Searching for life on Mars: selection of molecular targets for ESA's aurora ExoMars mission

Photochemical Evolution of Alanine in Association with the Martian Soil Analog Montmorillonite: Insights Derived from Experiments Conducted on the International Space Station

The Photochemistry on the Space Station (PSS) experiment was part of the European Space Agency's EXPOSE-R2 mission and was conducted on the International Space Station from 2014 to 2016. The PSS experiment investigated the properties of montmorillonite clay as a protective shield against degradation of organic compounds that were exposed to elevated levels of ultraviolet (UV) radiation in space. Additionally, we examined the potential for montmorillonite to catalyze UV-induced breakdown of the amino acid alanine and its potential to trap the resulting photochemical byproducts within its interlayers. We tested pure alanine thin films, alanine thin films protected from direct UV exposure by a thin cover layer of montmorillonite, and an intimate combination of the two substances forming an organoclay. The samples were exposed to space conditions for 15.5 months and then returned to Earth for detailed analysis. Concurrent ground-control experiments subjected identical samples to simulated solar light irradiation. Fourier-transform infrared (FTIR) spectroscopy quantified molecular changes by comparing spectra obtained before and after exposure for both the space and ground-control samples. To more deeply understand the photochemical processes influencing the stability of irradiated alanine molecules, we performed an additional experiment using time-resolved FTIR spectroscopy for a second set of ground samples exposed to simulated solar light. Our collective experiments reveal that montmorillonite clay exhibits a dual, configuration-dependent effect on the stability of alanine: while a thin cover layer of the clay provides UV shielding that slows degradation, an intimate mixture of clay and amino acid hastens the photochemical decomposition of alanine by promoting certain chemical reactions. This observation is important to understand the preservation of amino acids in specific extraterrestrial environments, such as Mars: cover mineral layer depths of several millimeters are required to effectively shield organics from the harmful effects of UV radiation. We also explored the role of carbon dioxide (CO2), a byproduct of alanine photolysis, as a tracer of the amino acid. CO2 can be trapped within clay interlayers, particularly in clays with small interlayer ions such as sodium. Our studies emphasize the multifaceted interactions between montmorillonite clay and alanine under nonterrestrial conditions; thus, they contribute valuable insights to broader astrobiological research questions.

Organic Products of Fatty Acid and Magnesium Sulfate Mixtures after Gamma Radiolysis: Implications for Missions to Europa

If ocean-derived materials are present at Europa's surface, they would represent accessible records of ocean chemistry and habitability, but such materials would be further processed by Europa's harsh radiation environment. In this study, saturated fatty acids were precipitated onto a Europa-relevant hydrated magnesium sulfate and exposed to gamma radiation doses up to 2 MGy at -196°C. Alkane chains, with carbon numbers one less than those of the starting fatty acids, were the most abundant radiolysis products in solvent and thermal extracts analyzed by gas chromatography mass spectrometry. Detections of monounsaturated fatty acids and combined radiolysis products were attributed to the experiment's Europa-like parameters. Additionally, elevated concentrations of shorter-chain saturated fatty acids suggest that gamma radiation induced charge remote fragmentation of the alkyl chains of some starting fatty acids under these experimental conditions. Quantitation of fatty acid concentrations in the irradiated samples enabled the calculation of a radiolysis constant that indicated exposure to a 5 MGy dose of gamma radiation would have resulted in a ∼90% loss of the initial fatty acid population. The samples were further studied by Raman spectroscopy and laser desorption and ionization mass spectrometry, which characterized the distribution of fatty acids and their radiolysis products on sulfate surfaces. The substantial loss of starting fatty acids typically seen with increasing radiation dose, along with the remarkable diversity of radiolysis products identified, suggests that the detection of fatty acids in irradiated sulfate deposits on Europa will be challenged by rapid destruction of any initial fatty acid populations and scrambling of their residual signals by a myriad of organic radiolysis products. If missions to Europa encounter sulfate deposits, targeting minimally irradiated units may still enable the detection of surviving fatty acid signatures that could inform about Europa's subsurface chemistry and habitability.

Resolution and quantification of carbohydrates by enantioselective comprehensive two-dimensional gas chromatography

Carbohydrates, in particular the d-enantiomers of ribose, 2-deoxyribose, and glucose, are essential to life's informational biopolymers (RNA/DNA) and for supplying energy to living cells through glycolysis. Considered to be potential biosignatures in the search of past or present life, our capacity to detect and quantify these essential sugars is crucial for future space missions to the Moon, Mars or Titan as well as for sample-return missions. However, the enantioselective analysis of carbohydrates is challenging and both research and routine applications, are lacking efficient methods that combine highly sensitive and reproducible detection with baseline enantioselective resolution and reliable enantiomeric excess (ee) measurements. Here, we present four different derivatization strategies in combination with multidimensional gas chromatography coupled to a reflectron time-of-flight mass spectrometer (GC×GC-TOF-MS) for the enantioselective resolution of C3 to C6 carbohydrates potentially suitable for sample-return analyses. Full mass spectral interpretation and calibration curves for one single-step (cyclic boronate derivatives) and three two-step derivatization protocols (aldononitrile-acetate, hemiacetalization-trifluoroacetylation, and hemiacetalization-permethylation) are presented for concentrations ranging from 1 to 50 pmol μL⁻1 with correlation coefficients R2 > 0.94. We compared several analytical parameters including reproducibility, sensitivity (LOD and LOQ), overall separation, chiral resolution (RS), mass spectrum selectivity, stability during long term storage, and reliability of ee measurements to guide the application-dependent selection of optimal separation and quantification performance.

UV photo-degradation of the secondary lichen substance parietin: A multi-spectroscopic analysis in astrobiology perspective

The cortical anthraquinone yellow-orange pigment parietin is a secondary lichen substance providing UV-shielding properties that is produced by several lichen species. In our work, the secondary metabolite has been extracted from air-dried thalli of Xanthoria parietina. The aims of this study were to characterize parietin absorbance through UV-VIS spectrophotometry and with IR spectroscopy and to evaluate its photodegradability under UV radiation through in situ reflectance IR spectroscopy to understand to what extent the substance may have a photoprotective role. This allows us to relate parietin photo-degradability to the lichen UV tolerance in its natural terrestrial habitat and in extreme environments relevant for astrobiology such as Mars. Extracted crystals were UV irradiated for 5.59 h under N2 flux. After the UV irradiation, we assessed relevant degradations in the 1614, 1227, 1202, 1160 and 755 cm-1 bands. However, in light of Xanthoria parietina survivability in extreme conditions such as space- and Mars-simulated ones, we highlight parietin UV photo-resistance and its relevance for astrobiology as photo-protective substance and possible bio-hint.

In Situ Real-Time Monitoring for Aseptic Drilling: Lessons Learned from the Atacama Rover Astrobiology Drilling Studies Contamination Control Strategy and Implementation and Application to the Icebreaker Mars Life Detection Mission

In 2019, the Atacama Rover Astrobiology Drilling Studies (ARADS) project field-tested an autonomous rover-mounted robotic drill prototype for a 6-Sol life detection mission to Mars (Icebreaker). ARADS drilled Mars-like materials in the Atacama Desert (Chile), one of the most life-diminished regions on Earth, where mitigating contamination transfer into life-detection instruments becomes critical. Our Contamination Control Strategy and Implementation (CCSI) for the Sample Handling and Transfer System (SHTS) hardware (drill, scoop and funnels) included out-of-simulation protocol testing (out-of-sim) for hardware decontamination and verification during the 6-Sol simulation (in-sim). The most effective five-step decontamination combined safer-to-use sterilants (3%_hydrogen-peroxide-activated 5%_sodium-hypochlorite), and in situ real-time verification by adenosine triphosphate (ATP) and Signs of Life Detector (SOLID) Fluorescence Immunoassay for characterization hardware bioburden and airborne contaminants. The 20- to 40-min protocol enabled a 4-log bioburden reduction down to <0.1 fmoles ATP detection limit (funnels and drill) to 0.2-0.7 fmoles (scoop) of total ATP. The (post-cleaning) hardware background was 0.3 to 1-2 attomoles ATP/cm2 (cleanliness benchmark background values) equivalent to ca. 1-10 colony forming unit (CFU)/cm2. Further, 60-100% of the in-sim hardware background was ≤3-4 bacterial cells/cm2, the threshold limit for Class <7 aseptic operations. Across the six Sols, the flux of airborne contaminants to the drill sites was ∼5 and ∼22 amoles ATP/(cm2·day), accounting for an unexpectedly high Fluorescence Intensity (FI) signal (FI: ∼6000) against aquatic cyanobacteria, but negligible anthropogenic contribution. The SOLID immunoassay also detected microorganisms from multiple habitats across the Atacama Desert (anoxic, alkaline/acidic microenvironments in halite fields, playas, and alluvial fans) in both airborne and post-cleaning hardware background. Finally, the hardware ATP background was 40-250 times lower than the ATP in cores. Similarly, the FI peaks (FImax) against the microbial taxa and molecular biomarkers detected in the post-cleaned hardware (FI: ∼1500-1600) were 5-10 times lower than biomarkers in drilled sediments, excluding significant interference with putative biomarker found in cores. Similar protocols enable the acquisition of contamination-free materials for ultra-sensitive instruments analysis and the integrity of scientific results. Their application can augment our scientific knowledge of the distribution of cryptic life on Mars-like grounds and support life-detection robotic and human-operated missions to Mars.

Genetic Biosignatures of Deep-Subsurface Organisms Preserved in Carbonates Over a 100,000 Year Timescale at a Surface-Accessible Mars Analog Site in Southeastern Utah

In recent years, strong evidence has emerged indicating the potential habitability of the subsurface of Mars. Occasional discharge events that bring subsurface fluids to the surface may carry with them the biological traces of subsurface organisms. Similar events are known to take place on Earth and are frequently associated with long-term mineralogical preservation of organic material, including DNA. Taking advantage of this process may allow for the development of life-detection strategies targeting biosignatures from the more habitable subsurface environment without the need for direct subsurface exploration. To test the potential for this approach to life-detection, we adapted a protocol to extract microbial DNA preserved in carbonate rocks and tested its efficacy in detecting subsurface organisms at a Mars analog site in southeastern Utah, USA, using samples from ancient and modern carbonate deposits associated with natural and artificial springs. Our results indicated that DNA from deep-subsurface organisms preserved in carbonate deposits can remain recoverable for up to 100,000 years, supporting life-detection strategies based on the detection of deep-subsurface biosignatures in surface-exposed rocks on Mars.

Fe-Rich Fossil Vents as Mars Analog Samples: Identification of Extinct Chimneys in Miocene Marine Sediments Using Raman Spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy

On Earth, the circulation of Fe-rich fluids in hydrothermal environments leads to characteristic iron mineral deposits, reflecting the pH and redox chemical conditions of the hydrothermal system, and is often associated with chemotroph microorganisms capable of deriving energy from chemical gradients. On Mars, iron-rich hydrothermal sites are considered to be potentially important astrobiological targets for searching evidence of life during exploration missions, such as the Mars 2020 and the ExoMars 2022 missions. In this study, an extinct hydrothermal chimney from the Jaroso hydrothermal system (SE Spain), considered an interesting geodynamic and mineralogical terrestrial analog for Mars, was analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The sample consists of a fossil vent in a Miocene shallow-marine sedimentary deposit composed of a marl substrate, an iron-rich chimney pipe, and a central space filled with backfilling deposits and vent condensates. The iron crust is particularly striking due to the combined presence of molecular and morphological indications of a microbial colonization, including mineral microstructures (e.g., stalks, filaments), iron oxyhydroxide phases (altered goethite, ferrihydrite), and organic signatures (carotenoids, organopolymers). The clear identification of pigments by resonance Raman spectroscopy and the preservation of organics in association with iron oxyhydroxides by Raman microimaging demonstrate that the iron crust was indeed colonized by microbial communities. These analyses confirm that Raman spectroscopy is a powerful tool for documenting the habitability of such historical hydrothermal environments. Finally, based on the results obtained, we propose that the ancient iron-rich hydrothermal pipes should be recognized as singular terrestrial Mars analog specimens to support the preparatory work for robotic in situ exploration missions to Mars, as well as during the subsequent interpretation of data returned by those missions.

Comparative study of methods for detecting extraterrestrial life in exploration mission of Mars and the solar system

The detection and analysis of extraterrestrial life are important issues of space science. Mars is among the most important planets to explore for extraterrestrial life, owing both to its physical properties and to its ancient and present environments as revealed by previous exploration missions. In this paper, we present a comparative study of methods for detecting extraterrestrial life and life-related substances. To this end, we have classified and summarized the characteristics targeted for the detection of extraterrestrial life in solar system exploration mission and the methods used to evaluate them. A summary table is presented. We conclude that at this moment (i) there is no realistic single detection method capable of concluding the discovery of extraterrestrial life, (ii) no single method has an advantage over the others in all respects, and (iii) there is no single method capable of distinguishing extraterrestrial life from terrestrial life. Therefore, a combination of complementary methods is essential. We emphasize the importance of endeavoring to detect extraterrestrial life without overlooking possible alien life forms, even at the cost of tolerating false positives. Summaries of both the targets and the detection methods should be updated continuously, and comparative studies of both should be pursued. Although this study assumes Mars to be a model site for the primary environment for life searches, both the targets and detection methods described herein will also be useful for searching for extraterrestrial life in any celestial environment and for the initial inspection of returned samples.

Chemical, Thermal, and Radiation Resistance of an Iron Porphyrin: A Model Study of Biosignature Stability

Metal complexes of porphyrins and porphyrin-type compounds are ubiquitous in all three domains of life, with hemes and chlorophylls being the best-known examples. Their diagenetic transformation products are found as geoporphyrins, in which the characteristic porphyrin core structure is retained and which can be up to 1.1 billion years old. Because of this, and their relative ease of detection, metalloporphyrins appear attractive as chemical biosignatures in the search for extraterrestrial life. In this study, we investigated the stability of solid chlorido(2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III) [FeCl(oep)], which served as a model for heme-like molecules and iron geoporphyrins. [FeCl(oep)] was exposed to a variety of astrobiologically relevant extreme conditions, namely: aqueous acids and bases, oxidants, heat, and radiation. Key results are: (1) the [Fe(oep)]⁺ core is stable over the pH range 0.0-13.5 even at 80°C; (2) the oxidizing power follows the order ClO^- > H₂O₂ > ClO₃^- > HNO₃ > ClO₄^-; (3) in an inert atmosphere, the iron porphyrin is thermally stable to near 250°C; (4) at high temperatures, carbon dioxide gas is not inert but acts as an oxidant, forming carbon monoxide; (5) a decomposition layer is formed on ultraviolet irradiation and protects the [FeCl(oep)] underneath; (6) an NaCl/NaHCO₃ salt mixture has a protective effect against X-rays; and (7) no such effect is observed when [FeCl(oep)] is exposed to iron ion particle radiation. The relevance to potential iron porphyrin biosignatures on Mars, Europa, and Enceladus is discussed.

Metabolomic Profile of the Fungus Cryomyces antarcticus Under Simulated Martian and Space Conditions as Support for Life-Detection Missions on Mars

The identification of traces of life beyond Earth (e.g., Mars, icy moons) is a challenging task because terrestrial chemical-based molecules may be destroyed by the harsh conditions experienced on extraterrestrial planetary surfaces. For this reason, studying the effects on biomolecules of extremophilic microorganisms through astrobiological ground-based space simulation experiments is significant to support the interpretation of the data that will be gained and collected during the ongoing and future space exploration missions. Here, the stability of the biomolecules of the cryptoendolithic black fungus Cryomyces antarcticus, grown on two Martian regolith analogues and on Antarctic sandstone, were analysed through a metabolomic approach, after its exposure to Science Verification Tests (SVTs) performed in the frame of the European Space Agency (ESA) Biology and Mars Experiment (BIOMEX) project. These tests are building a set of ground-based experiments performed before the space exposure aboard the International Space Station (ISS). The analysis aimed to investigate the effects of different mineral mixtures on fungal colonies and the stability of the biomolecules synthetised by the fungus under simulated Martian and space conditions. The identification of a specific group of molecules showing good stability after the treatments allow the creation of a molecular database that should support the analysis of future data sets that will be collected in the ongoing and next space exploration missions.

Preservation and Distributions of Covalently Bound Polyaromatic Hydrocarbons in Ancient Biogenic Kerogens and Insoluble Organic Macromolecules

The likelihood of finding pristine molecular biosignatures preserved in Earth's oldest rocks or on other planetary bodies is low, and new approaches are needed to assess the origins of highly altered and recalcitrant organic matter. In this study, we aim to understand the distributions and systematics of preservation of ancient polycyclic aromatic hydrocarbons (PAHs), as both free hydrocarbons and bound within insoluble macromolecules. We report the distributions of bound PAHs generated by catalytic hydropyrolysis from ancient biogenic kerogens and from insoluble organic matter (IOM) in high-temperature carbonaceous residues from pyrobitumens and synthetic coke. For biogenic kerogens, the degree of thermal maturity exerts the primary control on the preservation and distributions of the major five-ring and six-ring PAH compounds. This holds for both Precambrian and Phanerozoic rocks, thus source variation in primary biogenic organic matter inputs does not exert the major control on bound PAH. The IOM samples, predominantly residues from hydrocarbon cracking at high temperatures, preserve a bound PAH profile significantly distinct from ancient biogenic kerogens and characterized by an absence of perylene and higher abundance of large-ring condensed PAHs. Covalently bound PAH profiles offer promise as "last resort" molecular biosignatures for aiding the astrobiological search for ancient life.

Development of a Surface-Enhanced Raman Spectroscopic Methodology to Detect Immobilized Organic Materials in Biogeological Contexts

The likelihood of finding intact cellular structures on the surface or in the near subsurface of the martian regolith is slim, due in part to the intense bombardment of the surface by ionizing radiation from outer space. Given that this radiation is predicted to be so intense that it would render a living cell inactive within minutes, it is logical to search for evidence of microbial life by looking for molecules produced by the breakdown of cellular matter. This "pool" of molecules, known as biomarkers, consists of a range of species with various functionalities that make them likely to interact with minerals in the martian regolith. Raman spectroscopy, a molecularly specific analysis method utilized for detecting organic biomarkers among inorganic geomaterials, suffers from low signal intensity when the concentration of organics is as low as it appears to be on the martian surface. This article describes the utility of a surface-enhanced Raman spectroscopy (SERS) method used to detect extremely low levels of biomarkers that were passively adhered to mineral surfaces in a method that represents how this interaction would take place in a natural environment on Mars. The methodology showed promise for the detection of multiple classes of biomarkers.

Insights into the Survival Capabilities of Cryomyces antarcticus Hydrated Colonies after Exposure to Fe Particle Radiation

The modern concept of the evolution of Mars assumes that life could potentially have originated on the planet Mars, possibly during the end of the late heavy bombardment, and could then be transferred to other planets. Since then, physical and chemical conditions on Mars changed and now strongly limit the presence of terrestrial-like life forms. These adverse conditions include scarcity of liquid water (although brine solutions may exist), low temperature and atmospheric pressure, and cosmic radiation. Ionizing radiation is very important among these life-constraining factors because it damages DNA and other cellular components, particularly in liquid conditions where radiation-induced reactive oxidants diffuse freely. Here, we investigated the impact of high doses (up to 2 kGy) of densely-ionizing (197.6 keV/µm), space-relevant iron ions (corresponding on the irradiation that reach the uppermost layer of the Mars subsurface) on the survival of an extremophilic terrestrial organism-Cryomyces antarcticus-in liquid medium and under atmospheric conditions, through different techniques. Results showed that it survived in a metabolically active state when subjected to high doses of Fe ions and was able to repair eventual DNA damages. It implies that some terrestrial life forms can withstand prolonged exposure to space-relevant ion radiation.

The Complex Molecules Detector (CMOLD): A Fluidic-Based Instrument Suite to Search for (Bio)chemical Complexity on Mars and Icy Moons

Organic chemistry is ubiquitous in the Solar System, and both Mars and a number of icy satellites of the outer Solar System show substantial promise for having hosted or hosting life. Here, we propose a novel astrobiologically focused instrument suite that could be included as scientific payload in future missions to Mars or the icy moons: the Complex Molecules Detector, or CMOLD. CMOLD is devoted to determining different levels of prebiotic/biotic chemical and structural targets following a chemically general approach (i.e., valid for both terrestrial and nonterrestrial life), as well as their compatibility with terrestrial life. CMOLD is based on a microfluidic block that distributes a liquid suspension sample to three instruments by using complementary technologies: (1) novel microscopic techniques for identifying ultrastructures and cell-like morphologies, (2) Raman spectroscopy for detecting universal intramolecular complexity that leads to biochemical functionality, and (3) bioaffinity-based systems (including antibodies and aptamers as capture probes) for finding life-related and nonlife-related molecular structures. We highlight our current developments to make this type of instruments flight-ready for upcoming Mars missions: the Raman spectrometer included in the science payload of the ESAs Rosalind Franklin rover (Raman Laser Spectrometer instrument) to be launched in 2022, and the biomarker detector that was included as payload in the NASA Icebreaker lander mission proposal (SOLID instrument). CMOLD is a robust solution that builds on the combination of three complementary, existing techniques to cover a wide spectrum of targets in the search for (bio)chemical complexity in the Solar System.

The Responses of the Black Fungus Cryomyces Antarcticus to High Doses of Accelerated Helium Ions Radiation within Martian Regolith Simulants and Their Relevance for Mars

One of the primary current astrobiological goals is to understand the limits of microbial resistance to extraterrestrial conditions. Much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the Earth. The aim of this research was to study the impact of accelerated He ions (150 MeV/n, up to 1 kGy) as a component of the galactic cosmic rays on the black fungus C. antarcticus when mixed with Antarctic sandstones-the substratum of its natural habitat-and two Martian regolith simulants, which mimics two different evolutionary stages of Mars. The high dose of 1 kGy was used to assess the effect of dose accumulation in dormant cells within minerals, under long-term irradiation estimated on a geological time scale. The data obtained suggests that viable Earth-like microorganisms can be preserved in the dormant state in the near-surface scenario for approximately 322,000 and 110,000 Earth years within Martian regolith that mimic early and present Mars environmental conditions, respectively. In addition, the results of the study indicate the possibility of maintaining traces within regolith, as demonstrated by the identification of melanin pigments through UltraViolet-visible (UV-vis) spectrophotometric approach.

Carotenoid Raman Signatures Are Better Preserved in Dried Cells of the Desert Cyanobacterium Chroococcidiopsis than in Hydrated Counterparts after High-Dose Gamma Irradiation

Carotenoids are promising targets in our quest to search for life on Mars due to their biogenic origin and easy detection by Raman spectroscopy, especially with a 532 nm excitation thanks to resonance effects. Ionizing radiations reaching the surface and subsurface of Mars are however detrimental for the long-term preservation of biomolecules. We show here that desiccation can protect carotenoid Raman signatures in the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 even after high-dose gamma irradiation. Indeed, while the height of the carotenoids Raman peaks was considerably reduced in hydrated cells exposed to gamma irradiation, it remained stable in dried cells irradiated with the highest tested dose of 113 kGy of gamma rays, losing only 15-20% of its non-irradiated intensity. Interestingly, even though the carotenoid Raman signal of hydrated cells lost 90% of its non-irradiated intensity, it was still detectable after exposure to 113 kGy of gamma rays. These results add insights into the preservation potential and detectability limit of carotenoid-like molecules on Mars over a prolonged period of time and are crucial in supporting future missions carrying Raman spectrometers to Mars' surface.

MarsCAPE: Mars Communicated Through an Augmented, Physical Environment

In the last decade, vast amounts of planetary science data have been made available publicly often focused on Mars. Such data is typically disseminated via the web and made available through screen-based visualizations. However, this approach can make it difficult to convey the broader context of a feature of interest or the spatial arrangement of surface phenomena. To better support learning and engagement, we present and evaluate MarsCAPE: Mars Communicated through an Augmented, Physical Environment. MarsCAPE consists of physical models of the surface of Mars, augmented by projected information and visualizations. To assess its learning and engagement value, a structured workshop and formal evaluation were conducted. Participants reported a significant increase in knowledge, found the models engaging, and exhibited natural learning without prompting. Systems such as MarsCAPE have the potential to provide an interesting, educational way for the public to access planetary data that goes beyond the capabilities of on-screen visualizations.

Terraforming: synthetic biology's final frontier

Synthetic biology, the design and synthesis of synthetic biological systems from DNA to whole cells, has provided us with the ultimate tools for space exploration and colonisation. Herein, we explore some of the most significant advances and future prospects in the field of synthetic biology, in the context of astrobiology and terraforming.

Chiral metamaterials via Moiré stacking

Chiral metamaterials have attracted strong interest due to their versatile capabilities in spin-dependent light manipulation. Benefiting from advancements in nanofabrication and mechanistic understanding of chiroptical effects, chiral metamaterials have shown potential in a variety of applications including circular polarizers, chiral sensors, and chiroptical detectors. Recently, chiral metamaterials made by moiré stacking, superimposing two or more periodic patterns with different lattice constants or relative spatial displacement, have shown promise for chiroptical applications. The moiré chiral metamaterials (MCMs) take advantage of lattice-dependent chirality, giving cost-effective fabrication, flexible tunability, and reconfigurability superior to conventional chiral metamaterials. This feature article focuses on recent progress of MCMs. We discuss optical mechanisms, structural design, fabrication, and applications of the MCMs. We conclude with our perspectives on the future opportunities for the MCMs.

Detecting Nonvolatile Life- and Nonlife-Derived Organics in a Carbonaceous Chondrite Analogue with a New Multiplex Immunoassay and Its Relevance for Planetary Exploration

Potential martian molecular targets include those supplied by meteoritic carbonaceous chondrites such as amino acids and polycyclic aromatic hydrocarbons and true biomarkers stemming from any hypothetical martian biota (organic architectures that can be directly related to once living organisms). Heat extraction and pyrolysis-based methods currently used in planetary exploration are highly aggressive and very often modify the target molecules making their identification a cumbersome task. We have developed and validated a mild, nondestructive, multiplex inhibitory microarray immunoassay and demonstrated its implementation in the SOLID (Signs of Life Detector) instrument for simultaneous detection of several nonvolatile life- and nonlife-derived organic molecules relevant in planetary exploration and environmental monitoring. By utilizing a set of highly specific antibodies that recognize D- or L- aromatic amino acids (Phe, Tyr, Trp), benzo[a]pyrene (B[a]P), pentachlorophenol, and sulfone-containing aromatic compounds, respectively, the assay was validated in the SOLID instrument for the analysis of carbon-rich samples used as analogues of the organic material in carbonaceous chondrites or even Mars samples. Most of the antibodies enabled sensitivities at the 1-10 ppb level and some even at the ppt level. The multiplex immunoassay allowed the detection of B[a]P as well as aromatic sulfones in a water/methanol extract of an Early Cretaceous lignite sample (c.a., 140 Ma) representing type IV kerogen. No L- or D-aromatic amino acids were detected, reflecting the advanced diagenetic stage and the fossil nature of the sample. The results demonstrate the ability of the liquid extraction by ultrasonication and the versatility of the multiplex inhibitory immunoassays in the SOLID instrument to discriminate between organic matter derived from life and nonlife processes, an essential step toward life detection outside Earth.

Standoff ultracompact micro-Raman sensor for planetary surface explorations

We report the development of an innovative standoff ultracompact micro-Raman instrument that would solve some of the limitations of traditional micro-Raman systems to provide a superior instrument for future NASA missions. This active remote sensor system, based on a 532 nm laser and a miniature spectrometer, is capable of inspection and identification of minerals, organics, and biogenic materials within several centimeters (2-20 cm) at a high 10 μm resolution. The sensor system is based on inelastic (Raman) light scattering and laser-induced fluorescence. We report on micro-Raman spectroscopy development and demonstration of the standoff Raman measurements by acquiring Raman spectra in daylight at a 10 cm target distance with a small line-shaped laser spot size of 17.3 μm (width) by 5 mm (height).

Resistance of an Antarctic cryptoendolithic black fungus to radiation gives new insights of astrobiological relevance

The Antarctic black meristematic fungus Cryomyces antarcticus CCFEE 515 occurs endolithically in the McMurdo Dry Valleys of Antarctica, one of the best analogue for Mars environment on Earth. To date, this fungus is considered one of the best eukaryotic models for astrobiological studies and has been repeatedly selected for space experiments in the last decade. The obtained results are reviewed here, with special focus on responses to space relevant irradiation, UV radiation, and both sparsely and densely ionizing radiation, which represent the major injuries for a putative space-traveller. The remarkable resistance of this model organism to space stress, its radioresistance in particular, and mechanisms involved, significantly contributed to expanding our concept of limits for life and provided new insights on the origin and evolution of life in planetary systems, habitability, and biosignatures for life detection as well as on human protection during space missions.

Cryptoendolithic Antarctic Black Fungus Cryomyces antarcticus Irradiated with Accelerated Helium Ions: Survival and Metabolic Activity, DNA and Ultrastructural Damage

Space represents an extremely harmful environment for life and survival of terrestrial organisms. In the last decades, a considerable deal of attention was paid to characterize the effects of spaceflight relevant radiation on various model organisms. The aim of this study was to test the survival capacity of the cryptoendolithic black fungus Cryomyces antarcticus CCFEE 515 to space relevant radiation, to outline its endurance to space conditions. In the frame of an international radiation campaign, dried fungal colonies were irradiated with accelerated Helium ion (150 MeV/n, LET 2.2 keV/μm), up to a final dose of 1,000 Gy, as one of the space-relevant ionizing radiation. Results showed that the fungus maintained high survival and metabolic activity with no detectable DNA and ultrastructural damage, even after the highest dose irradiation. These data give clues on the resistance of life toward space ionizing radiation in general and on the resistance and responses of eukaryotic cells in particular.

Correlations Between Life-Detection Techniques and Implications for Sampling Site Selection in Planetary Analog Missions

We conducted an analog sampling expedition under simulated mission constraints to areas dominated by basaltic tephra of the Eldfell and Fimmvörðuháls lava fields (Iceland). Sites were selected to be "homogeneous" at a coarse remote sensing resolution (10-100 m) in apparent color, morphology, moisture, and grain size, with best-effort realism in numbers of locations and replicates. Three different biomarker assays (counting of nucleic-acid-stained cells via fluorescent microscopy, a luciferin/luciferase assay for adenosine triphosphate, and quantitative polymerase chain reaction (qPCR) to detect DNA associated with bacteria, archaea, and fungi) were characterized at four nested spatial scales (1 m, 10 m, 100 m, and >1 km) by using five common metrics for sample site representativeness (sample mean variance, group F tests, pairwise t tests, and the distribution-free rank sum H and u tests). Correlations between all assays were characterized with Spearman's rank test. The bioluminescence assay showed the most variance across the sites, followed by qPCR for bacterial and archaeal DNA; these results could not be considered representative at the finest resolution tested (1 m). Cell concentration and fungal DNA also had significant local variation, but they were homogeneous over scales of >1 km. These results show that the selection of life detection assays and the number, distribution, and location of sampling sites in a low biomass environment with limited a priori characterization can yield both contrasting and complementary results, and that their interdependence must be given due consideration to maximize science return in future biomarker sampling expeditions. Key Words: Astrobiology-Biodiversity-Microbiology-Iceland-Planetary exploration-Mars mission simulation-Biomarker. Astrobiology 17, 1009-1021.

The PanCam Instrument for the ExoMars Rover

The scientific objectives of the ExoMars rover are designed to answer several key questions in the search for life on Mars. In particular, the unique subsurface drill will address some of these, such as the possible existence and stability of subsurface organics. PanCam will establish the surface geological and morphological context for the mission, working in collaboration with other context instruments. Here, we describe the PanCam scientific objectives in geology, atmospheric science, and 3-D vision. We discuss the design of PanCam, which includes a stereo pair of Wide Angle Cameras (WACs), each of which has an 11-position filter wheel and a High Resolution Camera (HRC) for high-resolution investigations of rock texture at a distance. The cameras and electronics are housed in an optical bench that provides the mechanical interface to the rover mast and a planetary protection barrier. The electronic interface is via the PanCam Interface Unit (PIU), and power conditioning is via a DC-DC converter. PanCam also includes a calibration target mounted on the rover deck for radiometric calibration, fiducial markers for geometric calibration, and a rover inspection mirror. Key Words: Mars—ExoMars—Instrumentation—Geology—Atmosphere—Exobiology—Context. Astrobiology 17, 511–541.

Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures-ExoMars-Landing sites-Mars rover-Search for life. Astrobiology 17, 471-510.

The First Space-Related Study of a Kombucha Multimicrobial Cellulose-Forming Community: Preparatory Laboratory Experiments

Biofilm-forming microbial communities are known as the most robust assemblages that can survive in harsh environments. Biofilm-associated microorganisms display greatly increased resistance to physical and chemical adverse conditions, and they are expected to be the first form of life on Earth or anywhere else. Biological molecules synthesized by biofilm -protected microbiomes may serve as markers of the nucleoprotein life. We offer a new experimental model, a kombucha multimicrobial culture (KMC), to assess a structural integrity of a widespread microbial polymer - cellulose - as a biosignature of bacteria-producers for the multipurpose international project "BIOlogical and Mars Experiment (BIOMEX)", which aims to study the vitality of pro- and eukaryotic organisms and the stability of organic biomolecules in contact with minerals to analyze the detectability of life markers in the context of a planetary background. In this study, we aimed to substantiate the detectability of mineralized cellulose with spectroscopy and to study the KMC macrocolony phenotype stability under adverse conditions (UV, excess of inorganics etc.). Cellulose matrix of the KMC macrocolony has been mineralized in the mineral-water interface under assistance of KMC-members. Effect of bioleached ions on the cellulose matrix has been visible, and the FT-IR spectrum proved changes in cellulose structure. However, the specific cellulose band vibration, confirming the presence of β(1,4)-linkages between monomers, has not been quenched by secondary minerals formed on the surface of pellicle. The cellulose-based KMC macrocolony phenotype was in a dependence on extracellular matrix components (ionome, viriome, extracellular membrane vesicles), which provided its integrity and rigidness in a certain extent under impact of stressful factors.

Supercritical Carbon Dioxide Extraction of Coronene in the Presence of Perchlorate for In Situ Chemical Analysis of Martian Regolith

The analysis of the organic compounds present in the martian regolith is essential for understanding the history and habitability of Mars, as well as studying the signs of possible extant or extinct life. To date, pyrolysis, the only technique that has been used to extract organic compounds from the martian regolith, has not enabled the detection of unaltered native martian organics. The elevated temperatures required for pyrolysis extraction can cause native martian organics to react with perchlorate salts in the regolith and possibly result in the chlorohydrocarbons that have been detected by in situ instruments. Supercritical carbon dioxide (SCCO2) extraction is an alternative to pyrolysis that may be capable of delivering unaltered native organic species to an in situ detector. In this study, we report the SCCO2 extraction of unaltered coronene, a representative polycyclic aromatic hydrocarbon (PAH), from martian regolith simulants, in the presence of 3 parts per thousand (ppth) sodium perchlorate. PAHs are a class of nonpolar molecules of astrobiological interest and are delivered to the martian surface by meteoritic infall. We also determined that the extraction efficiency of coronene was unaffected by the presence of perchlorate on the regolith simulant, and that no sodium perchlorate was extracted by SCCO2. This indicates that SCCO2 extraction can provide de-salted samples that could be directly delivered to a variety of in situ detectors. SCCO2 was also used to extract trace native fluorescent organic compounds from the martian regolith simulant JSC Mars-1, providing further evidence that SCCO2 extraction may provide an alternative to pyrolysis to enable the delivery of unaltered native organic compounds to an in situ detector on a future Mars rover.

KEY WORDS

Biomarkers-Carbon dioxide-In situ measurement-Mars-Search for Mars' organics. Astrobiology 16, 703-714.

Preservation of Biomarkers from Cyanobacteria Mixed with Mars-Like Regolith Under Simulated Martian Atmosphere and UV Flux

The space mission EXPOSE-R2 launched on the 24th of July 2014 to the International Space Station is carrying the BIOMEX (BIOlogy and Mars EXperiment) experiment aimed at investigating the endurance of extremophiles and stability of biomolecules under space and Mars-like conditions. In order to prepare the analyses of the returned samples, ground-based simulations were carried out in Planetary and Space Simulation facilities. During the ground-based simulations, Chroococcidiopsis cells mixed with two Martian mineral analogues (phyllosilicatic and sulfatic Mars regolith simulants) were exposed to a Martian simulated atmosphere combined or not with UV irradiation corresponding to the dose received during a 1-year-exposure in low Earth orbit (or half a Martian year on Mars). Cell survival and preservation of potential biomarkers such as photosynthetic and photoprotective pigments or DNA were assessed by colony forming ability assays, confocal laser scanning microscopy, Raman spectroscopy and PCR-based assays. DNA and photoprotective pigments (carotenoids) were detectable after simulations of the space mission (570 MJ/m(2) of UV 200-400 nm irradiation and Martian simulated atmosphere), even though signals were attenuated by the treatment. The fluorescence signal from photosynthetic pigments was differently preserved after UV irradiation, depending on the thickness of the samples. UV irradiation caused a high background fluorescence of the Martian mineral analogues, as revealed by Raman spectroscopy. Further investigation will be needed to ensure unambiguous identification and operations of future Mars missions. However, a 3-month exposure to a Martian simulated atmosphere showed no significant damaging effect on the tested cyanobacterial biosignatures, pointing out the relevance of the latter for future investigations after the EXPOSE-R2 mission. Data gathered during the ground-based simulations will contribute to interpret results from space experiments and guide our search for life on Mars.

Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method

Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examined L-alanine, L-aspartic acid, L-cysteine, L-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for L-alanine (strongest intensity band: 832 cm(-1)), L-aspartic acid (938 cm(-1)), L-cysteine (679 cm(-1)), L-glutamine (1090 cm(-1)) and glycine (875 cm(-1)), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

Towards matrix-free femtosecond-laser desorption mass spectrometry for in situ space research

RATIONALE

There is an increasing interest in the quest for low molecular weight biomarkers that can be studied on extra-terrestrial objects by direct laser desorption mass spectrometry (LD-MS). Although molecular structure investigations have recently been carried out by direct LD-MS approaches, there is still a lack of suitable instruments for implementation on a spacecraft due to weight, size and power consumption demands. In this contribution we demonstrate the feasibility of LD-MS structural analysis of molecular species by a miniature laser desorption-ionization mass spectrometer (instrument name LMS) originally designed for in situ elemental and isotope analysis of solids in space research.

METHODS

Direct LD-MS studies with molecular resolution were carried out by means of a Laser Ablation/Ionization Mass Spectrometry (LIMS) technique. Two polymer samples served as model systems: neutral polyethylene glycol (PEG) and cationic polymerizates of imidazole and epichlorohydrin (IMEP). Optimal conditions for molecular fragmentation could be identified for both polymers by tuning the laser energy and the instrument-sample distance.

RESULTS

PEG and IMEP polymers show sufficient stability over a relatively wide laser energy range. Under mild LD conditions only moderate fragmentation of the polymers takes place so that valuable structural characterization based on fragment ions can be achieved. As the applied laser pulse energy rises, the abundance of fragment ions increases, reaches a plateau and subsequently drops down due to more severe fragmentation and atomization of the polymers. At this final stage, usually referred to as laser ablation, only elemental/isotope analysis can be achieved.

CONCLUSIONS

Our investigations demonstrate the versatility of the LMS instrument that can be tuned to favourable laser desorption conditions that successfully meet molecule-specific requirements and deliver abundant fragment ion signals with detailed structural information. Overall, the results show promise for use in similar studies on planetary surfaces beyond Earth where no or minimal sample preparation is essential.

AstRoMap European Astrobiology Roadmap

The European AstRoMap project (supported by the European Commission Seventh Framework Programme) surveyed the state of the art of astrobiology in Europe and beyond and produced the first European roadmap for astrobiology research. In the context of this roadmap, astrobiology is understood as the study of the origin, evolution, and distribution of life in the context of cosmic evolution; this includes habitability in the Solar System and beyond. The AstRoMap Roadmap identifies five research topics, specifies several key scientific objectives for each topic, and suggests ways to achieve all the objectives. The five AstRoMap Research Topics are • Research Topic 1: Origin and Evolution of Planetary Systems • Research Topic 2: Origins of Organic Compounds in Space • Research Topic 3: Rock-Water-Carbon Interactions, Organic Synthesis on Earth, and Steps to Life • Research Topic 4: Life and Habitability • Research Topic 5: Biosignatures as Facilitating Life Detection It is strongly recommended that steps be taken towards the definition and implementation of a European Astrobiology Platform (or Institute) to streamline and optimize the scientific return by using a coordinated infrastructure and funding system.

Survival of Antarctic Cryptoendolithic Fungi in Simulated Martian Conditions On Board the International Space Station

Dehydrated Antarctic cryptoendolithic communities and colonies of the rock inhabitant black fungi Cryomyces antarcticus (CCFEE 515) and Cryomyces minteri (CCFEE 5187) were exposed as part of the Lichens and Fungi Experiment (LIFE) for 18 months in the European Space Agency's EXPOSE-E facility to simulated martian conditions aboard the International Space Station (ISS). Upon sample retrieval, survival was proved by testing colony-forming ability, and viability of cells (as integrity of cell membrane) was determined by the propidium monoazide (PMA) assay coupled with quantitative PCR tests. Although less than 10% of the samples exposed to simulated martian conditions were able to proliferate and form colonies, the PMA assay indicated that more than 60% of the cells and rock communities had remained intact after the "Mars exposure." Furthermore, a high stability of the DNA in the cells was demonstrated. The results contribute to assessing the stability of resistant microorganisms and biosignatures on the surface of Mars, data that are valuable information for further search-for-life experiments on Mars.

KEY WORDS

Endoliths-Eukaryotes-Extremophilic microorganisms-Mars-Radiation resistance.

Implementation of microchip electrophoresis instrumentation for future spaceflight missions

We present a comprehensive discussion of the role that microchip electrophoresis (ME) instrumentation could play in future NASA missions of exploration, as well as the current barriers that must be overcome to make this type of chemical investigation possible. We describe how ME would be able to fill fundamental gaps in our knowledge of the potential for past, present, or future life beyond Earth. Despite the great promise of ME for ultrasensitive portable chemical analysis, to date, it has never been used on a robotic mission of exploration to another world. We provide a current snapshot of the technology readiness level (TRL) of ME instrumentation, where the TRL is the NASA systems engineering metric used to evaluate the maturity of technology, and its fitness for implementation on missions. We explain how the NASA flight implementation process would apply specifically to ME instrumentation, and outline the scientific and technology development issues that must be addressed for ME analyses to be performed successfully on another world. We also outline research demonstrations that could be accomplished by independent researchers to help advance the TRL of ME instrumentation for future exploration missions. The overall approach described here for system development could be readily applied to a wide range of other instrumentation development efforts having broad societal and commercial impact.

Chemical Composition of Micrometer-Sized Filaments in an Aragonite Host by a Miniature Laser Ablation/Ionization Mass Spectrometer

Detection of extraterrestrial life is an ongoing goal in space exploration, and there is a need for advanced instruments and methods for the detection of signatures of life based on chemical and isotopic composition. Here, we present the first investigation of chemical composition of putative microfossils in natural samples using a miniature laser ablation/ionization time-of-flight mass spectrometer (LMS). The studies were conducted with high lateral (∼15 μm) and vertical (∼20-200 nm) resolution. The primary aim of the study was to investigate the instrument performance on micrometer-sized samples both in terms of isotope abundance and element composition. The following objectives had to be achieved: (1) Consider the detection and calculation of single stable isotope ratios in natural rock samples with techniques compatible with their employment of space instrumentation for biomarker detection in future planetary missions. (2) Achieve a highly accurate chemical compositional map of rock samples with embedded structures at the micrometer scale in which the rock matrix is easily distinguished from the micrometer structures. Our results indicate that chemical mapping of strongly heterogeneous rock samples can be obtained with a high accuracy, whereas the requirements for isotope ratios need to be improved to reach sufficiently large signal-to-noise ratio (SNR).

UV-resistant yeasts isolated from a high-altitude volcanic area on the Atacama Desert as eukaryotic models for astrobiology

The Sairecabur volcano (5971 m), in the Atacama Desert, is a high-altitude extreme environment with high daily temperature variations, acidic soils, intense UV radiation, and low availability of water. Four different species of yeasts were isolated from this region using oligotrophic media, identified and characterized for their tolerance to extreme conditions. rRNA sequencing revealed high identity (>98%) to Cryptococcus friedmannii, Exophiala sp., Holtermanniella watticus, and Rhodosporidium toruloides. To our knowledge, this is the first report of these yeasts in the Atacama Desert. All isolates showed high resistance to UV-C, UV-B and environmental-UV radiation, capacity to grow at moderate saline media (0.75–2.25 mol/L NaCl) and at moderate to cold temperatures, being C. friedmannii and H. watticus able to grow in temperatures down to −6.5°C. The presence of pigments, analyzed by Raman spectroscopy, correlated with UV resistance in some cases, but there is evidence that, on the natural environment, other molecular mechanisms may be as important as pigmentation, which has implications for the search of spectroscopic biosignatures on planetary surfaces. Due to the extreme tolerances of the isolated yeasts, these organisms represent interesting eukaryotic models for astrobiological purposes.

The Significance of Microbe-Mineral-Biomarker Interactions in the Detection of Life on Mars and Beyond

The detection of biomarkers plays a central role in our effort to establish whether there is, or was, life beyond Earth. In this review, we address the importance of considering mineralogy in relation to the selection of locations and biomarker detection methodologies with characteristics most promising for exploration. We review relevant mineral-biomarker and mineral-microbe interactions. The local mineralogy on a particular planet reflects its past and current environmental conditions and allows a habitability assessment by comparison with life under extreme conditions on Earth. The type of mineral significantly influences the potential abundances and types of biomarkers and microorganisms containing these biomarkers. The strong adsorptive power of some minerals aids in the preservation of biomarkers and may have been important in the origin of life. On the other hand, this strong adsorption as well as oxidizing properties of minerals can interfere with efficient extraction and detection of biomarkers. Differences in mechanisms of adsorption and in properties of minerals and biomarkers suggest that it will be difficult to design a single extraction procedure for a wide range of biomarkers. While on Mars samples can be used for direct detection of biomarkers such as nucleic acids, amino acids, and lipids, on other planetary bodies remote spectrometric detection of biosignatures has to be relied upon. The interpretation of spectral signatures of photosynthesis can also be affected by local mineralogy. We identify current gaps in our knowledge and indicate how they may be filled to improve the chances of detecting biomarkers on Mars and beyond.

Selection of Portable Spectrometers for Planetary Exploration: A Comparison of 532 nm and 785 nm Raman Spectroscopy of Reduced Carbon in Archean Cherts

Knowledge and understanding of the martian environment has advanced greatly over the past two decades, beginning with NASA's return to the surface of Mars with the Pathfinder mission and its rover Sojourner in 1997 and continuing today with data being returned by the Curiosity rover. Reduced carbon, however, is yet to be detected on the martian surface, despite its abundance in meteorites originating from the planet. If carbon is detected on Mars, it could be a remnant of extinct life, although an abiotic source is much more likely. If the latter is the case, environmental carbonaceous material would still provide a source of carbon that could be utilized by microbial life for biochemical synthesis and could therefore act as a marker for potential habitats, indicating regions that should be investigated further. For this reason, the detection and characterization of reduced or organic carbon is a top priority for both the ESA/Roscosmos ExoMars rover, currently due for launch in 2018, and for NASA's Mars 2020 mission. Here, we present a Raman spectroscopic study of Archean chert Mars analog samples from the Pilbara Craton, Western Australia. Raman spectra were acquired with a flight-representative 532 nm instrument and a 785 nm instrument with similar operating parameters. Reduced carbon was successfully detected with both instruments; however, its Raman bands were detected more readily with 785 nm excitation, and the corresponding spectra exhibited superior signal-to-noise ratios and reduced background levels.

Effect of nontronite smectite clay on the chemical evolution of several organic molecules under simulated martian surface ultraviolet radiation conditions

Most of the phyllosilicates detected at the surface of Mars today are probably remnants of ancient environments that sustained long-term bodies of liquid water at the surface or subsurface and were possibly favorable for the emergence of life. Consequently, phyllosilicates have become the main mineral target in the search for organics on Mars. But are phyllosilicates efficient at preserving organic molecules under current environmental conditions at the surface of Mars? We monitored the qualitative and quantitative evolutions of glycine, urea, and adenine in interaction with the Fe(3+)-smectite clay nontronite, one of the most abundant phyllosilicates present at the surface of Mars, under simulated martian surface ultraviolet light (190-400 nm), mean temperature (218 ± 2 K), and pressure (6 ± 1 mbar) in a laboratory simulation setup. We tested organic-rich samples that were representative of the evaporation of a small, warm pond of liquid water containing a high concentration of organics. For each molecule, we observed how the nontronite influences its quantum efficiency of photodecomposition and the nature of its solid evolution products. The results reveal a pronounced photoprotective effect of nontronite on the evolution of glycine and adenine; their efficiencies of photodecomposition were reduced by a factor of 5 when mixed at a concentration of 2.6 × 10(-2) mol of molecules per gram of nontronite. Moreover, when the amount of nontronite in the sample of glycine was increased by a factor of 2, the gain of photoprotection was multiplied by a factor of 5. This indicates that the photoprotection provided by the nontronite is not a purely mechanical shielding effect but is also due to stabilizing interactions. No new evolution product was firmly identified, but the results obtained with urea suggest a particular reactivity in the presence of nontronite, leading to an increase of its dissociation rate.

Volcanogenic fluvial-lacustrine environments in iceland and their utility for identifying past habitability on Mars

The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing.

Biomarkers and their Raman spectroscopic signatures: a spectral challenge for analytical astrobiology

The remote robotic exploration of extraterrestrial scenarios for evidence of biological colonization in 'search for life' missions using Raman spectroscopy is critically dependent on two major factors: firstly, the Raman spectral recognition of characteristic biochemical spectral signatures in the presence of mineral matrix features; and secondly, the positive unambiguous identification of molecular biomaterials which are indicative of extinct or extant life. Both of these factors are considered here: the most important criterion is the clear definition of which biochemicals truly represent biomarkers, whose presence in the planetary geological record from an analytical astrobiological standpoint will unambiguously be indicative of life as recognized from its remote instrumental interrogation. Also discussed in this paper are chemical compounds which are associated with living systems, including biominerals, which may not in themselves be definitive signatures of life processes and origins but whose presence provides an indicator of potential life-bearing matrices.

Detection of macromolecules in desert cyanobacteria mixed with a lunar mineral analogue after space simulations

In the context of future exposure missions in Low Earth Orbit and possibly on the Moon, two desert strains of the cyanobacterium Chroococcidiopsis, strains CCMEE 029 and 057, mixed or not with a lunar mineral analogue, were exposed to fractionated fluencies of UVC and polychromatic UV (200–400 nm) and to space vacuum. These experiments were carried out within the framework of the BIOMEX (BIOlogy and Mars EXperiment) project, which aims at broadening our knowledge of mineral-microorganism interaction and the stability/degradation of their macromolecules when exposed to space and simulated Martian conditions. The presence of mineral analogues provided a protective effect, preserving survivability and integrity of DNA and photosynthetic pigments, as revealed by testing colony-forming abilities, performing PCR-based assays and using confocal laser scanning microscopy. In particular, DNA and pigments were still detectable after 500 kJ/m² of polychromatic UV and space vacuum (10⁻⁴ Pa), corresponding to conditions expected during one-year exposure in Low Earth Orbit on board the EXPOSE-R2 platform in the presence of 0.1 % Neutral Density (ND) filter. After exposure to high UV fluencies (800 MJ/m²) in the presence of minerals, however, altered fluorescence emission spectrum of the photosynthetic pigments were detected, whereas DNA was still amplified by PCR. The present paper considers the implications of such findings for the detection of biosignatures in extraterrestrial conditions and for putative future lunar missions.

Biota and biomolecules in extreme environments on Earth: implications for life detection on Mars

The three main requirements for life as we know it are the presence of organic compounds, liquid water, and free energy. Several groups of organic compounds (e.g., amino acids, nucleobases, lipids) occur in all life forms on Earth and are used as diagnostic molecules, i.e., biomarkers, for the characterization of extant or extinct life. Due to their indispensability for life on Earth, these biomarkers are also prime targets in the search for life on Mars. Biomarkers degrade over time; in situ environmental conditions influence the preservation of those molecules. Nonetheless, upon shielding (e.g., by mineral surfaces), particular biomarkers can persist for billions of years, making them of vital importance in answering questions about the origins and limits of life on early Earth and Mars. The search for organic material and biosignatures on Mars is particularly challenging due to the hostile environment and its effect on organic compounds near the surface. In support of life detection on Mars, it is crucial to investigate analogue environments on Earth that resemble best past and present Mars conditions. Terrestrial extreme environments offer a rich source of information allowing us to determine how extreme conditions affect life and molecules associated with it. Extremophilic organisms have adapted to the most stunning conditions on Earth in environments with often unique geological and chemical features. One challenge in detecting biomarkers is to optimize extraction, since organic molecules can be low in abundance and can strongly adsorb to mineral surfaces. Methods and analytical tools in the field of life science are continuously improving. Amplification methods are very useful for the detection of low concentrations of genomic material but most other organic molecules are not prone to amplification methods. Therefore, a great deal depends on the extraction efficiency. The questions “what to look for”, “where to look”, and “how to look for it” require more of our attention to ensure the success of future life detection missions on Mars.

Searching for life on Mars: degradation of surfactant solutions used in organic extraction experiments

Life-detection instruments on future Mars missions may use surfactant solutions to extract organic matter from samples of martian rocks. The thermal and radiation environments of space and Mars are capable of degrading these solutions, thereby reducing their ability to dissolve organic species. Successful extraction and detection of biosignatures on Mars requires an understanding of how degradation in extraterrestrial environments can affect surfactant performance. We exposed solutions of the surfactants polysorbate 80 (PS80), Zonyl FS-300, and poly[dimethylsiloxane-co-[3-(2-(2-hydroxyethoxy)ethoxy)propyl]methylsiloxane] (PDMSHEPMS) to elevated radiation and heat levels, combined with prolonged storage. Degradation was investigated by measuring changes in pH and electrical conductivity and by using the degraded solutions to extract a suite of organic compounds spiked onto grains of the martian soil simulant JSC Mars-1. Results indicate that the proton fluences expected during a mission to Mars do not cause significant degradation of surfactant compounds. Solutions of PS80 or PDMSHEPMS stored at -20 °C are able to extract the spiked standards with acceptable recovery efficiencies. Extraction efficiencies for spiked standards decrease progressively with increasing temperature, and prolonged storage at 60°C renders the surfactant solutions ineffective. Neither the presence of ascorbic acid nor the choice of solvent unequivocally alters the efficiency of extraction of the spiked standards. Since degradation of polysorbates has the potential to produce organic compounds that could be mistaken for indigenous martian organic matter, the polysiloxane PDMSHEPMS may be a superior choice of surfactant for the exploration of Mars.

Statistics provide guidance for indigenous organic carbon detection on Mars missions

Data from the Viking and Mars Science Laboratory missions indicate the presence of organic compounds that are not definitively martian in origin. Both contamination and confounding mineralogies have been suggested as alternatives to indigenous organic carbon. Intuitive thought suggests that we are repeatedly obtaining data that confirms the same level of uncertainty. Bayesian statistics may suggest otherwise. If an organic detection method has a true positive to false positive ratio greater than one, then repeated organic matter detection progressively increases the probability of indigeneity. Bayesian statistics also reveal that methods with higher ratios of true positives to false positives give higher overall probabilities and that detection of organic matter in a sample with a higher prior probability of indigenous organic carbon produces greater confidence. Bayesian statistics, therefore, provide guidance for the planning and operation of organic carbon detection activities on Mars. Suggestions for future organic carbon detection missions and instruments are as follows: (i) On Earth, instruments should be tested with analog samples of known organic content to determine their true positive to false positive ratios. (ii) On the mission, for an instrument with a true positive to false positive ratio above one, it should be recognized that each positive detection of organic carbon will result in a progressive increase in the probability of indigenous organic carbon being present; repeated measurements, therefore, can overcome some of the deficiencies of a less-than-definitive test. (iii) For a fixed number of analyses, the highest true positive to false positive ratio method or instrument will provide the greatest probability that indigenous organic carbon is present. (iv) On Mars, analyses should concentrate on samples with highest prior probability of indigenous organic carbon; intuitive desires to contrast samples of high prior probability and low prior probability of indigenous organic carbon should be resisted.

Lipids as universal biomarkers of extraterrestrial life

In 1965, James Lovelock published a general statement, based on thermodynamic chemical equilibrium principles, about how to detect extant or extinct life on a planet other than Earth. Nearly 50 years later, it is possible to make such measurements with robotic missions such as current and future Mars rovers, and probes to sample icy plumes of Enceladus or Europa. We make a specific recommendation that certain characteristic patterns in the composition of lipid hydrocarbons can only result from a biological process, because the signal arises from a universal requirement related to lipid bilayer fluidity and membrane stability. Furthermore, the pattern can be preserved over millions of years, and instrumentation is already available to be incorporated into flight missions.