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The presence of liquid water on the surface and subsurface of Mars has been of interest because liquid water is essential for life as we know it. While pure liquid water is typically not stable on ...

The Joint Workshop on Induced Special Regions convened scientists and planetary protection experts to assess the potential of inducing special regions through lander or rover activity. An Induced Special Region is defined as a place where the presence of the spacecraft could induce water activity and temperature to be sufficiently high and persist for long enough to plausibly harbor life. The questions the workshop participants addressed were: (1) What is a safe stand-off distance, or formula to derive a safe distance, to a purported special region? (2) Questions about RTGs (Radioisotope Thermoelectric Generator), other heat sources, and their ability to induce special regions. (3) Is it possible to have an infected area on Mars that does not contaminate the rest of Mars? The workshop participants reached a general consensus addressing the posed questions, in summary: (1) While a spacecraft on the surface of Mars may not be able to explore a special region during the prime mission, the safe stand-off distance would decrease with time because the sterilizing environment, that is the martian surface would progressively clean the exposed surfaces. However, the analysis supporting such an exploration should ensure that the risk to exposing interior portions of the spacecraft (i.e., essentially unsterilized) to the martian surface is minimized. (2) An RTG at the surface of Mars would not create a Special Region but the short-term result depends on kinetics of melting, freezing, deliquescence, and desiccation. While a buried RTG could induce a Special Region, it would not pose a long-term contamination threat to Mars, with the possible exception of a migrating RTG in an icy deposit. (3) Induced Special Regions can allow microbial replication to occur (by definition), but such replication at the surface is unlikely to globally contaminate Mars. An induced subsurface Special Region would be isolated and microbial transport away from subsurface site is highly improbable.

A strong, repeatable seasonal cycle in the background methane mixing ratio has been observed at the Gale Crater landing site of the Mars Science Laboratory rover with the Tunable Laser Spectrometer of the Sample Analysis at Mars instrument. However, as of yet, no physical process has been proposed that can explain both the timing and amplitude of the observations. Here we show that a one-dimensional numerical model considering adsorption onto and diffusion through the regolith can reproduce the variation, including a phase lag, if the regolith is impregnated with methane from a prior plume or supplied from below by microseepage. Combining the model results with geological constraints, we estimate that the amount of microseepage at Gale is at most 3 × 10−5 tonnes km−2 yr−1. Gale’s unique dynamical environment makes such seeps easier to detect in surface sampling measurements. Over most of the Martian surface, atmospheric mixing is stronger or atmospheric transport more effective, and we expect the amplitude of the seasonal cycle to be smaller for the same strength of seep. The seasonal cycle in the methane mixing ratio observed at Gale Crater on Mars can be explained by adsorption onto and diffusion through the regolith, suggests a one-dimensional numerical model with geological constraints.

Water vapor is likely being exchanged between the regolith and the atmosphere on Mars, according to evidence from multiple landing sites (including Gale Crater), satellite measurements and numerical modeling. The mechanism of this exchange is largely unknown but could involve the formation of water frost, the adsorption of thin films of water onto mineral surfaces, or the deliquescence or hydration of salts. Hydration, a solid-solid phase transition during which water molecules are incorporated into a crystal structure in stoichiometric amounts, is possible for many salts found at Gale Crater and elsewhere on Mars. These salts may therefore be acting as a source and sink for water vapor in the Martian regolith. Furthermore, salt hydration state may be used as a marker for the presence of liquid water on present-day Mars. For example, the hydrated, crystalline perchlorate and chloride salts detected at recurring slope lineae (RSL) locations have been proposed to form from liquid brines rather than by experiencing hydration by atmospheric water vapor. Here we use an environmental cell coupled to a Raman microscope to experimentally study the hydration and dehydration of magnesium chloride (MgCl2), calcium perchlorate (Ca(ClO4)2), and calcium chloride (CaCl2) with the goal of determining which of these salts are capable of experiencing hydration on diurnal time scales. Other potential hydration phase transitions of chlorine-containing salts are thought to be less likely. Specifically, we study the transition between magnesium chloride tetrahydrate and hexahydrate, anhydrous calcium perchlorate and hydrated calcium perchlorate, and calcium chloride dihydrate and hexahydrate. We find that under conditions measured by the REMS instrument at Gale Crater, some chlorine-containing salts can readily hydrate and other salts can readily dehydrate, but no salt system studied here is likely to undergo both processes at the surface on diurnal time scales. With respect to RSL formation, these experiments suggest that atmospheric hydration of these salt systems may be too slow or otherwise not feasible. Hence, hydrated salts formed recently at active RSL locations on Mars may indeed be an indicator of the presence of liquid water.

Chlorine is ubiquitous on Mars, some of it in the form of oxy-chlorine salts. Chlorine-containing salts have been found at several landing sites, including that of Phoenix and Curiosity, in the form of perchlorates and chlorides. Several intermediate states also exist, of which chlorate is the most stable. While perchlorates have received much attention in the past few years, chlorate salts are much less studied. The ratio of perchlorate to chlorate on Mars is not well-defined but may be approximately 1:1. Chlorate salts have similar properties to perchlorates: high solubility, low eutectic temperatures, and likely low deliquescence relative humidities. Laboratory studies were performed to determine the ability of sodium and magnesium chlorate salts to take up water vapor at low temperatures (296 K to 237 K). These studies were performed using a Raman microscope equipped with an environmental chamber and a single particle optical levitator equipped with a Raman spectrometer. The deliquescence of sodium chlorate (NaClO3) was found to be temperature-dependent with the average relative humidity (RH) values ranging from 68% RH at 296 K to 80% RH at 237 K. Additionally, there was a slight deviation between experimental deliquescence values for this salt and those predicted by equilibrium thermodynamics. The observed efflorescence (recrystallization) of NaClO3 occurred at lower RH values ranging from 18% RH at 264 K to 24% RH at 249 K, demonstrating the hysteresis common to salt recrystallization. Several experiments were performed below the reported eutectic temperature of NaClO3 which resulted in supercooling of the brine and depositional ice nucleation. Based on the supercooling effects observed during our experiments, a revised metastable eutectic temperature of 237 K is suggested for NaClO3 compared to the previously reported value of 252 K. Two phases of magnesium chlorate (Mg(ClO3)2) were observed and exhibited different water uptake behavior. The most common form of Mg(ClO3)2 appeared to be a hydrated, amorphous phase, Mg(ClO3)2 • X H2O(a) that continuously took up water when the RH was increased. This water uptake behavior was even observed at very low humidity values, 5.0 (±1.9)% RH, with little temperature dependence. This detectable water persisted down to RH values close to 0%, averaging 0.5 (±0.6)% RH with no visible temperature dependence. The deliquescence relative humidity (DRH) of the hexahydrate, Mg(ClO3)2 • 6 H2O, was found to range from 50.9 (± 7.5)% at 227 K to 55.8 (± 6.6)% at 224 K and was consistent with thermodynamic calculations. Under conditions measured by the Remote Environmental Monitoring Station (REMS) instrument at Gale Crater and conditions modeled in the shallow subsurface, magnesium chlorate, if present, likely interacts with water vapor during some diurnal cycles.

The Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) has now made continuous in-situ meteorological measurements for several martian years at Gale crater, Mars. Of importance in the search for liquid formation are REMS' measurements of ground temperature and in-air measurements of temperature and relative humidity, which is with respect to ice. Such data can constrain the surface and subsurface stability of brines. Here we use updated calibrations to REMS data and consistent relative humidity comparisons (i.e., w.r.t. liquid vs w.r.t. ice) to investigate the potential formation of surface and subsurface liquids throughout MSL's traverse. We specifically study the potential for the deliquescence of calcium perchlorate. Our data analysis suggests that surface brine formation is not favored within the first 1648 sols as there are only two times (sols 1232 and 1311) when humidity-temperature conditions were within error consistent with a liquid phase. On the other hand, modeling of the subsurface environment would support brine production in the shallow subsurface. Indeed, we find that the shallow subsurface for terrains with low thermal inertia ($\Gamma\lesssim 300$ J m$^{-2}$ K$^{-1}$ s$^{-1/2}$) may be occasionally favorable to brine formation through deliquescence. Terrains with $\Gamma\lesssim175$ J m$^{-2}$ K$^{-1}$ s$^{-1/2}$ and albedos of $\gtrsim0.25$ are the most apt to subsurface brine formation. Should brines form, they would occur around Ls 100$^{\circ}$. Their predicted properties would not meet the Special nor Uncertain Region requirements, as such they would not be potential habitable environments to life as we know it., Comment: 25 pages, 4 figures

Observed features such as recurring slope lineae suggest that liquid water may exist on the surface and near-subsurface of Mars today. The presence of this liquid water, likely in the form of a brine, has important implications for the present-day water cycle, habitability, and planetary protection policies. It is possible that this water is formed, at least partially, by deliquescence of salts, a process during which hygroscopic salts absorb water vapor from the atmosphere and form a saturated liquid brine. We performed laboratory experiments to examine the ability of Bacillus subtilis (B-168) spores, alone or mixed with calcium perchlorate salt (Ca(ClO

Perchlorate and chloride salts on Mars could readily absorb water vapor and deliquesce into aqueous solutions. The deliquescence relative humidity (RH) as well as the efflorescence (recrystallization) RH of several Mars-relevant salts are now well known; however, the conditions that could cause a brine to freeze are not well established. It is often assumed that ice formation will occur whenever the saturation with respect to ice, S ice , of the system is greater than or equal to unity; however, ice nucleation is often hindered due to a kinetic barrier. For ice to form, a critical cluster of the ice crystal must first be achieved, often requiring S ice > 1. Here we use a Raman microscope and an environmental cell to examine the RH and temperature conditions required for Mg(ClO 4 ) 2 and MgCl 2 brines to freeze into ice. By examining the salt phase present both optically and spectrally under different low temperature conditions, it is found that both salts exhibit S ice values much greater than unity, meaning that supersaturation readily occurs and brines can persist under conditions previously thought to lead to freezing. The RH range of ice formation for Mg(ClO 4 ) 2 from 218 to 245 K is 83–95%, respectively, corresponding to S ice = 1.30–1.54. The RH of ice formation for MgCl 2 ranges from 80 to 100% for temperatures between 221 and 252 K, corresponding to S ice = 1.30–1.35. In addition to ice nucleation, the deliquescence and efflorescence relative humidity values for MgCl 2 were determined. Two hydrates for MgCl 2 were observed, and exhibited different deliquescence relative humidity (DRH) values. The DRH for MgCl 2 ·4H 2 O was found to be 12.8 ± 0.3% at 243 K with slightly increasing DRH as temperature decreased. The DRH for MgCl 2 ·6H 2 O was found to be 31.3 ± 0.6% at 242 K with little temperature dependence. The DRH of MgCl 2 ·6H 2 O was measured below the previously reported eutectic, 240 K, suggesting that the eutectic might be incorrect or that there is a different relevant hydration state. The aqueous solutions of MgCl 2 recrystallized to the tetrahydrate at low RH in the range of 3–9% RH at temperatures 265–235 K. Together, the ice nucleation, DRH, and efflorescence relative humidity (ERH) results show that Mg(ClO 4 ) 2 and MgCl 2 brines on present day Mars may have the ability to exist for up to 2 h longer than previously predicted.

Synthetic lubricants are widely used for applications that require high thermal and oxidative stability. In order to facilitate new designs and applications for these fluids, we are measuring a suite of thermophysical and transport properties for lubricant base fluids and mixtures. As part of the property measurements, here, we report the global thermal decomposition kinetics of four polyol ester lubricant base oils, in addition to a fully qualified (MIL-PRF-23699) formulation. The fluids were heated in stainless steel ampule reactors and the extent of decomposition was measured by gas chromatography coupled with flame ionization detection (GC-FID), from which pseudo-first-order rate constants were derived. The rate constants for decomposition ranged from 1 × 10–8 s–1 at 500 K to 2 × 10–4 s–1 at 675 K. Arrhenius parameters across this temperature regime are also reported. Other techniques for chemical characterization applied in this work include gas chromatography with mass spectrometry (GC-MS), nuclear ...

There is significant interest in the potential existence of even small amounts of liquid brine on current Mars. It has been proposed that aqueous solutions could form on Mars via the deliquescence of hygroscopic salts in contact with atmospheric water vapor, and these hygroscopic salts have recently been detected in recurring slope linae (RSL). While past work has largely focused on perchlorate species, another Mars-relevant salt that has a low eutectic temperature and may be deliquescent is calcium chloride, CaCl 2 . This salt may be linked to RSL formation on Mars, and deliquescence of CaCl 2 is also known to be responsible for the only terrestrial RSL analog features known thus far: water tracks in the McMurdo Dry Valleys. Here we use Raman microscopy to monitor the low-temperature (223−273 K) deliquescence (solid to aqueous phase transition) and efflorescence (aqueous to solid phase transition) of two hydration states of CaCl 2 , the dihydrate and the hexahydrate. We find the deliquescence relative humidity (DRH) decreases with decreasing hydration state and with increasing temperature. Average DRH values over the temperature range studied are 15.8±3.5% RH for the dihydrate and 63.3±12.5% RH for the hexahydrate, making this salt at least as deliquescent as many perchlorate salts. A remarkable property of CaCl 2 is its ability to persist as metastable, supersaturated brine. Once an aqueous solution was formed, efflorescence (recrystallization) of the liquid did not occur until single-digit RH values were reached (3.9±2.4% RH on average). We show that temperature and relative humidity conditions in the martian subsurface are sufficient to allow deliquescence of CaCl 2 , and the resulting brines may persist for over half of a martian sol. Therefore, this salt could play a role in RSL formation, the martian water cycle, and have implications for the potential habitability of Mars.

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location.We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover.The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv).This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle.The large seasonal variation in the background and occurrences of higher temporary spikes (∼7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs., The authors thank the reviewers for constructive comments that greatly improved the manuscript. The research described here was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Funding: Funding from NASA’s Planetary Science Division is acknowledged by authors C.R.W., P.R.M., S.K.A., G.J.F., C.M., C.P.M., M.H.W., M.G.T., A.S., D.A., C.H.H., R.V.G., A.P., J.L.E., D.P.G., J.C.P., D.K., L.E.C., J.P.-G., S.C.R.R., M.D.S., D.M.H., M.L., J.C., R.W.Z., and A.R.V. R.N.-G. acknowledges funding from the National Autonomous University of Mexico and Consejo Nacional de Ciencia y Tecnología. J.E.M. and C.L.S. acknowledge funding from the Canadian Space Agency MSL participating scientist program. S.P.Sc. acknowledges funding from the UK Space Agency. A.-M.H. acknowledges funding from the Finnish Academy under grant 310509. J.P.-G. acknowledges funding from the Spanish Ministry of Economy and Competitiveness under contract ESP2016-79612-C3-1-R. Author contributions: C.R.W. and P.R.M. performed TLS-SAM instrument design, build, and testing (IDBT); surface operations (SO); test-bed activities (TBA); data analysis (DA); data correlations (DC); and science interpretation (SI). G.J.F. and C.M. performed IDBT, SO, TBA, and DA. S.K.A., J.E.M., C.P.M., C.L.S., A.S., D.A., B.S., P.J.C., C.F., P.-Y.M., R.V.G., C.H.H., A.P., J.L.E., D.P.G., S.P.Sa., and R.W.Z. performed SI. J.C. and A.R.V. performed SO. J.C.P., D.K., and L.E.C. performed IDBT. G.M., J.M.-T., J.G.-E., M.-P.Z., M.G.T., S.P.Sc., R.N.-G., A.V.-R., H.K., D.V.-M., M.D.S., A.-M.H., M.G., D.M.H., and M.L. performed DC. J.P.-G. and S.C.R.R. performed DC and SI. Competing interests: No potential conflicts of interest exist for any of the listed authors. Data and materials availability: The data described in this paper are publicly available from NASA’s Planetary Data System (PDS) under an arrangement with the Mars Science Laboratory (MSL) project at http://pds-geosciences.wustl.edu/missions/msl/sam. htm, under the run numbers given in table S2.

Due to their stability in low-temperature conditions, aqueous salt solutions are the favored explanation for potential fluid features observed on present-day Mars. A salt analog was developed to closely match the individual cation and anion concentrations at the Phoenix landing site as reported by the Wet Chemistry Laboratory instrument. “Instant Mars” closely replicates correct relative concentrations of magnesium, calcium, potassium, sodium, perchlorate, chloride, and sulfate ions. A Raman microscope equipped with an environmental cellprobed liquid water uptake and loss by Instant Mars particles in a Mars relevant temperature and relative humidity (RH) environment. Our experiments reveal that Instant Mars particles can form stable, aqueous solutions starting at 56 ± 5% RH between 235 K and 243 K and persist as a metastable, aqueous solution at or above 13 ± 5% RH. Particle levitation using an optical trap examined the phase state and morphology of suspended Instant Mars particles exposed to changing water vapor conditions at room temperature. Levitation experiments indicate that water uptake began at 42 ± 8% RH for Instant Mars particles at 293 K. As RH is decreased at 293 K, the aqueous Instant Mars particles transition into a crystalline solid at 18 ± 7% RH. These combined results demonstrate that Instant Mars can take up water vapor from the surrounding environment and transition into a stable, aqueous solution. Furthermore, this aqueous Instant Mars solution can persist as a metastable, supersaturated solution in low-RH conditions.

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.

The thermal decomposition kinetics of JP-7, JP-TS and JP-900 were studied, motivated by the need of the hypersonic vehicle community for a fuel that has a high degree of thermal stability. Decomposition reactions were performed at 375, 400, 425 and 450 °C in stainless-steel ampule reactors. In all cases, the pressure before decomposition was 34.5 MPa (5000 psi). Decomposition as a function of time at each temperature was quantified by analyzing the thermally stressed liquid phase using gas chromatography. These results were used to determine global first-order rate constants that approximate the overall decomposition rate of of each fuel. For JP-7, these first-order rate constants ranged from 1.79 × 10–5 s–1 at 375 °C to 3.02 × 10–4 s–1 at 450 °C. For JP-TS, the rate constants had values between 1.74 × 10–5 s–1 at 375 °C to 2.70 × 10–4 s–1 at 450 °C. For JP-900, the rate constants ranged from 1.03 × 10–5 s–1 at 375 °C to 3.60 × 10–4 s–1 at 450 °C. At all temperatures studied, these three fuels have simila...

The cetane number (CN) is a measure of the ignition quality of a fuel for compression-ignition engines according to the self-ignition delay. If the CN of a fuel is too low, chemical compounds known as CN improvers may be added to increase both the CN and performance of the fuel. The addition of CN improvers is dependent upon the detailed properties of the particular fuel. While many fuel properties are important for design, the vapor–liquid equilibrium, as described by volatility, is very sensitive to composition. In this work, we measured blends of diesel fuel with the following CN improvers: amyl nitrate, isoamyl nitrate, isoamyl nitrite, 2-ethylhexyl nitrate, and the multi-component CN improver PM-1, in diesel fuel by use of the advanced distillation curve (ADC) method to determine the amount of CN improver in the various distillate volume fractions. Tracking the CN improver throughout the volatility profile of diesel fuels provides valuable information for determining structural property relationships...

Recent surrogate diesel fuel mixture development identified the need for a multiply substituted, low cetane number, high molecular mass monocycloalkane component. On the basis of a thermophysical property evaluation and prediction, 1,3,5-triisopropylcyclohexane was chosen to serve this need. This fluid is not commercially available; therefore, very few thermophysical property measurements exist, and the thermal decomposition kinetics have not yet been investigated. In this work, we study the thermal decomposition kinetics of 1,3,5-triisopropylcyclohexane between 350 and 425 °C. The decomposition reactions were performed in stainless-steel ampule reactors. At each temperature, the extent of decomposition as a function of time was determined by analyzing the thermally stressed liquid phase by use of gas chromatography. These data were used to derive pseudo-first-order rate constants that ranged from 2.38 × 10–7 s–1 at 350 °C to 7.28 × 10–5 s–1 at 425 °C. The Arrhenius parameters of the thermal decomposition...

The use of fuel blends (incorporating fluids such as natural gas or gasoline) for compression ignition engines may aid in efforts to reduce nitrogen oxides (NOx) and particulate matter emission. The consideration and design of such blends is dependent upon the detailed properties of the particular blend. In this work, we measured blends of 10, 20, 30, 50, 70, 80, and 90% (v/v) gasoline in diesel fuel by use of the advanced distillation curve (ADC) method to determine the hydrocarbon classifications in the various volume fractions. This allows us to track the hydrocarbon families throughout the volatility profile and, most importantly, observe changes in the aromatic content of the distillate cuts. In addition, we have used the composition explicit data channel (a unique capability to sample composition throughout the distillation curve) of the ADC to access thermochemical data, and related this to the temperature data grid reported earlier. This was done by calculating a composite enthalpy of combustion b...

In recent years, environmental considerations, the potential for supply disruptions, and rising fuel prices have led to the development of turbine fuels produced from non-petroleum feedstocks. To determine the suitability of an alternative turbine fuel, it is important to characterize the fuel properties and assess the degree of departure of the alternative fuel characteristics from those of petroleum-derived fuels. One very important property to use for this purpose is the volatility, as expressed by the distillation curve. In this paper, we present advanced distillation curve measurements of three prototype alternative turbine fuels and compare the distillation curve, composition, and combustion enthalpy to those of the petroleum-derived turbine fuels JP-8 and JP-10. We studied a hydrotreated fuel derived from chicken fat, a fuel composed of hydrogenated pinene dimers derived from turpentine, and a gas–liquid fuel produced from natural gas via the Fischer–Tropsch process. We found that the distillation ...

In recent years, environmental considerations, the potential for supply disruptions, and rising fuel prices have led to the development of alternative diesel fuels produced from nonpetroleum feedstocks. It is important to characterize the properties of these fuels in order to assess the degree of departure of the alternative fuels from the petroleum-derived fuels. One of the most important properties to use for this purpose is the volatility, as expressed by the distillation curve. In this paper, we present advanced distillation curve measurements of three prototype alternative diesel fuels and compare the distillation curve, composition, and combustion enthalpy to those of petroleum-derived diesel fuel. We studied two Fischer–Tropsch diesel fuels, one synthesized from coal-derived gas and one produced from natural gas, and one renewable diesel fuel composed of hydrotreated animal and vegetable fats. We found that the distillation curves of the three alternative diesel fuels are similar to those of petrol...

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.

It has been reported by several groups that methane in the Martian atmosphere is both spatially and temporally variable. Gough et al. (2010) suggested that temperature dependent, reversible physical adsorption of methane onto Martian soils could explain this variability. However, it is also useful to consider if there might be chemical destruction of methane (and compensating sources) operating on seasonal time scales. The lifetime of Martian methane due to known chemical loss processes is long (on the order of hundreds of years). However, observations constrain the lifetime to be 4 years or less, and general circulation models suggest methane destruction must occur even faster ( 2 ·H 2 O 2 and JSC-Mars-1 with H 2 O 2 , were able to oxidize the complex organic compounds (sugars and amino acids) used in the Viking Labeled Release experiments, these analogs were unable to oxidize methane to carbon dioxide within a 72 h experiment. Sodium and magnesium perchlorate, salts that were recently discovered at the Phoenix landing site and are potential strong oxidants, were not observed to directly oxidize either the organic solution or methane. The upper limit reaction coefficient, α , was found to be −17 for methane loss on TiO 2 ·H 2 O 2 and −17 for methane loss on JSC-Mars-1 with H 2 O 2 . Unless the depth of soil on Mars that contains H 2 O 2 is very deep (thicker than 500 m), the lifetime of methane with respect to heterogeneous oxidation by H 2 O 2 is probably greater than 4 years. Therefore, reaction of methane with H 2 O 2 on Martian soils does not appear to be a significant methane sink, and would not destroy methane rapidly enough to cause the reported atmospheric methane variability.

Recent observations suggest methane in the martian atmosphere is variable on short spatial and temporal scales. However, to explain the variability by loss reactions requires production rates much larger than expected. Here, we report results of laboratory studies of methane adsorption onto JSC-Mars-1, a martian soil simulant, and suggest that this process could explain the observations. Uptake coefficient (γ) values were measured as a function of temperature using a high-vacuum Knudsen cell able to simulate martian temperature and pressure conditions. Values of γ were measured from 115 to 135 K, and the data were extrapolated to higher temperatures with more relevance to Mars. Adsorptive uptake was found to increase at lower temperatures and larger methane partial pressures. Although only sub-monolayer methane surface coverage is likely to exist under martian conditions, a very large mineral surface area is available for adsorption as atmospheric methane can diffuse meters into the regolith. As a result, significant methane may be temporarily lost to the regolith on a seasonal time scale. As this weak adsorption is fully reversible, methane will be re-released into the atmosphere when surface and subsurface temperatures rise and so no net loss of methane occurs. Heterogeneous interaction of methane with martian soil grains is the only process proposed thus far which contains both rapid methane loss and rapid methane production mechanisms and is thus fully consistent with the reported variability of methane on Mars.

Mineral aerosol is of interest due to its physiochemical impacts on the Earth's atmosphere. However, adsorbed organics could influence the chemical and physical properties of atmospheric mineral particles and alter their impact on the biosphere and climate. In this work, the heterogeneous uptake of a series of small organic acids on the swelling clay, Na-montmorillonite, was studied at 212 K as a function of relative humidity (RH), organic acid pressure and clay mass. A high vacuum chamber equipped with a quadrupole mass spectrometer and a transmission Fourier transform infrared spectrometer was used to detect the gas and condensed phases, respectively. Our results show that while the initial uptake efficiency was found to be independent of organic acid pressure, it increased linearly with increasing clay mass. Thus, the small masses studied allow access to the entire surface area of the clay sample with minimal effects due to surface saturation. Additionally, results from this study show that the initial uptake efficiency for butanoic (butyric) acid on the clay increases by an order of magnitude as the RH is raised from 0% to 45% RH at 212 K while the initial uptake efficiency of formic, acetic and propanoic (propionic) acids increases only slightly at higher humidities. However, the initial uptake efficiency decreases significantly in a short amount of time due to surface saturation effects. Thus, although the initial uptake efficiencies are appropriate for initial times, the fact that the uptake efficiency will decrease over time as the surface saturates should be considered in atmospheric models. Surface saturation results in sub-monolayer coverage of organic acid on montmorillonite under dry conditions and relevant organic acid pressures that increases with increasing humidity for all organic acids studied. Additionally, the presence of large organic acids may slightly enhance the water content of the clay above 45% RH. Our results indicate that heterogeneous uptake of organic acids on swelling clay minerals provides an important irreversible heterogeneous sink for these species.

Biosynthetic valencene, premnaspirodiene, and natural caryophyllene were hydrogenated and evaluated as high performance fuels. The parent sesquiterpenes were then isomerized to complex mixtures of hydrocarbons with the heterogeneous acid catalyst Nafion SAC-13. High density fuels with net heats of combustion ranging from 133-141 000 Btu gal(-1), or up to 13% higher than commercial jet fuel could be generated by this approach. The products of caryophyllene isomerization were primarily tricyclic hydrocarbons which after hydrogenation increased the fuel density by 6%. The isomerization of valencene and premnaspirodiene also generated a variety of sesquiterpenes, but in both cases the dominant product was δ-selinene. Ab initio calculations were conducted to determine the total electronic energies for the reactants and products. In all cases the results were in excellent agreement with the experimental distribution of isomers. The cetane numbers for the sesquiterpane fuels ranged from 20-32 and were highly dependent on the isomer distribution. Specific distillation cuts may have the potential to act as high density diesel fuels, while use of these hydrocarbons as additives to jet fuel will increase the range and/or time of flight of aircraft. In addition to the ability to generate high performance renewable fuels, the powerful combination of metabolic engineering and heterogeneous catalysis will allow for the preparation of a variety of sesquiterpenes with potential for pharmaceutical, flavor, and fragrance applications.

International audience; The mechanisms that can induce short term variations of methane in the Martian atmosphere, and thus explain the observations currently available, are yet to be discovered. Seasonal exchange with the regolith, caused by reversible adsorption, is expected to induce both spatial and time variability without the need for additional sources and sinks, thus avoiding difficulties raised by other scenarios. However, a comprehensive view of the role of reversible exchanges with the subsurface was still lacking. We have investigated the efficiency of such a process by implementing a coupled subsurface-atmosphere transport module in a Global Climate Model, taking into account both the thermodynamics and the kinetics of the adsorption process. It is based on recent experimental data on the adsorption of methane. We show that even with an optimistic set of parameters, and although the regolith can potentially take up a large fraction of the atmospheric reservoir, the seasonal variability induced by exchange with the subsurface is very limited. If a local plume is detected, however, the apparent decay rate of methane in the atmosphere can be affected by the regolith uptake. This study could be extended to any trace gas reacting with the regolith, to help interpret future in situ or orbital measurements.

Although critical to atmospheric modeling of stratospheric ozone depletion, selective heterogeneous nuclei that promote the formation of Type Ia polar stratospheric clouds (PSCs) are largely unknown. While mineral particles are known to be good ice nuclei, it is currently not clear whether they are also good nuclei for PSCs. In the present study, a high-vacuum chamber equipped with transmission Fourier transform infrared spectroscopy and a quadrupole mass spectrometer was used to study heterogeneous nucleation of nitric acid trihydrate (NAT) on two clay minerals-Na-montmorillonite and kaolinite-as analogs of atmospheric terrestrial and extraterrestrial minerals. The minerals are first coated with a 3:1 supercooled H2O/HNO3 solution prior to the observed nucleation of crystalline NAT. At 220 K, NAT formation was observed at low SNAT values of 12 and 7 on kaolinite and montmorillonite clays, respectively. These are the lowest SNAT values reported in the literature on any substrate. However, NAT nucleation exhibited significant temperature dependence. At lower temperatures, representative of typical polar stratospheric conditions, much higher supersaturations were required before nucleation was observed. Our results suggest that NAT nucleation on mineral particles, not previously treated with sulfuric acid, may not be an important nucleation platform for Type Ia PSCs under normal polar stratospheric conditions.

Perchlorate salts, recently discovered on Mars, are known to readily absorb water vapor from the atmosphere and deliquesce into the aqueous phase at room temperature. Here we study the deliquescence (crystalline solid to liquid transition) and efflorescence (liquid to crystalline solid transition) of perchlorate salts at low temperatures relevant to Mars. A Raman microscope and environmental cell were used to determine the deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of NaClO4 and Mg(ClO4)2 as a function of temperature and hydration state. We find that the deliquescence of anhydrous NaClO4 is only slightly dependent on temperature and occurs at ∼38% RH. The DRH of NaClO4⋅H2O increases with decreasing temperature from 51% at 273 K to 64% at 228 K. The DRH of Mg(ClO4)2⋅6H2O also increases with decreasing temperature from 42% at 273 K to 55% at 223 K. The efflorescence of both NaClO4 and Mg(ClO4)2 salt solutions occurs at a lower RH than deliquescence due to the kinetic inhibition of crystallization. For all temperatures studied, the ERH values of NaClO4 and Mg(ClO4)2 are 13% and 19%, respectively. These results indicate perchlorate salts can exist as metastable, supersaturated solutions over a wide range of RH and temperature conditions. Summer diurnal temperature and relative humidity cycles at low latitudes on Mars could allow the surface salts to be aqueous for several hours per day.