The Sample Analysis at Mars (SAM) instrument suite detected SO2, H2S, OCS, and CS2 from similar to 450 to 800 degrees C during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a Martian surface sample during in situ EGA. SO2 (similar to 3-22 mu mol) is consistent with the thermal decomposition of Fe sulfates or Ca sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O-2 or H2O in the SAM oven are another candidate SO2 source. H2S (similar to 41-109nmol) is consistent with interactions of H2O, H-2 and/or HCl with reduced sulfur phases and/or SO2 in the SAM oven. OCS (similar to 1-5nmol) and CS2 (similar to 0.2-1nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe sulfates imply interaction with acid solutions whereas Ca sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of Martian surface materials.

The characterization of any organic molecules on Mars is a top-priority objective for the ExoMars European Space Agency-Russian Federal Space Agency joint mission. The main instrument for organic analysis on the ExoMars rover is the Mars Organic Molecule Analyzer (MOMA).

C-13/C-12 and N-15/N-14 isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce C-13 and N-15 isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both C-13 and N-15 due to galactic cosmic rays (GCRs) exposure can vary within 1.5-6 atoms/cm(3)/s depending on rocks' depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5-10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the "light," potentially "biological" C-13/C-12 ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e. g., 100 million years), cosmogenic changes in N-15/N-14 ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (N-15/N-14). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed.

Decomposition of oxalic acid in the presence of water was examined in a hydrothermal diamond-anvil cell up to 800 degrees C and 970-1480 MPa as a function of oxygen fugacity to assess its usefulness as a C-O-H fluid source in petrologic experiments. Fluid, vapor, and solid species were identified in situ at elevated temperature and pressure with Raman spectroscopy and optical microscopy. Under oxidizing conditions (buffered by the reaction NiO <-> Ni+1/2O(2)), oxalic acid decomposes to carbon dioxide and water. Under reducing conditions (buffered by the reaction Mo+O-2 <-> MoO2), oxalic acid decomposes to methane and hydrogen. Under unbuffered conditions, at intermediate oxygen fugacity (similar to O to 1 log units below the fayalite-quartz-magnetite buffer), oxalic acid disproportionates to graphite and minor methane and carbon dioxide. The results from the Ni-NiO-buffered and Mo-MoO2-buffered experiments result in observed fluid species that are similar to those predicted by previous investigations. However, there are substantial differences between our results and previous studies of oxalic acid decomposition in the unbuffered experiment that was within a log unit of the fayalite-magnetite-quartz (FMQ) buffer. These include the detection of aqueous C-H species at temperatures as low as 400 degrees C and a solid graphite-like phase at 800 degrees C. These differences can be explained if we consider that aqueous H-2 in our experiment reacted to form the C-H species, instead of being lost via diffusion through the H-2-permeable capsules used in previous studies. Consequently, for experiments within about 1 log unit of the FMQ buffer curve, oxalic acid is likely a poor choice for a C-O-H fluid source because the formation of graphitic carbon would result in significant deviations from the expected C-O-H fluid composition and concentration (i.e., CO2+H2O). At oxygen fugacities outside a log unit of FMQ, the observed fluid species are similar to those predicted by previous investigations and the use of oxalic acid as a C-O-H fluid source is permissible from the perspective of oxygen fugacity, although other system parameters (e.g., sample geometries, capsule thickness, capsule materials, gasket materials, wall thickness) must still be considered.

Motivation: This article presents Thresher, an improved technique for finding peak height thresholds for automated rRNA intergenic spacer analysis (ARISA) profiles. We argue that thresholds must be sample dependent, taking community richness into account. In most previous fragment analyses, a common threshold is applied to all samples simultaneously, ignoring richness variations among samples and thereby compromising cross-sample comparison. Our technique solves this problem, and at the same time provides a robust method for outlier rejection, selecting for removal any replicate pairs that are not valid replicates.

Table of Contents

An interesting characteristic of the pyroclastic glass bead deposits, select impact produced lithologies such as the "rusty rock" 66095, and unique lunar soils from the Apollo 16 landing site, is their unusual enrichments in Pb-204, Cd, Bi, Br, I, Ge, Sb, Tl, Zn, and Cl which indicates that portions of these sample contain a substantial volatile component. Sample 66095, a fine-grained, subophitic to ophitic polymict melt breccia, also hosts a pervasive low-temperature, volatile-rich, oxy-hydrated mineral assemblage. The volatile element enrichments in these assorted lunar lithologies have been attributed to a variety of extra-lunar and lunar processes, whereas the oxyhydration in 66095 has long been thought to represent either terrestrial alteration of lunar chlorides and Fe-Ni metal to beta FeO(OH,Cl) or indigenous lunar processes. In 66095, Cl is accommodated in FeO(OH,Cl), phosphates, and chlorides and is heterogeneously distributed. The low-temperature alteration occurs as rims around Fe-Ni metal and sulfide grains, and as dispersed grains in the adjacent matrix. Micro-Raman and transmission electron microscope (TEM) imaging indicate that akaganeite (beta FeO(OH,Cl)) is the dominant Fe0(OH) polymorph and is intergrown with goethite (alpha FeO(OH)) and hematite (alpha Fe2O3). TEM observations indicate a well-defined "nanometer-scale" stratigraphy" to the alteration. For example, kamacite (body centered cubic) --> face-centered cubic (fcc) Fe-Ni alloy --> lawrencite (FeCl2) --> akaganeite. The lunar lawrencite (Fe,Ni)Cl-2 in 66095 does not react directly to akaganeite on Earth. Rather, lawrencite exposed to terrestrial conditions reacts to form an amorphous Fe- and Cl-bearing phase, nano-crystalline goethite, and hematite. The morphology of these terrestrial alteration products is significantly different than that of the akaganeite occurring in 66095. The chlorine isotopic compositions of these volatile-rich samples are enriched in heavy Cl. For 66095, the delta Cl-32 ranges from +14.0 parts per thousand to +15.6 parts per thousand, whereas the delta Cl-32 for the volatile-rich A16 soils ranges from +5.6 parts per thousand to +15.7 parts per thousand. Based on these data it appears likely that the volatile element enrichments and the Cl isotopic fractionation observed in 66095 and the Apollo 16 soils did not result from extra-lunar additions, but are most likely indigenous to the Moon. Lawrencite was deposited on mineral surfaces at approximately 650 degrees C to 570 degrees C from a metal-chloride-bearing, H-poor gas phase. This gas phase was also responsible for the transport of other metals (e.g. Zn, Cu, Pb, Fe). The fractionation of Cl isotopes in the rusty rock can be attributed to fumarole processes in a low-H system. The origin and formation of the akaganeite is more enigmatic. The Cl-isotopes are consistent with it replacing lawrencite. However, numerous nanometer-scale observations are not consistent with a terrestrial origin and indicate multiple episodes of oxyhydration. (C) 2014 Elsevier Ltd. All rights reserved.

The Cometary Sampling and Composition (COSAC) experiment onboard the Philae lander is a combined Gas Chromatograph-Mass Spectrometer targeted to determine the organic composition of the nucleus of comet 67P/Churyumov-Gerasimenko. The COSAC flight-model mass spectrometer (FM-MS) was scheduled to sample volatile organic species from 67P's coma prior to Philae's detachment from the Rosetta orbiter in November 2014. It was again scheduled to sample subsequent to Philae's touchdown but prior to drilling operations, thereby retrieving measurements of volatiles from the surface of an unperturbed nucleus. This article evaluates the competence of COSAC mass spectrometers in identifying volatile organic species in both cometary and laboratory-simulated environments. The evaluation was conducted on an operationally optimized COSAC flight spare model mass spectrometer (FS-MS) maintained in ultra-high vacuum. The FS-MS obtained analytical measurements by "sniffing" several organic molecule mixtures of diverse chemical functional groups and molecules with broader molecular masses introduced into the vacuum vessel housing the instrument. The results demonstrate that COSAC produces mass fragmentation patterns of organic species similar to those in calibration standard mass spectra; it is able to identify various organic species within mixtures present at low concentrations (100 ppm); and it can identify fragmentation patterns of non-introduced unknown species and those with high molecular masses within organic mixtures. These observations successfully substantiate the potential of the FM-MS to make qualitative measurements of organic species both in the rarefied environment of the coma and in the relatively enriched nucleus surface. (C) 2014 Elsevier Ltd. All rights reserved.