/° covering most of Mars surface. This product has several advantages. First, it can be used to instantaneously extract atmospheric- and aerosol-corrected near-infrared (NIR) spectra from any location on Mars. Second, several new data maps can be built as discussed here. That includes new global mineral distributions, quantitative mineral abundance distributions and maps of Martian surface chemistry (wt% oxide) detailed in a companion paper (Riu et al, 2018). Here we present the method to derive the global hyperspectral cube from several hundred millions of spectra. Global maps of some mafic minerals are then shown, and compared to previous works.


Experimental hydrothermal alteration of basaltic glass with relevance to Mars.

Sætre, C. et al. (2019).  Meteoritics and Planetary Science.  ISSN 1086-9379.

Phyllosilicates, carbonates, zeolites, and sulfates on Mars give clues about the planet's past environmental conditions, but little is known about the specific conditions in which these minerals formed within the crust and at the surface. The aim of the present study was to gain increased understanding on the formation of secondary phases by hydrothermal alteration of basaltic glass. The reaction processes were studied under varying conditions (temperature, pCO2, water:rock ratio, and fluid composition) with relevance to aqueous hydrothermal alteration in fully and partly saturated Martian basalt deposits. Analyses made on reaction products using X‐ray diffraction (XRD) and scanning electron microscope (SEM) were compared with near infrared spectroscopy (NIR) to establish relative detectability and spectral signatures. This study demonstrates that comparable alteration minerals (phyllosilicates, carbonates, zeolites) form from vapor condensing on mineral surfaces in unsaturated sediments and not only in fully water‐saturated sediments. In certain environments where water vapor might be present, it can alter the basaltic bedrock to a suite of authigenic phases similar to those observed on the Martian surface. For the detection of the secondary phases, XRD and SEM‐EDS were found to be superior to NIR for detecting and characterizing zeolites. The discrepancy in detectability of zeolites between NIR and XRD/SEM‐EDS might indicate that zeolites on Mars are more abundant than previously thought.


Planetary Terrestrial Analogues Library (PTAL) project: Raman data overview

Veneranda et al (2019)

The multianalytical study of terrestrial analogues is a useful strategy to deepen the knowledge about the geological and environmental evolution of Mars and other extraterrestrial bodies. In spite of the increasing importance that laser‐induced breakdown spectroscopy (LIBS), near‐infrared spectroscopy (NIR), and Raman techniques are acquiring in the field of space exploration, there is a lack Web‐based platform providing free access to a wide multispectral database of terrestrial analogue materials. The Planetary Terrestrial Analogues Library (PTAL) project aims at responding to this critical need by developing and providing free Web accessibility to LIBS, NIR, and Raman data from more than 94 terrestrial analogues selected according to their congruence with Martian geological contexts. In this framework, the present manuscript provides the scientific community with a complete overview of the over 4,500 Raman spectra collected to feed the PTAL database. Raman data, obtained through the complementary use of laboratory and spacecraft‐simulator systems, confirmed the effectiveness of this spectroscopic technique for the detection of major and minor mineralogical phases of the samples, the latter being of critical importance for the recognition of geological processes that could have occurred on Mars and other planets. In light of the forthcoming missions to Mars, the results obtained through the Raman Laser Spectrometer (RLS) ExoMars Simulator offer a valuable insight on the scientific outcome that could derive from the RLS spectrometer that will soon land on Mars as part of the ExoMars rover payload.


Spectroscopic study of olivine-bearing rocks and its relevance to the ExoMars rover mission

Veneranda et al, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 223 (2019) 117360

We present the compositional analysis of three terrestrial analogues of Martian olivine-bearing rocks derived from both laboratory and flight-derived analytical instruments. In the first step, state-of-the-art spectroscopic (XRF, NIR and Raman) and diffractometric (XRD) laboratory systemswere complementary used. Besides providing a detailed mineralogical and geochemical characterization of the samples, results comparison shed light on the advantages ensured by the combined use of Raman and NIR techniques, being these the spectroscopic instruments that will soon deploy (2021) on Mars as part of the ExoMars/ESA rover payload. In order to extrapolate valuable indicators of the mineralogical data that could derive from the ExoMars/Raman Laser Spectrometer (RLS), laboratory results were then compared with the molecular data gathered through the RLS ExoMars Simulator. Beside correctly identifying all major phases (feldspar, pyroxene and olivine), the RLS ExoMars Simulator confirmed the presence of additional minor compounds (i.e. hematite and apatite) that were not detected by complementary techniques. Furthermore, concerning the in-depth study of olivine grains, the RLS ExoMars simulator
was able to effectively detect the shifting of the characteristic double peak around 820 and 850 cm−1, from which the Fe\\Mg content of the analyzed crystals can be extrapolated. Considering that olivine is one of the main mineral phases of the ExoMars landing site (Oxia Planum), this study suggests that the ExoMars/RLS system has the potential to provide detailed information about the elemental composition of olivine on Mars.


Detection of Carbonates in Martian Weathering Profiles

Bultel et al (2019)

Noachian surfaces on Mars exhibit vertical assemblages of weathering horizons termed as weathering profiles; this indicates that surface water caused alteration of the rocks that required a different, warmer climate than today. Evidence of this early Martian climate with CO2 vapor as the main component causing greenhouse warming has been challenged by the lack of carbonate in these profiles. Here we report the analysis of Compact Reconnaissance Imaging Spectrometer for Mars L‐detector data leading to the detections of carbonates using a spectral signature exclusively attributed to them. The carbonates are collocated with hydroxylated minerals in weathering profiles over the Martian surface. The origin of CO2 for the formation of carbonates could be the atmosphere. The widespread distribution of weathering profiles with carbonates over the surface of the planet suggest global interactions between fluids containing carbonate/bicarbonate ions with the surface of Mars in the presence of atmospheric water until around 3.7 billion years ago.


Deposition of >3.7 Ga clay-rich strata of the Mawrth Vallis Group, Mars, in lacustrine, alluvial, and aeolian environments

Lowe et al. (2019) GSA Bulletin

The presence of abundant phyllosilicate minerals in Noachian (>3.7 Ga) rocks on Mars has been taken as evidence that liquid water was stable at or near the surface early in martian history. This study investigates some of these clay-rich strata exposed in crater rim and inverted terrain settings in the Mawrth Vallis region of Mars. In Muara crater the 200-m-thick, clay-rich Mawrth Vallis Group (MVG) is subdivided into five informal units numbered 1 (base) to 5 (top). Unit 1 consists of interbedded sedimentary and volcanic or volcaniclastic units showing weak Fe/Mg-smectite alteration deposited in a range of subaerial depositional settings. Above a major unconformity eroded on Unit 1, the dark-toned sediments of Unit 2 and lower Unit 3 are inferred to represent mainly wind-blown sand. These are widely interlayered with and draped by thin layers of light-toned sediment representing fine suspended-load aeolian silt and clay. These sediments show extensive Fe/Mg-smectite alteration, probably reflecting subaerial weathering. Upper Unit 3 and units 4 and 5 are composed of well-layered, fine-grained sediment dominated by Al-phyllosilicates, kaolinite, and hydrated silica. Deposition occurred in a large lake or arm of a martian sea. In the inverted terrain 100 km to the NE, Unit 4 shows very young slope failures suggesting that the clay-rich sediments today retain a significant component of water ice. The MVG provides evidence for the presence of large, persistent standing bodies of water on early Mars as well as a complex association of flanking shoreline, alluvial, and aeolian systems. Some of the clays, especially the Fe/Mg smectites in upper units 1 and 2 appear to have formed through subaerial weathering whereas the aluminosilicates, kaolinite, and hydrated silica of units 3, 4, and 5 formed mainly through alteration of fine sediment in subaqueous environments.


Experimental reproduction of the martian weathering profiles argues for a dense Noachian CO2 atmosphere.

Viennet, J.-C., B. Bultel, S.C. Werner (2019)

On Mars, mineral sequences have been detected and they are composed of a top layer of Al-rich clay minerals, then (Al, Fe)-rich clay minerals and a bottom layer composed of (Mg, Fe)-rich clay minerals. By analogy with Earth, such sequences are interpreted as weathering profiles formed by the interaction of acidic solutions in equilibrium with the atmosphere and the parent rock. Thus, understanding of the aqueous solution composition leading to the above mineral description allows deciphering the atmosphere composition. We designed an experimental column system with three levels containing powdered basaltic rock to test the influence of different acidic fluids on the mineralogical formation. Five solutions were used: H2SO4 and HCl at pH 3 in equilibrium with N2 atmosphere, pure water in equilibrium with 0.1 and 1 atmospheric pressure CO2 leading to pH values of 3.9 and 4.4, respectively and a H2SO4 solution at pH 3 in equilibrium with 0.1 atmospheric pressure CO2 leading to a pH value of 2.98. The results obtained show that the content of Al-rich clay minerals and the evolution from Al, (Al, Fe) to (Fe, Mg)-rich clay minerals formed are better reproduced with an originally high pCO2. Hence, we suggest that acidic alteration driven by a dense CO2 atmosphere reproduced better the observed martian weathering profiles. The experiments involving CO2 led to the formation of carbonates. Their identification by near infrared (NIR) detection methods is challenged, because the laboratory NIR spectra acquired on the experimental products show that: (i) the absorption bands related to carbonates are very weak, and (ii) the strongest feature at 3.95 μm is beyond the CRISM NIR range. Such carbonate formation is consistent with the recent carbonate detection at a planetary scale in weathering profiles, which goes toward that the weathering profiles could have been formed under a dense CO2-rich atmosphere as suggested also by climatic models.


Dioctahedral Phyllosilicates Versus Zeolites and Carbonates Versus Zeolites Competitions as Constraints to Understanding Early Mars Alteration Conditions

Viennet et al. (2017) Journal of Geophysical Research: Planets, Volume 122, Issue 11, pp. 2328-2343

Abstract: Widespread occurrence of Fe,Mg-phyllosilicates has been observed on Noachian Martian terrains. Therefore, the study of Fe,Mg-phyllosilicate formation, in order to characterize early Martian environmental conditions, is of particular interest to the Martian community. Previous studies have shown that the investigation of Fe,Mg-smectite formation alone helps to describe early Mars environmental conditions, but there are still large uncertainties in terms of pH range, oxic/anoxic conditions, etc. Interestingly, carbonates and/or zeolites have also been observed on Noachian surfaces in association with the Fe,Mg-phyllosilicates. Consequently, the present study focuses on the dioctahedral/trioctahedral phyllosilicate/carbonate/zeolite formation as a function of various CO2 contents (100% N2, 10% CO2/90% N2, and 100% CO2), from a combined approach including closed system laboratory experiments for 3 weeks at 120°C and geochemical simulations. The experimental results show that as the CO2 content decreases, the amount of dioctahedral clay minerals decreases in favor of trioctahedral minerals. Carbonates and dioctahedral clay minerals are formed during the experiments with CO2. When Ca-zeolites are formed, no carbonates and dioctahedral minerals are observed. Geochemical simulation aided in establishing pH as a key parameter in determining mineral formation patterns. Indeed, under acidic conditions dioctahedral clay minerals and carbonate minerals are formed, while trioctahedral clay minerals are formed in basic conditions with a neutral pH value of 5.98 at 120°C. Zeolites are favored from pH ≳ 7.2. The results obtained shed new light on the importance of dioctahedral clay minerals versus zeolites and carbonates versus zeolites competitions to better define the aqueous alteration processes throughout early Mars history.