Abundance and Isotopic Composition of Gases in the Martian Atmosphere: First Results from the Mars Curiosity Rover

Repeated measurements of the composition of the Mars atmosphere from Curiosity Rover yield a (40)Ar/N2 ratio 1.7 times greater and the (40)Ar/(36)Ar ratio 1.6 times smaller than the Viking Lander values in 1976. The unexpected change in (40)Ar/N2 ratio probably results from different instrument characteristics although we cannot yet rule out some unknown atmospheric process. The new (40)Ar/(36)Ar ratio is more aligned with Martian meteoritic values. Besides Ar and N2 the Sample Analysis at Mars instrument suite on the Curiosity Rover has measured the other principal components of the atmosphere and the isotopes. The resulting volume mixing ratios are: CO2 0.960(+/- 0.007); (40)Ar 0.0193(+/- 0.0001); N2 0.0189(+/- 0.0003); O2 1.45(+/- 0.09) x 10(exp -3); and CO 5.45(+/- 3.62) x 10(exp 4); and the isotopes (40)Ar/(36)Ar 1.9(+/- 0.3) x 10(exp 3), and delta (13)C and delta (18)O from CO2 that are both several tens of per mil more positive than the terrestrial averages. Heavy isotope enrichments support the hypothesis of large atmospheric loss. Moreover, the data are consistent with values measured in Martian meteorites, providing additional strong support for a Martian origin for these rocks

Primordial argon isotope fractionation in the atmosphere of Mars measured by the SAM instrument on Curiosity and implications for atmospheric loss

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102170/1/grl51048.pd

The Search for Nitrates on Mars by the Sample Analysis at Mars (SAM) Instrument

Planetary models suggest that nitrogen was abundant in the early Martian atmosphere as N2 but it was lost by sputtering and photochemical loss to space, impact erosion, and chemical oxidation to nitrates. A nitrogen cycle may exist on Mars where nitrates, produced early in Mars' history, may have been later decomposed back into N2 by the current impact flux. Nitrates are a fundamental source of nitrogen for terrestrial microorganisms, and they have evolved metabolic pathways to perform both oxidation and reduction to drive a complete biological nitrogen cycle. Therefore, the characterization of nitrogen in Martian soils is important to assess habitability of the Martian environment, particularly with respect to the presence of nitrates. The only previous mission that was designed to search for soil nitrates was the Phoenix mission but N-containing species were not detected by TEGA or the MECA WCL. Nitrates have been tentatively identified in Nakhla meteorites, and if nitrogen was oxidized on Mars, this has important implications for the habitability potential of Mars. Here we report the results from the Sample Analysis at Mars (SAM) instrument suite aboard the Curiosity rover during the first year of surface operations in Gale Crater. Samples from the Rocknest aeolian deposit and sedimentary rocks (John Klein) were heated to approx 835degC under helium flow and the evolved gases were analyzed by MS and GC-MS. Two and possibly three peaks may be associated with the release of m/z 30 at temperatures ranging from 180degC to 500degC. M/z 30 has been tentatively identified as NO; other plausible contributions include CH2O and an isotopologue of CO, 12C18O. NO, CH2O, and CO may be reaction products of reagents (MTBSTFA/DMF) carried from Earth for the wet chemical derivatization experiments with SAM and/or derived from indigenous soil nitrogenated organics. Laboratory analyses indicate that it is also possible that <550degC evolved NO is produced via reaction of HCl with nitrates arising from the decomposition of perchlorates. All sources of m/z 30 whether it be martian or terrestrial will be considered and their implications for Mars will be discussed

Hydrogen isotope geochemistry of SNC meteorites

We report the yields and hydrogen isotopic compositions of water extracted by stepwise heating of eight whole-rock SNC meteorites. D/H values are consistent with terrestrial water at low temperatures and increase with temperature to values that far exceed terrestrial. The data are consistent with the water in the samples originating from two sources: a terrestrial component/contaminant, released largely at low temperature, and an extraterrestrial component, released at high temperature. The variation in δD values of the high-temperature hydrogen (∼+250 to +900 for the nakhlites, ∼+1200 to +2100 for the shergottites, and ∼+800 for ALH84001) could represent true variation of the δD of the extra-terrestrial water in the samples, or may reflect varying contributions of the terrestrial endmember, even at high temperature. The high δD values are consistent with a martian origin for the meteorites since the current martian atmosphere contains water with a δD of ∼+4000. The presence of alteration products in at least some of the samples suggests the D-enriched water was probably incorporated into the rocks through interaction at low temperature with aqueous crustal fluids that had exchanged with the martian atmosphere. Chassigny contains water that has terrestrial δD values at all temperatures (with the possible exception of the highest temperature step, with δD up to ∼+50), suggesting contamination of this sample by terrestrial water. Carbon and oxygen isotopic results for CO_2 extracted by stepwise heating are also reported. These data are consistent with formation of carbonates in the SNC meteorites by secondary processes on Mars (from fluids that had exchanged C and O with the atmosphere), perhaps in the same alteration events that formed the D-enriched minerals

Petrogenesis of the new lherzolitic shergottite Grove Mountains 99027: Constraints of petrography, mineral chemistry, and rare earth elements

We report petrography, mineral chemistry, and microdistribution of rare earth elements (REE) in a new lherzolitic shergottite, Grove Mountains (GRV) 99027. The textural relationship and REE patterns of minerals suggest precipitation of cumulus olivine and chromite, followed by equilibrium crystallization of a closed system with a bulk composition of the inferred intercumulus melt. Subsolidus equilibrium temperatures of pyroxenes and olivine range from 1100 to 1210 degrees C, based on a two-pyroxene thermometry and Ca partitioning between augite and olivine. Oxygen fugacity of the parent magma is 1.5-2.5 (av. 2.0 +/- 0.4) log units below the quartz-fayalite-magnetite (QFM) buffer at 960-1360 degrees C, according to the olivine-orthopyroxene-chromite barometer. The ilmenite-chromite barometer and thermometer show much wider ranges of oxygen fugacity (1.0-7.0 log unit below QFM) and temperature (1130-480 degrees C), suggesting subsolidus equilibration of the oxides at low temperatures, probably due to deep burial of GRV 99027 on Mars. The low oxygen fugacity and LREE depletion of the parent magma of GRV 99027 suggest low contamination by martian crust.Characteristics of GRV 99027 demonstrate similarity of lherzolitic shergottites, suggesting a high possibility of launch pairing or a homogeneous upper mantle of Mars if they were ejected by individual impact events. However, GRV 99027 probably experienced severe post-shock thermal metamorphism in comparison with other lherzolitic shergottites, based on the re-crystallization of maskelynite, the homogeneity of minerals, and the low subsolidus equilibrium temperatures between chromite and ilmenite.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Oxygen Isotopic Constraints on the Genesis of Carbonates from Martian Meteorite ALH84001

Ion microprobe oxygen isotopic measurements of a chemically diverse suite of carbonates from Martian meteorite ALH84001 are reported. The δ^(18)O values are highly variable, ranging from +5.4 to +25.3‰, and are correlated with major element compositions of the carbonate. The earliest-forming (Ca-rich) carbonates have the lowest δ^(18)O values and the late-forming (Mg-rich) carbonates have the highest δ^(18)O values. Two models are presented which can explain the isotopic variations. The carbonates could have formed in a water rich environment at relatively low, but highly variable temperatures. In this open-system case the lower limit to the temperature variation is ∼125°C, with fluctuations of over 250°C possible within the constraints of the model. Alternatively, the data can be explained by a closed-system model in which the carbonates precipitated from a limited amount of CO_2-rich fluid. This scenario can reproduce the isotopic variations observed at a range of temperatures, including relatively high temperatures (> 500°C). Thus the oxygen isotopic compositions do not provide unequivocal evidence for formation of the carbonates at low temperature. Although more information is needed in order to distinguish between the models, neither of the implied environments is consistent with biological activity. Thus, we suggest that features associated with the carbonates which have been interpreted to be the result of biological activity were most probably formed by inorganic processes

Oxygen Isotopic Constraints on the Genesis of Carbonates from Martian Meteorite ALH84001

Ion microprobe oxygen isotopic measurements of a chemically diverse suite of carbonates from Martian meteorite ALH84001 are reported. The δ^(18)O values are highly variable, ranging from +5.4 to +25.3‰, and are correlated with major element compositions of the carbonate. The earliest-forming (Ca-rich) carbonates have the lowest δ^(18)O values and the late-forming (Mg-rich) carbonates have the highest δ^(18)O values. Two models are presented which can explain the isotopic variations. The carbonates could have formed in a water rich environment at relatively low, but highly variable temperatures. In this open-system case the lower limit to the temperature variation is ∼125°C, with fluctuations of over 250°C possible within the constraints of the model. Alternatively, the data can be explained by a closed-system model in which the carbonates precipitated from a limited amount of CO_2-rich fluid. This scenario can reproduce the isotopic variations observed at a range of temperatures, including relatively high temperatures (> 500°C). Thus the oxygen isotopic compositions do not provide unequivocal evidence for formation of the carbonates at low temperature. Although more information is needed in order to distinguish between the models, neither of the implied environments is consistent with biological activity. Thus, we suggest that features associated with the carbonates which have been interpreted to be the result of biological activity were most probably formed by inorganic processes

Oxygen isotope and 26Al-26Mg systematics of aluminum-rich chondrules from unequilibrated enstatite chondrites

Correlated in situ analyses of the oxygen and magnesium isotopic compositions of aluminum-rich chondrules from unequilibrated enstatite chondrites were obtained using an ion microprobe. Among eleven aluminum-rich chondrules and two plagioclase fragments measured for 26Al-26Mg systematics, only one aluminum-rich chondrule contains excess 26Mg from the in situ decay of 26Al; the inferred initial ratio (26Al/27Al)o = (6.8 +/- 2.4) x 10^(-6) is consistent with ratios observed in chondrules from carbonaceous chondrites and unequilibrated ordinary chondrites.The oxygen isotopic compositions of five aluminum-rich chondrules and one plagioclase fragment define a line of slope ~0.6 +/- 0.1 on a three-oxygen-isotope diagram, overlapping the field defined by ferromagnesian chondrules in enstatite chondrites but extending to more 16O-rich compositions with a range in delta-18O of about ~12 ppm. Based on their oxygen isotopic compositions, aluminum-rich chondrules in unequilibrated enstatite chondrites are probably genetically related to ferromagnesian chondrules and are not simple mixtures of materials from ferromagnesian chondrules and calcium-aluminum-rich inclusions (CAIs).Relative to their counterparts from unequilibrated ordinary chondrites, aluminum-rich chondrules from unequilibrated enstatite chondrites show a narrower oxygen isotopic range and much less resolvable excess 26Mg from the in situ decay of 26Al, probably resulting from higher degrees of equilibration and isotopic exchange during post-crystallization metamorphism. However, the presence of 26Al-bearing chondrules within the primitive ordinary, carbonaceous, and now enstatite chondrites suggests that 26Al was at least approximately homogeneously distributed across the chondrite-forming region.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202