Article

# The origins of perchlorate in the Martian soil

Authors:
• NASA Jet Propulsion Laboratory, California Institute of Technology
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## Abstract

Perchlorate (ClO4−) has been detected on Mars, but its production and distribution are unclear. Mechanisms requiring atmospheric chlorine are insufficient for measured concentrations. We conducted studies under Mars conditions using halite (NaCl) alone, soil simulants consisting of silica (SiO2), Fe2O3, Al2O3, and TiO2. After 170 h irradiation, samples analyzed by ion chromatography (IC) showed ClO4− and ClO3− present in all samples. When SiO2 was added, yield increased from 2 to 42 nmol and 0.4 to 2.6 nmol, respectively. We attribute this to SiO2 and metal oxides acting as photocatalysts, generating O2− radicals from O2 which react with chloride. Results show ClO4− and ClO3− can be produced photochemically on Cl minerals without atmospheric chlorine or aqueous conditions, and explain high concentration of ClO4− and ClO4−/Cl− ratios detected by Phoenix. They provide evidence that its distribution on Mars is dictated by distribution of chlorine and provide insight into the oxidizing nature of the soil and its potential effects on organics.

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... As a result, perchlorate has been invoked to explain observations such as recurring slope lineae (e.g., Chevrier & Rivera-Valentin, 2012;McEwen et al., 2011) and putative sub-polar cap liquid water (Orosei et al., 2018). Perchlorate may act as an electron acceptor for microbes (McKay et al., 2013;Oren et al., 2014), and may destroy organic molecules via interaction with intermediate oxidation steps during perchlorate formation (Carrier & Kounaves, 2015), interaction with ionizing radiation (Quinn et al., 2013), or during analytical heating of a sample (Lasne et al., 2016;ten Kate, 2010), impacting the search for potential biosignatures. ...
... However, decomposition of perchlorate occurs under exposure to ionizing radiation (Prince & Johnson, 1965a;Quinn et al., 2013;Turner et al., 2016). While UV interactions have been proposed as a formation mechanism for perchlorate (e.g., Carrier & Kounaves, 2015;Wilson et al., 2016), this thermodynamically unfavorable process occurs only when a local energy minimum is encountered. The radiolysis breakdown described above allows the kinetic barrier to be broken so that thermodynamically favorable decomposition can occur. ...
... As the drilled bedrock samples and scooped samples are not distinguishable in these analyses, there are two straightforward possibilities: either perchlorate is present in both, evidenced only by the release of O 2 , There is also no apparent enrichment in O 2 release in these samples ( Figure S3), suggesting that perchlorate is no more abundant in surface materials than near-surface materials. The perchlorate formation mechanism on Mars is debated and may involve irradiation of the surface (Carrier & Kounaves, 2015;Wilson et al., 2016;Zhao et al., 2018), atmospheric interactions Smith et al., 2014), or electrochemical processes . Each of these mechanisms would likely result in enrichment of perchlorate at the surface. ...
Article
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Perchlorate (ClO₄⁻) was discovered in Martian soil by the Phoenix lander, with important implications for potential Martian biology, photochemistry, aqueous chemistry, and the chlorine cycle on Mars. Perchlorate was subsequently reported in both loose sediment and bedrock samples analyzed by the Sample Analysis at Mars instrument onboard the Curiosity rover in Gale crater based on a release of O₂ at 200–500°C. However, the continually wet paleoenvironment recorded by the sedimentary rocks in Gale crater was not conducive to the deposition of highly soluble salts. Furthermore, the preservation of ancient perchlorate to the modern day is unexpected due to its low thermodynamic stability and radiolytic decomposition associated with its long exposure to radioactivity and cosmic radiation. We therefore investigate alternative sources of O₂ in Sample Analysis at Mars analyses including superoxides, sulfates, nitrate, and nanophase iron and manganese oxides. Geochemical evidence and oxygen release patterns observed by Curiosity are inconsistent with each of these alternatives. We conclude that perchlorate is indeed the most likely source of the detected O2 release at 200–500°C, but contend that it is unlikely to be ancient. Rather than being associated with the lacustrine or early diagenetic environment, the most likely origin of perchlorate in the bedrock is late stage addition by downward percolation of water through rock pore space during transient wetting events in the Amazonian. The conclusion that the observed perchlorate in Gale crater is most likely Amazonian suggests the presence of recent liquid water at the modern surface.
... Perchlorate presence would be a global challenge due to its detection at various locations on Mars, such as the Northern hemisphere, Gale Crater, possibly in the Vikings landing sites [8], and areas covered by Mars Reconnaissance Orbiter (MRO) in 2015 [9]. Furthermore, it is estimated that perchlorate is distributed superficially throughout the soil on a worldwide scale [10], [11], reducing the opportunities for plants to grow and with high probabilities to 1.1 Objectives a) Lowering the concentration of perchlorate in the analog Martian soil by 95% b) Concentrate 80% of perchlorate in the solution for future uses. c) Lowering the analog Martian soil conductivity below 2.5 dS/m. ...
... mg/Kg) [7]; on Mars, the soil itself has higher quantities of perchlorate (about 0.5 -1%) [8]. In the northern hemisphere, the Phoenix detected this salt perhaps in the form of magnesium perchlorate hexahydrate (Mg(ClO4)2.6H2O) and calcium perchlorate (Ca(ClO4)2), also believed to be detected in Gale Crater by Curiosity [8], [11]. ...
Conference Paper
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One of the main technological challenges for enabling human settlements on Mars is the development of agriculture. Water, carbon, oxygen, and nutrients needed for plant development are already present mainly in the form of ice below the surface, CO2 in the atmosphere, and nutrients in the regolith. On the other hand, the Mars Odyssey mission discovered that the Martian regolith, due to its formation process, contains high amounts of chlorine and harmful minerals for the growth of plants. Perchlorate salts were detected by Phoenix Lander, and by Curiosity on Gale Crater, in values from 0.5 to 1 wt%. Since chlorine is widespread, perchlorate salts are expected to be present throughout the Martian regolith at high concentrations. The method presented here, named REDMARS, eliminates 99% of perchlorate from a Martian analog regolith. This experiment was carried out during the Asclepios analog space mission in Switzerland and is based on hydro-metallurgical techniques. Briefly, the perchlorate salts voluntarily added to the sample are first dissolved by washing with water. Then, the sediment and solution are separated by a filtration stage. Finally, the solution is treated by an ion exchange column with an appropriate anion exchange resin to remove 85% of the perchlorate, which would allow water reused. It used a soil sample extracted from the Pampas de La Joya desert in Peru, with mineralogical features similar to what is expected in the Martian low latitudes. Implementing the REDMARS methodology during an analog mission showed that it is effective and safe to use. This method is a potential first step in enabling the use of the Martian regolith in agricultural activities. Furthermore, the stored perchlorate could be used as an essential source of oxygen and propellant, making it an attractive mining resource on Mars, and the potential application of perchlorate for In-Situ resources utilization (ISRU).
... Under Mars ambient conditions both ClO 4 and ClO 3 can be photochemically produced on Cl-bearing mineral surfaces, most likely due to silicate (SiO 2 ) and/or metal-oxides acting as photocatalysts to generate radicals such as O 2 -, which can then react with chloride (Yen et al., 2000;Carrier and Kounaves, 2015). During this process, several oxychlorine intermediates such as hypochlorite (ClO -), chlorite (ClO 2 -), chlorate (ClO 3 -), and chlorine dioxide (ClO 2 ) gas, as well as radicals such as OCl, Cl, O 2 -, and OH are also likely generated . ...
... Glycine+sand displayed increased degradation in all the samples under both Mars ambient and humid conditions compared to the glycine film. This is likely the result of silica sand particles providing a larger surface area and therefore more reactive sites (Carrier and Kounaves, 2015). It has been shown that the presence of water (usually 10-1000 ppm in the atmosphere) is necessary for amino acid degradation under Mars ambient conditions, while the absolute level of water does not seem to affect the reaction rate significantly (ten Kate et al., 2006). ...
Article
The degradation of glycine (Gly), proline (Pro), and tryptophan (Trp) was studied under simulated Mars conditions during UV-driven production of oxychlorines and compared under Mars ambient and humid conditions, as films, and with addition of sodium chloride (NaCl), sodium chlorate (NaClO3), and sodium perchlorate (NaClO4) salts. It was shown that glycine sustained no significant destruction in either of the non-salt samples under Mars ambient or humid conditions. However, its degradation increased in the presence of any of the three salts and under both conditions though more under humid conditions. Proline degradation followed the order No Salt > NaCl > NaClO3 > NaClO4 under Mars ambient conditions but the reverse order under Mars humid conditions. A mechanism is proposed to explain how water and silica participate in these degradation reactions and how it is strongly influenced by the identity of the salt and its ability to promote deliquescence. No difference was observed for tryptophan between Mars ambient and humid conditions, or for the different salts, suggesting its degradation mechanism is different compared to glycine and proline. The results reported here will help to better understand the survival of amino acids in the presence of oxychlorines and UV on Mars and thus provide new insights for the detection of organic compounds on future Mars missions.
... One hypothesis suggests that the perchlorates were produced on the surface whereby Martian surface minerals catalyze the photochemical oxidation of chlorides to perchlorates (Schuttlefield et al., 2011;Kim et al., 2013). It was shown that in chloride-containing Martian soil simulants, perchlorates are produced in the presence of ultraviolet light (Carrier and Kounaves, 2015). Another formation mechanism might be through the reaction of atmospheric oxidants probably on dust particles in the arid environment on Mars (Catling et al., 2010). ...
... Several direct measurements of UV irradiance have been made by the Curiosity rover, showing that the maximum total UV flux at the Gale Crater may be closer to 20 J/(s·m 2 ), which is less severe than the typically modeled irradiance level but is still not favorable for surface habitability [11]. Additional factors, such as ionizing radiation, the presence of oxidants or other reactive species in the atmosphere, and regolith on Mars, would appear to make the long-term survival of organisms or organic biosignatures on the surface highly unlikely [15][16][17][18][19][20]. ...
Article
Full-text available
The success of an astrobiological search for life campaign on Mars, or other planetary bodies in the Solar System, relies on the detectability of past or present microbial life traces, namely, biosignatures. Spectroscopic methods require little or no sample preparation, can be repeated almost endlessly, and can be performed in contact or even remotely. Such methods are therefore ideally suited to use for the detection of biosignatures, which can be confirmed with supporting instrumentation. Here, we discuss the use of Raman and Fourier Transform Infrared (FT-IR) spectroscopies for the detection and characterization of biosignatures from colonies of the fungus Cryomyces antarcticus, grown on Martian analogues and exposed to increasing doses of UV irradiation under dried conditions. The results report significant UV-induced DNA damage, but the non-exceeding of thresholds for allowing DNA amplification and detection, while the spectral properties of the fungal melanin remained unaltered, and pigment detection and identification was achieved via complementary analytical techniques. Finally, this work found that fungal cell wall compounds, likely chitin, were not degraded, and were still detectable even after high UV irradiation doses. The implications for the preservation and detection of biosignatures in extraterrestrial environments are discussed.
... Like Earth, Mars experienced a global-scale redox transition billions of years ago. On Mars, the oxidation of Fe 2+ was ultimately governed by atmospheric loss 41 , which would have resulted in increased ultraviolet exposure and greater concentration of oxychlorine species 42 . Mars' global oxidization event was therefore driven by abiotic chemical processes. ...
Article
Full-text available
Reduced greenhouse gases such as methane (CH4) and hydrogen (H2) might be the only tenable solution to explain warming of the ancient Martian climate, but direct geological evidence that a reduced atmosphere actually existed on Mars has been lacking. Here we report widespread, strong Fe loss in chemically weathered bedrock sections in the Mawrth Vallis region and other 3–4-billion-year-old terrains on Mars. The separation of Fe from Al in Martian palaeosols, which is comparable to trends observed in palaeosols before the Great Oxidation Event on Earth, suggests that the ancient Martian surface was chemically weathered under a reducing greenhouse atmosphere. Although for different reasons than on Earth, Mars underwent an oxidation event of its own in the late Noachian that forever changed the geological path of the planet. A comparative analysis of weathered bedrock in the Mawrth Vallis region of Mars and on Hainan Island, China, provides geological evidence for a reduced greenhouse atmosphere on early Mars, as there was on early Earth.
... This effort accelerated after Curiosity also identified perchlorate (Glavin et al. 2013) and its distribution was posited to be widespread on Mars (Clark & Kounaves 2016). Much of the Article number, page 6 of 14 K.S. Olsen et al.: Reappearance of HCl in the atmosphere of Mars experimental work done concerning chlorides on Mars supports the formation of perchlorates directly on the surface over long periods (e.g., Rao et al. 2012a;Carrier & Kounaves 2015;Zhao et al. 2018;Civiš et al. 2019), often demonstrating direct pathways to convert NaCl to ClO − 4 . Catling et al. (2010) proposed an atmospheric source of surface perchlorate that is the end-product of ancient atmospheric HCl of volcanic origin. ...
Article
Hydrogen chloride was discovered in the atmosphere of Mars for the first time during the global dust storm in Mars year (MY) 34 (July 2018) using the Atmospheric Chemistry Suite mid-infrared channel (ACS MIR) on the ExoMars Trace Gas Orbiter. The simultaneity of variations in dust and HCl, and a correlation between water vapour and HCl, led to the proposal of a novel surface-atmosphere coupling analogous to terrestrial HCl production in the troposphere from salt aerosols. After seasonal dust activity restarted in MY 35 (August 2020), we have been monitoring HCl activity to determine whether such a coupling was validated. Here we present a new technique for analysing the absorption features of trace gases close to the ACS MIR noise level and report that HCl mixing ratios are observed to rapidly increase in both hemispheres coincidentally with the onset of the MY 35 perihelion dust season. We present the temporal evolution of the vertical distribution of HCl (0.1–6 ppbv) and of dust activity in both hemispheres. We also report two observations of >2 ppbv HCl below 10 km in the northern hemisphere during the aphelion period.
... Moreover, two additional components of the Martian surface, iron oxides and hydrogen peroxide, were shown to act in synergy with irradiated perchlorates to cause a 10.8-fold increase in cell death when compared with cells exposed to UV radiation for 60 seconds. Interestingly, the distribution of perchlorates in the Martian regolith may be driven by the distribution of chlorine and the photocatalytic ability of silicon dioxide and other metal oxides, suggesting that areas may exist where the perchlorate concentration may vary [36]. ...
Article
Full-text available
The recent success of the Mars 2020 project and the high quality images relayed back to Earth have provided further impetus and expectations for human missions to Mars. To support space agency and private enterprise plans to establish a sustainable colony on Mars in the 2030s, synthetic biology may play a vital role to enable astronaut self-sufficiency. In this review, we describe some aspects of where synthetic biology may inform and guide in situ resource utilisation strategies. We address the nature of Martian regolith and describe methods by which it may be rendered fit for purpose to support growth and yield of bioengineered crops. Lastly, we illustrate some examples of innate human adaptation which may confer characteristics desirable in the selection of colonists and with a future looking lens, offer potential targets for human enhancement.
... It has been suggested that production pathways for perchlorate on Mars are similar to Earth, primarily photochemically in the upper atmosphere via oxidation of chlorine by ozone [36]. But because of the low amount of Ozone in the Martian atmosphere, mechanisms involving surface components are probable [37]. For example, perchlorates may form from the radiolysis of surface component caused by galactic cosmic rays, causing a sublimation of chlorine oxide in atmosphere, where final oxidation to perchloric acid is performed by some sources of active Oxigen (i.e. ...
Chapter
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The discovery by the Lander Phoenix (summer 2008) that the Mars polar soil is rich of perchloric acid salts (Na, Mg, Ca perchlorate) strongly could change the interpretation of the Martian experiment of 14CO2 release (LR, Labeled release experiment), performed in 70’s by both Viking Landers. The LR experiment gave substantially positive results but, at that time, possibility of Martian bacteria was ruled out because the CGMS instruments on board of both Vikings didn’t detect any trace of complex organic molecules. But Martian organics exist and were found in fair quantities by Curiosity, landed inside the Gale crater on 2012. So it is likely that Viking CGMS, working at about 500°C, could not see any organic substances (natural or bacterial) because, at that temperature, perchlorates decompose, releasing Oxygen that destroyed organics BEFORE their detection. In any case, the discovery of keragenic compounds by Curiosity, could also be indication of a presence of archea bacteria in the distant past of Mars, when the atmosphere of the Red Planet was wetter and denser than now.
... All known ClO 4 À production mechanisms (photochemical, ozone oxidation, plasma oxidation) produce ClO 3 À in at least equimolar amounts, and in aqueous solutions in much higher amounts, compared to ClO 4 À (Rao et al., 2010a;Jackson et al., 2018;Kang et al., 2006;Carrier and Kounaves et al., 2015;Schuttlefield et al., 2011;Wu et al., 2018;Zhao et al., 2018). Sources of anthropogenic ClO 3 À are well known, but sources of naturally occurring ClO 3 À are less understood. ...
Article
Full-text available
Natural chlorate (ClO3⁻) is widely distributed in terrestrial and extraterrestrial environments. To improve understanding of the origins and distribution of ClO3⁻, we developed and tested methods to determine the multi-dimensional isotopic compositions (δ¹⁸O, Δ¹⁷O, δ³⁷Cl, ³⁶Cl/Cl) of ClO3⁻ and then applied the methods to samples of natural nitrate-rich caliche-type salt deposits in the Atacama Desert, Chile, and Death Valley, USA. Tests with reagents and artificial mixed samples indicate stable-isotope ratios were minimally affected by the purification processes. Chlorate extracted from Atacama samples had δ¹⁸O = +7.0 to +11.1 ‰, Δ¹⁷O = +5.7 to +6.4 ‰, δ³⁷Cl = -1.4 to +1.3 ‰, and ³⁶Cl/Cl = 48 x 10⁻¹⁵ to 105 x 10⁻¹⁵. Chlorate from Death Valley samples had δ¹⁸O = -6.9 to +1.6 ‰, Δ¹⁷O = +0.4 to +2.6 ‰, δ³⁷Cl = +0.7 to +1.0 ‰, and ³⁶Cl/Cl = 18 x 10⁻¹⁵ to 49 x 10⁻¹⁵. Positive Δ¹⁷O values of natural ClO3⁻ indicate that its production involved reaction with O3, while its Cl isotopic composition is consistent with a tropospheric or near-surface source of Cl. The Δ¹⁷O and δ¹⁸O values of natural ClO3⁻ are positively correlated, as are those of ClO4⁻ and NO3⁻ from the same localities, possibly indicating variation in the relative contributions of O3 as a source of O in the formation of the oxyanions. Additional isotopic analyses of ClO3⁻ could provide stronger constraints on its production mechanisms and/or post-formational alterations, with applications for environmental forensics, global biogeochemical cycling of Cl, and the origins of oxyanions detected on Mars.
... Perchlorate (ClO 4 − ) has been directly detected at two landing sites on Mars at concentrations between 0.5 and 1% (Hecht et al., 2009;Navarro-Gonzalez et al., 2013) suggesting that ClO 4 − could be globally distributed on the planet, in surface 10 cm layer of the regolith (Davila et al., 2013). Hypotheses of the origin of perchlorates in the Mars regolith during photochemical reactions with the participation of halite and other chlorine-containing minerals were proposed (Carrier and Kounaves, 2015). The presence of perchlorates in the regolith of Mars is considered among the main factors limiting the survival of terrestrial microorganisms (Quinn et al., 2013;Wadsworth and Cockell, 2017). ...
Article
Previously conducted space missions revealed the presence of perchlorates, which are known to have a high oxidizing potential in Martian regolith, at the level of 0.5%. Due to hygroscopic properties and crystallization features of perchlorate-containing solutions, assumptions leading to the possibility of the existence of liquid water in the form of brines, which can contribute to the vital activity of microorganisms, have been made. At the same time, high concentrations of perchlorates can inhibit the growth of microorganisms and cause their death. Previously performed studies have discovered the presence of highly diverse microbial communities in terrestrial perchlorate-containing soils and have also demonstrated the stability and activity of some prokaryotes cultured on highly concentrated perchlorates media (over 10%). Nevertheless, the limits of microbial tolerance to perchlorates and whether microbial communities are able to withstand the effects of high concentrations of perchlorates remain uncertain. The aim of this research was to study the reaction of microbial communities of hot-arid and cryo-arid soils and sedimentary rocks to the adding of a highly concentrated solution of sodium perchlo-rate (5%) in situ. An increase in the total number of prokaryotes, the number of metabolically active Bacteria and Archaea, and the variety of the consumed substrates were revealed. It was observed that in samples incubated with sodium perchlorate, a high taxonomic diversity of the microbial community is preserved at a level comparable to control sample. The study shows that the presence of high concentrations of sodium perchlorate (5%) in the soil does not lead to the death or significant inhibition of microbial communities.
... Following its generation and deposition on the surface, perchlorate interactions with regolith are capable of forming Mg− and Na− perchlorate salts in a process that has been occurring for at least 3 billion years [5,11]. With atmospheric circulation and wind transport of sediments, perchlorate salts are hypothesized to be present over the entire surface of Mars [16][17][18]. This presents a global problem to future human habitation of Mars. ...
Article
Full-text available
Perchlorate (ClO4−) is globally enriched in Martian regolith at levels commonly toxic to plants. Consequently, perchlorate in Martian regolith presents an obstacle to developing agriculture on Mars. Here, we assess the effect of perchlorate at different concentrations on plant growth and germination, as well as metal release in a simulated Gusev Crater regolith and generic potting soil. The presence of perchlorate was uniformly detrimental to plant growth regardless of growing medium. Plants in potting soil were able to germinate in 1 wt.% perchlorate; however, these plants showed restricted growth and decreased leaf area and biomass. Some plants were able to germinate in regolith simulant without perchlorate; however, they showed reduced growth. In Martian regolith simulant, the presence of perchlorate prevented germination across all plant treatments. Soil column flow-through experiments of perchlorate-containing Martian regolith simulant and potting soil were unable to completely remove perchlorate despite its high solubility. Additionally, perchlorate present in the simulant increased metal/phosphorous release, which may also affect plant growth and biochemistry. Our results support that perchlorate may modify metal availability to such an extent that, even with the successful removal of perchlorate, Martian regolith may continue to be toxic to plant life. Overall, our study demonstrates that the presence of perchlorate in Martian regolith provides a significant challenge in its use as an agricultural substrate and that further steps, such as restricted metal availability and nutrient enrichment, are necessary to make it a viable growing substrate.
... Since the amount of ClO 3 − expected to be present in Martian near-surface systems is limited (<1 wt.%, not accounting for regeneration processes [70][71][72][73][74][75]), understanding its actual capacity to oxidize dissolved Fe(II) in Mars-relevant fluids might better constrain iron oxidation processes and the resulting products. The number of moles of Fe(II) oxidized per mole of ClO 3 − ions relative to its maximum, theoretical capacity of 6:1 (Equation (1)), is referred to as the "stoichiometric efficiency". ...
Article
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Chlorate is an important Cl-bearing species and a strong potential Fe(II) oxidant on Mars. Since the amount of oxychlorine species (perchlorate and chlorate) detected on Mars is limited (<~1 wt.%), the effectiveness of chlorate to produce iron oxides depends heavily on its oxidizing capacity. Decomposition of chlorate or intermediates produced during its reduction, before reaction with Fe(II) would decrease its effective capacity as an oxidant. We thus evaluated the capacity of chlorate to produce Fe(III) minerals in Mars-relevant fluids, via oxidation of dissolved Fe(II). Each chlorate ion can oxidize 6 Fe(II) ions under all conditions investigated. Mass balance demonstrated that 1 wt.% chlorate (as ClO3−) could produce approximately 6 to 12 wt.% Fe(III) or mixed valent mineral products, with the amount varying with the formula of the precipitating phase. The mineral products are primarily determined by the fluid type (chloride- or sulfate-rich), the solution pH, and the rate of Fe(II) oxidation. The pH at the time of initial mineral nucleation and the amount of residual dissolved Fe(II) in the system exert important additional controls on the final mineralogy. Subsequent diagenetic transformation of these phases would yield 5.7 wt.% hematite per wt.% of chlorate reacted, providing a quantitative constraint on the capacity of chlorate to generate iron oxides on Mars.
... Being lifted to high altitudes, chlorine-bearing molecules at the surface of airborne dust may break up under the effect of UV irradiation into gas-phase compounds, including chlorine. The potential to oxidize mineral chlorides by the action of UV radiation has been demonstrated in the laboratory (36), but more experimental work is required to determine the abundance of chloride radicals that could be released to the gas phase by such processes. ...
Article
Full-text available
A major quest in Mars’ exploration has been the hunt for atmospheric gases, potentially unveiling ongoing activity of geophysical or biological origin. Here, we report the first detection of a halogen gas, HCl, which could, in theory, originate from contemporary volcanic degassing or chlorine released from gas-solid reactions. Our detections made at ~3.2 to 3.8 micron with the Atmospheric Chemistry Suite and confirmed with Nadir and Occultation for Mars Discovery instruments onboard the ExoMars Trace Gas Orbiter, reveal widely distributed HCl in the 1- to 4-ppbv range, 20 times greater than previously reported upper limits. HCl increased during the 2018 global dust storm and declined soon after its end, pointing to the exchange between the dust and the atmosphere. Understanding the origin and variability of HCl shall constitute a major advance in our appraisal of martian geo- and photochemistry.
... Reactions on the surface of metal oxides have also been proposed in which the irradiation by UV radiation would oxidize chloride ions present on the surface to form perchlorate (Schuttlefield et al. 2011). Laboratory studies have demonstrated the formation of perchlorate and chlorate ions from UV irradiation of NaCl in regolith samples composed of Fe2O3, Al2O3, TiO2, and SiO2 which were consistent with the ClO4 -:Clratio measured by Phoenix (Carrier & Kounaves 2015). Perchlorate could also be formed during the irradiation of CO2 ices by SEP and GCR (Kim et al. 2013). ...
Thesis
The question of if terrestrial life is alone in the universe is a philosophical and scientific question that has captivated humanity since ancient times. This thesis approaches its science and technical questions from the idea that life is composed of, and generates, organic matter. This thesis focuses on the search for organic matter on the surface of Mars by gas chromatography-mass spectrometry (GC-MS) onboard the Viking Lander, the future ExoMars Mars Organic Molecule Analyser (MOMA) experiment, and with applications to the Sample Analysis at Mars (SAM) experiment onboard the Mars Science Laboratory (MSL). In this thesis, the Viking GC-MS data sets have been reexamined and evidence is presented for the presence of chlorobenzene, a potential reaction product of martian carbon and martian chlorine during pyrolysis. The performance of the ExoMars MOMA integrated chromatographic system is assessed by experiments carried out with a laboratory setup that reproduces the flight configuration and mimics in situ operating conditions. Results demonstrate the ability of the GC subsystem to identify a wide range of organic and inorganic volatile compounds, including biomolecular signatures, within the constrained operating conditions of MOMA. Next, the MOMA GC-MS pyrolysis and wet chemistry protocol is explored with a more complex set of samples in which organic compounds are adsorbed to amontmorillonite mineral matrix across concentrations and with or without the addition of magnesium perchlorate. This study shows that the MOMA GC-MS package enables detection of each target organic molecule or its products in the presence of the clay mineral. Finally, perspectives are presented on the specific complexities to more complex natural samples (e.g., suites of species, trace organics) and to space experimentation (e.g., complex gas processing systems, adsorption/desorption trapping) that can present unique challenges for Mars surface experiments in the strict identification of target compounds such as amino acids. The results presented in this thesis reevaluate the interpretation of past Mars GC-MS mission data and will collectively aid in the implementation of Mars surface operations and the interpretation of potential data obtained by ExoMars’s MOMA experiment. In addition, this thesis offers results and discussion that can be applied to the interpretation of the SAM GC-MS analysis currently operating on Mars.
... Mapping by the Mars Odyssey Gamma Ray Spectrometer has revealed that chlorine is ubiquitous on the surface of Mars, particularly at low latitudes (Keller et al., 2006), implying that (per)chlorates are equivalently widespread (Carrier and Kounaves, 2015). Although we do not know the extent to which (per)chlorates pervaded the Martian regolith at $1500-1200 Ma, the relative lack of geologic activity during the Amazonian implies that the (per)chlorate distribution was comparable to today. ... Article The past Martian atmosphere is often compared to the Archean Earth’s as both were dominated by CO2-rich and O2-poor chemistries. Archean Earth rocks preserve mass-independently fractionated sulfur isotopes (S-MIF; non-zero Δ³³S and Δ³⁶S), originating from photochemistry in an anoxic atmosphere. Thus, Martian crustal rocks might also be expected to preserve a S-MIF signature, providing insights into past atmospheric chemistry. We have used secondary ion mass spectrometry (SIMS) to investigate in situ, the sulfur isotope systematics of NWA 8171 (paired to NWA 7034), a Martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near-surface regolith setting. In this meteorite, pyrite grains have a weighted mean of Δ³³S of -0.14 ± 0.08 ‰ and Δ³⁶S = -0.70 ± 0.40 ‰ (2 s.e.m.), so the S-MIF signature is subtle. Sulfur isotope data for four additional shergottites yield Δ³³S values that are not resolvable from zero, as in previous studies of shergottites. At first glance the result for the polymict breccia might seem surprising, but no Martian meteorite yet has yielded a S-MIF signature akin to the large deviations seen on Earth. We suggest that S-MIF-bearing aerosols (H2SO4 and S8) were produced when volcanic activity pushed a typically oxidising Martian atmosphere into a reduced state. After rain-out of these aerosols, S8 would tend to be oxidised by chlorate, dampening the S-MIF signal, which might be somewhat retained in the more abundant photolytic sulfate. Then in the regolith, mixing of aqueous surface-derived sulfate with igneous sulfide (the latter with zero MIF), to form the abundant pyrite seen in NWA 8171, would further dampen the S-MIF signal. Nonetheless, the small negative Δ³³S anomalies seen in Martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times. This volcanically-driven atmospheric evolution would tend to produce high levels of carbonyl sulfide (OCS). Given that OCS is a relatively long-lived strong greenhouse gas, the S-MIF signal implies that volcanism periodically generated warmer conditions, perhaps offering an evidence-based solution to the young wet Mars paradox. ... These concentrations are considerably higher than those found in terrestrial analogs, such as the Atacama Desert soil surface where it is only 0.03 wt% (Navarro-González et al., 2009) and a maximum of 0.004 wt% in cores and powder samples down to 5 mdepth (Parro et al., 2011a), the soils of the Antarctic Dry Valleys at 10 −5 wt% (Kounaves et al., 2014) or in the Devon Island ice cap (Nunavut, Canada) at 2 × 10 −7 wt% (Furdui and Tomassini, 2010). The discovery of perchlorates in the Martian soil has important implications for the detection of organics because the powerful oxidizing properties of perchlorate promote combustion of organics in pyrolytic experiments (Hecht et al., 2009;Carrier and Kounaves, 2015). As such, both the 1976 Viking missions (Klein, 1974) and the Phoenix Lander in 2008 (Hoffman et al., 2008), using gas chromatography-mass spectrometry (GC-MS) instrumentation, failed to detect organics on the surface of Mars, and until very recently, the presence of organic matter on the Red Planet was unclear (Freissinet et al., 2015). ... Article Full-text available Perchlorate anions are produced by chemical industries and are important contaminants in certain natural ecosystems. Perchlorate also occurs in some natural and uncontaminated environments such as the Atacama Desert, the high Arctic or the Antarctic Dry Valleys, and is especially abundant on the surface of Mars. As some bacterial strains are capable of using perchlorate as an electron acceptor under anaerobic conditions, their detection is relevant for environmental monitoring on Earth as well as for the search for life on Mars. We have developed an antibody microarray with 20 polyclonal antibodies to detect perchlorate-reducing bacteria (PRB) strains and two crucial and highly conserved enzymes involved in perchlorate respiration: perchlorate reductase and chlorite dismutase. We determined the cross-reactivity, the working concentration, and the limit of detection of each antibody individually and in a multiplex format by Fluorescent Sandwich Microarray Immunoassay. Although most of them exhibited relatively high sensitivity and specificity, we applied a deconvolution method based on graph theory to discriminate between specific signals and cross-reactions from related microorganisms. We validated the system by analyzing multiple bacterial isolates, crude extracts from contaminated reactors and salt-rich natural samples from the high Arctic. The PRB detecting chip (PRBCHIP) allowed us to detect and classify environmental isolates as well as to detect similar strains by using crude extracts obtained from 0.5 g even from soils with low organic-matter levels (<103 cells/g of soil). Our results demonstrated that PRBCHIP is a valuable tool for sensitive and reliable detection of perchlorate-reducing bacteria for research purposes, environmental monitoring and planetary exploration. ... This is an important finding for all extraterrestrial environments with natural occurring perchlorates. This might not only include Mars, but any planetary bodies with a relatively dry surface (to avoid leaching of salts) and increased UV radiation (to oxidize chlorides (Carrier and Kounaves, 2015)). For example, spectral data indicates the presence of perchlorates at the surface of the icy moon Europa (Ligier et al., 2016), which could entail delivery of perchlorates to Europa´s subsurface ocean (Hand et al. 2007). ... Thesis Full-text available The availability of liquid water on Mars is one of the key factors for its habitability. While there is strong morphological and geochemical evidence for the existence of large water bodies on the surface of Early Mars, at the present time, the planet is dry, cold and hostile. However, liquid water might still be found in niches like cold brines. These are especially relevant for Mars since several hygroscopic salts have been detected in the Martian regolith which cause a significant freezing point depression of water and, hence, enhance the habitability range of Mars to subzero temperatures. Formation of these brines could occur through deliquescence, i.e. water absorption by these salts followed by dissolution of the salts in the absorbed water. This process might has already been observed on Mars, namely by the formation of Recurring Slope Lineae (RSL) which are dark, flow-like features extending downslope from bedrock outcrops. In this study, both the formation process of RSL caused by deliquescence of various perchlorate (ClO4-) and chloride (Cl-) salts, and the survivability of the halo- and cryotolerant bacterial strain Planococcus halocryophilus within brines has been investigated. It was found that measuring electrical conductivity (EC) is an excellent method for following the process of deliquescence-induced RSL formation. The results of these experiments revealed that the darkening of soil typical for RSL can occur very fast, e.g. after 2.5 hours for soil containing calcium perchlorate (Ca(ClO4)2) under the provided experimental conditions (25°C, 70–85% RH), and requires only small amounts of intergranular water. In contrast, the formation of larger amounts of bulk water requires substantially longer, e.g. 17 days for soil containing magnesium perchlorate (Mg(ClO4)2) under the same experimental conditions. This suggests that RSL on Mars do actually not represent flows of briny water but a rewetting of salt-cemented soils generated by the evaporation of water tracks that flowed down the hills at a time when Mars had a warmer and wetter climate. The brines that formed via deliquescence were too concentrated to enable growth of P. halocryophilus within them. However, an enhanced survivability with decreasing temperature was observed. This effect was most pronounced in calcium chloride (CaCl2) containing samples. Additionally, we found that the presence of sodium chloride (NaCl) is beneficial for the survival of P. halocryophilus during freeze/thaw cycles. To enable bacterial growth in these salty samples a dilution of the brines is necessary. Hence, the maximum salt concentration suitable for growth at 25°C and 4°C was determined for six Cl- and ClO4- salts. The results showed an increased CaCl2 tolerance of P. halocryophilus at 4°C compared to 25°C, while the tolerances to other salts were similar or lower at 4°C compared to 25°C. The highest ClO4- tolerance reported to date was found with 12 wt% NaClO4 at 25°C. Growth of P. halocryophilus under these salty conditions yielded serval stress responses like cell clustering, formation of nanofilaments, cell encrustation, and formation of different cell colony morphologies. Putting all together, this study provides important and coherent insights in the formation and habitability of brines as they might occur on Mars. The results of a large set of experiments give an impression on how life on Mars could have adapted to its cold and salty environmental conditions and what influence different salt species and variations in temperature and salt concentration might have. ... L'étude de la matière organique sur Mars reste peu aisée en raison de la forte capacité d'altération que présente l'environnement de la planète. Premièrement, le sol de Mars contient des composés chimiques très oxydants tels que des perchlorates (Carrier & Kounaves, 2015), qui peuvent fortement biaiser les mesures in situ. En effet, le climat aride et froid actuel de Mars, inhibe les éventuelles réactions chimiques entre la matière organique et les oxydants. ... Thesis Depuis une vingtaine d'années, la spectroscopie de réflectance proche-infrarouge appliquée à la planétologie a révolutionné notre vision des surfaces planétaires, grâce notamment à la découverte de phyllosilicates à la surface de Mars par les instruments OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) à bord de la sonde européenne Mars Express, et CRISM (Compact Reconnaissance Infrared Spectrometer for Mars) embarqué sur la sonde Mars Reconnaissance Orbiter, en 2005 et 2007. Ces deux missions spatiales ont ouvert la voie à l'étude approfondie de toutes les surfaces planétaires dans le proche-infrarouge (entre 1 et 5 µm), à la recherche de leur composition minéralogique et des processus d'altération passés et présents.Dans l'optique d'équiper toute sonde interplanétaire, voire même in-situ, avec des spectromètres proche-infrarouge, il est nécessaire de développer une nouvelle génération d'instruments à la fois compacts et performants. L'AOTF (Acousto-Optic Tunable Filter) utilisé en tant que monochromateur est une technologie-clé sur laquelle pourront s'appuyer ces instruments. Les deux spectromètres au coeur de ma thèse, IRS (Infrared Spectrometer) équipant l'instrument combiné SuperCam à bord du rover Perseverance, et ExoCam, au stade de R&T à l'Institut d'Astrophysique Spatiale, exploitent le potentiel de ce composant pour produire des données scientifiques de haute qualité avec un volume réduit.Ma thèse a ainsi contenu deux volets principaux : la préparation et la réalisation de l'étalonnage radiométrique des modèles de vol et de qualification de IRS/SuperCam, et le développement d'un simulateur d'observations infrarouge pour les futures opérations du rover Perseverance d'une part ; et l'étude des performances de l'imagerie hyperspectrale proche-infrarouge utilisant l'AOTF en transmission avec le programme de R&T ExoCam, accompagnée du développement d'un modèle radiométrique du banc de R&T permettant de projeter les résultats obtenus sur table à de futures opérations dans l'espace. ... However, these studies did not even consider the possibility that salts could also be deposited from the vapors emitted during volcanic degassing (Glotch et al., 2010;Naughton et al., 1974) known to occur in the early history of Mars. Nor that formation of perchlorates could even be an ongoing process, produced photochemically on Cl minerals without atmospheric chlorine or aqueous conditions, occurring wherever chloride-bearing mineral phases exist (Carrier & Kounaves, 2015). ... Article Full-text available Abstract Existing data returned in >40 years of planetary missions to Mars provided a good basis to understand that an ocean never existed on the surface of the planet during its whole history. The presence of environmental indicators like unaltered jarosite and olivine deposited by the early volcanic activity can be seen as evidence that liquid water was never abundant nor widespread on the surface of Mars since the pre‐Noachian or Noachian at least. There is a dramatic mismatch with the water equivalent volume of the outflow channels sources with the volume needed to form an ocean. The ubiquitous presence of large volcanoes, with their huge lava fields exactly where liquid water was claimed to be abundant during the Noachian age, makes now very clear that lava and not water was involved in the formation of the outflow channels and the fluvial networks. As a consequence, cheaper robotic exploration might be favored with respect to the ambitious human exploration program planned for Mars. Unless enough water supplies will be brought to the equatorial regions from the poles through long pipelines, or from nearby asteroids through cargo ships, it will be very difficult to exploit the rich equatorial resources brought up from the mantle by the massive volcanism that characterized the early history of the planet. Digging deeply the equatorial regions searching for water would be too expensive, of uncertain reward, and thus unpractical. ... A variety of pathways have been proposed for the perchlorate synthesis on Mars. ese pathways may involve photochemical reactions [15], electrostatic discharge [16], and oxidation-reduction reactions [17]. Perchlorates and chloride salts in the Martian regolith are extensively investigated because they can absorb water from the atmosphere forming hydrates [18], by absorption, and then liquid brines, through deliquescence [19,20]. ... Article Full-text available Tribocorrosion is a degradation phenomenon of material surfaces subjected to the combined action of mechanical loading and corrosion attack caused by the environment. Although corrosive chemical species such as materials like chloride atoms, chlorides, and perchlorates have been detected on the Martian surface, there is a lack of studies of its impact on materials for landed spacecraft and structures that will support surface operations on Mars. Here, we present a series of experiments on the stainless-steel material of the ExoMars 2020 Rosalind Franklin rover wheels. We show how tribocorrosion induced by brines accelerates wear on the materials of the wheels. Our results do not compromise the nominal ExoMars mission but have implications for future long-term surface operations in support of future human exploration or extended robotic missions on Mars. ... One hypothesis suggests that the perchlorates were produced on the surface whereby Martian surface minerals catalyze the photochemical oxidation of chlorides to perchlorates (Schuttlefield et al., 2011;Kim et al., 2013). It was shown that in chloride-containing Martian soil simulants, perchlorates are produced in the presence of ultraviolet light (Carrier and Kounaves, 2015). Another formation mechanism might be through the reaction of atmospheric oxidants probably on dust particles in the arid environment on Mars (Catling et al., 2010). ... Chapter Full-text available Five bacterial (facultatively) anaerobic strains, namely Buttiauxella sp. MASE-IM-9, Clostridium sp. MASE-IM-4, Halanaerobium sp. MASE-BB-1, Trichococcus sp. MASE-IM-5, and Yersinia intermedia MASE-LG-1 isolated from different extreme natural environments were subjected to Mars relevant environmental stress factors in the laboratory under controlled conditions. These stress factors encompassed low water activity, oxidizing compounds, and ionizing radiation. Stress tests were performed under permanently anoxic conditions. The survival rate after addition of sodium perchlorate (Na-perchlorate) was found to be species-specific. The inter-comparison of the five microorganisms revealed that Clostridium sp. MASE-IM-4 was the most sensitive strain (D₁₀-value (15 min, NaClO₄) = 0.6 M). The most tolerant microorganism was Trichococcus sp. MASE-IM-5 with a calculated D₁₀-value (15 min, NaClO₄) of 1.9 M. Cultivation in the presence of Na-perchlorate in Martian relevant concentrations up to 1 wt% led to the observation of chains of cells in all strains. Exposure to Na-perchlorate led to a lowering of the survival rate after desiccation. Consecutive exposure to desiccating conditions and ionizing radiation led to additive effects. Moreover, in a desiccated state, an enhanced radiation tolerance could be observed for the strains Clostridium sp. MASE-IM-4 and Trichococcus sp. MASE-IM-5. These data show that anaerobic microorganisms from Mars analogue environments can resist a variety of Martian-simulated stresses either individually or in combination. However, responses were species-specific and some Mars-simulated extremes killed certain organisms. Thus, although Martian stresses would be expected to act differentially on microorganisms, none of the expected extremes tested here and found on Mars prevent the growth of anaerobic microorganisms. ... were performed at 25 °C and 1 bar. A simulant Mars atmosphere (99.99% CO 2 ) or Earth atmosphere (dry ambient air) was continuously flushed through the chamber at a rate of 0.7 l min −1 throughout the experiments. We used the 254 nm UV wavelength because the UVC range (200-280 nm) is more effective than UVA or UVB at oxidizing Cl − to ClO x − (ref.14 ) ... Article Full-text available Perchlorate (ClO4⁻) and possibly chlorate (ClO3⁻) are considered to be ubiquitous on Mars1–5, and the ClO3⁻/ClO4⁻ abundance ratio has critical implications for the redox conditions6,7, aqueous environments8,9 and habitability on Mars¹⁰. However, factors that control the ClO3⁻/ClO4⁻ generation ratios are not well established. Here we expose mixtures of halite salt (NaCl) with Fe sulfates, Fe (hydr)oxides and Fe³⁺ montmorillonite to ultraviolet radiation or ozone in an Earth or CO2 atmosphere and show that Fe secondary mineralogy is the dominant factor controlling the ClO3⁻/ClO4⁻ generation ratio: the sulfates and montmorillonite mixtures produce much higher yields of ClO4⁻ than of ClO3⁻, whereas the opposite is true for the (hydr)oxide mixtures. Consistent with previous studies11–18, our results indicate that the physical state of chloride (Cl⁻) (that is, solid, liquid or gas) and the characteristics of the co-occurring minerals (for example, semiconductivity, surface area, acidity) have the greatest influence, whereas oxidation sources (ultraviolet radiation or ozone) and atmospheric composition induce only secondary effects. We conclude that, under the hyperarid climate and widespread Fe (hydr)oxide abundances prevailing on Mars since the Amazonian period¹⁹, Cl⁻ oxidation should produce yields of ClO3⁻ that are orders of magnitude higher than those of ClO4⁻, highlighting the importance of ClO3⁻ in the surficial environments and habitability of modern Mars compared with ClO4⁻. ... I n situ methods of chemical analysis on the surfaces of planetary bodies are of primary importance in current space research and promise to significantly increase the scientific return from these missions (Knight et al., 2000;Wurz et al., 2012;Horneck et al., 2016). From the current perspective, Mars is a cold desert with an intense flux of ionizing radiation at the surface (Hassler et al., 2014), high ultraviolet (UV) flux, chemical reactivity of soils (Carrier and Kounaves, 2015), and considered to be largely uninhabitable (Fairén et al., 2010). However, scientific analysis and modeling suggest that life could survive in the subsurface and imply the possible existence of rock-hosted life in the deep subsurface (Stamenković et al., 2019), where liquid water may be present (Orosei et al., 2018). ... Article The investigation of chemical composition on planetary bodies without significant sample processing is of importance for nearly every mission aimed at robotic exploration. Moreover, it is a necessary tool to achieve the longstanding goal of finding evidence of life beyond Earth, for example, possibly preserved microbial remains within martian sediments. Our Laser Ablation Ionization Mass Spectrometer (LIMS) is a compact time-of-flight mass spectrometer intended to investigate the elemental, isotope, and molecular composition of a wide range of solid samples, including e.g., low bulk density organic remains in microfossils. Here, we present an overview of the instrument and collected chemical spectrometric data at the micrometer level from a Precambrian chert sample (1.88 Ga Gunflint Formation, Ontario, Canada), which is considered to be a martian analogue. Data were collected from two distinct zones-a silicified host area and a carbon-bearing microfossil assemblage zone. We performed these measurements using an ultrafast pulsed laser system (pulse width of ∼180 fs) with multiple wavelengths (infrared [IR]-775 nm, ultraviolet [UV]-387 nm, UV-258 nm) and using a pulsed high voltage on the mass spectrometer to reveal small organic signals. We investigated (1) the chemical composition of the sample and (2) the different laser wavelengths' performance to provide chemical depth profiles in silicified media. Our key findings are as follows: (1) microfossils from the Gunflint chert reveal a distinct chemical composition compared with the host mineralogy (we report the identification of 24 elements in the microfossils); (2) detection of the pristine composition of microfossils and co-occurring fine chemistry (rare earth elements) requires utilization of the depth profiling measurement protocol; and (3) our results show that, for analysis of heterogeneous material from siliciclastic deposits, siliceous sinters, and cherts, the most suitable wavelength for laser ablation/Ionization is UV-258 nm. ... Magnesium perchlorate appears correlated with both the magnesium chloride distribution and the exogenic plasma bombardment centred on the trailing apex (Figure 14). This is consistent with the endogenic magnesium chloride being converted to magnesium perchlorate under the high radiation ion bombardment in the trailing hemisphere around Dyfed Regio (Carrier & Kounaves 2015;Ligier et al. 2016). ... Preprint Full-text available We present maps of surface composition of Europa's anti-jovian hemisphere acquired using high spatial resolution IFU multi-spectral data from the SPHERE instrument on the Very Large Telescope (0.95 to 1.65$\mu$m) and the NIMS instrument on the Galileo orbiter (0.7 to 5.2$\mu$m). Spectral modelling was performed using a Markov Chain Monte Carlo method to estimate endmember abundances and to quantify their associated uncertainties. Modelling results support the leading-trailing hemisphere difference in hydrated sulphuric acid abundances caused by exogenic plasma bombardment. Water ice grains are found to be in the 100$\mu\$m to 1mm range, with larger grains present on the trailing hemisphere, consistent with radiation driven sputtering destroying smaller grains. Modelling best estimates suggest a mixture of sulphate and chlorinated salts, although uncertainties derived from the MCMC modelling suggest that it is difficult to confidently detect individual salt abundances with low spectral resolution spectra from SPHERE and NIMS. The high spatial resolution offered by SPHERE allows the small scale spatial distribution (<150km) of potential species to be mapped, including ground-based detection of lineae and impact features. This could be used in combination with other higher spectral resolution observations to confirm the presence of these species.
... The combined presence of large amounts of ROS in the surrounding medium and hypersalinity-hyperacidity might impose an even more serious challenge for life. Sodium perchlorate is a chaotropic salt primarily formed on Earth through the oxidation of atmospheric chlorine by ozone and/or oxygen-containing radicals found in the stratosphere, but it is also formed under high UV irradiation of NaCl in the presence of silica, conditions that are met on the surface of Mars (76). These conditions also occur in Dallol, often considered an analog of Mars (49), although perchlorates are likely much less abundant than the ferrous and ferric chloride complexes dominant in Dallol brines. ...
Article
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Determining the precise limits of life in polyextreme environments is challenging. Studies along gradients of polyextreme conditions in the Dallol protovolcano area (Danakil salt desert, Ethiopia) showed the occurrence of archaea-dominated communities (up to 99%) in several hypersaline systems but strongly suggested that life did not thrive in the hyperacidic (pH ;0), hypersaline (;35% [wt/ vol],) and sometimes hot (up to 108°C) ponds of the Dallol dome. However, it was recently claimed that archaea flourish in these brines based on the detection of one Nanohaloarchaeotas 16S rRNA gene and fluorescent in situ hybridization (FISH) experiments with archaea-specific probes. Here, we characterized the diversity of microorganisms in aerosols over Dallol, and we show that, in addition to typical bacteria from soil/dust, they transport halophilic archaea likely originating from neighboring hypersaline ecosystems. We also show that cells and DNA from cultures and natural local halophilic communities are rapidly destroyed upon contact with Dallol brine. Furthermore, we confirm the widespread occurrence of mineral particles, including silica-based biomorphs, in Dallol brines. FISH experiments using appropriate controls show that DNA fluorescent probes and dyes unspecifically bind to mineral precipitates in Dallol brines; cellular morphologies were unambiguously observed only in nearby hypersaline ecosystems. Our results show that airborne cell dispersal and unspecific binding of fluorescent probes are confounding factors likely affecting previous inferences of archaea thriving in Dallol. They highlight the need for controls and the consideration of alternative abiotic explanations before safely drawing conclusions about the presence of life in polyextreme terrestrial or extraterrestrial systems.
... The surface of Mars is an inimical place for organic molecules: Along with being cold, dry, and airless, the soil contains strong oxidants such as perchlorates (Carrier & Kounaves, 2015) and the varied mineralogy offers different levels of preservation, all of which have been studied using laboratory analogs, summarized in Table 1. Organic material can also be selectively eliminated by the pressures and temperatures of meteorite impacts, which have occurred throughout Martian history and have been proposed as a natural drill for sampling the subsurface (Montgomery et al., 2016). ...
Article
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Recent space missions have identified organics, chlorinated and non‐chlorinated, on Mars. Understanding the origin, current state and reactivity of this carbonaceous material is critical to efforts to detect organic signatures of possible past life on Mars. Environmental effects such as ultraviolet radiation, pressure, diagenesis, aqueous activity, and presence of perchlorates have been assessed previously using analog experiments. To this list, Fox, et al. adds and quantifies the effect of galactic cosmic rays and solar winds on organic material on the surface and in the near subsurface of Mars. Their work, using laboratory analog materials and radiation, shows that the same organic acids, formic and oxalic acid, are produced after exposure equivalent to that over Martian history at depths of less than 5 cm, independent of mineral matrix or starting organic materials. These experiments suggest that planned subsurface exploration using the drill on the Rosalind Franklin Rover (ExoMars) will sample organic material which has not been altered by cosmic rays, although it may have been exposed to other environmental factors such as water or salts.
... One hypothesis suggests that the perchlorates were produced on the surface whereby Martian surface minerals catalyze the photochemical oxidation of chlorides to perchlorates (Schuttlefield et al., 2011;Kim et al., 2013). It was shown that in chloride-containing Martian soil simulants, perchlorates are produced in the presence of ultraviolet light (Carrier and Kounaves, 2015). Another formation mechanism might be through the reaction of atmospheric oxidants probably on dust particles in the arid environment on Mars (Catling et al., 2010). ...
Article
Five bacterial (facultatively) anaerobic strains, namely Buttiauxella sp. MASE-IM-9, Clostridium sp. MASE-IM-4, Halanaerobium sp. MASE-BB-1, Trichococcus sp. MASE-IM-5, and Yersinia intermedia MASE-LG-1 isolated from different extreme natural environments were subjected to Mars relevant environmental stress factors in the laboratory under controlled conditions. These stress factors encompassed low water activity, oxidizing compounds, and ionizing radiation. Stress tests were performed under permanently anoxic conditions. The survival rate after addition of sodium perchlorate (Na-perchlorate) was found to be species-specific. The inter-comparison of the five microorganisms revealed that Clostridium sp. MASE-IM-4 was the most sensitive strain (D10-value (15 min, NaClO4) = 0.6 M). The most tolerant microorganism was Trichococcus sp. MASE-IM-5 with a calculated D10-value (15 min, NaClO4) of 1.9 M. Cultivation in the presence of Na-perchlorate in Martian relevant concentrations up to 1 wt% led to the observation of chains of cells in all strains. Exposure to Na-perchlorate led to a lowering of the survival rate after desiccation. Consecutive exposure to desiccating conditions and ionizing radiation led to additive effects. Moreover, in a desiccated state, an enhanced radiation tolerance could be observed for the strains Clostridium sp. MASE-IM-4 and Trichococcus sp. MASE-IM-5. These data show that anaerobic microorganisms from Mars analogue environments can resist a variety of Martian-simulated stresses either individually or in combination. However, responses were species-specific and some Mars-simulated extremes killed certain organisms. Thus, although Martian stresses would be expected to act differentially on microorganisms, none of the expected extremes tested here and found on Mars prevent the growth of anaerobic microorganisms.
... Perchlorate salts have been detected in martian soil (Hecht et al., 2009;Kounaves et al., 2010Kounaves et al., , 2014Glavin et al., 2013), where they may occasionally be dissolved by thin water films or small amounts of meltwater (Cull et al., 2010). Martian perchlorate chemistry is believed to be linked to the chemistry of hypochlorite and chlorate, which is why these two anions are also believed to occur on Mars (Hanley et al., 2012;Quinn et al., 2013;Carrier and Kounaves, 2015;Clark and Kounaves, 2016). ...
Article
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.
... The surface of Mars is an inimical place for organic molecules: along with being cold, 53 dry, and airless, the soil contains strong oxidants such as perchlorates (Carrier et al., 2015) and 54 the varied mineralogy offers different levels of preservation, all of which have been studied 55 using laboratory analogs, summarized in Table 1. Organic material can also be selectively 56 eliminated by the pressures and temperatures from asteroid impacts, which have occurred 57 throughout Martian history and have been proposed as a natural drill for sampling the subsurface 58 (Montgomery et al., 2016). ...
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Tribocorrosion is a degradation phenomenon of material surfaces subjected to the combined action of mechanical loading and corrosion attack caused by the environment. Although corrosive chemical species such as materials like chloride atoms, chlorides and perchlorates have been detected on the Martian surface, there is a lack of studies of its impact on materials for landed spacecraft and structures that will support surface operations on Mars. Here we present a series of experiments on the stainless-steel material of the ExoMars 2020 Rosalind Franklin rover wheels. We show how tribocorrosion induced by brines accelerate wear on the materials of the wheels. Our results do not compromise the nominal ExoMars mission but have implications for future long-term surface operations in support of future human exploration or extended robotic missions on Mars.
Article
Anticipated human missions to Mars require a methodical understanding of the unconsolidated bulk sediment that mantles its surface, given its role as an accessible resource for water and as a probable substrate for food production. However, classifying martian sediment as soil has been pursued in an ad-hoc fashion, despite emerging evidence from in situ missions for current and paleo-pedological processes. Here we find that in situ sediment at Gusev, Meridiani and Gale are consistent with pedogenesis related to comminuted basalts mixing with older phyllosilicates – perhaps of pluvial origin -- and sulfates. Furthermore, a notable presence of hydrated amorphous phases indicates significant chemical weathering that mirrors pedogenesis at extreme environments on Earth. Effects of radiation and reactive oxygen species are also reminiscent of such soils at Atacama and Mojave. Some related phases, like perchlorates and Fe-sulfates, may sustain brine-driven weathering in modern martian soils. Meanwhile, chemical diversity across in situ and regional soils suggests many different soil types and processes. But the two main soil classification systems –the World Reference Base for Soil Resources (WRB) and the U.S. Soil Taxonomy – only inadequately account for such variability. While WRB provides more process insight, it needs refinement to represent variability of martian soils even at the first level of categorical detail. That will provide a necessary reference for future missions when identifying optimal pedological protocols to systematically survey martian soil. Updating Earth-based soil classification systems for this purpose will also advance soil taxonomy as a research field.
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Chlorine is one of the highly mobile elements that participated in early aqueous chemistry and later alteration in Mars history. Our new experimental results suggest that chlorine could cycle on present‐day Mars between the atmosphere and surface, driven by multiphase redox plasma chemistry induced by current Martian dust activity (dust storms, dust devils, and grain saltation). We present two sets of experimental results that demonstrate the instantaneous release of chlorine from seven common chlorides during a medium strength electrostatic discharge (ESD) process that induced plasma chemistry in a Mars environmental chamber. Results include (1) the direct detection of a plasma emission line at 837.8 nm of the first excited state of the Cl atom (Cl‐I) by in situ plasma spectroscopy during the ESD process for MgCl2, FeCl2, and AlCl3 and (2) the characterization of Cl‐bearing phases in the films deposited on the upper electrode after 7 hr of ESD exposure on each of seven chlorides (NaCl, KCl, CaCl2, MgCl2, FeCl2, AlCl3, and FeCl3), using Raman spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive X‐ray (EDX) spectroscopy, and X‐ray photoelectron spectroscopy (XPS). This study is part of a series of laboratory investigations on the Martian atmosphere and surface interaction induced by electrochemistry.
Thesis
From the vast microbial diversity of the three domains of life, a fraction of microorganisms (in particular some Archaea) have adapted to the most extreme conditions. Since most extreme environments are characterised by multiple stress factors (e.g. hot and acidic hydrothermal springs, saline and alkaline lakes, etc.), some extremophiles are in fact polyextremophiles. Nevertheless, there is no microorganism known to be adapted simultaneously to a very low pH (<1) and high salinity (and possibly high temperature). Either there are no molecular adaptations capable of withstanding certain combinations of pH and salinity, or this absence is related to the rarity of hyperacidic and hypersaline (and hot) environments, leaving them unexplored.The salt desert of the Danakil Depression (Afar region) in Ethiopia lies at the confluence of three tectonic plates in the East African Rift. In the middle of this geologically active zone, the Dallol geothermal dome and its surroundings offer a rare combination of physicochemical parameters, with high salt levels (20 to 78%, rich in Mg2+/Ca2+ or Na+(/Fe2+/3+)) and neutral to negative pH values (~6 to -1.5). Therefore, these sites provide a good model for studying microbial communities along these rare and unique parameter gradients. Over the last four years, we have collected 235 samples (solids, liquids, plankton biomass) from the different sites in and around the Dallol dome. In situ and ex situ physicochemical measurements have enabled us to characterise each environment and estimate its theoretical habitability based on previously known life-limiting conditions. We then proceeded to DNA purification of the samples and amplified and sequenced 16S/18S rRNA genes in order to characterize the microbial diversity, which we compared with databases and classified phylogenetically. We also completed our study by using a flow cytometer (for multiparametric analysis), and microscope observations (optical, scanning electron and confocal laser scanning).Hypersaline (~30% salts, dominated by NaCl) and slightly acidic (pH 4-6) environments showed a very high diversity of microorganisms, dominated by Archaea (at least 80% of the total sequences) in particular Halobacteria and Nanohaloarchaeota, frequently associated in hypersaline environments. We observed that the increase in acidity and salinity was associated with an increase in the proportion of Archaea (especially Nanohaloarchaeota). A better adaptation of halophilic archaea compared to bacteria could explain their prevalence. Concerning nanohaloarchaea, their higher proportion could be linked to their suspected role as haloarchaea ectosymbionts: in the case of a mutualistic relationship, their association could favour the adaptation to more extreme conditions; in the case of a parasitic relationship, the rise of acidity and salinity may weaken the host and increase the parasite prevalence. No trace of microbial life has been found in the most polyextreme environments (salinity 20-78%, pH -1 to 3). For some sites, we interpret that the chaotropicity, water activity and ionic strength values related to the composition and concentration of salts (minimum 50%, rich in Mg2+/Ca2+) are limiting for microbial life. For others, such as the Dallol dome, it could be the combination of hypersalinity and hyperacidity (pH~0) that make it inhospitable, without excluding the possible presence of sterilising chemical compounds. As environments with low or absent biomass are sensitive to biocontamination (local or laboratory), we have also tried to estimate the impact of this biocontamination on the study of the multi-extreme sites of Dallol and its surroundings. We thus propose a rigorous protocol, based on the use of cross-analyses and positive/negative controls in all our experiments in order to separate endogenous and exogenous DNA, and to distinguish cells from abiotic mineral biomorphs in our samples.
Article
Organic compounds have been delivered to the surface of Mars via meteorites, comets and interplanetary dust particles for billions of years. Determining the effects of high energy radiation and galactic cosmic radiation (GCR) on these organic compounds is critical for understanding the potential for the preservation of organic molecules associated with past or present life, and where to look for possible chemical bio- signatures during future Mars missions. Understanding how these effects are attenuated by the mineral matrix and the depth at which they are buried have been challenging to determine in situ on Mars. There have been very few experimental studies on the survival of organic compounds under radiation from a gamma source under realistic conditions, and their interpretation until now has been difficult due to the lack of data for actual radiation levels on Mars. Using the in-situ data obtained by the MSL/RAD instrument to anchor the dose calculations, here we show that the N-heterocycles purine and uracil, crucial components of biochemical processes in extant living systems, mixed with calcite, anhydrite, and kaolinite as Mars analogue minerals can survive the effects of radiation with a dose corresponding to ~500,000 years on Martian surface. The extent of survival varied not only with the nature of the organic compound, but its depth from the surface. These results provide new experimental data for the degree of protection offered by the regolith, in conjunction with minerals, for organic compounds that may be present on Mars.
Article
Perchlorate (ClO4⁻) is widespread in the solar system having been detected on Earth, on Mars, in chondrite meteorites and in lunar samples. On Mars, perchlorates expand the potential for habitable conditions by lowering the freezing point of liquid water in the formation of brines. In future manned space exploration their presence poses a hazard to human health, however, it also represents opportunities as a source of oxygen and fuel. Despite their prevalence, the mechanism(s) of perchlorate formation in different solar system environments are poorly understood. Here we demonstrate that perchlorate can be generated through the mechanical activation of silicates in the presence of chloride.
Article
Natural perchlorate (ClO4⁻) exists in many places on Earth, in lunar regolith, meteorites, and on the surface of Mars. Terrestrial natural ClO4⁻ has widely variable Cl and O stable isotopic compositions (δ³⁷Cl, δ¹⁸O, Δ¹⁷O). The δ¹⁸O and Δ¹⁷O values of ClO4⁻ from the most hyper-arid locations co-vary. ClO4⁻ from less arid areas has relatively little ¹⁷O excess and poor Δ¹⁷O-δ¹⁸O correlation. ClO4⁻ from the Atacama Desert has unusually low δ³⁷Cl (< -10‰) and exhibits a positive correlation between δ³⁷Cl and δ¹⁸O, while the δ³⁷Cl of ClO4⁻ from all other locations varies between -5 and +7 ‰ with no δ³⁷Cl-δ¹⁸O covariation. To evaluate the impact of different precursors (ClOx) and reaction pathways on the isotopic composition of ClO4⁻, we measured the isotopic composition of ClO4⁻ produced in the laboratory by UV or O3 mediated aqueous oxidation of Cl⁻, OCl⁻, ClO2⁻, and ClO2° as well as O3 mediated oxidation of dry NaCl. ClOx oxidation in aqueous or dry systems enriched in O3 produced ClO4⁻ with Δ¹⁷O values that generally increased with the number of O atoms required and included evidence that the site-specific ¹⁷O anomaly in O3 was preferentially transferred to ClO4⁻. Based on the inferred number of O atoms sourced from O3, and known Cl and O reaction pathways, it appears that ClO2° and ClO3* were required intermediates in the production of ClO4⁻ in the O3 experiments. ClOx aqueous oxidation by UV irradiation produced ClO4⁻ with a large range of δ¹⁸O values and little or no ¹⁷O anomaly. ClO3⁻ was produced to a much greater extent than ClO4⁻ in all experiments except dry oxidation of NaCl by O3. The isotopic composition of ClO3⁻ was distinct from that of ClO4⁻ produced from the same initial reactants. Combined results of O3 and UV mediated reactions largely bracketed the range of natural ClO4⁻ δ¹⁸O and Δ¹⁷O values as well as δ³⁷Cl values of non-Atacama natural samples, but no conditions produced the low δ³⁷Cl values of Atacama ClO4⁻. Our results indicate that variation in production mechanisms, possibly combined with isotopically variable precursors, could be responsible for much of the observed isotopic variation in natural ClO4⁻ and ClO3⁻.
Article
Chlorine is ubiquitous on Mars, some of it in the form of oxy-chlorine salts. Chlorine-containing salts have been found at several landing sites, including that of Phoenix and Curiosity, in the form of perchlorates and chlorides. Several intermediate states also exist, of which chlorate is the most stable. While perchlorates have received much attention in the past few years, chlorate salts are much less studied. The ratio of perchlorate to chlorate on Mars is not well-defined but may be approximately 1:1. Chlorate salts have similar properties to perchlorates: high solubility, low eutectic temperatures, and likely low deliquescence relative humidities. Laboratory studies were performed to determine the ability of sodium and magnesium chlorate salts to take up water vapor at low temperatures (296 K to 237 K). These studies were performed using a Raman microscope equipped with an environmental chamber and a single particle optical levitator equipped with a Raman spectrometer. The deliquescence of sodium chlorate (NaClO3) was found to be temperature-dependent with the average relative humidity (RH) values ranging from 68% RH at 296 K to 80% RH at 237 K. Additionally, there was a slight deviation between experimental deliquescence values for this salt and those predicted by equilibrium thermodynamics. The observed efflorescence (recrystallization) of NaClO3 occurred at lower RH values ranging from 18% RH at 264 K to 24% RH at 249 K, demonstrating the hysteresis common to salt recrystallization. Several experiments were performed below the reported eutectic temperature of NaClO3 which resulted in supercooling of the brine and depositional ice nucleation. Based on the supercooling effects observed during our experiments, a revised metastable eutectic temperature of 237 K is suggested for NaClO3 compared to the previously reported value of 252 K. Two phases of magnesium chlorate (Mg(ClO3)2) were observed and exhibited different water uptake behavior. The most common form of Mg(ClO3)2 appeared to be a hydrated, amorphous phase, Mg(ClO3)2 • X H2O(a) that continuously took up water when the RH was increased. This water uptake behavior was even observed at very low humidity values, 5.0 (±1.9)% RH, with little temperature dependence. This detectable water persisted down to RH values close to 0%, averaging 0.5 (±0.6)% RH with no visible temperature dependence. The deliquescence relative humidity (DRH) of the hexahydrate, Mg(ClO3)2 • 6 H2O, was found to range from 50.9 (± 7.5)% at 227 K to 55.8 (± 6.6)% at 224 K and was consistent with thermodynamic calculations. Under conditions measured by the Remote Environmental Monitoring Station (REMS) instrument at Gale Crater and conditions modeled in the shallow subsurface, magnesium chlorate, if present, likely interacts with water vapor during some diurnal cycles.
Article
Microbial communities have been explored in various terrestrial subsurface ecosystems, showing metabolic potentials that could generate noteworthy morphological and molecular biosignatures. Recent advancements in bioinformatic tools have allowed for descriptions of novel and yet-to-be cultivated microbial lineages in different ecosystems due to the genome reconstruction approach from metagenomic data. Using shotgun metagenomic data, we obtained metagenome-assembled genomes related to cultivated and yet-to-be cultivated prokaryotic lineages from a silica and iron-rich cave (Monte Cristo) in Minas Gerais State, Brazil. The Monte Cristo Cave has been shown to possess a high diversity of genes involved with different biogeochemical cycles, including reductive and oxidative pathways related to carbon, sulfur, nitrogen, and iron. Three genomes were selected for pangenomic analysis, assigned as Truepera sp., Ca. Methylomirabilis sp., and Ca. Koribacter sp. based on their lifestyles (radiation resistance, anaerobic methane oxidation, and potential iron oxidation). These bacteria exhibit genes involved with multiple DNA repair strategies, starvation, and stress response. Because these groups have few reference genomes deposited in databases, our study adds important genomic information about these lineages. The combination of techniques applied in this study allowed us to unveil the potential relationships between microbial genomes and their ecological processes with the cave mineralogy and highlight the lineages involved with anaerobic methane oxidation, iron oxidation, and radiation resistance as functional models for the search for extant life-forms outside our planet in silica- and iron-rich environments and potentially on Mars.
Article
The electrostatic discharge (ESD) induced by Martian dust activities (dust storms, dust devils, and grain saltation) has been recently proposed as a powerful geological agent to modify the structure and chemistry of Martian salts. Here, we performed new experiments to simulate gas discharge in Martian dust activity in a Mars chamber to investigate the modifications of chloride exposed to a medium strength ESD process. The structural, chemical and spectral features of NaCl before and after ESD exposure were systematically characterized with multiple analysis methods. On the basis of the experimental results, we found that 1) the colorless NaCl precursor subjected to ESD exposure subsequently displayed violet/blue color, indicating the presence of color centers; 2) the color centers (VK centers and Na colloids) in NaCl cause strong and characteristic spectral features in the visible to near-infrared reflectance spectra and Raman spectra; and 3) the relative density of color centers (VK centers and Na colloids) in NaCl gradually changes with increasing ESD duration. Our results also suggest that preferential Cl was released within NaCl crystals during the ESD process, and new phases ClO3−, ClO4−, and CO32− formed, which is consistent with previous studies (Wang et al., 2020b; Wu et al., 2018). We interpreted that preferential Cl release within NaCl crystals should be associated with the decomposition of VK centers and the sputtering process. We also proposed that the chemically active Cl species released from solid NaCl crystals is an essential part of the overall reaction pathway of perchlorate formation on Mars. Chloride exposed to the radiation environment at the Martian surface may also contain color centers, shedding light on the detection of normally featureless chlorides on Mars.
Article
The absence of significant detectable signatures of organic molecules in the atmosphere and on the surface of Mars is a major unsolved puzzle. One possible explanation is that perchlorate-rich Martian soils, activated by solar ultraviolet (UV) radiation, create an environment favorable for the rapid oxidation of organics such as alkanes (including methane or CH4). In this paper, we measured product formation rates from the methane-perchlorate-UV system at room temperature. Our results show that magnesium perchlorate (Mg(ClO4)2•6H2O) surfaces exposed to UV light at wavelengths reaching the Mars' surface accelerate the decomposition of methane (CH4), resulting in the formation of carbon dioxide (CO2), carbon monoxide (CO), and volatile chlorine oxides. The production rates for CO2 and CO on UV-activated perchlorate surfaces are 2.5 and 4.5 times higher, respectively, than in the absence of perchlorate. In addition, with UV radiation exposure, perchlorate (ClO4⁻) decomposes to chlorate (ClO3⁻) and chlorine oxides. These results are incorporated into a simple box model to estimate the near-surface atmospheric methane lifetime. The model gives a lifetime on the order of hours to months depending on assumptions, substantially shorter than ~300 yrs. calculated from methane loss by gas-phase chemistry alone.
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Samples returned from Mars would be placed under quarantine at a Sample Receiving Facility (SRF) until they are considered safe to release to other laboratories for further study. The process of determining whether samples are safe for release, which may involve detailed analysis and/or sterilization, is expected to take several months. However, the process of breaking the sample tube seal and extracting the headspace gas will perturb local equilibrium conditions between gas and rock and set in motion irreversible processes that proceed as a function of time. Unless these time-sensitive processes are understood, planned for, and/or monitored during the quarantine period, scientific information expected from further analysis may be lost forever. At least four processes underpin the time-sensitivity of Mars returned sample science: (1) degradation of organic material of potential biological origin, (2) modification of sample headspace gas composition, (3) mineral-volatile exchange, and (4) oxidation/reduction of redox-sensitive materials. Available constraints on the timescales associated with these processes supports the conclusion that an SRF must have the capability to characterize attributes such as sample tube headspace gas composition, organic material of potential biological origin, as well as volatiles and their solid-phase hosts. Because most time-sensitive investigations are also sensitive to sterilization, these must be completed inside the SRF and on timescales of several months or less. To that end, we detail recommendations for how sample preparation and analysis could complete these investigations as efficiently as possible within an SRF. Finally, because constraints on characteristic timescales that define time-sensitivity for some processes are uncertain, future work should focus on: (1) quantifying the timescales of volatile exchange for core material physically and mineralogically similar to samples expected to be returned from Mars, and (2) identifying and developing stabilization or temporary storage strategies that mitigate volatile exchange until analysis can be completed.
Article
We present maps of surface composition of Europa’s anti-Jovian hemisphere acquired using high spatial resolution IFU multispectral data from the SPHERE instrument on the Very Large Telescope (0.95–1.65 μ m) and the NIMS instrument on the Galileo orbiter (0.7–5.2 μ m). Spectral modeling was performed using a Markov Chain Monte Carlo method to estimate endmember abundances and to quantify their associated uncertainties. Modeling results support the leading–trailing hemisphere difference in hydrated sulfuric acid abundances caused by exogenic plasma bombardment. Water-ice grains are found to be in the 100 μ m–1 mm range, with larger grains present on the trailing hemisphere, consistent with radiation-driven sputtering destroying smaller grains. Modeling best estimates suggest a mixture of sulfate and chlorinated salts, although uncertainties derived from the MCMC modeling suggest that it is difficult to confidently detect individual salt abundances with low spectral resolution spectra from SPHERE and NIMS. The high spatial resolution offered by SPHERE allows the small-scale spatial distribution (<150 km) of potential species to be mapped, including ground-based detection of lineae and impact features. This could be used in combination with other higher spectral resolution observations to confirm the presence of these species.
Article
Salts and basalt are widespread on the surface of Mars. Therefore, basalt-brine interactions may have significant effects on both the aqueous history of the planet, and near-surface alteration assemblages. Raman spectra were collected from McKinney Basalt samples that were immersed in eight near-saturated brines composed of Na-Cl-H2O, Na-SO4-H2O, Na-ClO4-H2O, Mg-Cl-H2O, Mg-SO4-H2O, and two salt mixtures (Mg-Cl-SO4-H2O and Na-ClO4-SO4-H2O), as well as ultra-pure water for up to one year. Secondary minerals were observed in the Raman specta, including iron oxides, hydrated sulfates, amorphous silica, phosphates, and carbonates. Detection of these secondary minerals demonstrates the utility of Raman spectroscopy to identify basalt-brine alteration assemblages on Mars. This work also demonstrates that major classes of alteration phases can be distinguished using Raman spectra with resolution similar to those expected from the Raman instruments aboard the Perseverance and Rosalind Franklin Mars rovers. In addition, observations of carbonate minerals within alteration assemblages suggest CO2 from the atmosphere readily reacted with ions released from the basalt during alteration in near-saturated brines.
Thesis
Au carrefour des disciplines, l’exobiologie a pour objet la vie dans l’Univers. Parmi ses thématiques, la question des limites du vivant se pose avec celle de l’habitabilité des environnements extraterrestres. Proches de ces limites, les extrêmophiles terrestres peuplant les environnements extrêmes telles les cheminées hydrothermales ou la Mer Morte, indiquent que la présence d’eau liquide reste une condition nécessaire à la vie. Sa recherche dans le Système Solaire et au-delà demeure donc une priorité en exobiologie, justifiant l’intérêt porté aux océans subglaciaires des lunes glacées ainsi qu’aux saumures Martiennes.Les océans subglaciaires renferment, de loin, la majeure partie de l’eau liquide dans le Système Solaire et certaines, comme Encelade, pourraient présenter des cheminées hydrothermales dans leurs abysses. Sur Terre, les cheminées hydrothermales sont des biotopes indépendants de la surface, complexes et productifs malgré les conditions de pression et de température extrêmes qui les caractérisent. Ils constituent donc des modèles de premier ordre pour une hypothétique vie sur les lunes glacées. Des différences potentielles de conditions physico-chimiques viennent cependant limiter cette analogie. En particulier, la pression dans les abysses d’Europe pourrait excéder celle rencontrée au niveau des cheminées hydrothermales terrestres. La vie est-elle compatible avec de telles conditions ?Dans un premier projet, nous avons étudié les effets des hautes pressions (HP) à une échelle moléculaire en utilisant comme principal modèle l’ADN polymérase (ADNpol) B de l’archée hyperthermophile abyssale Pyrococcus abyssi. En utilisant des rapporteurs fluorescents de diverses natures et un fluorimètre couplé à une enceinte HP, nous avons étudié les effets des pressions allant de 0,1 à 100MPa sur l’activité de cette enzyme et comparé sa sensibilité aux HP à celles d’autres ADNpols thermostables. Nous démontrons que les HP inhibent directement l’activité des ADNpols et que cette inhibition peut être largement compensée par une augmentation de la température. Les implications exobiologiques et concernant l’adaptation aux HP chez les organismes abyssaux sont par ailleurs discutées.Plus proche de la Terre, un autre type d’environnement pourrait abriter de l’eau liquide dans le Système Solaire : les saumures Martiennes. Présentes de manière transitoire à la surface et de façon plus pérenne dans les environnements souterrains, ces saumures se caractérisent par une salinité importante et l’abondance de composés chaotropes comme les ions Mg2+, Ca2+ et ClO42-. Sur Terre, les environnements hypersalins comme la Mer Morte ou les bassins de saumures abyssaux sont peuplés par des microorganismes spécialisés appelés halophiles. Les plus extrêmes d’entre eux sont des archées de la classe Halobacteria qui présentent des traits caractéristiques, comme l’accumulation intracellulaire de KCl et l’acidification des protéines, et constituent des modèles de choix en exobiologie.Dans un deuxième projet, nous avons comparé les propriétés du protéome entier, et non de protéines modèles isolées, entre cinq archées hyperhalophiles issues d’environnements différents. Cette comparaison a été réalisée en utilisant diverses méthodes, analyse statistique des séquences, protéomique, dosage des ions intracellulaires ou encore diffusion des neutrons, et a notamment permis le développement d’une méthode biophysique de caractérisation de la dépendance au sel du protéome. Nous avons révélé des différences significatives de propriétés intrinsèques du protéome et de l’environnement intracellulaire entre les cinq souches qui soulignent le lien entre l’adaptation à l’environnement et l’adaptation moléculaire chez les halophiles. La réponse du protéome à des sels caractéristiques des saumures Martiennes présente également des implications exobiologiques concernant la recherche de traces de vie sur Mars.
Article
The formation and stability of brines on the surface of present-day Mars remains an important question to resolve the astrobiological potential of the red planet. Although modeling and experimental work have constrained the processes controlling the stability of single-salt brines exhibiting low freezing temperatures, such as calcium perchlorate, the Martian regolith is far more complex because multiple salts coexist in various concentrations, leading to brines whose behavior remains untested. Here we modeled the stability of complex brines of compositions determined from the Phoenix lander’s Wet Chemistry Laboratory. We find that such brines would form in equilibrium with sodium and magnesium perchlorates, chlorides, and calcium chlorate, but never calcium perchlorate, which has been widely considered as the most likely to produce brines on Mars. Furthermore, we find that only chlorate-rich brines can potentially remain liquid, for small periods of time, at temperatures compatible with those measured by the Phoenix lander. Therefore, liquid brines remain overly unstable under present-day Martian conditions and are unlikely to contribute to surface geomorphological activity, such as recurring slope lineae. In these conditions, of cold and salty brines, the present-day Martian surface remains highly unhabitable.
Article
We use the freezing point depressing magnesium and calcium perchlorates in Martian regolith to redistribute ground ice by residual liquid water migration following the initial emplacement of ground ice by vapour deposition. This residual liquid water is moved by forces generated by periodic surface temperatures that decay with depth in conjunction with the geothermal vertical temperature gradient. We examine the period means of the bulk water speeds with depth and the mean divergence of the bulk water speeds, which relates to the rate of change in ice content in the regolith. Silt and clay rich regoliths behave differently. In silty regolith, for the short 1.88 a period and for longer 50 ka (precession) and 120 ka (obliquity) temperature cycles, there is a mean movement of liquid perchlorate aqueous solution that results in formation of near surface excess ice layers. The excess ice formed by the seasonal 1.88a period is confined at high latitudes to the upper meter of regolith. For the longer periods, there is a well-defined surface temperature region where near surface thick (≥40 m) excess ice layers form; (from 192 K to 210 K). For mean surface temperatures <192 K no near surface thick excess ice layers formed, but deeper layers are predicted and followed. The formation of excess ice layers in silt near the surface is controlled by the relationship between the temperature cycles, geothermal gradient and the eutectic temperature of the perchlorate (eg. ~198 K for Ca and ~ 205 K for Mg perchlorate). At a given depth if the periodic temperature is below the eutectic then there is nearly no liquid water left and what there is has much higher viscosity. The sudden change in the liquid water amount and viscosity with temperature generates net average water speeds in silts that are two orders larger than in clays.
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The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles.
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The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles. Key Points First in situ evidence of nonterrestrial organics in Martian surface sediments Chlorinated hydrocarbons identified in the Sheepbed mudstone by SAM Organics preserved in sample exposed to ionizing radiation and oxidative condition
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Evidence for deliquescence of perchlorate salts has been discovered in the Martian polar region while possible brine flows have been observed in the equatorial region. This appears to contradict the idea that bulk deliquescence is too slow to occur during the short periods of the Martian diurnal cycle during which conditions are favorable for it. We conduct laboratory experiments to study the formation of liquid brines at Mars environmental conditions. We find that when water vapor is the only source of water, bulk deliquescence of perchlorates is not rapid enough to occur during the short periods of the day during which the temperature is above the salts’ eutectic value, and the humidity is above the salts’ deliquescence value. However, when the salts are in contact with water ice, liquid brine forms in minutes, indicating that aqueous solutions could form temporarily where salts and ice coexist on the Martian surface and in the shallow subsurface.
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In extremely arid regions on Earth, such as the Atacama Desert, nitrate, sulfate and perchlorate salts form in the atmosphere and accumulate on the surface from dry deposition according to diagnostic evidence in their oxygen isotopes. Salts of similar oxyanions should have formed in the atmosphere of Mars because of comparable photochemical reactions. We use a 1-D photochemical model to calculate the deposition rates of sulfate, nitrogen oxyanions, and perchlorate from Mars’ atmosphere, given a plausible range of volcanic fluxes of sulfur- and chlorine-containing gases in the past. To calculate integrated fluxes over time, we assume that throughout the last 3 byr (the Amazonian eon), the typical background atmosphere would have been similar to today’s cold and dry environment. If the soil has been mixed by impact perturbations to a characteristic depth of ∼2 m during this time, given a time-average volcanic flux 0.1% of the modern terrestrial volcanic flux, the model suggests that the soil would have accumulated 1.0–1.7 wt.% SO42- and 0.2–0.4 wt.% N in the form of pernitrate (peroxynitrate) or nitrate. The calculated sulfate concentration is consistent with in situ observations of soils from rovers and landers and orbital gamma ray spectroscopy. However, nitrates or pernitrates are yet to be detected. The modeled formation of perchlorate via purely gas-phase oxidation of volcanically-derived chlorine is insufficient by orders of magnitude to explain 0.4–0.6 wt.% ClO4- measured by NASA’s Phoenix Lander. The far smaller amount of ozone in the martian atmosphere compared to the terrestrial atmosphere and the colder, drier conditions are the cause of lower rates of gas phase oxidation of chlorine volatiles to perchloric acid. Our calculations imply that non-gas-phase processes not included in the photochemical model, such as heterogeneous reactions, are likely important for the formation of perchlorate and are yet to be identified.
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We studied the low-temperature properties of sodium and magnesium perchlorate solutions as potential liquid brines at the Phoenix landing site. We determined their theoretical eutectic values to be 236 ± 1 K for 52 wt% sodium perchlorate and 206 ± 1 K for 44.0 wt% magnesium perchlorate. Evaporation rates of solutions at various concentrations were measured under martian conditions, and range from 0.07 to 0.49 mm h-1 for NaClO4 and from 0.06 to 0.29 mm h-1 for Mg(ClO4)2. The extrapolation to Phoenix landing site conditions using our theoretical treatment shows that perchlorates are liquid during the summer for at least part of the day, and exhibit very low evaporation rates. Moreover, magnesium perchlorate eutectic solutions are thermodynamically stable over vapour and ice during a few hours a day. We conclude that liquid brines may be present and even stable for short periods of time at the Phoenix landing site.
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The detection and identification of organic molecules on Mars are of prime importance to establish the existence of a possible ancient prebiotic chemistry or even a biological activity. To date, however, no complex organic compounds have been detected on Mars. The harsh environmental conditions at the surface of Mars are commonly advocated to explain this nondetection, but few studies have been implemented to test this hypothesis. To investigate the nature, abundance, and stability of organic molecules that could survive under such environmental conditions, we exposed, in low Earth orbit, organic molecules of martian astrobiological relevance to solar UV radiation (>200 nm). The experiment, called UVolution, was flown on board the Biopan ESA module, which was situated outside a Russian Foton automated capsule and exposed to space conditions for 12 days in September 2007. The targeted organic molecules [alpha-aminoisobutyric acid (AIB), mellitic acid, phthalic acid, and trimesic acid] were exposed with, and without, an analogous martian soil. Here, we present experimental results of the impact of solar UV radiation on the targeted molecules. Our results show that none of the organic molecules studied seemed to be radiotolerant to the solar UV radiation when directly exposed to it. Moreover, the presence of a mineral matrix seemed to increase the photodestruction rate. AIB, mellitic acid, phthalic acid, and trimesic acid should not be considered as primary targets for in situ molecular analyses during future surface missions if samples are only collected from the first centimeters of the top surface layer.
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The detection and identification of organic molecules on Mars are of primary importance to establish the existence of a possible ancient prebiotic chemistry or even biological activity. The harsh environmental conditions at the surface of Mars could explain why the Viking probes-the only efforts, to date, to search for organics on Mars-detected no organic matter. To investigate the nature, abundance, and stability of organic molecules that could survive such environmental conditions, we developed a series of experiments that simulate martian surface environmental conditions. Here, we present results with regard to the impact of solar UV radiation on various carboxylic acids, such as mellitic acid, which are of astrobiological interest to the study of Mars. Our results show that at least one carboxylic acid, mellitic acid, could produce a resistant compound-benzenehexacarboxylic acid-trianhydride (C(12)O(9))-when exposed to martian surface radiation conditions. The formation of such products could contribute to the presence of organic matter in the martian regolith, which should be considered a primary target for in situ molecular analyses during future surface missions.
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GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life.
Chapter
Carbon delivered to the Earth by interplanetary dnst particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concent rat on of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.
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The Viking Landers were unable to detect evidence of life on Mars but, instead, found a chemically reactive soil capable of decomposing organic molecules. This reactivity was attributed to the presence of one or more as-yet-unidentified inorganic superoxides or peroxides in the martian soil. Using electron paramagnetic resonance spectroscopy, we show that superoxide radical ions (O2 –) form directly on Mars-analog mineral surfaces exposed to ultraviolet radiation under a simulated martian atmosphere. These oxygen radicals can explain the reactive nature of the soil and the apparent absence of organic material at the martian surface.
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Using the Mars Exploration Rover Opportunity, we have compiled one of the first field geologic maps on Mars while traversing the Noachian terrain along the rim of the 22-km diameter Endeavour crater (Lat -2° 16’ 33”, Long -5° 10’ 51”). In situ mapping of the petrographic, elemental, structural, and stratigraphic characteristics of outcrops and rocks distinguishes four mappable bedrock lithologic units. Three of these rock units pre-date the surrounding Burns formation sulfate-rich sandstones and one, the Matijevic formation, represents conditions on early Mars pre-dating the formation of Endeavour crater. The stratigraphy assembled from these observations includes several geologic unconformities. The differences in lithologic units across these unconformities record changes in the character and intensity of the Martian aqueous environment over geologic time. Water circulated through fractures in the oldest rocks over periods long enough that texturally and elementally significant alteration occurred in fracture walls. These oldest pre-Endeavour rocks and their network of mineralized and altered fractures were preserved by burial beneath impact ejecta and were subsequently exhumed and exposed. The alteration along joints in the oldest rocks, and the mineralized veins and concentrations of trace metals in overlying lithologic units is direct evidence that copious volumes of mineralized and/or hydrothermal fluids circulated through the early Martian crust. The wide range in intensity of structural and chemical modification from outcrop to outcrop along the crater rim shows that the ejecta of large (>8 km in diameter) impact craters is complex. These results imply that geologic complexity is to be anticipated in other areas of Mars where cratering has been a fundamental process in the local and regional geology and mineralogy.
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H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO2. Concurrent evolution of O2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.
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Recurring Slope Lineae (RSL) are active features on Mars that might require flowing water. Most examples observed through 2011 formed on steep, equator-facing slopes in the southern mid-latitudes. They form and grow during warm seasons and fade and often completely disappear during colder seasons, but recur over multiple Mars years. They are recognizable by their incremental growth, relatively low albedo and downhill orientation. We examined all images acquired by HiRISE during Ls 250–10° (slightly longer than southern summer, Ls 270–360°) of Mars years 30–31 (03/2011–10/2011), and supplemented our results with data from previous studies to better understand the geologic context and characteristics of RSL. We also confirmed candidate and likely sites from previous studies and discovered new RSL sites. We report 13 confirmed RSL sites, including the 7 in McEwen et al. (McEwen et al. [2011]. Science 333(6043), 740–743]. The observed seasonality, latitudinal and slope orientation preferences, and THEMIS brightness temperatures indicate that RSL require warm temperatures to form. We conclude that RSL are a unique phenomenon on Mars, clearly distinct from other slope processes that occur at high latitudes associated with seasonal CO2 frost, and episodic mass wasting on equatorial slopes. However, only 41% (82 out of 200) of the sites that present apparently suitable conditions for RSL formation (steep, equator-facing rocky slopes with bedrock exposure) in the southern mid-latitudes (28–60°S) contain any candidate RSL, with confirmed RSL present only in 7% (13 sites) of those locations. Significant variability in abundance, size and exact location of RSL is also observed at most sites, indicating additional controls such as availability of water or salts that might be playing a crucial role.
Article
The results from the Viking mission in the mid 1970s provided evidence that the martian surface contained oxidants responsible for destroying organic compounds. In 2008 the Phoenix Wet Chemistry Lab (WCL) found perchlorate (ClO4-) in three soil samples at concentrations from 0.5 to 0.7 wt%. The detection of chloromethane (CH3Cl) and dichloromethane (CH2Cl2) by the Viking pyrolysis gas chromatograph–mass spectrometer (GC–MS) may have been a result of ClO4- at that site oxidizing either terrestrial organic contaminates or, if present, indigenous organics. Recently, the Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity directly measured the presence of CH3Cl, CH2Cl2 and, along with measurements of HCl and oxygen, indirectly indicate the presence of ClO4-. However, except for Phoenix, no other direct measurement of the ClO4- anion in martian soil or rock has been made. We report here ion chromatographic (IC) and isotopic analyses of a unique sawdust portion of the martian meteorite EETA79001 that show the presence by mass of 0.6 ± 0.1 ppm ClO4-, 1.4 ± 0.1 ppm ClO3-, and 16 ± 0.2 ppm NO3- at a quantity and location within the meteorite that is difficult to reconcile with terrestrial contamination. The sawdust sample consists of basaltic material with a minor salt-rich inclusion in a mass ratio of ∼300:1, thus the salts may be 300 times more concentrated within the inclusion than the whole sample. The molar ratios of NO3-:ClO4- and Cl-:ClO4-, are very different for EETA79001 at ∼40:1 and 15:1, respectively, than the Antarctic soils and ice near where the meteorite was recovered at ∼10,000:1 and 5000:1, respectively. In addition, the isotope ratios for EETA79001 with δ15N = −10.48 ± 0.32‰ and δ18O = +51.61 ± 0.74‰ are significantly different from that of the nearby Miller Range blue ice with δ15N = +102.80 ± 0.14‰ and δ18O = +43.11 ± 0.64‰. This difference is notable, because if the meteorite had been contaminated with nitrate from the blue ice, the δ15N values should be the same. More importantly, the δ15N is similar to the uncontaminated Tissint Mars meteorite with δ15N = −4.5‰. These findings suggest a martian origin of the ClO4-, ClO3- and NO3- in EETA79001, and in conjunction with previous discoveries, support the hypothesis that they are present and ubiquitous on Mars. The presence of ClO3- in EETA79001 suggests the accompanying presence of other highly oxidizing oxychlorines such as ClO2- or ClO−, produced both by UV oxidation of Cl− and γ- and X-ray radiolysis of ClO4-. Since such intermediary species may contribute to oxidization of organic compounds, only highly refractory and/or well-protected organics are likely to survive. The global presence of ClO4-, ClO3-, and NO3-, has broad implications for the planet-wide water cycle, formation of brines, human habitability, organics, and life.
Article
Chlorate (ClO3-) is an intermediate oxidation species between chloride (Cl-) and perchlorate (ClO4-), both of which were found at the landing site by the Wet Chemistry Lab (WCL). The chlorate ion is almost as stable as perchlorate, and appears to be associated with perchlorate in most terrestrial reservoirs (e.g. Atacama and Antarctica). It is possible that chlorate contributed to the ion sensor response on the WCL, yet was masked by the strong perchlorate signal. However, very little is known about chlorate salts and their effect on the stability of water. We performed evaporation rate experiments in our Mars simulation chamber, which enabled us to determine the activity of water for various concentrations. From this we constructed solubility diagrams for NaClO3, KClO3, Mg(ClO3)2 and Ca(ClO3)2, and determined the Pitzer parameters for each salt. Chlorate salt eutectic temperatures range from 270 K (KClO3) to 204 K (Mg(ClO3)2). Modeling the addition of chlorate to the initial WCL solutions shows that it precipitates in concentrations comparable to other common salts, such as gypsum and epsomite, and implies that chlorates may play an important role in the wet chemistry on Mars.
Data
A single scoop of the Rocknest aeolian deposit was sieved (<150 mu m), and four separate sample portions, each with a mass of similar to 50mg, were delivered to individual cups inside the Sample Analysis at Mars (SAM) instrument by the Mars Science Laboratory rover's sample acquisition system. The samples were analyzed separately by the SAM pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes. Several chlorinated hydrocarbons including chloromethane, dichloromethane, trichloromethane, a chloromethylpropene, and chlorobenzene were identified by SAM above background levels with abundances of similar to 0.01 to 2.3nmol. The evolution of the chloromethanes observed during pyrolysis is coincident with the increase in O-2 released from the Rocknest sample and the decomposition of a product of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA), a chemical whose vapors were released from a derivatization cup inside SAM. The best candidate for the oxychlorine compounds in Rocknest is a hydrated calcium perchlorate (Ca(ClO4)(2)nH(2)O), based on the temperature release of O-2 that correlates with the release of the chlorinated hydrocarbons measured by SAM, although other chlorine-bearing phases are being considered. Laboratory analog experiments suggest that the reaction of Martian chlorine from perchlorate decomposition with terrestrial organic carbon from MTBSTFA during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by SAM. Chlorobenzene may be attributed to reactions of Martian chlorine released during pyrolysis with terrestrial benzene or toluene derived from 2,6-diphenylphenylene oxide (Tenax) on the SAM hydrocarbon trap. At this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons, nor do we exclude the possibility that future SAM analyses will reveal the presence of organic compounds native to the Martian regolith.
Article
A bacterial isolate, strain perc1ace, was shown to reduce the ground water contaminant perchlorate (ClO{sub 4}{sup {minus}}) to levels < 0.005 mg L{sup {minus}1} when grown on acetate under anaerobic conditions. The ability of perc1ace to simultaneously reduce perchlorate and another ground water pollutant, nitrate (NO{sub 3}{sup {minus}}), was examined in batch studies and in a sand packed column under saturated flow conditions. Nitrate removal was monitored using ion chromatography, and perchlorate removal was monitored using a perchlorate specific electrode or ion chromatography, depending on the study. In batch studies, the reduction of 0.089, 0.92, 12.0, and 122 mg L{sup {minus}1} perchlorate was examined in the presence and absence of 62 mg L{sup {minus}1} NO{sub 3}{sup {minus}}. Perchlorate was reduced more rapidly in the absence of NO{sub 3}{sup {minus}} than in its presence. However, both perchlorate and NO{sub 3}{sup {minus}} were reduced by more than 10-fold within 48 h. A sand-packed column inoculated with perc1ace simulated a flow-through biotreatment system for water contaminated with a low level of perchlorate and a much higher level of NO{sub 3}{sup {minus}}. Biotreatment could reduce perchlorate to < 0.005 mg L{sup {minus}1} in a 3 h residence time. The addition of NO{sub 3}{sup {minus}} initially decreased the efficiency of perchlorate removal, however within 1 d the biotreatment system had adjusted such that there was complete removal of perchlorate and the reduction of NO{sub 3}{sup {minus}} to < 1 mg L{sup {minus}1}.
Article
The most comprehensive search for organics in the Martian soil was performed by the Viking Landers. Martian soil was subjected to a thermal volatilization process to vaporize and break organic molecules, and the resultant gases and volatiles were analyzed by gas chromatography-mass spectrometry. Only water at 0.1–1.0 wt% was detected, with traces of chloromethane at 15 ppb, at Viking landing site 1, and water at 0.05–1.0 wt% and carbon dioxide at 50–700 ppm, with traces of dichloromethane at 0.04–40 ppb, at Viking landing site 2. These chlorohydrocarbons were considered to be terrestrial contaminants, although they had not been detected at those levels in the blank runs. Recently, perchlorate was discovered in the Martian Arctic soil by the Phoenix Lander. Here we show that when Mars-like soils from the Atacama Desert containing 32 ± 6 ppm of organic carbon are mixed with 1 wt% magnesium perchlorate and heated, nearly all the organics present are decomposed to water and carbon dioxide, but a small amount is chlorinated, forming 1.6 ppm of chloromethane and 0.02 ppm of dichloromethane at 500°C. A chemical kinetics model was developed to predict the degree of oxidation and chlorination of organics in the Viking oven. Reinterpretation of the Viking results therefore suggests ≤0.1% perchlorate and 1.5–6.5 ppm organic carbon at landing site 1 and ≤0.1% perchlorate and 0.7–2.6 ppm organic carbon at landing site 2. The detection of organics on Mars is important to assess locations for future experiments to detect life itself.
Article
Environmental context. Perchlorate, a well-known thyroid disruptor with both man-made and natural sources represents a major environmental problem in the United States but little information is available concerning the source of natural perchlorate. Previous research has demonstrated that perchlorate can be produced from exposure of some chlorine compounds to ultraviolet radiation, but no information was available how quickly or comparatively how much perchlorate was formed. The results of the present study can be used to evaluate the potential impact of ultraviolet processes on the overall occurrence of perchlorate in the environment. Abstract. The present study provides new and important information on perchlorate (ClO4–) formation through ultraviolet (UV) photodissociation of unbuffered chlorite (ClO2–) solutions from the standpoint of kinetics under three different wavelength regimes having maximum emissions, λe,max, at 235.7, 300 and 350 nm. ClO4– production rates and yields were in general found to be inversely related, with higher yields and lower rates at higher wavelengths, and vice versa. A simple kinetic model for ClO4– production as a function of the ClO2– first-order decay constant and starting concentration was fitted to the experimental data, resulting in the calculation of a rate constant, k2, which is a function of light-source characteristics. Further, a conceptual scheme for ClO4– formation via photochemical reactions between oxychlorine species was proposed based on the experimental results and available literature. The present study is a further step towards understanding the formation of ClO4– from the photolysis of its precursors.
Article
Perchlorate salts, recently discovered on Mars, are known to readily absorb water vapor from the atmosphere and deliquesce into the aqueous phase at room temperature. Here we study the deliquescence (crystalline solid to liquid transition) and efflorescence (liquid to crystalline solid transition) of perchlorate salts at low temperatures relevant to Mars. A Raman microscope and environmental cell were used to determine the deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of NaClO4 and Mg(ClO4)2 as a function of temperature and hydration state. We find that the deliquescence of anhydrous NaClO4 is only slightly dependent on temperature and occurs at ~38% RH. The DRH of NaClO4·H2O increases with decreasing temperature from 51% at 273K to 64% at 228K. The DRH of Mg(ClO4)2·6H2O also increases with decreasing temperature from 42% at 273K to 64% at 223K. The efflorescence of both NaClO4 and Mg(ClO4)2 salt solutions occurs at a lower RH than deliquescence due to the kinetic inhibition of crystallization. For all temperatures studied, the ERH values of NaClO4 and Mg(ClO4)2 are 13% and 19%, respectively. These results indicate perchlorate salts can exist as metastable, supersaturated solutions over a wide range of RH and temperature conditions. Summer diurnal temperature and relative humidity cycles at low latitudes on Mars could allow the surface salts to be aqueous for several hours per day.
Article
Abstract Results from the Viking biology experiments indicate the presence of reactive oxidants in martian soils that have previously been attributed to peroxide and superoxide. Instruments on the Mars Phoenix Lander and the Mars Science Laboratory detected perchlorate in martian soil, which is nonreactive under the conditions of the Viking biology experiments. We show that calcium perchlorate exposed to gamma rays decomposes in a CO2 atmosphere to form hypochlorite (ClO(-)), trapped oxygen (O2), and chlorine dioxide (ClO2). Our results show that the release of trapped O2 (g) from radiation-damaged perchlorate salts and the reaction of ClO(-) with amino acids that were added to the martian soils can explain the results of the Viking biology experiments. We conclude that neither hydrogen peroxide nor superoxide is required to explain the results of the Viking biology experiments. Key Words: Mars-Radiolysis-Organic degradation-in situ measurement-Planetary habitability and biosignatures. Astrobiology 13, xxx-xxx.
Article
Carbon dioxide (CO2) rich chlorine-bearing ices were exposed to energetic electrons in laboratory simulation experiments to investigate the formation of chlorine oxides (ClxOy) in the condensed phase on Mars. The radiolysis-induced synthesis of chlorine oxides (ClxOy) was complementarily monitored online and in situ via infrared spectroscopy (IR) and quadrupole mass spectrometry (QMS). Three discrete chlorine oxides were identified: chorine dioxide (OClO), dichlorine monoxide (ClOCl), and chloryl chloride (ClClO2). Higher irradiation doses support the facile production of ClO3- and ClO2-bearing high-order chlorine oxides. We attribute manifolds of chlorine oxides, as invoked herein, to the potential origin of perchlorates as found on Mars.
Article
The Phoenix Mars lander measured perchlorate as a key soluble anion in the soil at an abundance of ~1wt%. Here, we discuss how the perchlorate was likely formed from atmospheric oxidants acting on chlorine-bearing species in Mars' arid environment.