Search

Cassini’s Visible and Infrared Mapping Spectrometer (VIMS) has provided evidence of several different hydrocarbons on the surface of Titan using seven atmospheric windows. Methane (CH4) and ethane (C2H6) are suggested to exist in both the liquid and solid states on Titan. Even if the average surface temperature (90–94 K) of Titan is clearly in the liquid stability field of both CH4 and C2H6, the particles can condense in the atmosphere (∼65 km for C2H6 and lower stratosphere for CH4 Anderson et al. in Icarus, 243:129–138, 2014) and precipitate allowing them to melt and/or sublimate. It is also suggested that these liquids can freeze on the surface due to evaporative cooling. We conducted a laboratory study at Titan surface conditions to determine the phase change of CH4 and C2H6 and to test if they would freeze on the surface of Titan. Using NIR reflectance spectroscopy, we calculated the reflectivity ratio ( $R_{\mathrm{solid}}/R_{\mathrm{liquid}}$ ) of CH4 and C2H6 of 1.08 and 1.36, respectively, suggesting an 8% increase in reflectivity for CH4 and a 36% increase for C2H6 during phase change. The low albedo in liquid phase for both CH4 and C2H6 is consistent with observations made by VIMS in both Titan’s northern and southern latitudes. We also find the evaporation rate of amorphous CH4 close to Titan conditions, which is $9.0 \pm 0.3 \times 10^{-5}~\mbox{kg}\,\mbox{s}^{-1}\,\mbox{m}^{-2}$ at 87 K and we estimated a sublimation rate of $0.22 \times 10^{-5}~\mbox{kg}\,\mbox{s}^{-1}\,\mbox{m}^{-2}$ at 83 K for a 1.5 bar N2 atmosphere. The freezing rate of ∼46 m/year for C2H6 was observed whereas, for CH4, we observed that CH4 does not freeze at 87 K due to a high N2 dissolution rate. However, the viscosity of CH4 increases with a decreasing temperature that results in amorphous CH4. The results show a remarkable difference between the formation of ice for two liquids with different N2 dissolution rates. Consequently, using the results obtained from the laboratory study we predict that the observed change is albedo during and after rainfall on Titan is caused by CH4 due to evaporative cooling processes.

In this study, the solubility of acetylene (or ethyne, C2H2) and ethylene (or ethene, C2H4) in liquid methane (CH4) and ethane (C2H6) has been experimentally determined at Titan surface temperature (90 K) and pressure (1.5 bars). As predicted by theoretical models, the solubilities of acetylene and ethylene are very large at Titan temperature and these species are most likely to be abundantly present in the lakes and as evaporites on the shores or dry lake beds. Our results indicate the solubility of 4.9 × 10−2 mole fraction for acetylene in methane and 48 × 10−2 mole fraction in ethane; for ethylene, 5.6 × 10−1 mole fraction in methane and 4.8 × 10−1 mole fraction in ethane. Assuming the mole fractions from atmospheric models in the lower stratosphere and equilibrium with the surface, we determined that the lakes on Titan that cover ∼400,000 km2 are not saturated. The liquid lakes on Titan act as an important reservoir for both acetylene and ethylene. Assuming difference of methane and ethane content in the lakes at different latitudes, the difference in solubility in liquid methane and ethane, solutes in lakes may change with the temporal evolution (such as; evaporation and condensation) over seasons and geological time scales.

Hydrated chlorine salts are expected to exist on a variety of planetary bodies, including inner planets such as Mars and outer planet satellites such as Europa. However, detection by remote sensing has been limited due to a lack of comparison data in spectral libraries. In addition, at low temperatures spectral features of many H2O-bearing species deviate from their room temperature behavior. Thus, we acquired spectra of NaCl, NaClO4·nH2O, MgCl2·nH2O, Mg(ClO4)2·6H2O, and Mg(ClO3)2·6H2O from 0.35 to 2.5 µm at both 298 and 80 K to observe the effects of temperature on diagnostic spectral features. In the near-infrared, the strongest spectral features often arise from water molecules. Increasing hydration states increases the depth and width of water bands. Interestingly, at low temperature these bands become narrower with sharper, better defined minima, allowing individual bands to be more easily resolved. We also measured frozen eutectic solutions of NaCl, MgCl2, and KCl. We show that while care must be taken to acquire laboratory spectra of all hydrated phases at the relevant conditions (e.g., temperature and pressure) for the planetary body being studied, chlorine salts do possess distinct spectral features that should allow for their detection by remote sensing.

Calcium perchlorate (Ca(ClO4)2) is a highly deliquescent salt that may exist on the surface of present-day Mars; however, its water uptake properties have not been well characterized at temperatures and relative humidity conditions relevant to Mars. Here, we quantify the deliquescent relative humidity (DRH) and efflorescent relative humidity (ERH) of Ca(ClO4)2 as a function of temperature (223–273 K) to elucidate its behavior on the surface of Mars. A Raman microscope equipped with an environmental cell was used to simulate Mars relevant temperature and relative humidity conditions and monitor deliquescence (solid to aqueous) and efflorescence (aqueous to solid) phase transitions of Ca(ClO4)2. Deliquescence and efflorescence were monitored visually using optical images and spectroscopically using Raman microscopy. We find that there is a wide range of deliquescence RH values between 5% and 55% RH. This range is due to the formation of hydrates in different temperatures regimes, with the higher DRH values occurring at the lowest temperatures. Experimental deliquescence results were compared to a thermodynamic model for three hydration states of Ca(ClO4)2. The model predicts that the higher hydration states deliquesce at a higher RH than the lower hydration states. Calcium perchlorate was found to supersaturate, with lower ERH values than DRH values. The ERH results were less dependent on temperature with an average 15 ± 4%, but values as low as 3 ± 2% were measured at 273 K. Levitation experiments were performed on single particles of Ca(ClO4)2 and Mg(ClO4)2 at 298 K. While efflorescence was observed around 15% RH for Mg(ClO4)2, the efflorescence of Ca(ClO4)2 was not observed, even when exposed to 1% RH at 298 K. Additionally, a 17-h experiment was conducted to simulate a martian subsurface diurnal cycle. This demonstrated Ca(ClO4)2 aqueous solutions can persist without efflorescing for the majority of a martian sol, up to 17 h under Mars temperature heating rates and RH conditions. We find that Ca(ClO4)2 aqueous solutions could persist for most of the martian sol under present-day conditions. The aqueous phase stability and metastability quantified for Ca(ClO4)2 under Mars relevant temperature and relative humidity conditions has important implications for the water cycle and the stability of liquid water on present day Mars.

A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.

Perchlorate salts, known to exist on Mars, can readily absorb water vapor and deliquesce into aqueous solutions even at low temperatures. The multiple soluble ionic species, such as chloride salts, present in the Martian subsurface may affect this deliquescence. Here we study the deliquescence (solid to aqueous transition) and efflorescence (aqueous to solid transition) of three perchlorate/chloride mixtures: KClO 4 /KCl at 253 K, NaClO 4 /NaCl at 243 and 253 K, and Mg(ClO 4 ) 2 /MgCl 2 at 243 and 253 K. A Raman microscope with an environmental cell was used to monitor the phase transitions of internally mixed ClO − 4 /Cl − particles as a function of the perchlorate mole fraction. The eutonic relative humidity (where deliquescence begins to occur regardless of ClO − 4 mole fraction), deliquescence relative humidity (DRH, where complete deliquescence occurs), and efflorescence relative humidity (ERH) were measured for several perchlorate mole ratios for each cation system. At the temperatures studied, the eutonic relative humidity was measured to be 28% RH for Mg(ClO 4 ) 2 /MgCl 2 mixtures, 38% RH for NaClO 4 /NaCl mixtures, and 82% RH for KClO 4 /KCl mixtures. The DRH depends on the perchlorate mole ratio, but is below the DRH of the least deliquescent (highest DRH) pure salt. When humidity is lowered around an aqueous salt mixture, we find that efflorescence occurs at an RH below the DRH due to the kinetic inhibition of crystallization. The ERH values of the salt solutions were as low as 5% RH for Mg(ClO 4 ) 2 /MgCl 2 mixtures, as low as 13% RH for NaClO 4 /NaCl mixtures, and as low as 66% RH for KClO 4 /KCl mixtures. The low eutonic RH values for the Na + and Mg 2+ perchlorate/chloride mixtures are important: wherever Mg(ClO 4 ) 2 and MgCl 2 or NaClO 4 and NaCl coexist at the temperatures studied, mixtures will contain a stable aqueous phase above 28 or 38% RH, respectively, regardless of the perchlorate mole fraction. This liquid water may persist until 5 or 13% RH, respectively.

Recent geomorphological observations as well as chemical and thermodynamic studies demonstrate that liquid water should be stable today on the Martian surface at some times of the day. In Martian conditions, brines would be particularly more stable than pure water because salts can depress the freezing point and lower the evaporation rate of water. Despite this evidence, no clear spectral signature of liquid has been observed so far by the hyperspectral imaging spectrometers OMEGA and CRISM. However, past spectral analysis lacks a good characterization of brines׳ spectral signatures. This study thus aims to determine how liquid brines can be detected on Mars by spectroscopy. In this way, laboratory experiments were performed for reproducing hydration and dehydration cycles of various brines while measuring their spectral signatures. The resulting spectra first reveal a very similar spectral evolution for the various brine types and pure water, with the main difference observed at the end of the dehydration with the crystallization of various hydrated minerals from brines. The main characteristic of this spectral behavior is an important decoupling between the evolution of albedo and hydration bands depths. During most of the wetting/drying processes, spectra usually display a low albedo associated with shallow water absorption band depths. Strong water absorption band depth and high albedo are respectively only observed when the surface is very wet and when the surface is very dry. These experiments can thus explain why the currently active Martian features attributed to the action of a liquid are only associated with low albedo and very weak spectral signatures. Hydration experiments also reveal that deliquescence occurs easily even at low temperature and moderate soil water vapor pressure and could thus cause seasonal darkening on Mars. These experiments demonstrate that the absence of water absorptions in CRISM in the middle afternoon does not rule out water activity and suggest future spectral investigations to identify water on the Martian surface.

We analyze the recalibrated in situ humidity measurements by the Phoenix lander, which landed at 68.2°N, 234.3°E and operated from Ls 78° through Ls 148°, ∼152 sols. Vapor pressures demonstrate significant day–night variations with values ranging from 0.005 Pa to 0.37 Pa, an order of magnitude lower than previously reported, and evening derived enthalpies less than that for a purely ice deposition-driven process, suggesting other water vapor sinks may contribute to the near-surface humidity at the martian polar regions.

Ligeia Mare, the second largest sea on Titan, resides in an endorheic basin dominated by seas in the northeastern polar region. Ligeia's shoreline morphology resembles terrestrial man-made reservoirs where water is dammed and valleys are flooded. Here we describe the mare and surrounding geologically diverse terrain including rugged highlands and lowlands, incised valleys, and smooth plains. Observations include active processes evidenced by drainage flow directions, areal extent of rivers and river valleys, sediment volume estimates, and varied drainage patterns. Headward erosion has carved valley and ridge systems in the flanks of the highlands, while the more distal highland plateau is mostly uncut by rivers or extensive erosion and contains smaller lakes, lakebeds, and mottled terrain.

Lattice-gas cellular automata are often considered as a particular case of cellular automata in which additional constraints apply, such as conservation of particles or spatial exclusion. But what about their updating? How to deal with non-perfect synchrony? Novel definitions of asynchronism are proposed that respect the specific hypotheses of lattice-gas models. These definitions are then applied to a swarming rule in order to explore the robustness of the global emergent behaviour. In particular, we compare the synchronous and asynchronous case, and remark that a paradoxical phenomenon, the anti-alignment of particles, is no longer observed when a small but not infinitesimal amount of asynchronism is added.

Isothermal microcalorimetry is a quick and simple method of determining the effect an additive or additive combination has on the parasitic reactions occurring as a function of state of charge. It can easily discriminate exactly where in the voltage range the additive is providing a benefit with just a single cycle. As a demonstrative example, the effect of varying concentrations of vinylene carbonate (VC) on a LiCoO2/graphite cell is examined. Machine-made pouch cells were used such that the cells were nominally identical except for the concentration of VC. The measured heat flow for the different cells is then identical except for the heat flow that results from parasitic reactions. It is shown that the presence of VC reduces parasitic reactions above 3.9 V, and continues to reduce these reactions with increasing state of charge. The heat flow during open circuit conditions at the top of charge also shows that the presence of VC dramatically reduces the heat due to parasitic reactions. Lithium-ion batteries are being used in an increasing number of applications that are demanding higher energy densities and longer lifetimes. The use of electrolyte additives is a common method that has shown to extend calendar and cycle life and reduce parasitic reactions such as the consumption of active lithium in forming and repairing the solid electrolyte interphase (SEI), electrolyte oxidation, transition metal dissolution, electrode damage, etc. 1 However, it is not very well understood how these additives are functioning and exactly where in the charge-discharge cycle they prove advantageous. One such example is with the popular additive, vinylene carbonate (VC). Several studies 2‐7 report that the increase in full cell lifetime is caused by VC being reduced on the surface of graphite, which forms a more stable SEI. More recent studies 8‐13 have challenged this thought, reporting that the benefit of VC arises primarily from limitingelectrolyteoxidationandpossibletransitionmetaldissolution reactionsatthepositiveelectrode.Therefore,itisofdistinctinterestto be able to determine the voltage-dependent advantage of a particular additive or additive combination, which can aid in the understanding of how these additives are extending lifetimes. Recently the technique of isothermal microcalorimetry has been combinedwithelectrochemicalmeasurements,whichhasbeenusedto examine the thermal behavior of several lithium-ion chemistries. 14‐21 More recently, Krause et al. 22 showed how to use this technique to separate the various contributions to the thermal power and isolate parasitic energy. In this paper, this technique is used to qualitatively compare the heat flow between cells that only vary in concentration of additive. In this case, with all other sources being identical, the measured difference in heat flow arises from differences in parasitic heat. This is done as a function of state of charge, providing a simple and quick method of determining exactly where and to what extent the additive is reducing parasitic reactions. As a demonstrative example, the effect of varying concentrations of VC on a LiCoO2/graphite cell is examined. Experimental General.— Machine-made 225 mAh LiCoO2 (LCO)/graphite pouch cells 0.4 cm thick × 2 cm wide × 3 cm high (obtained from Pred Materials Co.) were provided dry. The pouches were then filled with 0.75 g of 1M LiPF6 in 3:7 ethylene carbonate (EC):ethylmethyl carbonate (EMC) (Novolyte Technologies, now BASF) with various amounts of VC (Novolyte Technologies, now BASF) additive (0%, 0.5%, 2%, and 4% by weight) and then vacuum sealed. The electrodes

As a result of measurements acquired by the Cassini–Huygens mission of Titan’s near surface atmospheric composition and temperature, Titan conditions can now be simulated in the laboratory and samples can subsequently be subjected to those conditions. Titan demonstrates an active hydrological-like cycle with its thick atmosphere, dynamic clouds, polar lakes of methane and ethane, moist regolith, and extensive fluvial erosive features. Unlike Earth, Titan’s hydrological-like cycle likely involves several constituents, primarily methane and ethane. Here the properties of a new Titan simulation facility are presented, including conceptual methodology, design, implementation, and performance results. The chamber maintains Titan’s surface temperature and pressure, and the sample cryogenic liquids undergoing experimentation are condensed within the chamber itself. During the experiments, the evaporation rates of the sample liquids are directly determined by continually measuring mass. Constituents are analyzed utilizing a Fourier Transform Infrared Spectroscopy (FTIR), and vapor concentrations are determined using a gas chromatograph fitted with a Flame Ionization Detector (FID). All pertinent data is logged via computer. Under laboratory conditions, the direct measurements of the evaporation rates of methane, ethane, and mixtures thereof can be achieved. Among the processes to be studied are the effects of regolith on transport from the subsurface to the atmosphere, the freezing point depression effects of dissolved nitrogen, and the solubility of various relevant organic compounds.

Thin films of Si1−xOx were produced using combinatorial sputtering methods. X-ray diffraction studies of these films show that they are amorphous or nanostructured. The effect of oxygen content on the electrochemical performance of these materials was studied. The reversible specific capacity (between 0.005 and 0.9 V) agrees with the assumption that Si1−xOx is made up of amorphous silicon, which can react to form Li3.75Si, and amorphous SiO2, which reacts to form Li4SiO4. The irreversible capacity increases with oxygen content when measured to a potential limit of 0.9 V vs Li/Li+ but further Li can be extracted from sites presumably near oxygen up to a potential of 2.0 V vs Li/Li+. However, such potentials for the negative electrode would not be reached in a full Li-ion cell. This work shows that the oxygen content in Si1−xOx should be optimized to produce materials with a reasonable active/inactive ratio in order to have electrodes with the desired specific capacity, an appropriate irreversible capacity and an appropriate amount of inactive phase to buffer volume expansion.

The measured heat flow of graphite/NMC lithium ion cells under charging conditions show a characteristic and easily identifiable signal at the onset of lithium plating on the graphite electrode. A marked decrease in heatflow signals the full lithiation of the graphite host. The origin of this signal is shown to arise from the combined effects of entropy and cell over potentials. This signal allows for an accurate measure of the maximum amount of lithium intercalation possible in the host. Metallic lithium deposition begins within 5‐7 mAh/g after the heat flow begins to decrease. Two different types of graphite were examined; G25 and MCMB. The onset of lithium plating was detected at 336 mAh/g for the G25 graphite and 297 mAh/g for the MCMB graphite, yielding empirical formulas of Li0.888C6 and Li0.804C6, respectively. The effect of plated lithium on the electrode/electrolyte reactivity was also examined by precise measurement of the coulombic efficiency, parasitic thermal energy and cell capacity fade. These measurements then allowed for the calculation of the efficiency of lithium plating on the graphite surface: 0.98 and 0.97 for G25 and MCMB graphites, respectively.

[1] Phyllosilicates have been identified in some of the most highly cratered Noachian terrains on Mars. To study the effects of such impacts on the properties of phyllosilicates, we experimentally shocked six phyllosilicate minerals relevant to the Martian surface: montmorillonite, nontronite, kaolinite, prehnite, chlorite, and serpentine. The shock-treated samples were analyzed with X-ray diffraction (XRD), near- and mid-infrared (NIR and MIR) spectroscopy, Raman spectroscopy, cathodoluminescence (CL), and the shock pressures and temperatures in some were modeled using Autodyn modeling software. XRD data show that the structure of each mineral, except prehnite, underwent partial structural deformation or amorphization. We also found that while the NIR spectra of shocked samples were very similar to that of the original sample, the MIR spectra changed significantly. This may explain some of the discrepancies between CRISM/OMEGA data (NIR) and TES/THEMIS (MIR) observations of phyllosilicates on Mars. Quartz was identified as a secondary phase in the XRD of shocked chlorite.

Investigations of the mechanical properties of planetary analog materials are of great importance to improve future mission success and to enhance our understanding of the history and evolution of planetary surfaces and subsurfaces. Determining the stratigraphy of the subsurface using drills and penetrometers implies knowing the mechanical properties of the regolith. Therefore, we investigated the mechanical properties of Martian regolith analogs (JSC Mars-1 and an unaltered basaltic soil from Mojave desert). Penetration force is dependent on the bearing capacity factor (Nq) and the angle of internal friction which is found to be function of the level of compaction and increases with relative density. The bearing capacity factor (Nq) showed an exponential trend with the angle of internal friction. For Mojave soil, (Nq) increased from 64 to 338 with φ increasing from 32 to 41.3° while (Nq) increased from 161 to 3347 with φ increasing from 39.4 to 54.7° for JSC Mars-1. Based on estimation of the bearing capacity factor and the angle of internal friction, we predicted the force of penetration under the Martian gravity using a 1.2 cm diameter penetrometer. Under a bulk density of 1240 and 1500 kg m−3 in JSC Mars-1 and Mojave soil, 460 and 200 N is the estimated force to reach a depth of about 20 cm deep. Based on this investigation, distinguishing between different regolith layers on the subsurface of Mars is possible and observable using penetration force.

International audience; Liquid water may exist on the Martian surface today, albeit transiently and in a metastable state under the low atmospheric surface pressure. However, the identification of liquid water on Mars from observed morphological changes is hampered by our limited understanding of how metastable liquids interact with sediments. Here, we present lab experiments in which a block of ice melts and seeps into underlying sediment, and the resulting downslope fluid propagation and sediment transport are tracked. In experiments at Martian surface pressure, we find that pure water boils as it percolates into the sediment, inducing grain saltation and leading to wholesale slope destabilization: a hybrid flow mechanism involving both wet and dry processes. For metastable brines, which are more stable under Martian conditions than pure water, saltation intensity and geomorphological impact are reduced; however, we observed channel formation in some briny flow experiments that may be analogous to morphologies observed on Mars. In contrast, under terrestrial-like experimental conditions, there is little morphological impact of seeping water or brine, which are both stable. We propose that the hybrid flow mechanism operating in our experiments under Martian surface pressure could explain observed Martian surface changes that were originally interpreted as the products of either dry or wet processes.

Acetylene is thought to be abundant on Titan according to most photochemical models. While detected in the atmosphere, its likely presence at the surface still lacks physical evidence. It is thought that solid acetylene could be a major component of Titan’s lakes shorelines and dry lakebed, detected as the 5 μm-bright deposits with the Cassini/VIMS instrument. Acetylene could also be present under its liquid form as dissolved solids in Titan’s methane–ethane lakes, as emphasized by thermodynamics studies. This paper is devoted to the near-infrared spectroscopy study of acetylene under solid and liquid phases between 1 and 2.2 μm, synthesized in a Titan simulation chamber that is able to reproduce extreme temperature conditions. From experiments, we observed a ∼10% albedo increase between liquid acetylene at 193–188 K and solid acetylene at 93 K. Using the NIR spectroscopy technique we successfully calculated the reflectivity ratio of solid/liquid acetylene as 1.13. The second difference we observed between liquid and solid acetylene is a shift in the major absorption band detected at 1.54 μm, the shift of ∼0.01 μm occurring toward higher wavelength. In order to assess the detectability of acetylene on Titan using the Cassini/VIMS instrument, we adapted our spectra to the VIMS spectral resolution. The spectral band at 1.55 μm and a negative slope at 2.0 μm falls in the Cassini/VIMS atmospheric windows over several VIMS infrared spectels, thus Cassini/VIMS should be able to detect acetylene.

Clays form on Earth by near-surface weathering, precipitation in water bodies within basins, hydrothermal alteration (volcanic- or impact-induced), diagenesis, metamorphism, and magmatic precipitation. Diverse clay minerals have been detected from orbital investigation of terrains on Mars and are globally distributed, indicating geographically widespread aqueous alteration. Clay assemblages within deep stratigraphic units in the Martian crust include Fe/Mg smectites, chlorites and higher temperature hydrated silicates. Sedimentary clay mineral assemblages include Fe/Mg smectites, kaolinite, and sulfate, carbonate, and chloride salts. Stratigraphic sequences with multiple clay-bearing units have an upper unit with Al-clays and a lower unit with Fe/Mg-clays. The typical restriction of clay minerals to the oldest, Noachian terrains indicates a distinctive set of processes involving water-rock interaction that was prevalent early in Mars history and may have profoundly influenced the evolution of Martian geochemical systems. Current analyses of orbital data have led to the proposition of multiple clay-formation mechanisms, varying in space and time in their relative importance. These include near-surface weathering, formation in ice-dominated near-surface groundwaters, and formation by subsurface hydrothermal fluids. Near-surface, open system formation of clays would lead to fractionation of Mars’ crustal reservoir into an altered crustal reservoir and a sedimentary reservoir, potentially involving changes in the composition of Mars’ atmosphere. In contrast, formation of clays in the subsurface by either aqueous alteration or magmatic cooling would result in comparatively little geochemical fractionation or interaction of Mars’ atmospheric, crustal, and magmatic reservoirs, with the exception of long-term sequestration of water. Formation of clays within ice would have geochemical consequences intermediate between these endmembers. We outline the future analyses of orbital data, in situ measurements acquired within clay-bearing terrains, and analyses of Mars samples that are needed to more fully elucidate the mechanisms of martian clay formation and to determine the consequences for the geochemical evolution of the planet.

International audience; Typically viewed as a deterministic model of spatial computing, cellular automata are here considered as a collective system subject to the noise inherent to natural computing. The classical updating scheme is replaced by stochastic versions which either randomly update cells or disrupt the cell-to-cell transmission of information. We then use the novel updating schemes to probe the behaviour of Elementary Cellular Automata, and observe a wide variety of results. We study these behaviours in the scope of macroscopic statistical phenomena and microscopic analysis. Finally, we discuss the possibility to use updating schemes to probe the robustness of complex systems.

Copper substituted lithium iron phosphate, with the olivine structure, has been synthesized hydrothermally as dark-brown single crystals with 15% of the iron sites occupied by cupric ions. Single crystal X-ray diffraction and magnetic susceptibility,combined with Li solid state NMR studies performed on powder sample, showed that 5% of the lithium ions also reside on the iron site, giving the formula Li0.95[(Fe2+)0.70(Fe3+)0.10(Cu2+)0.15Li0.05)]PO4. The compound exhibits anisotropic magnetic susceptibility and orders antiferromagnetically at 48 K. The magnetic moments are aligned along [010] as in LiFePO4. The optical measurements indicate that the dark brown color originates from interionic d-d transitions. A part of the lithium ions can be cycled in an electrochemical cell, corresponding to the oxidation/reduction of the iron ions. An onset of a second electrochemical process is observed at about 4.1 V, tentatively attributed to the removal of Li ions from the Fe site. The first principles calculations i...

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 NaClO 4 and Mg(ClO 4 ) 2 as a function of temperature and hydration state. We find that the deliquescence of anhydrous NaClO 4 is only slightly dependent on temperature and occurs at ~ 38% RH. The DRH of NaClO 4 ·H 2 O increases with decreasing temperature from 51% at 273 K to 64% at 228 K. The DRH of Mg(ClO 4 ) 2 ·6H 2 O also increases with decreasing temperature from 42% at 273 K to 64% at 223 K. The efflorescence of both NaClO 4 and Mg(ClO 4 ) 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 NaClO 4 and Mg(ClO 4 ) 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.

The nakhlites Martian meteorites contain small proportions of Cu-Fe-Ni sulfide minerals; we have studied these sulfides in Northwest Africa (NWA) 998, Nakhla, Governador Valadares, and NWA 817 with optical microscopy, scanning electron microscope, and electron microprobe. The meteorites studied are thought to derive from the bottom, inner part and top of hypothetical nakhlite lava flow(s), respectively. Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are uniformly low (0.02 to 0.05 ± 0.03 vol%), i.e., a factor 5 lower than in shergottites. Sulfides occur within the glassy mesostasis, as composite two-phase Fe-Ti oxide-sulfide grains, intimately associated with interstitial grains or locally enclosed in postcumulus melt inclusions (e.g., Governador Valadares) in olivine. They exhibit a uniform low-Ni monoclinic pyrrhotite composition ± chalcopyrite. There is a gradation of sulfide grain sizes and textures across the nakhlites flow(s): droplets in NWA 817, resorbed blebs in Governador Valadares; more massive, true intercumulus blebs in Nakhla and NWA 998. These nakhlites also show evidence for sulfide weathering. Hot desert finds (e.g., NWA 998 and NWA 817) show a few percent fracture-filling iron (oxy) hydroxides of likely terrestrial origin. Original sulfides are 50% altered in our NWA 998 section, with iron (oxy) hydroxides at grain boundaries and as complete pseudomorphs. The compositions of unaltered pyrrhotites are homogeneous, close to that of the monoclinic endmember Fe7S8, and are too sulfur-rich to have been in chemical equilibrium with the late-magmatic redox state fixed by the fayalite-magnetite-quartz buffer. Therefore, the compositions of the pyrrhotites must have been altered during the later stages of magmatic crystallization, by assimilation of S-rich regolith and hydrothermal circulation.

An ESA-ASI organized workshop on the Martian methane brought together nearly one hundred enthusiastic participants to ESRIN, Frascati, Italy from world over – two thirds from Europe, one-fifth from the US, and the rest from other places. The program comprised thirteen hours of oral presentations, two hours of posters, and, most noteworthy, about five hours of discussions, over a three-day period from November 25th through the 27th, 2009. The topics cast a wide net, ranging from earth-based and space observations to their implications for potential geology and biology, from models and supporting laboratory measurements to future exploration of Mars. This is a synopsis of the main themes covered at the Workshop, many of which are discussed in detail in peerreviewed papers in this special issue.

The detection of phyllosilicates and sulfates on Mars has revealed a complex aqueous history which suggests distinct geochemical environments separated temporally and spatially. Recent observations by MRO CRISM in Mawrth Vallis have shown that phyllosilicate deposits exhibit a specific stratigraphy, which remains incompletely understood. Moreover, MER Spirit has evidenced association between phyllosilicates, amorphous silica and sulfates. We investigated the hypothesis that these parageneses resulted from the acidic weathering of older phyllosilicate deposits. We exposed nontronite (Fe-rich smectite), montmorillonite (Al-rich smectite) and kaolinite to H 2 SO 4 solutions at pH 0, 2 and 4, and at a temperature of 60 °C. After the acid treatment, a combination of mineralogical techniques was used to assess the degree of alteration of the three phyllosilicate minerals. XRF, XRD and ESEM measurements show that nontronite was the most unstable when acid leached, followed by montmorillonite and then kaolinite. Progressive acidic leaching of nontronite leads to alteration of the phyllosilicate to amorphous silica, along with Fe-sulfate and anatase, and the formation of an acidic Al,Fe-rich solution. Alteration of montmorillonite resulted in the formation of Fe-, Al-, Ca- and Mg-sulfates, and a Al-rich leaching solution. Comparatively, leaching of kaolinite resulted in the formation of Al-sulfates and a Al-rich solution as well, with only slight alteration of the primary mineralogical features. The effects of acid leaching of the phyllosilicates were also observed in NIR reflectance spectra, allowing a comparison with CRISM spectra from Mawrth Vallis. Based on our results, we propose a new model where acid leaching of mixed phyllosilicate deposits leads to kaolinite overlaying montmorillonite, which in turn caps Fe,Mg-smectites. Leaching of cations and subsequent evaporation leads to sulfate deposits, as supported by geochemical modeling, while amorphous silica remains as a residue. Depending on the intensity (pH) and length of exposure of acidic leaching, our model can explain the stratigraphic distribution of phyllosilicates, and the association of sulfates, silica and smectites.

The Optical Probe for Regolith Analysis (OPRA) is a spike-shaped subsurface analytical probe that will be delivered to a planet, asteroid, or cometary body by a lander and/or rover. OPRA will be pushed down into the subsurface to record near infrared spectra as a function of depth down to maximum of 50 cm. Therefore, knowledge of the required penetration force to specific depths can be helpful in estimating the length of the probe. Test probes covering the anticipated diameter (2.5, 1.9, 1.2 and 0.9 cm diameter) and tip angle (T.A. = 30°, 60°, 90° and 120°) of OPRA were inserted mechanically into dry playground sand. The results showed that tip angle does not have a major effect, while probe diameter and density of the regolith are the most important parameters. Increasing probe diameter from 0.9 to 1.9 cm (i.e. a factor of 2) leads to an increase in penetration force from 200 to 1000 N (i.e. a factor of 5) at 20 cm depth. An increase in bulk density (B.D.) from 1550 to 1700 kg m −3 leads to an increase in penetration force from 10 to 200 N at 20 cm depth. Bearing capacity theory was used to explain the downward movement of the penetrometer through regolith and showed good agreement with the experimental results. This model was then used to take into account the effect of gravity on other planetary bodies. We observed a good agreement between the theoretical model and results from penetration testings on the Moon by the Apollo missions. Since the maximum allowed force for penetration is the weight of the lander/rover on their targeted planetary surface, our results put a strong constraint on the maximum reachable depth without endangering the whole mission.

To test the effects of meteorite impacts on martian phyllosilicate deposits, we heated two smectites (nontronite and montmorillonite) to temperatures ranging from 350 °C to 1150 °C for durations of 4–24 h in two different atmospheres, under air and a steady flow of CO 2 . Samples were analyzed using X-ray diffraction (XRD) and near-infrared (NIR) and mid-infrared (MIR) reflectance spectroscopy. Interlayer water was lost after heating to temperatures of ∼400 °C. Between 400 °C and 700 °C, nontronite converted to an intermediary phase which conserved the XRD pattern of untreated nontronite with the exception of the 0 0 1 peak. Nanocrystalline high-temperature phases formed for both smectites at temperatures between 700 °C and 1000 °C. Finally, after being heated to temperatures above ∼1100 °C, the samples melted and recrystallized into secondary phases. Secondary high-temperature phases included sillimanite and cristobalite for both smectites plus hematite for nontronite. NIR and MIR reflectance spectra significantly evolved with increasing temperature. NIR spectra of smectites showed that 1.4 and 1.9 μm bands decrease in intensity and disappear above 700 °C. Similarly, the 2.2–2.3 μm metal–OH band showed a decrease in intensity as well as an overall shift towards lower wavelengths (for nontronite) due to the thermal resistance of the Al–OH bond compared to the Fe–OH bond. NIR spectra of montmorillonite showed a gradual increase in band depth up to temperatures between 500 °C and 600 °C, then decreased with increasing temperature. In the MIR spectra of samples heated to temperatures above ∼1100 °C, newly formed bands confirmed the secondary phases identified by XRD. Similarities between the NIR spectra of our heated samples and the phyllosilicates in some martian craters imply that these phyllosilicates were altered by the impact-generated heat and thus were not formed post-impact. In addition, NIR reflectance spectra provide a proxy for shock temperatures of smectites up to 700 °C while MIR is optimum for identification of high-temperature phases of smectites above 700 °C.

The crystalline Li–Si phases: LiSi, Li12Si7, Li7Si3, Li13Si4, Li15Si4, Li21Si5, and Li22Si5 are studied using density functional theory. Charge transfer is evaluated using the Atoms in Molecules method (Bader charge analysis), showing that the Li atoms donate approximately 0.73 electrons to Si atoms in all crystalline Li–Si phases. The electronic structures of the Li–Si phases are studied using both total and projected densities of states. Results confirm the understanding of Li–Si structures as Zintl-like phases. Phonon density of states are calculated for all structures and thermodynamic properties are calculated in the context of the harmonic approximation. Phonon contributions to the free energy of formation cause a loss of stability with increasing temperature which is more pronounced in the LiSi and Li15Si4 phases compared to their neighboring phases.

Dynamic models of the martian polar caps are in abundance, but most rely on the assumption that the rate of sublimation of CO 2 ice can be calculated from heat transfer and lack experimental verification. We experimentally measured the sublimation rate of pure CO 2 ice under simulated martian conditions as a test of this assumption, developed a model based on our experimental results, and compared our model's predictions with observations from several martian missions (MRO, MGS, Viking). We show that sun irradiance is the primary control for the sublimation of CO 2 ice on the martian poles with the amount of radiation penetrating the surface being controlled by variations in the optical depth, ensuring the formation and sublimation of the seasonal cap. Our model confirmed by comparison of MGS-MOC and MRO-HiRISE images, separated by 2–3 martian years, shows that ∼0.4 m are currently being lost from the south perennial cap per martian year. At this rate, the ∼2.4-m-thick south CO 2 perennial cap will disappear in about 6–7 martian years, unless a short-scale climatic cycle alters this rate of retreat.

Roumaite, (Ca,Na‚□) 3 (Ca,REE,Na) 4 (Nb,Ti)[Si 2 O 7 ] 2 (OH)F 3 , a new mineral species, occurs as a late-stage product in cavities of peralkaline nepheline syenites on Rouma Island, in the Los Archipelago, in Guinea; associated minerals are aegirine, albite, analcime, arfvedsonite, catapleiite, a eudialyte-group member, microcline, sodalite, sphalerite, steacyite and villiaumite. Roumaite is monoclinic, space group Cc , with cell parameters a 7.473(2), b 11.294(2), c 18.778(4) A, β 101.60(2)°, V 1552.5(6) A 3 , Z = 4. The modular structure of roumaite consists of stacks of tobermorite-like layers, “octahedral” layers and disilicate groups; it is closely related to dovyrenite.

We have investigated the evaporation of concentrated magnesium and ferrous sulfate, and magnesium and ferric chloride brines as possible sources for liquid water on the surface of Mars, with special emphasis on the effect of freezing and crystallization of solutions. Experimental evaporation rates range from 0.04 mm h− 1 for 25 wt.% MgSO4 at 271.9 K, to 0.19 mm h− 1 for 18 wt.% FeSO4 at 270.5 K. For chloride solutions, evaporation rates range from 0.09 mm h− 1 for 40 wt.% FeCl3 at 261.34 K, to 0.43 mm h− 1 for 20 wt.% MgCl2 at 267.2 K. These evaporation rates are significantly lower than for pure water, i.e. 1.35 mm h− 1 at 273 K. Using the Pitzer ion interaction model, we show that the decrease in evaporation rate is due to lower water activity in concentrated solutions, down to 0.91 for saturated MgSO4 and 0.97 for saturated FeSO4, at their eutectic temperatures. For saturated MgCl2 and FeCl3, the calculated water activities are 0.57 and 0.60 at their respective eutectic temperatures. In addition, we show that the water activity drops significantly when salts are crystallizing, down to 0.17 and 0.21 for MgSO4 and FeSO4, respectively. Our experiments and calculations show that the water activity and evaporation rate are dependent on the hydration state of the precipitating salt, which is in turn controlled by the temperature and the relative humidity. Low-hydration state salts precipitate at lower humidity, with lower evaporation rates. Our study suggests that martian brines could remain stable for longer periods of time, at low temperatures and low humidity, than previously thought. Brines formed from these salts would be a more stable source of water on Mars, thus beneficial for any putative martian life, past and/or present.

Gullies are widespread on slopes on the surface of Mars and have been investigated by numerous authors, yet their formation processes remain elusive. In an attempt to understand the possibility of a water-based origin for these forms, we undertook a series of flume experiments at Earth surface temperatures and pressures. Our objectives were to produce forms that resemble those most commonly observed on Mars, documenting their morphometric characteristics and identifying any statistically significant relationships between form and controlling factors of slope and flow rate. Experiments were conducted in a 1×1.5 m2 flume filled with medium grain size sand. The experiments were run over a slope angle range of 10–30°, corresponding to the range for gullies on Mars. Water from a constant-head tank fed through 5 mm silicone hose to a rotameter and then released just below the surface at the top of the slope. Gullies were produced at slope angle values of 10°, 20°, and 30° and flow rate values of 445, 705, 965, and 1260 mL min−1 at each angle. Eighteen parameters were identified and subsequently measured on each gully produced in the flume. Gully forms were successfully reproduced and displayed development of the fundamental morphological components observed on Mars: alcove, channel, and apron. Slope–gully form relationships for each component revealed the following results: higher slope angles formed shorter gullies with thicker apron deposits. Moreover, longer gullies were seen at higher flow rates. We concluded that forms visually similar to those observed on Mars can be created by water in the laboratory flume under terrestrial conditions. Morphometric parameters can be measured and permit identification of controlling factors. Experimental simulation of gullies appears possible with proper scaling of experimental parameters. Although not directly scalable to Mars, flume gully parameters may be used to develop numerical models in the future.

We have studied the sublimation of ice and water vapor transport through various thicknesses of clay (

We have studied the effect of wind velocity on the sublimation rate of pure water ice under martian conditions. Measurements were made for wind velocities ranging from 0.7 to 11.4 m s −1 , a typical range observed by the meteorological instruments on the surface of Mars, and at − 15 ° C a value typical of the daily high temperature for most of the year at the Pathfinder landing site. At this temperature, and for a low-humidity environment (relative humidity around 1%) sublimation rates increase following a linear trend of equation E S = 0.68 + 0.025 V ( E S is the sublimation rate in mm h −1 and V is the wind speed in m s −1 ). In high relative humidity (30–35%) atmospheres, the effect of wind velocity is negligible, and the sublimation rate remains nearly constant at 0.33 ± 0.04 mm h −1 . Pure forced convection theory did not provide a satisfying description of the data in terms of the range of values and their wind speed dependency. Therefore, a new semi-empirical expression for the sublimation rate that combines free and forced convection was developed using analogy with heat transfer models. Using this expression, sublimation rates of ice as a function of wind velocity for any temperature can be calculated. In general, temperature is more important that wind speed and atmospheric humidity in determining the rate of sublimation of ice on Mars.

In order to advance our understanding of the long-term stability of subsurface ice, the diurnal martian water cycle, and implications for liquid water, we determined diffusion coefficients and adsorption kinetics for the water vapor produced by the sublimation of ice buried beneath various layers of fine-grained ( 1.56 ± 0.53 × 10 −4 , 2.05 ± 0.82 × 10 −4 , and 3.42 ± 1.36 × 10 −4 m 2 s −1 for the 52.6 ± 8.3 at 270 K for 39.0 ± 6.4 at 267 K for 63–125 μm, and 54.3 ± 9.3 at 266 K for 125–250 μm, resulting in surface areas of 2.6 ± 0.1 × 10 4 , 1.7 ± 0.3 × 10 4 , 1.5 ± 0.3 × 10 4 m 2 kg −1 , respectively. These results suggest that while diffusion is too rapid to explain the purported diurnal cycle in water content of the atmosphere, adsorption is efficient and rapid, and does provide an effective mechanism to explain such a cycle. The present diffusion data suggest that very thin, 10 h at ∼224 K, just above the freezing point of saturated CaCl2. Temperatures can remain above ∼224 K over most of the planet, which means that water, even as saturated brine, will sublimate before the freezing point is reached and liquid could be formed. On the other hand, 1 m ice layers below 1 m of fine-grained basaltic regolith at 235 K and 10 Pa of atmospheric water could last 600 to 1300 years. At deeper depths and lower temperatures, ice could last since the last major obliquity change 400,000 years ago.

Protein adsorption on solid surfaces can be easily and accurately quantified by electron microprobe analysis using wavelength dispersive spectroscopy (WDS) to detect the carbon and nitrogen atoms within the protein. The method was calibrated by measurements of the carbon and nitrogen WDS signals for sputtered carbon and C0.72N0.28 films of known mass per unit area. Fibrinogen adsorption isotherms on silicon wafers and sputtered Ni film samples were studied using this method. The sensitivities for fibrinogen are about 20 ng/cm2 using carbon WDS, and about 60 ng/cm2 using nitrogen WDS with a circular electron beam of 50 μm diameter. The fibrinogen adsorption results on Si and Ni are in agreement with reported values in the literature. This study suggests that WDS studies are a reliable way to rapidly and automatically screen metallic biomaterials, including combinatorial libraries, in a quantitative manner for their protein affinity.

There is abundant evidence that liquid water once existed on the surface of Mars. Today's martian atmosphere is too thin to sustain the sort of greenhouse effect that could create a climate warm enough to support liquid water but, one theory goes, there may have been a carbon dioxide-rich atmosphere in the past. The apparent absence of carbonates and the low escape rates of carbon dioxide, however, have argued against that explanation. Now a thermodynamic study of clay minerals recently discovered by the OMEGA spectro-imaging instrument on-board Mars Express, has provided a clearer picture of the primitive geochemical conditions on Mars. What emerges is an atmosphere with very low carbon dioxide levels. Other greenhouse gases — methane seems the most likely — may therefore have been involved in sustaining a warm and wet climate on Mars. The apparent absence of carbonates and the low escape rates of carbon dioxide are indicative of an early Martian atmosphere with low levels of carbon dioxide. Calculations of aqueous equilibria of phyllosilicates that were recently observed on Mars now suggest low partial pressure of carbon dioxide at the time. This implies that other greenhouse gases may have played a key role in sustaining a warm and wet climate on early Mars. Images of geomorphological features that seem to have been produced by the action of liquid water have been considered evidence for wet surface conditions on early Mars1. Moreover, the recent identification of large deposits of phyllosilicates, associated with the ancient Noachian terrains2,3 suggests long-timescale weathering4 of the primary basaltic crust by liquid water2,5. It has been proposed that a greenhouse effect resulting from a carbon-dioxide-rich atmosphere sustained the temperate climate required to maintain liquid water on the martian surface during the Noachian6,7. The apparent absence of carbonates and the low escape rates of carbon dioxide8, however, are indicative of an early martian atmosphere with low levels of carbon dioxide. Here we investigate the geochemical conditions prevailing on the surface of Mars during the Noachian period using calculations of the aqueous equilibria of phyllosilicates. Our results show that Fe3+-rich phyllosilicates probably precipitated under weakly acidic to alkaline pH, an environment different from that of the following period, which was dominated by strongly acid weathering9 that led to the sulphate deposits identified on Mars10,11,12. Thermodynamic calculations demonstrate that the oxidation state of the martian surface was already high, supporting early escape of hydrogen. Finally, equilibrium with carbonates implies that phyllosilicate precipitation occurs preferentially at a very low partial pressure of carbon dioxide. We suggest that the possible absence of Noachian carbonates more probably resulted from low levels of atmospheric carbon dioxide, rather than primary acidic conditions13. Other greenhouse gases may therefore have played a part in sustaining a warm and wet climate on the early Mars.

Small amounts of methane have been detected in the atmosphere of Mars, though the actual sources of the gas remain unknown. Thermodynamic conditions on Mars suggest that gas clathrate hydrate deposits might exist at the polar caps and in some areas of the planetary subsurface. We review the literature available on the detection of methane in the martian atmosphere and the presence of gas clathrate hydrates on Mars. The possibility of martian methane clathrate deposits is established, and initial sources for the sequestered methane are discussed. Based on correlated data and information from disparate sources, we conclude that subsurface methane clathrate deposits are a possible immediate source for the observed atmospheric methane on Mars.

International audience; The Martian surface is covered by a fine-layer of oxidized dust responsible for its red color in the visible spectral range (Bibring et al., 2006;Morris et al., 2006). In the near infrared, the strongest spectral feature is located between 2.6 and 3.6μm and is ubiquitously observed on the planet (Jouglet et al., 2007;Milliken et al., 2007). Although this absorption has been studied for many decades, its exact attribution and its geological and climatic implications remain debated. We present new lines of evidence from laboratory experiments, orbital and landed missions data, and characterization of the unique Martian meteorite NWA 7533, all converging toward the prominent role of hydroxylated ferric minerals. Martian breccias (so-called “Black Beauty” meteorite NWA7034 and its paired stones NWA7533 and NWA 7455) are unique pieces of the Martian surface that display abundant evidence of aqueous alteration that occurred on their parent planet (Agee et al., 2013). These dark stones are also unique in the fact that they arose from a near surface level in the Noachian southern hemisphere (Humayun et al., 2013). We used IR spectroscopy, Fe-XANES and petrography to identify the mineral hosts of hydrogen in NWA 7533 and compare them with observations of the Martian surface and results of laboratory experiments. The spectrum of NWA 7533 does not show mafic mineral absorptions, making its definite identification difficult through NIR remote sensing mapping. However, its spectra are virtually consistent with a large fraction of the Martian highlands. Abundant NWA 7034/7533 (and paired samples) lithologies might abound on Mars and might play a role in the dust production mechanism.

Titan's polar lakes are thought to be predominantly composed of liquid ethane and methane; however, little is known on the ratio of these hydrocarbons in the lakes, and the stability and dynamics of these mixtures. Here we provide the first experimental constraints under Titan surface conditions of liquid hydrocarbon mixture evaporation. Our results are relevant to Titan's polar temperatures and pressures (∼92 K and 1.5 bar), and cover a wide range of methane–ethane compositions. We show that evaporation is negligible for pure ethane, but increases nearly linearly with increasing methane concentration. Early dissolution of N2 results in ternary mixtures evaporating, which is modeled by a ‘hybrid’ thermodynamic equilibrium approach combining Perturbed-Chain Statistical Associating Fluid Theory with a diffusion and buoyancy-driven mass flux model. The approach follows the experimental evaporation rate measurements presented in this study, and allows for the calculation of the corresponding liquid methane–ethane–nitrogen ratios. Such results along with Cassini inferred lake evaporation rates can be used to estimate the composition of Titan's polar liquids, and may have implications on their origin. Our results suggest that Ontario Lacus is predominantly composed of ethane (>50–80 mol%), indicating it may be a residual lake following extensive seasonal methane evaporation, and/or might be in contact with a subsurface liquid reservoir.

International audience; This paper illustrates how the multi-agent approach, or paradigm, can help in the modeling and the simulation of smart grids in the context ofMS4SG (a joint project between LORIA-INRIA and EDF R&D). Smart grids simulations need to integrate together pre-existing and heterogeneous models and their simulation software; for example modeling tools of the power grids, of telecommunication networks, and of the information and decision systems. This paper describes the use of MECSYCO as a valid approach to integrate these heterogeneous models in a multi-agent smart grid simulation platform. Several use cases show the ability of MECSYCO to effectively take into account the requirements of smart grids simulation in MS4SG.

The topic of this work is the problem solving issue using simple interacting entities. The main difficulty of such a method stems from the paradox between the complexity of the problem, on one side, and the conceptual and functional simplicity of the entities on the other side. In order to overcome this paradox, we propose a method based on a reactive multi-agent system. This solving principle points out the importance of the interaction, and their integration in the agents' environment. As for the use of such a system to solve a real problem, the environment plays a key role. First, it represents the problem to solve on both topological and dynamical points of view. Second, it takes action into the solving process by determining the collective evolution of the agents thanks to the implementation of a system's Physics. In this paper, we describe the solving model we propose and its validation through experimental test performed both on simulation and with real targets.

Visible and near-infrared spectroscopic properties have been measured on elemental iron experimentally weathered in simulated Martian atmosphere and correlated to mineralogical compositions determined by X-ray diffraction. Two main features are observed in the reflectance spectra, corresponding to two deep bands located at 0.9 and 3.1 μm, respectively the iron band and the hydration band. In early weathering stages both Fe2+ and Fe3+ bands are identified. In addition, whereas the water band position does not change with time, the Fe2+ band disappears, and the Fe3+ band shifts towards longer wavelength (from 0.88 to 0.92 μm) because of transition from Fe2+ phases (siderite) to Fe3+ phases (ferrihydrite and goethite). Apart from these spectral signatures, other bands more specific of each phase are not clearly evidenced, especially for siderite. This is due to relatively low abundance of siderite (

A short critical review is provided on two questions linking magnetism and possible early life on Mars: (1) Did Mars have an Earth-like internal magnetic field, and, if so, during which period and was it a requisite for life? (2) Is there a connection between iron minerals in the martian regolith and life? We also discuss the possible astrobiological implications of magnetic measurements at the surface of Mars using two proposed instruments. A magnetic remanence device based on magnetic field measurements can be used to identify Noachian age rocks and lightning impacts. A contact magnetic susceptibility probe can be used to investigate weathering rinds on martian rocks and identify meteorites among the small regolith rocks. Both materials are considered possible specific niches for microorganisms and, thus, potential astrobiological targets. Experimental results on analogues are presented to support the suitability of such in situ measurements.

A new method for the production of four-component (element or compound) combinatorial thin films is presented. The combinatorial thin film consists of nine continuous four-component regions producing planes in quaternary composition space. The method allows for the coverage of large continuous regions of quaternary or pseudoquaternary systems. The magnetron sputtering deposition method is mechanically simple and uses existing infrastructure. New software for the visualization of quaternary data is also presented. This software allows the straightforward identification of composition-dependent properties such as x-ray diffraction intensities. The new production method and software are demonstrated with a four-element combinatorial thin film containing Si, Sn, Co and C.

Magmatic sulfide mineralogy has been studied in 2 olivine-phyric shergottites (DaG 476 and SaU 005) and 4 basaltic shergottites (Zagami, Shergotty, Los Angeles, and NWA 480). Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are high (0.16 to 0.53 area percent) and correlate positively with abundances of Fe-Ti oxides. Sulfides are mesostasis minerals, being mostly interstitial grains or locally enclosed in post-cumulus melt inclusions (e.g., SaU 005) in olivine. Sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of Cu sulfides (chalcopyrite and/or cubanite). Hot desert finds (e.g., DaG 476) show abundant fracture-filling iron (oxy)hydroxides of probable terrestrial origin. Unaltered sulfides show metal-rich hexagonal pyrrhotite compositions with metal/sulfur (M/ S) ratio ranging between 0.936 ± 0.005 and 0.962 ± 0.01. This compositional range corresponds to the two-phase structural domain 2C + nC of the Fe-S system; however, the high-temperature disordered hexagonal 1C pyrrhotite structure would be in better agreement with magnetic properties of shergottites. Ni contents in pyrrhotite increase from Los Angeles (

Magnetic properties of 26 (of 32) unpaired Martian meteorites (SNCs) are synthesized to further constrain the lithology carrying Martian magnetic crustal sources. Magnetic properties of ultramafic cumulates (i.e., Chassigny, Allan Hills [ALH] 84001) and lherzolitic shergottites (ALH 77005, Lewis Cliff [LEW] 88516) are one or two orders of magnitude too weak to account for the crustal magnetizations, assuming magnetization in an Earth-like field. Nakhlites and some basaltic shergottites, which are the most magnetic SNCs, show the right intensity. Titanomagnetite is the magnetic carrier in the nakhlites (7 meteorites), whereas in most basaltic shergottites (11 meteorites) it is pyrrhotite. Dhofar (Dho) 378, Los Angeles, and NWA 480/1460 and 2046 are anomalous basaltic shergottites, as their magnetism is mainly due to titanomagnetite. Pyrrhotite should be among the candidate minerals for the magnetized Noachian crust.