133 results found
Naz N, Liu D, Harandi BF, et al., 2022, Microbial Growth in Martian Soil Simulants Under Terrestrial Conditions: Guiding the Search for Life on Mars, ASTROBIOLOGY, Vol: 0, Pages: 1-12, ISSN: 1531-1074
MacKenzie SM, Neveu M, Davila AF, et al., 2022, Science Objectives for Flagship-Class Mission Concepts for the Search for Evidence of Life at Enceladus, ASTROBIOLOGY, Vol: 22, Pages: 685-712, ISSN: 1531-1074
Liu D, Kounaves SP, 2021, Degradation of amino acids on Mars by UV irradiation in the presence of chloride and oxychlorine salts, Astrobiology, Vol: 21, Pages: 793-801, ISSN: 1531-1074
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.
Schulze-Makuch D, Lipus D, Arens FL, et al., 2021, Microbial Hotspots in Lithic Microhabitats Inferred from DNA Fractionation and Metagenomics in the Atacama Desert, MICROORGANISMS, Vol: 9
MacKenzie SM, Neveu M, Davila AF, et al., 2021, The enceladus orbilander mission concept: Balancing return and resources in the search for life, Planetary Science Journal, Vol: 2
Enceladus’s long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon’s surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.
Welsh H, Gueorguieva G-A, Kounaves S, et al., 2020, Stable nitrogen and oxygen isotope fractionation during precipitation of nitrate salt from saturated solutions., Rapid Commun Mass Spectrom, Vol: 34
RATIONALE: Nitrate is an oxyanion similar to CO3 - and thus should undergo stable N and O isotope fractionation during dissolution or precipitation. This process should dominate abiotic soil nitrate processes in hyperarid regions of Earth and possibly Mars. METHODS: The N and O isotope fractionations during the precipitation of nitrate salt from saturated solutions at ~20°C were determined by two methods: rapid precipitation by antisolvent crystallization and slow uninhibited precipitation in a desiccator. In the antisolvent crystallization procedure, increasing volumes of acetone were added to samples of saturated sodium and strontium nitrate solutions to instantaneously precipitate nitrate salt. In the slow procedure (requiring weeks), slow evaporative water loss drove the process. RESULTS: There was little difference between the two procedures. Using a Rayleigh model, the calculated N fractionation (15 εproduct-residual ) ranged from 1.69‰ to 2.77‰, whereas for O, the 18 εproduct-residual values were between 1.27‰ and 4.61‰. The N isotope fractionation between NO3 - and the metal solid is similar to that between C in dissolved CO3 -2 and carbonates. We found that O versus N isotope plots of soil nitrate in a cold/dry Antarctic chronosequence had slopes similar to those from the experiments, revealing abiotic transport. In the Atacama Desert, where the soil nitrates are a mix of biological and tropospheric nitrate, there is an inverse relationship between soil N and O isotopes. These two relationships were compared with the isotope composition of nitrate from Martian meteorite EETA79001. CONCLUSIONS: While the N and O isotope composition of the Martian nitrate is remarkably similar to that of the present Atacama Desert, the interpretation of the slope of the O versus N isotopes remains ambiguous due to the limited number of samples. Additional NO3 samples from Martian meteorites are needed to address the question of
Kounaves S, Liu D, Naz N, 2020, Comparative Study of the Ability of Three Martian Simulants to Support Bacterial Growth, AGU
Maus D, Heinz J, Schirmack J, et al., 2020, Methanogenic archaea can produce methane in deliquescence-driven Mars analog environments, Scientific Reports, Vol: 10, ISSN: 2045-2322
The current understanding of the Martian surface indicates that briny environments at the near-surface are temporarily possible, e.g. in the case of the presumably deliquescence-driven Recurring Slope Lineae (RSL). However, whether such dynamic environments are habitable for terrestrial organisms remains poorly understood. This hypothesis was tested by developing a Closed Deliquescence System (CDS) consisting of a mixture of desiccated Martian Regolith Analog (MRA) substrate, salts, and microbial cells, which over the course of days became wetted through deliquescence. The methane produced via metabolic activity for three methanogenic archaea: Methanosarcina mazei, M. barkeri and M. soligelidi, was measured after exposing them to three different MRA substrates using either NaCl or NaClO4 as a hygroscopic salt. Our experiments showed that (1) M. soligelidi rapidly produced methane at 4 °C, (2) M. barkeri produced methane at 28 °C though not at 4 °C, (3) M. mazei was not metabolically reactivated through deliquescence, (4) none of the species produced methane in the presence of perchlorate, and (5) all species were metabolically most active in the phyllosilicate-containing MRA. These results emphasize the importance of the substrate, microbial species, salt, and temperature used in the experiments. Furthermore, we show here for the first time that water provided by deliquescence alone is sufficient to rehydrate methanogenic archaea and to reactivate their metabolism under conditions roughly analogous to the near-subsurface Martian environment.
Liu D, Kounaves SP, 2019, The Role of Titanium Dioxide (TiO2) in the Production of Perchlorate (ClO4-) from Chlorite (ClO2- and Chlorate (ClO3-) on Earth and Mars, ACS EARTH AND SPACE CHEMISTRY, Vol: 3, Pages: 1678-1684, ISSN: 2472-3452
Montgomery W, Jaramillo EA, Royle S, et al., 2019, Effects of oxygen-containing salts on the detection of organic biomarkers on Mars and in terrestrial analogue soils, Astrobiology, Vol: 19, Pages: 711-721, ISSN: 1531-1074
The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO4- ) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds, but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present, or at extremely low levels, should be re-examined.
Jaramillo EA, Royle S, Claire M, et al., 2019, Indigenous organic-oxidized fluid interactions in the tissint Mars meteorite, Geophysical Research Letters, Vol: 46, Pages: 3090-3098, ISSN: 0094-8276
The observed fall and rapid recovery of the Tissint Mars meteorite has provided minimally contaminated samples of the Martian surface. We report analyses of Tissint for organic compounds by pyrolysis‐gas chromatography‐mass spectrometry and for soluble salts by ion chromatography. Pyrolysis‐gas chromatography‐mass spectrometry analysis shows the presence of organic compounds similar to those in the Mars EETA79001 and Nakhla meteorites. The organic profile is dominated by aromatic hydrocarbons, including oxygen and nitrogen‐containing aromatics, and sulfur‐containing species including thiophenes. The soluble salts in Tissint are dominated by sulfate and various oxidation states of chlorine, including perchlorate. The organic compounds and salts in the soils from the Tissint recovery strewn field differ significantly from those found in Tissint suggesting minimal terrestrial contamination. Our results support the hypothesis that the soluble inorganic components of Tissint are most likely a result of indigenous fluid inclusion, thus providing a glimpse into the composition of early Martian fluids.
Royle SH, Tan J, Kounaves SP, et al., 2018, Survivability of 1-chloronapthalene during simulated early diagenesis – Implications for chlorinated hydrocarbon detection on Mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 2790-2802, ISSN: 2169-9097
All missions to Mars which have attempted to detect organic molecules have detected simple chlorohydrocarbons, the source of which has yet to be firmly established. This study assessed the likelihood of these chlorinated molecules being indigenous to the sedimentary units in which they were detected or if they were chlorinated during analysis. The survivability of 1-chloronapthalene was examined via hydrous pyrolysis experiments and its de-chlorination kinetics were determined. The results of these experiments were used to model the survivability of this simple chlorohydrocarbon under Mars-relevant diagenetic conditions using the Sheepbed mudstone unit as a case study. It was found that 1-chloronapthalene was rapidly dechlorinated under Noachian conditions and thus the detected Martian chlorohydrocarbons are unlikely to be ancient and probably formed within the rover’s sample handling chain during analysis.
Oberlin EA, Claire MW, Kounaves SP, 2018, Evaluation of the Tindouf Basin Region in Southern Morocco as an analog site for soil geochemistry on Noachian Mars, Astrobiology, Vol: 18, Pages: 1318-1328, ISSN: 1531-1074
Locations on Earth that provide insights into processes that may be occurring or may have occurred throughout martian history are often broadly deemed “Mars analog environments.” As no single locale can precisely represent a past or present martian environment, it is important to focus on characterization of terrestrial processes that produce analogous features to those observed in specific regions of Mars or, if possible, specific time periods during martian history. Here, we report on the preservation of ionic species in soil samples collected from the Tindouf region of Morocco and compare them with the McMurdo Dry Valleys of Antarctica, the Atacama Desert in Chile, the martian meteorite EETA79001, and the in situ Mars analyses from the Phoenix Wet Chemistry Laboratory (WCL). The Moroccan samples show the greatest similarity with those from Victoria Valley, Beacon Valley, and the Atacama, while being consistently depleted compared to University Valley and enriched compared to Taylor Valley. The NO3/Cl ratios are most similar to Victoria Valley and Atacama, while the SO4/Cl ratios are similar to those from Beacon Valley, Victoria Valley, and the Atacama. While perchlorate concentrations in the Moroccan samples are typically lower than those found in samples of other analog sites, conditions in the region are sufficiently arid to retain oxychlorines at detectable levels. Our results suggest that the Tindouf Basin in Morocco can serve as a suitable analogue for the soil geochemistry and subsequent aridification of the Noachian epoch on Mars.
Royle SH, Oberlin E, Watson JS, et al., 2018, Perchlorate‐driven combustion of organic matter during pyrolysis‐gas chromatography‐mass spectrometry: implications for organic matter detection on earth and mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 1901-1909, ISSN: 2169-9097
The search for life on Mars targets the detection of organic matter from extant or extinct organisms. Current protocols use thermal extraction procedures to transfer organic matter to mass spectrometer detectors. Oxidizing minerals on Mars, such as perchlorate, interfere with organic detection by thermal extraction. Thermal decomposition of perchlorate releases oxygen which promotes combustion of organic carbon. We have assessed the minimum mass ratio of organic carbon to perchlorate required to detect organic matter by thermal extraction and mass spectrometry. Locations on Mars with organic carbon to perchlorate ratios above 4.7-9.6 should be targeted. Because habitability is enhanced by the presence of liquid water and because perchlorate is a water soluble salt, locations on Mars with evidence of past or recent liquid water are high priority targets.
Kounaves S, Oberlin E, 2018, Volatiles Measured by the Phoenix Lander at the Northern Plains of Mars, Volatiles in the Martian Crust, Editors: Filiberto, Schwenzer, Publisher: Elsevier, ISBN: 9780128041918
The science goals of the Phoenix lander were to verify near-surface H2O ice surrounding the north polar cap, characterize the shallow icy soil and overlying soil deposits, document the high latitude surface and atmospheric environments, and evaluate the habitability. These goals guided payload selection which included; the Thermal and Evolved Gas Analyzer (TEGA), consisting of eight differential scanning calorimetry (DSC) cells coupled to a magnetic-sector mass spec (MS) for identification and quantification of organics and inorganics in the atmosphere and minerals; the Wet Chemistry Laboratory (WCL) to analyze the soil chemistry at the surface and depth to better understand the history of the water, habitability, chemical energy sources, and the general geochemistry including SO42-, Cl-, Br-, I-, NO3-, and ClO4-; and the Thermal and Electrical Conductivity Probe (TECP), mounted near the end of the 2.3 m Robotic Arm (RA), to characterize, control, distribution, and exchange of H2O between the atmosphere and subsurface. These instruments provided a wealth of data about volatiles, especially, sulfur, carbon, chlorine, and water. A significant discovery was that the dominant chlorine (Cl) phase in the soil was perchlorate (ClO4-) at ~ 0.6 wt% at a ratio of ClO4- to Cl- of 6:1. The production of ClO4- on Cl-mineral surfaces would result in highly oxidizing intermediates (ClO-, ClO2, •OCl, •Cl, •OH), capable of destroying or altering organics. Results also showed that the soil contained a 3:2 ratio of Ca(ClO4)2 to Mg(ClO4)2, strongly supporting the conclusion that the Phoenix site has been extremely arid for at least ~ 600 Myr. Other results included; ~ 1.3 wt% SO42-, most likely as a hydrated MgSO4, limiting the S phases to predominantly insoluble sulfur compounds; isotopic composition for atmospheric CO2 of δ13CVPDB = -2.5 ± 4.3‰ and δ18OVSMOW = 31.0 ±5.7‰, notably lacking in 13C; and calcium rich carbonate pha
Heinz J, Schirmack J, Airo A, et al., 2018, Enhanced Microbial Survivability in Subzero Brines., Astrobiology, Vol: 18, ISSN: 1531-1074
It is well known that dissolved salts can significantly lower the freezing point of water and thus extend habitability to subzero conditions. However, most investigations thus far have focused on sodium chloride as a solute. In this study, we report on the survivability of the bacterial strain Planococcus halocryophilus in sodium, magnesium, and calcium chloride or perchlorate solutions at temperatures ranging from +25°C to -30°C. In addition, we determined the survival rates of P. halocryophilus when subjected to multiple freeze/thaw cycles. We found that cells suspended in chloride-containing samples have markedly increased survival rates compared with those in perchlorate-containing samples. In both cases, the survival rates increase with lower temperatures; however, this effect is more pronounced in chloride-containing samples. Furthermore, we found that higher salt concentrations increase survival rates when cells are subjected to freeze/thaw cycles. Our findings have important implications not only for the habitability of cold environments on Earth but also for extraterrestrial environments such as that of Mars, where cold brines might exist in the subsurface and perhaps even appear temporarily at the surface such as at recurring slope lineae. Key Words: Brines-Halophile-Mars-Perchlorate-Subzero-Survival. Astrobiology 18, xxx-xxx.
Schulze-Makuch D, Wagner D, Kounaves SP, et al., 2018, A transitory microbial habitat in the hyperarid Atacama desert, Proceedings of the National Academy of Sciences, Vol: 115, Pages: 2670-2675, ISSN: 0027-8424
Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: (i) a physico-chemical characterization of the soil habitability after an exceptional rain event, (ii) identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], (iii) measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and (iv) microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today’s extreme hyperaridity.
Royle SH, Montgomery W, Kounaves SP, et al., 2017, Effect of hydration state of Martian perchlorate salts on their decomposition temperatures during thermal extraction, Journal of Geophysical Research: Planets, Vol: 122, Pages: 2793-2802, ISSN: 2169-9097
Three Mars missions have analyzed the composition of surface samples using thermal extraction techniques. The temperatures of decomposition have been used as diagnostic information for the materials present. One compound of great current interest is perchlorate, a relatively recently discovered component of Mars' surface geochemistry that leads to deleterious effects on organic matter during thermal extraction. Knowledge of the thermal decomposition behavior of perchlorate salts is essential for mineral identification and possible avoidance of confounding interactions with organic matter. We have performed a series of experiments which reveal that the hydration state of magnesium perchlorate has a significant effect on decomposition temperature, with differing temperature releases of oxygen corresponding to different perchlorate hydration states (peak of O2 release shifts from 500 to 600°C as the proportion of the tetrahydrate form in the sample increases). Changes in crystallinity/crystal size may also have a secondary effect on the temperature of decomposition, and although these surface effects appear to be minor for our samples further investigation may be warranted. A less than full appreciation of the hydration state of perchlorate salts during thermal extraction analyses could lead to misidentification of the number and the nature of perchlorate phases present.
Clark BC, Kounaves SP, 2017, Evidence for the distribution of perchlorates on Mars (vol 15, pg 311, 2015), INTERNATIONAL JOURNAL OF ASTROBIOLOGY, Vol: 16, Pages: 236-236, ISSN: 1473-5504
Weber AW, ONeil GD, Kounaves SP, 2017, Solid contact ion-selective electrodes for in situ measurements at high pressure, Analytical Chemistry, Vol: 89, Pages: 4803-4807, ISSN: 0003-2700
Solid contact polymeric ion-selective electrodes (SC-ISEs) have been fabricated using microporous carbon (μPC) as the ion-to-electron transducer, loaded with a liquid membrane cocktail containing both ionophore and additive dissolved in plasticizer. These SC-ISEs were characterized and shown to be suitable for analysis in aqueous environments at pressures of 100 bar. Potassium ISEs, prepared in this manner, showed excellent performance at both atmospheric and elevated pressures, as evaluated by their response slopes and potential stability. These novel SC-ISEs were shown to be capable of measuring K+ at pressures under which traditional liquid-filled ISEs fail. Furthermore, the effect of pressure on the response of these sensors had little or no effect on potential, sensitivity, or limit of detection. High pressure sensor calibrations were performed in standard solutions as well as simulated seawater samples to demonstrate their usefulness as sensors in a deep-sea environment. These novel SC-ISE sensors show promise of providing the ability to make in situ real-time measurements of ion-fluxes near deep-ocean geothermal vents.
Clark BC, Kounaves SP, 2016, Evidence for the distribution of perchlorates on Mars, INTERNATIONAL JOURNAL OF ASTROBIOLOGY, Vol: 15, Pages: 311-318, ISSN: 1473-5504
Heinz J, Schulze-Makuch D, Kounaves SP, 2016, Deliquescence-induced wetting and RSL-like darkening of a Mars analogue soil containing various perchlorate and chloride salts, Geophysical Research Letters, Vol: 43, Pages: 4880-4884, ISSN: 0094-8276
Recurring slope lineae (RSL) are flow-like features on Mars characterized by a local darkening of the soil thought to be generated by the formation and flow of liquid brines. One possible mechanism responsible for forming these brines could be the deliquescence of salts present in the Martian soil. We show that the JSC Mars-1a analogue soil undergoes a darkening process when salts dispersed in the soil deliquesce, but forming continuous liquid films and larger droplets takes much longer than previously assumed. Thus, RSL may not necessarily require concurrent flowing liquid water/brine or a salt-recharge mechanism, and their association with gullies may be the result of previously flowing water and deposited salts during an earlier warmer and wetter period. In addition, our results show that electrical conductivity measurements correlate well with the deliquescence rates and provide better overall characterization than either Raman spectroscopy or estimates based on deliquescence relative humidity.
Mars landed and orbiter missions have instrumentation capable of detecting oxychlorine phases(e.g. perchlorate, chlorate) on the surface. Perchlorate (*0.6 wt%) was first detected by the Wet ChemistryLaboratory in the surface material at the Phoenix Mars Landing site. Subsequent analyses by the ThermalEvolved Gas Analyser aboard the same lander detected an oxygen release (*465°C) consistent with thethermal decomposition of perchlorate. Recent thermal analysis by the Mars Science Laboratory’s SampleAnalysis at Mars instrument has also indicated the presence of oxychlorine phases (up to 1.2 wt%) in GaleCrater materials. Despite being at detectable concentrations, the Chemistry and Mineralogy (CheMin) Xraydiffractometer has not detected oxychlorine phases. This suggests that Gale Crater oxychlorine may existas poorly crystalline phases or that perchlorate/chlorate mixtures exist, so that individual oxychlorineconcentrations are below CheMin detection limits (*1 wt%). Although not initially designed to detectoxychlorine phases, reinterpretation of Viking Gas Chromatography/Mass Spectrometer data also suggestthat oxychlorine phases are present in the Viking surface materials. Remote near-infrared spectral analysesby the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument indicate that at leastsome martian recurring slope lineae (RSL) have spectral signatures consistent with the presence of hydratedperchlorates or chlorates during the seasons when RSL are most extensive. Despite the thermal emissionspectrometer, Thermal Emission Imaging System, Observatoire pour la Minéralogie, l’Eau, les Glaces etl’Activité and CRISM detection of hundreds of anhydrous chloride (*10–25 vol%) deposits, expectedassociated oxychlorine phases (>5–10 vol%) have not been detected. Total Cl and oxychlorine data sets fromthe Phoenix Lander and the Mars Science Laboratory missions could be used to develop oxychlorineversus tota
O'Neil GD, Fouskaki M, Kounaves SP, et al., 2015, The use of graphene oxide as a fixed charge carrier in ion-selective electrodes, ELECTROCHEMISTRY COMMUNICATIONS, Vol: 55, Pages: 51-54, ISSN: 1388-2481
Schulze-Makuch D, Rummel JD, Benner SA, et al., 2015, Nearly Forty Years after Viking: Are We Ready for a New Life-Detection Mission?, ASTROBIOLOGY, Vol: 15, Pages: 413-419, ISSN: 1531-1074
Carrier BL, Kounaves SP, 2015, The origins of perchlorate in the Martian soil, Geophysical Research Letters, Vol: 42, Pages: 3739-3745, ISSN: 0094-8276
Perchlorate (ClO4 ) has been detected on Mars, but its production and distribution are unclear.Mechanisms requiring atmospheric chlorine are insufficient for measured concentrations. We conductedstudies 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 SiO2was added, yield increased from 2 to 42 nmol and 0.4 to 2.6 nmol,respectively. We attribute this to SiO2and metal oxides acting as photocatalysts, generating O2 radicalsfrom O2which react with chloride. Results show ClO4 and ClO3 can be produced photochemically onCl 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 bydistribution of chlorine and provide insight into the oxidizing nature of the soil and its potential effectson organics.
Fang D, Oberlin E, Ding W, et al., 2015, A Common-Factor Approach for Multivariate Data Cleaning with an Application to Mars Phoenix Mission Data
Data quality is fundamentally important to ensure the reliability of data forstakeholders to make decisions. In real world applications, such as scientificexploration of extreme environments, it is unrealistic to require raw datacollected to be perfect. As data miners, when it is infeasible to physicallyknow the why and the how in order to clean up the data, we propose to seek theintrinsic structure of the signal to identify the common factors ofmultivariate data. Using our new data driven learning method, the common-factordata cleaning approach, we address an interdisciplinary challenge onmultivariate data cleaning when complex external impacts appear to interferewith multiple data measurements. Existing data analyses typically process onesignal measurement at a time without considering the associations among allsignals. We analyze all signal measurements simultaneously to find the hiddencommon factors that drive all measurements to vary together, but not as aresult of the true data measurements. We use common factors to reduce thevariations in the data without changing the base mean level of the data toavoid altering the physical meaning.
O'Neil GD, Weber AW, Buiculescu R, et al., 2014, Electrochemistry of Aqueous Colloidal Graphene Oxide on Pt Electrodes, LANGMUIR, Vol: 30, Pages: 9599-9606, ISSN: 0743-7463
Kounaves SP, Chaniotakis NA, Chevrier VF, et al., 2014, Identification of the perchlorate parent salts at the Phoenix Mars landing site and possible implications, ICARUS, Vol: 232, Pages: 226-231, ISSN: 0019-1035
Kounaves SP, Carrier BL, O'Neil GD, et al., 2014, Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: Implications for oxidants and organics, ICARUS, Vol: 229, Pages: 206-213, ISSN: 0019-1035
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