Present-day thermal and water activity environment of the Mars Sample Return collection

The Mars Sample Return mission intends to retrieve a sealed collection of rocks, regolith, and atmosphere sampled from Jezero Crater, Mars, by the NASA Perseverance rover mission. For all life-related research, it is necessary to evaluate water availability in the samples and on Mars. Within the first Martian year, Perseverance has acquired an estimated total mass of 355 g of rocks and regolith, and 38 μmoles of Martian atmospheric gas. Using in-situ observations acquired by the Perseverance rover, we show that the present-day environmental conditions at Jezero allow for the hydration of sulfates, chlorides, and perchlorates and the occasional formation of frost as well as a diurnal atmospheric-surface water exchange of 0.5-10 g water per m2 (assuming a well-mixed atmosphere). At night, when the temperature drops below 190 K, the surface water activity can exceed 0.5, the lowest limit for cell reproduction. During the day, when the temperature is above the cell replication limit of 245 K, water activity is less than 0.02. The environmental conditions at the surface of Jezero Crater, where these samples were acquired, are incompatible with the cell replication limits currently known on Earth.

Solubility Data of Potential Salts in the MgO-CaO-SO2-H2O-O2 System for Process Modeling

This review studies unwanted precipitation reactions, which can occur in SO2 absorption processes using a magnesium hydroxide slurry. Solubility data of potential salts in the MgO-CaO-SO2-H2O system are evaluated. The reviewed data can serve as a reliable basis for process modeling of this system used to support the optimization of the SO2 absorption process. This study includes the solubility data of MgSO3, MgSO4, Mg(OH)2, CaSO3, CaSO4, and Ca(OH)2 as potential salts. The solubility is strongly dependent on the state of the precipitated salts. Therefore, this review includes studies on the stability of different forms of the salts under different conditions. The solubility data in water over temperature serve as a base for modeling the precipitation in such system. Furthermore, influencing factors such as pH value, SO2 content and the co-existence of other salts are included and available data on such dependencies are reviewed. Literature data evaluated by the International Union of Pure and Applied Chemistry (IUPAC) are revisited and additional and newer studies are supplemented to obtain a solid base of accurate experimental values. For temperatures higher than 100 °C the available data are scarce. For a temperature range from 0 to 100 °C, the reviewed investigations and data provide a good base to evaluate and adapt process models for processes in order to map precipitations issues accurately.

Unanticipated Side Effects of Stratospheric Albedo Modification Proposals Due to Aerosol Composition and Phase

The Earth has now warmed ~1.0 °C since the period 1850–1900, due in large part to the anthropogenic addition of greenhouse gases to the atmosphere. Most strategies to address this warming have called for a reduction of emissions and, often, accompanying removal of greenhouse gases. Other proposals suggest masking the increased radiative forcing by an increase in particles and/or clouds to increase scattering of incoming solar radiation. Two related recent proposals have suggested addition of calcite particles to the stratosphere, which one model suggests may enhance ozone. Here we show that the interaction of calcite with acidic materials in the stratosphere results in a more complex aerosol than has been previously considered, including aqueous and hydrate phases that can lead to ozone loss. Our study suggests particle addition to the stratosphere could also perturb global radiative balance by affecting high altitude cloud formation and properties. Experimental and modeling results suggest particles will act as the nucleation sites for polar stratospheric cloud ice and, after sedimentation into the troposphere, impact cirrus clouds in the absence of other efficient ice nucleating particles. These results show that an overly simplistic set of assumptions regarding intentional particle emissions to the atmosphere can lead to incorrect estimates of the radiative effect and fail to identify unintended consequences.

Heterogeneous Occupancy and Vibrational Dynamics of Spatially Patterned Water Molecules

We performed first-principles molecular dynamics simulations of relatively dilute aqueous solutions of sulfate and thiosulfate dianions to analyze the structure, dynamics, and vibrational spectral properties of water molecules around the solute, especially the spatially patterned solvent molecules in the first solvation layer and the extended layers. This study also involves the investigation of dynamics of dangling OH groups in these layers and their role in patterning the water molecules around the dianions. Structural evaluation of the systems is carried out by radial distribution functions, number integrals, and spatial distribution functions. The lifetime of dangling OH groups inside the solvation shell is compared more to that of the bulk. By constructing the O-H groups in three ensembles (S1, S2, and S3) around the anion, we show that the frequency distribution of OH modes in the S1 ensemble show red-shifting for both sulfate and thiosulfate. The O-H groups in the S2 ensemble of the sulfate-water system show red-shifting by 10 cm^-1, while in the case of thiosulfate-water, these O-H groups show blue-shifting by 8 cm^-1. The water molecules in S1 and S2 subensembles have slower dynamics compared to those in the bulk (S3). The dynamics of various kinds of hydrogen bonds were characterized by hydrogen bond population correlation functions. The spectral diffusion of solvation shell O-H modes was performed through a frequency-time correlation function. We find a significant amount of orientational retardation of water molecules in the S1 layer and moderate retardation in the S2 layer as compared to that in the bulk, S3 layer. All these findings, the red shift of the OH stretching frequency in S1 and S2 layers, slowing down of the orientational dynamics of OH vectors in S1 and S2 layers, and less diffusivity of water in S1 and S2 layers, show the long-range kosmotropic effect of multivalent sulfate and thiosulfate oxyanions. Due to the long-range effect, heterogeneous occupancy of water molecules is observed, and the water molecules are found to arrange in a patterned manner in the vicinity of anions with varied local density.

Mapping magnesium sulfate salts from saline mine discharge with airborne hyperspectral data

Managing saline water discharges from mining operations is a global environmental challenge. Measuring the location and extent of surface efflorescence can indicate solute movement before changes in electrical conductivity (EC) are detected in waterways. We hypothesised through the use of a case study that ground-based reflectance spectrometry and airborne hyperspectral (450-2500 nm) analysis of surface efflorescence could be a rapid method for monitoring large regions of the surrounding environment, including downstream of remote mines. X-ray diffraction and X-ray fluorescence were used to determine mineralogy and elemental composition of surface salts around a uranium mine. Salt samples were found to be mixtures of magnesium sulfate. The reflectance of field spectra varied depending on the hydration of the mineral, mainly hexahydrite and starkeyite. A constrained energy minimisation technique was used to match the field reflectance spectra to the airborne data. Airborne matches were confirmed at the field sampling sites and surrounds. Salts were also detected at lower matches at mine water irrigation areas where excess mine water had previously been applied. Hence, hyperspectral remote sensing is a potentially rapid and sensitive method for mapping magnesium sulfates over large areas in operating and rehabilitated mines. It was successfully demonstrated as a tool for monitoring and assessment of efflorescence as a result of saline processes.

A slow-cooling-rate in situ cell for long-duration studies of mineral precipitation in cold aqueous environments on Earth and other planetary bodies

Liquid oceans and ice caps, along with ice crusts, have long been considered defining features of the Earth, but space missions and observations have shown that they are in fact common features among many of the solar system's outer planets and their satellites. Interactions with rock-forming materials have produced saline oceans not dissimilar in many respects to those on Earth, where mineral precipitation within frozen seawater plays a significant role in both determining global properties and regulating the environment in which a complex ecosystem of extremophiles exists. Since water is considered an essential ingredient for life, the presence of oceans and ice on other solar system bodies is of great astrobiological interest. However, the details surrounding mineral precipitation in freezing environments are still poorly constrained, owing to the difficulties of sampling and ex situ preservation for laboratory analysis, meaning that predictive models have limited empirical underpinnings. To address this, the design and performance characterization of a transmission-geometry sample cell for use in long-duration synchrotron X-ray powder diffraction studies of in situ mineral precipitation from aqueous ice-brine systems are presented. The cell is capable of very slow cooling rates (e.g. 0.3°C per day or less), and its performance is demonstrated with the results from a year-long study of the precipitation of the hydrated magnesium sulfate phase meridianiite (MgSO4·11H2O) from the MgSO4-H2O system. Evidence from the Mars Rover mission suggests that this hydrated phase is widespread on the present-day surface of Mars. However, as well as the predicted hexagonal ice and meridianiite phases, an additional hydrated sulfate phase and a disordered phase are observed.

MgSO4·11H2O and MgCrO4·11H2O based on time-of-flight neutron single-crystal Laue data

Hexaaquamagnesium(II) sulfate pentahydrate, [Mg(H2O)6]SO4·5H2O, and hexaaquamagnesium(II) chromate(II) pentahydrate, [Mg(H2O)6][CrO4]·5H2O, are isomorphous, being composed of hexaaquamagnesium(II) octahedra, [Mg(H2O)6](2+), and sulfate (chromate) tetrahedral oxyanions, SO4(2-) (CrO4(2-)), linked by hydrogen bonds. There are two symmetry-inequivalent centrosymmetric octahedra: M1 at (0, 0, 0) donates hydrogen bonds directly to the tetrahedral oxyanion, T1, at (0.405, 0.320, 0.201), whereas the M2 octahedron at (0, 0, ½) is linked to the oxyanion via five interstitial water molecules. Substitution of Cr(VI) for S(VI) leads to a substantial expansion of T1, since the Cr-O bond is approximately 12% longer than the S-O bond. This expansion is propagated through the hydrogen-bonded framework to produce a 3.3% increase in unit-cell volume; the greatest part of this chemically induced strain is manifested along the b* direction. The hydrogen bonds in the chromate compound mitigate ~20% of the expected strain due to the larger oxyanion, becoming shorter (i.e. stronger) and more linear than in the sulfate analogue. The bifurcated hydrogen bond donated by one of the interstitial water molecules is significantly more symmetrical in the chromate analogue.

Experimentally determined standard thermodynamic properties of synthetic MgSO(4)·4H(2)O (Starkeyite) and MgSO(4)·3H(2)O: a revised internally consistent thermodynamic data set for magnesium sulfate hydrates

The enthalpies of formation of synthetic MgSO(4)·4H(2)O (starkeyite) and MgSO(4)·3H(2)O were obtained by solution calorimetry at T=298.15 K. The resulting enthalpies of formation from the elements are [Formula: see text] (starkeyite)=-2498.7±1.1 kJ·mol(-1) and [Formula: see text] (MgSO(4)·3H(2)O)=-2210.3±1.3 kJ·mol(-1). The standard entropy of starkeyite was derived from low-temperature heat capacity measurements acquired with a physical property measurement system (PPMS) in the temperature range 5 K<T<300 K: [Formula: see text] (starkeyite)=254.48±2.0 J·K(-1)·mol(-1). Additionally, differential scanning calorimetry (DSC) measurements with a Perkin Elmer Diamond DSC in the temperature range 270 K<T<300 K were performed to check the reproducibility of the PPMS measurements around ambient temperature. The experimental C(p) data of starkeyite between 229 and 303 K were fitted with a Maier-Kelley polynomial, yielding C(p)(T)=107.925+0.5532·T-1048894·T(-2). The hydration state of all Mg sulfate hydrates changes in response to local temperature and humidity conditions. Based on recently reported equilibrium relative humidities and the new standard properties described above, the internally consistent thermodynamic database for the MgSO(4)·nH(2)O system was refined by a mathematical programming (MAP) analysis. As can be seen from the resulting phase diagrams, starkeyite is metastable in the entire T-%RH range. Due to kinetic limitations of kieserite formation, metastable occurrence of starkeyite might be possible under martian conditions.