The Wet Chemistry Laboratory on the Phoenix Mars Lander performed aqueous chemical analyses of martian soil from the polygon-patterned northern plains of the Vastitas Borealis. The solutions ...contained approximately 10 mM of dissolved salts with 0.4 to 0.6% perchlorate (ClO₄) by mass leached from each sample. The remaining anions included small concentrations of chloride, bicarbonate, and possibly sulfate. Cations were dominated by Mg²⁺ and Na⁺, with small contributions from K⁺ and Ca²⁺. A moderately alkaline pH of 7.7 ± 0.5 was measured, consistent with a carbonate-buffered solution. Samples analyzed from the surface and the excavated boundary of the approximately 5-centimeter-deep ice table showed no significant difference in soluble chemistry.
Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products. With ...this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants. A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas‐solid reactions. Because perchlorate‐rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate. We investigated gas phase pathways using a 1‐D photochemical model. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate.
Organic and inorganic carbon isotope records reflect the burial of organic carbon over geological timescales. Permanent burial of organic carbon in the crust or mantle oxidizes the surface ...environment (atmosphere, ocean and biosphere) by removing reduced carbon. It has been claimed that both organic and inorganic carbon isotope ratios have remained approximately constant throughout Earth's history, thereby implying that the flux of organic carbon burial relative to the total carbon input has remained fixed and cannot be invoked to explain the rise of atmospheric oxygen (Schidlowski, 1988; Catling and others, 2001; Holland, 2002; Holland, 2009; Kump and others, 2009; Rothman, 2015). However, the opposite conclusion has been drawn from the same carbon isotope record (Des Marais and others, 1992; Bjerrum and Canfield, 2004). To test these opposing claims, we compiled an updated carbon isotope database and applied both parametric and non-parametric statistical models to the data to quantify trends and mean-level changes in fractional organic carbon burial with associated uncertainties and confidence levels. We first consider a conventional mass-balance model where carbon input to surficial reservoirs is balanced by burial of sedimentary carbonates and organic carbon. For this model, statistical analysis implies fractional organic burial has increased over Earth history by a factor of 1.5 relative to organic burial at 3.6 Ga, with the 95 percent confidence interval ranging from factors of 1.2 to 2.0. An increase in organic burial by a factor of 1.2 cannot explain the rise of oxygen, whereas an increase by a factor of 2 could conceivably explain the rise of oxygen. There is, however, a highly significant and well constrained increase in organic burial from the Proterozoic to the Phanerozoic. We also analyze changes in the difference between carbonate and organic carbon isotopic ratios over Earth history. There is a statistically significant increase in this difference from the early to late Archean, possibly caused by increased biological fractionation due to methanotrophic recycling. This transition is consistent with the evolution of oxygenic photosynthesis at 2.8 Ga or earlier. Finally, we explore how these conclusions change if we modify the traditional mass balance model to include other carbon cycle fluxes, specifically ocean crust carbonatization and authigenic carbonates. Because the size of these fluxes has a large, poorly constrained range, our statistical analysis with this uncertainty implies that the carbon isotope record does not constrain the history of organic burial at all. However, it remains possible that the magnitude of these additional processes has been inconsequential throughout geologic time, in which case conclusions from the conventional model would be valid.
•Supercooling of 10–15°C is common in MgSO4, MgCl2, NaCl, and NaClO4 solutions.•Mg(ClO4)2 and Ca(ClO4)2 vitrify near −120°C.•Glasses are potentially important for habitability and the preservation of ...organics.
Salt solutions on Mars can stabilize liquid water at low temperatures by lowering the freezing point of water. The maximum equilibrium freezing-point depression possible, known as the eutectic temperature, suggests a lower temperature limit for liquid water on Mars; however, salt solutions can supercool below their eutectic before crystallization occurs. To investigate the magnitude of supercooling and its variation with salt composition and concentration, we performed slow cooling and warming experiments on pure salt solutions and saturated soil-solutions of MgSO4, MgCl2, NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2. By monitoring solution temperatures, we identified exothermic crystallization events and determined the composition of precipitated phases from the eutectic melting temperature. Our results indicate that supercooling is pervasive. In general, supercooling is greater in more concentrated solutions and with salts of Ca and Mg. Slowly cooled MgSO4, MgCl2, NaCl, and NaClO4 solutions investigated in this study typically supercool 5–15°C below their eutectic temperature before crystallizing. The addition of soil to these salt solutions has a variable effect on supercooling. Relative to the pure salt solutions, supercooling decreases in MgSO4 soil-solutions, increases in MgCl2 soil-solutions, and is similar in NaCl and NaClO4 soil-solutions. Supercooling in MgSO4, MgCl2, NaCl, and NaClO4 solutions could marginally extend the duration of liquid water during relatively warm daytime temperatures in the martian summer. In contrast, we find that Mg(ClO4)2 and Ca(ClO4)2 solutions do not crystallize during slow cooling, but remain in a supercooled, liquid state until forming an amorphous glass near −120°C. Even if soil is added to the solutions, a glass still forms during cooling. The large supercooling effect in Mg(ClO4)2 and Ca(ClO4)2 solutions has the potential to prevent water from freezing over diurnal and possibly annual cycles on Mars. Glasses are also potentially important for astrobiology because of their ability to preserve pristine cellular structures intact compared to solutions that crystallize.
Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) ...has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725°C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.
We perform a suite of smoothed particle hydrodynamics simulations to investigate in detail the results of a giant impact on the young Uranus. We study the internal structure, rotation rate, and ...atmospheric retention of the post-impact planet, as well as the composition of material ejected into orbit. Most of the material from the impactor's rocky core falls in to the core of the target. However, for higher angular momentum impacts, significant amounts become embedded anisotropically as lumps in the ice layer. Furthermore, most of the impactor's ice and energy is deposited in a hot, high-entropy shell at a radius of ∼3 R⊕. This could explain Uranus' observed lack of heat flow from the interior and be relevant for understanding its asymmetric magnetic field. We verify the results from the single previous study of lower resolution simulations that an impactor with a mass of at least 2 M⊕ can produce sufficiently rapid rotation in the post-impact Uranus for a range of angular momenta. At least 90% of the atmosphere remains bound to the final planet after the collision, but over half can be ejected beyond the Roche radius by a 2 or 3 M⊕ impactor. This atmospheric erosion peaks for intermediate impactor angular momenta (∼3 × 1036 kg m2 s−1). Rock is more efficiently placed into orbit and made available for satellite formation by 2 M⊕ impactors than 3 M⊕ ones, because it requires tidal disruption that is suppressed by the more massive impactors.
Chemical analyses of three Martian soil samples were performed using the Wet Chemistry Laboratories on the 2007 Phoenix Mars Scout Lander. One soil sample was obtained from the top ∼2 cm (Rosy Red) ...and two were obtained at ∼5 cm depth from the ice table interface (Sorceress 1 and Sorceress 2). When mixed with water in a ∼1:25 soil to solution ratio (by volume), a portion of the soil components solvated. Ion concentrations were measured using an array of ion selective electrodes and solution conductivity using a conductivity cell. The measured concentrations represent the minimum leachable ions in the soil and do not take into account species remaining in the soil. Described is the data processing and analysis for determining concentrations of seven ionic species directly measured in the soil/solution mixture. There were no significant differences in concentrations, pH, or conductivity, between the three samples. Using laboratory experiments, refinement of the surface calibrations, and modeling, we have determined a pH for the soil solution of 7.7(±0.3), under prevalent conditions, carbonate buffering, and PCO2 in the cell headspace. Perchlorate was the dominant anion in solution with a concentration for Rosy Red of 2.7(±1) mM. Equilibrium modeling indicates that measured Ca2+ at 0.56(±0.5) mM and Mg2+ at 2.9(±1.5) mM, are consistent with carbonate equilibrium for a saturated solution. The Na+ and K+ were 1.4(±0.6), and 0.36(±0.3) mM, respectively. Results indicate that the leached portion of soils at the Phoenix landing site are slightly alkaline and dominated by carbonate and perchlorate. However, it should be noted that there is a 5–15 mM discrepancy between measured ions and conductivity and another species may be present.
The Wet Chemistry Laboratory (WCL) on the Phoenix Mars Scout Lander analyzed soils for soluble ions and found Ca2+, Mg2+, Na+, K+, Cl−, SO42−, and ClO4−. The salts that gave rise to these ions can be ...inferred using aqueous equilibrium models; however, model predictions are sensitive to the initial solution composition. This is problematic because the WCL data is noisy and many different ion compositions are possible within error bounds. To better characterize ion concentrations, we reanalyzed WCL data using improvements to original analyses, including Kalman optimal smoothing and ion-pair corrections. Our results for Rosy Red are generally consistent with previous analyses, except that Ca2+ and Cl− concentrations are lower. In contrast, ion concentrations in Sorceress 1 and Sorceress 2 are significantly different from previous analyses. Using the more robust Rosy Red WCL analysis, we applied equilibrium models to determine salt compositions within the error bounds of the reduced data. Modeling with FREZCHEM predicts that WCL solutions evolve Ca–Mg–ClO4-rich compositions at low temperatures. These unusual compositions are likely influenced by limitations in the experimental data used to parameterize FREZCHEM. As an alternative method to evaluate salt assemblages, we employed a chemical divide model based on the eutectic temperatures of salts. Our chemical divide model predicts that the most probable salts in order of mass abundance are MgSO4·11H2O (meridianiite), MgCO3·nH2O, Mg(ClO4)2·6H2O, NaClO4·2H2O, KClO4, NaCl·2H2O (hydrohalite), and CaCO3 (calcite). If ClO3− is included in the chemical divide model, then NaClO3 precipitates instead of NaClO4·2H2O and Mg(ClO3)2·6H2O precipitates in addition to Mg(ClO4)2·6H2O. These salt assemblages imply that at least 1.3wt.% H2O is bound in the soil, noting that we cannot account for water in hydrated insoluble salts or deliquescent brines. All WCL solutions within error bounds precipitate Mg(ClO4)2·6H2O and/or Mg(ClO3)2·6H2O salts. These salts have low eutectic temperatures and are highly hygroscopic, which suggests that brines will be stable in soils for much of the Martian summer.
Cyanide plays a critical role in origin of life hypotheses that have received strong experimental support from cyanide-driven synthesis of amino acids, nucleotides, and lipid precursors. However, ...relatively high cyanide concentrations are needed. Such cyanide could have been supplied by reaction networks in which hydrogen cyanide in early Earth’s atmosphere reacted with iron to form ferrocyanide salts, followed by thermal decomposition of ferrocyanide salts to cyanide. Using an aqueous model supported by new experimental data, we show that sodium ferrocyanide salts precipitate in closed-basin, alkaline lakes over a wide range of plausible early Earth conditions. Such lakes were likely common on the early Earth because of chemical weathering of mafic or ultramafic rocks and evaporative concentration. Subsequent thermal decomposition of sedimentary sodium ferrocyanide yields sodium cyanide (NaCN), which dissolves in water to form NaCN-rich solutions. Thus, geochemical considerations newly identify a particular geological setting and NaCN feedstock nucleophile for prebiotic chemistry.
H₂O at the Phoenix Landing Site Smith, P.H; Tamppari, L.K; Arvidson, R.E ...
Science (American Association for the Advancement of Science),
07/2009, Volume:
325, Issue:
5936
Journal Article
Peer reviewed
The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5° and 148°). A shallow ice table was ...uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H₂O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO₃, aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.
PDF
