Solid-Phase Microextraction for Organic Contamination Control Throughout Assembly and Operational Phases of Space Missions.

Space missions concerned with life detection contain highly sensitive instruments for the detection of organics. Terrestrial contamination can interfere with signals of indigenous organics in samples and has the potential to cause false-positive biosignature detections, which may lead to incorrect suggestions of the presence of life elsewhere in the solar system. This study assessed the capability of solid-phase microextraction (SPME) as a method for monitoring organic contamination encountered by spacecraft hardware during assembly and operation. SPME-gas chromatography-mass spectrometry (SPME-GC-MS) analysis was performed on potential contaminant source materials, which are commonly used in spacecraft construction. The sensitivity of SPME-GC-MS to organics was assessed in the context of contaminants identified in molecular wipes taken from hardware surfaces on the ExoMars Rosalind Franklin rover. SPME was found to be effective at detecting a wide range of common organic contaminants that include aromatic hydrocarbons, aliphatic hydrocarbons, nitrogen-containing compounds, alcohols, and carbonyls. A notable example of correlation of contaminant with source material was the detection of benzenamine compounds in an epoxy adhesive analyzed by SPME-GC-MS and in the ExoMars rover surface wipe samples. The current form of SPME-GC-MS does not enable quantitative evaluation of contaminants, nor is it suitable for the detection of every group of organic molecules relevant to astrobiological contamination concerns, namely large and/or polar molecules such as amino acids. However, it nonetheless represents an effective new monitoring method for rapid, easy identification of organic contaminants commonly present on spacecraft hardware and could thus be utilized in future space missions as part of their contamination control and mitigation protocols.

Mineral Matrix Effects on Pyrolysis Products of Kerogens Infer Difficulties in Determining Biological Provenance of Macromolecular Organic Matter at Mars.

Ancient martian organic matter is likely to take the form of kerogen-like recalcitrant macromolecular organic matter (MOM), existing in close association with reactive mineral surfaces, especially iron oxides. Detecting and identifying a biological origin for martian MOM will therefore be of utmost importance for life-detection efforts at Mars. We show that Type I and Type IV kerogens provide effective analogues for putative martian MOM of biological and abiological (meteoric) provenances, respectively. We analyze the pyrolytic breakdown products when these kerogens are mixed with mineral matrices highly relevant for the search for life on Mars. We demonstrate that, using traditional thermal techniques as generally used by the Sample Analysis at Mars and Mars Organic Molecule Analyser instruments, even the breakdown products of highly recalcitrant MOM are transformed during analysis in the presence of reactive mineral surfaces, particularly iron. Analytical transformation reduces the diagnostic ability of this technique, as detected transformation products of both biological and abiological MOM may be identical (low molecular weight gas phases and benzene) and indistinguishable. The severity of transformational effects increased through calcite < kaolinite < hematite < nontronite < magnetite < goethite. Due to their representation of various habitable aqueous environments and the preservation potential of organic matter by iron, it is not advisable to completely avoid iron-rich strata. We conclude that hematite-rich localities, with evidence of extensive aqueous alteration of originally reducing phases, such as the Vera Rubin Ridge, may be relatively promising targets for identifying martian biologically sourced MOM.

Transformation of Cyanobacterial Biomolecules by Iron Oxides During Flash Pyrolysis: Implications for Mars Life-Detection Missions.

Answering the question of whether life ever existed on Mars is a key goal of both NASA's and ESA's imminent Mars rover missions. The obfuscatory effects of oxidizing salts, such as perchlorates and sulfates, on organic matter during thermal decomposition analysis techniques are well established. Less well studied are the transformative effects of iron oxides and (oxy)hydroxides, which are present in great abundances in the martian regolith. We examined the products of flash pyrolysis-gas chromatography-mass spectrometry (a technique analogous to the thermal techniques employed by past, current, and future landed Mars missions) which form when the cyanobacteria Arthrospira platensis are heated in the presence of a variety of Mars-relevant iron-bearing minerals. We found that iron oxides/(oxy)hydroxides have transformative effects on the pyrolytic products of cyanobacterial biomolecules. Both the abundance and variety of molecular species detected were decreased as iron substrates transformed biomolecules, by both oxidative and reductive processes, into lower fidelity alkanes, aromatic and aryl-bonded hydrocarbons. Despite the loss of fidelity, a suite that contains mid-length alkanes and polyaromatic hydrocarbons and/or aryl-bonded molecules in iron-rich samples subjected to pyrolysis may allude to the transformation of cyanobacterially derived mid-long chain length fatty acids (particularly unsaturated fatty acids) originally present in the sample. Hematite was found to be the iron oxide with the lowest transformation potential, and because this iron oxide has a high affinity for codeposition of organic matter and preservation over geological timescales, sampling at Mars should target sediments/strata that have undergone a diagenetic history encouraging the dehydration, dihydroxylation, and oxidation of more reactive iron-bearing phases to hematite by looking for (mineralogical) evidence of the activity of oxidizing, acidic/neutral, and either hot or long-lived fluids.

Pyrolysis of Carboxylic Acids in the Presence of Iron Oxides: Implications for Life Detection on Missions to Mars.

The search for, and characterization of, organic matter on Mars is central to efforts in identifying habitable environments and detecting evidence of life in the martian surface and near surface. Iron oxides are ubiquitous in the martian regolith and are known to be associated with the deposition and preservation of organic matter in certain terrestrial environments, thus iron oxide-rich sediments are potential targets for life-detection missions. The most frequently used protocol for martian organic matter characterization (also planned for use on ExoMars) has been thermal extraction for the transfer of organic matter to gas chromatography-mass spectrometry (GC-MS) detectors. For the effective use of thermal extraction for martian samples, it is necessary to explore how potential biomarker organic molecules evolve during this process in the presence of iron oxides. We have thermally decomposed iron oxides simultaneously with (z)-octadec-9-enoic and n-octadecanoic acids and analyzed the products through pyrolysis-GC-MS. We found that the thermally driven dehydration, reduction, and recrystallization of iron oxides transformed fatty acids. Overall detectability of products greatly reduced, molecular diversity decreased, unsaturated products decreased, and aromatization increased. The severity of this effect increased as reduction potential of the iron oxide and inferred free radical formation increased. Of the iron oxides tested hematite showed the least transformative effects, followed by magnetite, goethite, then ferrihydrite. It was possible to identify the saturation state of the parent carboxylic acid at high (0.5 wt %) concentrations by the distribution of n-alkylbenzenes in the pyrolysis products. When selecting life-detection targets on Mars, localities where hematite is the dominant iron oxide could be targeted preferentially, otherwise thermal analysis of carboxylic acids, or similar biomarker molecules, will lead to enhanced polymerization, aromatization, and breakdown, which will in turn reduce the fidelity of the original biomarker, similar to changes normally observed during thermal maturation.

Artificial Maturation of Iron- and Sulfur-Rich Mars Analogues: Implications for the Diagenetic Stability of Biopolymers and Their Detection with Pyrolysis-Gas Chromatography-Mass Spectrometry.

Acidic iron- and sulfur-rich streams are appropriate analogues for the late Noachian and early Hesperian periods of martian history, when Mars exhibited extensive habitable environments. Any past life on Mars may have left behind diagnostic evidence of life that could be detected at the present day. For effective preservation, these remains must have avoided the harsh radiation flux at the martian surface, survived geological storage for billions of years, and remained detectable within their geochemical environment by analytical instrument suites used on Mars today, such as thermal extraction techniques. We investigated the detectability of organic matter within sulfur stream sediments that had been subjected to artificial maturation by hydrous pyrolysis. After maturation, the samples were analyzed by pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) to determine whether organic matter could be detected with this commonly used technique. We find that macromolecular organic matter can survive the artificial maturation process in the presence of iron- and sulfur-rich minerals but cannot be unambiguously distinguished from abiotic organic matter. However, if jarosite and goethite are present in the sulfur stream environment, they interfere with the py-GC-MS detection of organic compounds in these samples. Clay reduces the obfuscating effect of the oxidizing minerals by providing nondeleterious adsorption sites. We also find that after a simple alkali and acid leaching process that removes oxidizing minerals such as iron sulfates, oxides, and oxyhydroxides, the sulfur stream samples exhibit much greater organic responses during py-GC-MS in terms of both abundance and diversity of organic compounds, such as the detection of hopanes in all leached samples. Our results suggest that insoluble organic matter can be preserved over billions of years of geological storage while still retaining diagnostic organic information, but sample selection strategies must either avoid jarosite- and goethite-rich outcrops or conduct preparative chemistry steps to remove these oxidants prior to analysis by thermal extraction techniques.

Solid Phase Micro Extraction: Potential for Organic Contamination Control for Planetary Protection of Life-Detection Missions to the Icy Moons of the Outer Solar System.

Conclusively detecting, or ruling out the possibility of, life on the icy moons of the outer Solar System will require spacecraft missions to undergo rigorous planetary protection and contamination control procedures to achieve extremely low levels of organic terrestrial contamination. Contamination control is necessary to avoid forward contamination of the body of interest and to avoid the detection of false-positive signals, which could either mask indigenous organic chemistry of interest or cause an astrobiological false alarm. Here we test a new method for rapidly and inexpensively assessing the organic cleanliness of spaceflight hardware surfaces using solid phase micro extraction (SPME) fibers to directly swab surfaces. The results suggest that the method is both time and cost efficient. The SPME-gas chromatography-mass spectrometry (SPME-GC-MS) method is sensitive to common midweight, nonpolar contaminant compounds, for example, aliphatic and aromatic hydrocarbons, which are common contaminants in laboratory settings. While we demonstrate the potential of SPME for surface sampling, the GC-MS instrumentation restricts the SPME-GC-MS technique's sensitivity to larger polar and nonvolatile compounds. Although not used in this study, to increase the potential range of detectable compounds, SPME can also be used in conjunction with high-performance liquid chromatography/liquid chromatography-mass spectrometry systems suitable for polar analytes (Kataoka et al., 2000). Thus, our SPME method presents an opportunity to monitor organic contamination in a relatively rapid and routine way that produces information-rich data sets.

Effects of Oxygen-Containing Salts on the Detection of Organic Biomarkers on Mars and in Terrestrial Analog Soils.

The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO4-) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes. Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water-insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present or were present at extremely low levels should be reexamined.

Biological Contamination Prevention for Outer Solar System Moons of Astrobiological Interest: What Do We Need to Know?

To ensure that scientific investments in space exploration are not compromised by terrestrial contamination of celestial bodies, special care needs to be taken to preserve planetary conditions for future astrobiological exploration. Significant effort has been made and is being taken to address planetary protection in the context of inner Solar System exploration. In particular for missions to Mars, detailed internationally accepted guidelines have been established. For missions to the icy moons in the outer Solar System, Europa and Enceladus, the planetary protection requirements are so far based on a probabilistic approach and a conservative estimate of poorly known parameters. One objective of the European Commission-funded project, Planetary Protection of Outer Solar System, was to assess the existing planetary protection approach, to identify inherent knowledge gaps, and to recommend scientific investigations necessary to update the requirements for missions to the icy moons.