11 research outputs found
Constraining the preservation of organic compounds in Mars analog nontronites after exposure to acid and alkaline fluids
The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as âtreated nontronitesâ) under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditionsEuropean Commission | Ref. FP7 n. 307496European Commission | Ref. H2020 n. 818602Ministerio de EconomĂa | Ref. MDM-2017-0737Ministerio de EconomĂa | Ref. ESP2017-89053-C2-1-
Tracking the weathering of basalts on Mars using lithium isotope fractionation models
An edited version of this paper was published by AGU. Copyright (2015) American Geophysical UnionLithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt-forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium - 7Li and 6Li - have a large relative mass difference (âŒ15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals - the source of Li - and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's historyData supporting our models and calculations are available as supporting information. The research leading to these results is a contribution from the Project âicyMARSââ, funded by the European Research Council, Starting Grant no 307496. This work was also partially supported by the European FEDER program and the Spanish Ministry of Science (MICINN) through the project CGL2011â30079. Comments by R. James and four anonymous reviewers helped us to clarify and strengthen our wor
Pyrite nanoparticles as a Fenton-like reagent for in situ remediation of organic pollutants
The Fenton reaction is the most widely used advanced oxidation process (AOP) for wastewater treatment. This study reports on the use of pyrite nanoparticles and microparticles as Fenton reagents for the oxidative degradation of copper phthalocyanine (CuPc) as a representative contaminant. Upon oxidative dissolution in water, pyrite (FeS2) particles can generate H2O2 at their surface while simultaneously promoting recycling of Fe3+ into Fe2+ and vice versa. Pyrite nanoparticles were synthesized by the hot injection method. The use of a high concentration of precursors gave individual nanoparticles (diameter: 20 nm) with broader crystallinity at the outer interfaces, providing a greater number of surface defects, which is advantageous for generating H2O2. Batch reactions were run to monitor the kinetics of CuPc degradation in real time and the amount of H2O2. A markedly greater degradation of CuPc was achieved with nanoparticles as compared to microparticles: at low loadings (0.08 mg/L) and 20 h reaction time, the former enabled 60% CuPc removal, whereas the latter enabled only 7% removal. These results confirm that the use of low concentrations of synthetic nanoparticles can be a cost effective alternative to conventional Fenton procedures for use in wastewater treatment, avoiding the potential risks caused by the release of heavy metals upon dissolution of natural pyrites
Long-lasting habitable periods in Gale crater constrained by glauconitic clays
International audienc
Hygroscopic Salts and the Potential for Life on Mars
13 pĂĄginas, ilustraciones y tablas estadĂsticas.Hygroscopic salts have been detected in soils in the northern latitudes of Mars, and widespread chloride-bearing
evaporitic deposits have been detected in the southern highlands. The deliquescence of hygroscopic minerals
such as chloride salts could provide a local and transient source of liquid water that would be available for
microorganisms on the surface. This is known to occur in the Atacama Desert, where massive halite evaporites
have become a habitat for photosynthetic and heterotrophic microorganisms that take advantage of the deliquescence
of the salt at certain relative humidity (RH) levels. We modeled the climate conditions (RH and
temperature) in a region on Mars with chloride-bearing evaporites, and modeled the evolution of the water
activity (aw) of the deliquescence solutions of three possible chloride salts (sodium chloride, calcium chloride,
and magnesium chloride) as a function of temperature. We also studied the water absorption properties of the
same salts as a function of RH. Our climate model results show that the RH in the region with chloride-bearing
deposits on Mars often reaches the deliquescence points of all three salts, and the temperature reaches levels
above their eutectic points seasonally, in the course of a martian year. The aw of the deliquescence solutions
increases with decreasing temperature due mainly to the precipitation of unstable phases, which removes ions
from the solution. The deliquescence of sodium chloride results in transient solutions with aw compatible with
growth of terrestrial microorganisms down to 252 K, whereas for calcium chloride and magnesium chloride it
results in solutions with aw below the known limits for growth at all temperatures. However, taking the limits of
aw used to define special regions on Mars, the deliquescence of calcium chloride deposits would allow for the
propagation of terrestrial microorganisms at temperatures between 265 and 253 K, and for metabolic activity (no
growth) at temperatures between 253 and 233 K.This work was supported by grants CGL2006-04658/BOS
and CGL2007-62875/BOS from the Spanish Ministry of Science
and Innovation and grant PIE-631A from the CSIC
(Spanish Research Council), and by the Helmholtz Association
through the research alliance ââPlanetary Evolution and
Life.ââ We greatly appreciate the comments and suggestions
of Dennis Powers and an anonymous reviewer, which
greatly improved the original manuscript.Peer reviewe
Constraining the preservation of organic compounds in Mars analog nontronites after exposure to acid and alkaline fluids
The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as âtreated nontronitesâ) under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditions
Stability against freezing of aqueous solutions on early Mars
4 pages.Many features of the Martian landscape are thought to have been formed by liquid water flow and water-related mineralogies on the surface of Mars are widespread and abundant. Several lines of evidence, however, suggest that Mars has been cold with mean global temperatures well below the freezing point of pure water. Martian climate modellers considering a combination of greenhouse gases at a range of partial pressures find it challenging to simulate global mean Martian surface temperatures above 273 K, and local thermal sources cannot account for the widespread distribution of hydrated and evaporitic minerals throughout the Martian landscape. Solutes could depress the melting point of water in a frozen Martian environment, providing a plausible solution to the early Mars climate paradox. Here we model the freezing and evaporation processes of Martian fluids with a composition resulting from the weathering of basalts, as reflected in the chemical compositions at Mars landing sites. Our results show that a significant fraction of weathering fluids loaded with Si, Fe, S, Mg, Ca, Cl, Na, K and Al remain in the liquid state at temperatures well below 273 K. We tested our model by analysing the mineralogies yielded by the evolution of the solutions: the resulting mineral assemblages are analogous to those actually identified on the Martian surface. This stability against freezing of Martian fluids can explain saline liquid water activity on the surface of Mars at mean global temperatures well below 273 K.Peer reviewe