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The identification of geochemical bio-signatures is important for assessing whether life existed on early Mars. In this paper, experimental microbiology and thermochemical modelling were combined to identify potential inorganic bio-signatures for life detection on early Mars. An analogue mixed microbial community from an analogue terrestrial fluvio-lacustrine environment similar to an ancient lacustrine system at Gale Crater was used to study microbial dissolution of a basalt regolith simulant and the formation of bio-signatures over a short time frame (1°month) at 14°C, 2 bar. Microbial growth influenced element dissolution (Mg, Fe, Mn, Ca and K) and the formation of morphologies and Fe-Si amorphous layers on mineral surfaces. Thermochemical models were performed at 14°C, 2 bar; the results were compared with experimental data to predict bio-signatures that would occur over geological timescales. The pH was varied to simulate abiotic and biotic experimental conditions. Model results suggest that, at water to rock ratios of 100 to 38, a less complex secondary mineral assemblage forms during biotic dissolution compared to abiotic weathering. Carbonates, quartz, pyrite and hydroxyapatite form under biotic conditions, whereas in the abiotic system magnetite and phyllosilicates would also precipitate. These results could be used to distinguish between abiotic and biotic basalt weathering processes, aiding the interpretation of data from Mars exploration missions.

The primary mineral olivine and its alteration products, serpentine and magnesite, have been reported from several locales on Mars. The mineralogical similarity of the altered ultramafic rocks on Earth makes them a potential analogue that can provide significant insight into the serpentinization and carbonation processes on Mars. This serpentine-magnesite assemblage is significant in astrobiology because serpentinization is known for the formation of simple organic molecules like methane from inorganic precursors. An association of olivine-serpentine-magnesite is widely distributed in the Salem Ultramafic Complex (SUC) in Southern India. We used hyperspectral, Laser Raman, and Fourier-transform infrared (FTIR) techniques to characterize this mineral association in the SUC. The visible and near-infrared (VNIR) spectra of all the serpentine samples show a narrow and strong absorption feature at 1.4 ​μm and an in-depth feature at 2.35 ​μm. Magnesite samples have broad and strong features at 1.4 ​μm, 2.3 ​μm, and 2.5 ​μm. The obtained spectra were compared with their Martian counterparts using the Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) type spectral library. Raman spectroscopy is used to differentiate serpentine polymorphs. The major polymorph in the area is antigorite, which shows intense Raman peaks at 682 ​cm−1, 371 ​cm−1, and 228 ​cm−1, and weak peaks at 635 ​cm−1 and 1040 ​cm−1. The Raman peaks at 1096 ​cm−1 and 326 ​cm−1 are typical of magnesite. FTIR spectra from the serpentine samples are characterized by the absorption feature at 3680 ​cm−1 indicative of antigorite, formed due to hydroxyl stretching. Diagnostic absorption features of magnesite are observed at 748 ​cm−1, 877 ​cm−1, 1427 ​cm−1, 1826 ​cm−1, and 2358 ​cm−1. The results from this study can be applied to future missions to validate orbital spectroscopic data, instrument calibration purposes, and data interpretation. • The Serpentine-magnesite assemblage in Salem Ultramafic Complex (SUC) in Southern India is considered as a potential Martian analogue site. • Spectral and chemical characterization of the serpentine-magnesite assemblage. • The study compares serpentine-magnesite assemblage of SUC to those of Mars from an astrobiological and geochemical point of view. • Future Mars missions can use the results to validate orbital spectroscopic data, for instrument calibration purposes, and for data interpretation. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • We present a review of the terrestrial analogue studies performed by the ERICA group. • Details about planetary mission simulations are also provided. • The main results gathered from the use of multiple analytical systems are compared. • Pros and cons expected by the use of Raman spectrometers on Mars are presented. • The work aims to support the interpretation of data returned from Mars2020 and ExoMars rovers. [ABSTRACT FROM AUTHOR]

Abstract: In the coastal desert of southern Peru, sequential high-resolution satellite images document the presence of short-lived and long-lived dust devil tracks. Dust devil tracks in the study region remain visible for less than 6 months in one area and for more than 4 years in another area. Short-lived tracks are generally darker than the surrounding ground surface. The brightness of long-lived tracks is often equal to that of their surroundings; they become visible due to a brighter edge along their margins. Different modes of formation related to ground surface properties are suggested to explain the differences in persistence and appearance. Dark, short-lived dust devil tracks are ascribed to the removal of silt-sized material from largely sand-sized surface materials. Long-lived tracks with bright margins are ascribed to coarser surface materials and the fallout of sand-sized particles along the track edges. Locating suitable areas on Earth for the study of dust devil tracks and distinguishing between different types of dust devil tracks is expected to further promote terrestrial analogue studies for Martian dust devil streaks. [Copyright &y& Elsevier]

Abstract: Near Eagle Plains, northern Yukon, Canada, acidic Ca–Fe–Mg sulfate waters are discharging year-long from disturbed permafrosted sandstone bedrock overlying pyritiferous black shales. These acidic waters are precipitating gypsum with minor amounts of jarosite-K (Na), schwertmannite and hematite. This mineral assemblage is similar to that observed at Meridiani Planum (and other location on Mars), making this site a valuable analogue for low-temperature sulfate geochemistry and mineral formation on Mars. Stable O–S isotope analysis of the acidic waters near Eagle Plains revealed that the oxygen in the dissolved sulfate is mostly derived from water (ca. 70%), suggesting that the sulfide oxidation process could be in part biomediated (i.e., accelerated by acidophilic Fe-oxidizing bacteria). However, unlike the dissolved sulfate in the waters, the formation of the Ca–Fe–SO4 minerals appears to be purely abiotic. The stable O–S isotope composition of the sulfate minerals is well within the predicted equilibrium range at low temperature, suggesting that they formed through physico-chemical processes (i.e., evaporation or freezing). Low-temperature geochemical modeling with FREZCHEM and PHREEQC suggests that the mineral assemblage at Eagle Plains precipitated mainly through the freezing of Ca–Fe–Mg–SO4 acidic waters, rather than through evaporation during the dry summer season, although the latter is still possible. This suggests that the sulfate mineral assemblage observed on Mars could have also formed under a periglacial-type climate. Considering that the active layer in the zone affected by acid drainage does not freeze-over during winter, the residual talik offers a localized niche environment to support acidophilic microorganisms. Overall, the fact that acid drainage is presently active near Eagle Plains allows the direct observation of the low-temperature geochemical processes responsible for generating acid drainage conditions and precipitation of gypsum, schwertmannite, jarosite-K, jarosite-Na, goethite and hematite. [Copyright &y& Elsevier]

[Display omitted] • Fe and Al-rich Cr-spinels are characteristic of the Sittampundi Anorthosite Complex (SAC) in southern India. • Variations in Cr-spinel chemistry are manifested in their spectral features. • SAC Cr-spinels show compositional resemblance to Fe- and Cr-bearing spinels on the Moon. • Cr-spinels in SAC are proposed as functional analogues to similar lunar spinels. The spectroscopic techniques such as Laser Raman, Fourier Transform Infrared (FTIR), and hyperspectral have been used widely to understand the mineral chemistry and crystal structure and identify the functional phases and organic molecules in geological materials on Earth and other planetary bodies. The present study used these spectroscopic techniques combined with X-ray Diffraction (XRD) and Electron Probe Micro Analysis (EPMA) to understand the spectral-compositional relationships of the Cr-spinel (Chromian spinel) present in chromitite bodies associated with Sittampundi Anorthosite Complex (SAC), southern India. The bands/lenses of Cr-spinel are found as layers (few centimeters to 6 m thick) intercalated with anorthosites and clinopyroxenites of the SAC. The cumulate Cr-spinels of the study area exhibit compositions ranging between Al-chromite and Cr-spinel. Fe-, Al-rich Cr-spinel is a characteristic of the SAC with Cr 2 O 3 content ranging from ~32–37 wt% and Cr# (Cr/[Cr + Al]) in the 0.44 to 0.53 range. The XRD spectra of these Cr-spinels have shown characteristic peaks corresponding to its constituent phases, with the highest peak at 36.11°. The observed longward shift in the Raman A 1g peak (~705–714 cm−1) is likely to be caused by the substitution of Al3+ in the spinel structure. The Raman A 1g peak position near 705 cm−1 in the spectra is attributed to the coexistence of (Mg, Fe) in the tetrahedral site and (Al, Cr) in the octahedral site. The broader and stronger 2 µm band position in the hyperspectral data is at relatively shorter wavelengths than typical Cr-spinels due to enhanced Al content (Al 2 O 3 ~ 25 wt%) in the SAC samples. The 2 µm band position is observed to have a longward shift with increasing Cr 2 O 3 and Cr# abundances and a corresponding shortward shift with enhanced Al 2 O 3 content in Cr-spinels. The linear relationship between the 2 µm band position and Cr/Al abundances indicates that this absorption band is significant in distinguishing Cr-spinels from Al-spinels. Based on spectral and compositional resemblance, Fe- and Al-rich Cr-spinels in SAC are considered as probable terrestrial (functional) analogues for similar lunar spinel compositions given that evidence-based correlation of intricate processes involved in their formation under the lunar and terrestrial conditions. The present study demonstrates the approach of applying spectrochemical characteristics of terrestrial analogue spinels for remote identification of lunar spinels and retrieving their compositional ranges from the spectral reflectance parameters. [ABSTRACT FROM AUTHOR]

• The ExoMars mission to Mars was simulated at the Tabernas Desert (ExoFiT trials) • Raman spectrometers were used the laboratory to analyse the drilled cores. • The main mineralogical phases were successfully detected in-situ by the RLS EQM-2. • The RLS ExoMars simulator detected additional minerals and organic compounds. • The suitability of Raman spectroscopy for space exploration missions was disclosed. 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. [ABSTRACT FROM AUTHOR]

As space agencies plan for the continuous deployment of rovers and landers to planetary bodies such as the Moon and Mars, an in-depth, quantitative, and qualitative understanding of the observations is essential. One objective of planetary exploration focuses on planetary geochemistry and biochemistry with an emphasis on the search for possible biosignatures and related minerals. To this end, we present the elemental quantification of samples from the CanMars analogue sample return mission conducted in Hanksville, UT, USA. Measurements were carried out in a laboratory at York University, Canada, using the Laser-induced Breakdown Spectroscopy Raman Sensor (LiRS) instrument- a breadboard for a future space concept. A linear Mixture Model (LMM) was used to quantify the abundance of major elements of 10 samples from the resulting Laser-induced Breakdown Spectroscopy LIBS spectra with a calibration set based on the sample mineralogy. We assessed the quantification achieved by LiRS and the LMM by error analysis, which resulted in root mean squared error, absolute error, and percentage relative error of less than 1.299 % ± 0.114% (wt%), 0.959 ± 0.010 (wt%), and 9.613 % ± 1.914% (of wt%), respectively. The results in question suggest that by complementing information obtained from various sources such as Raman spectroscopy, X-ray diffraction, and Reflectance spectroscopy, the quantification of LIBS may be significantly improved, from which subsequent geochemical inferences may be made. Within the scope of the CanMars analogue mission, these results show an advancement over past results with possible implications for ongoing and future sample return missions such as the OSIRIS-REx and the Mars2020 Perseverance Rover. • Collection of samples analogous to Mars. • Elemental quantification of geological samples obtained from the CanMars field Campaign. • Application of the Linear Mixture Model to LIBS spectra obtained from the LIRS instrument. • Validation of geological inference for future in situ spectrochemical analyses. [ABSTRACT FROM AUTHOR]

Clay minerals have been detected on Mars to outcrop mainly as alteration of ancient bedrock, and secondarily, as deposition from aqueous environments or interlayered with evaporitic deposits on Mars. In order to better constrain the alteration environments, we focused on the process to form clays from volcanic rocks and experimentally reproduced it at different temperature and pH. A fresh, holocrystalline alkali-basalt sample collected in the Mount Etna volcanic sequence has been used as analogue of the Martian unaltered bedrock. Previous works considered only volcanic glass or single mineral, but this may not reflect the full environmental conditions. Instead, we altered the bulk rock and analyzed the changes of primary minerals to constrain the minimum environmental parameters to form clays. We observed that under acidic aqueous solution (pH ~ 3.5–5.0) and moderate temperature (~150–175 °C), clinopyroxene and plagioclase are altered in smectite in just a few days, while higher temperature appear to favor oxides formation regardless of pH. Plagioclases can also be transformed in zeolite, commonly found in association with clays on Mars. This transformation may occur even at very shallow depth if a magmatic source is close or hydrothermalism is triggered by meteoritic impact. [ABSTRACT FROM AUTHOR]