^1,2Andrew M. Turner, ^1,2Matthew J. Abplanalp, ^1,2Ralf I. Kaiser
The Astrophysical Journal 820, 127 Link to Article [http://dx.doi.org/10.3847/0004-637X/820/2/127]
¹Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA
²W. M. Keck Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA

Perchlorates—inorganic compounds carrying the perchlorate ion (${\mathrm{ClO}}_{4}{}^{-}$)—were discovered at the north polar landing site of the Phoenix spacecraft and at the southern equatorial landing site of the Curiosity Rover within the Martian soil at levels of 0.4–0.6 wt%. This study explores in laboratory experiments the temperature-dependent decomposition mechanisms of hydrated perchlorates—namely magnesium perchlorate hexahydrate (Mg(ClO4)2centerdot6H2O)—and provides yields of the oxygen-bearing species formed in these processes at Mars-relevant surface temperatures from 165 to 310 K in the presence of galactic cosmic-ray particles (GCRs). Our experiments reveal that the response of the perchlorates to the energetic electrons is dictated by the destruction of the perchlorate ion (${\mathrm{ClO}}_{4}{}^{-}$) and the inherent formation of chlorates (${\mathrm{ClO}}_{3}{}^{-}$) plus atomic oxygen (O). Isotopic substitution experiments reveal that the oxygen is released solely from the perchlorate ion and not from the water of hydration (H2O). As the mass spectrometer detects only molecular oxygen (O2) and no atomic oxygen (O), atomic oxygen recombines to molecular oxygen within the perchlorates, with the overall yield of molecular oxygen increasing as the temperature drops from 260 to 160 K. Absolute destruction rates and formation yields of oxygen are provided for the planetary modeling community.

¹Mia B. Olsen, ¹Daniel Wielandt, ¹Martin Schiller, ¹Elishevah M.M.E. Van Kooten, ¹Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.07.011]
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350, Denmark
Copyright Elsevier

We report on the petrology, magnesium isotopes and mass-independent 54Cr/52Cr compositions (μ54Cr) of 42 chondrules from CV (Vigarano and NWA 3118) and CR (NWA 6043, NWA 801 and LAP 02342) chondrites. All sampled chondrules are classified as type IA or type IAB, have low 27Al/24Mg ratios (0.04 to 0.27) and display little or no evidence for secondary alteration processes. The CV and CR chondrules show variable 25Mg/24Mg and 26Mg/24Mg values corresponding to a range of mass-dependent fractionation of ∼500 ppm (parts per million) per atomic mass unit. This mass-dependent Mg isotope fractionation is interpreted as reflecting Mg isotope heterogeneity of the chondrule precursors and not the result of secondary alteration or volatility-controlled processes during chondrule formation. The CV and CR chondrule populations studied here are characterized by systematic deficits in the mass-independent component of 26Mg (μ26Mg∗) relative to the solar value defined by CI chondrites, which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26Al compared to the canonical 26Al/27Al of ∼5 × 10–5. Model initial 26Al/27Al values of CV and CR chondrules vary from (1.5±4.0) × 10–6 to (2.2±0.4) × 10–5. The CV chondrules display significant μ54Cr variability, defining a range of compositions that is comparable to that observed for inner Solar System primitive and differentiated meteorites. In contrast, CR chondrites are characterized by a narrower range of μ54Cr values restricted to compositions typically observed for bulk carbonaceous chondrites. Collectively, these observations suggest that the CV chondrules formed from precursors that originated in various regions of the protoplanetary disk and were then transported to the accretion region of the CV parent asteroid whereas CR chondrule predominantly formed from precursor with carbonaceous chondrite-like μ54Cr signatures. The observed μ54Cr variability in chondrules from CV and CR chondrites suggest that the matrix and chondrules did not necessarily formed from the same reservoir. The coupled μ26Mg∗ and μ54Cr systematics of CR chondrules establishes that these objects formed from a thermally unprocessed and 26Al-poor source reservoir distinct from most inner Solar System asteroids and planetary bodies, possibly located beyond the orbits of the gas giants. In contrast, a large fraction of the CV chondrules plot on the inner Solar System correlation line, indicating that these objects predominantly formed from thermally-processed, 26Al-bearing precursor material akin to that of inner Solar System solids, asteroids and planets.

¹L. Ilsedore Cleeves, ²Edwin A. Bergin, ³Conel M. O’D. Alexander, ²Fujun Du, ¹Dawn Graninger, ¹Karin I. Öberg, ⁴Tim J. Harries
The Astrophysical Journal, Volume 819, Number 1 Link to Article [http://dx.doi.org/10.3847/0004-637X/819/1/13]
¹Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
²Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA
³DTM, Carnegie Institution of Washington, Washington, DC 20015, USA
⁴Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK

Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues about their original formation environment. The organic materials in primitive solar system bodies generally have higher D/H ratios and show greater D/H variation when compared to D/H in solar system water. We propose this difference arises at least in part due to (1) the availability of additional chemical fractionation pathways for organics beyond that for water, and (2) the higher volatility of key carbon reservoirs compared to oxygen. We test this hypothesis using detailed disk models, including a sophisticated, new disk ionization treatment with a low cosmic-ray ionization rate, and find that disk chemistry leads to higher deuterium enrichment in organics compared to water, helped especially by fractionation via the precursors CH2D+/CH3+. We also find that the D/H ratio in individual species varies significantly depending on their particular formation pathways. For example, from ~20–40 au, CH4 can reach ${\rm{D}}/{\rm{H}}\sim 2\times {10}^{-3}$, while D/H in CH3OH remains locally unaltered. Finally, while the global organic D/H in our models can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir, our models are unable to reproduce the most deuterium-enriched organic materials in the solar system, and thus our model requires some inheritance from the cold interstellar medium from which the Sun formed.

¹F. Fontani, ¹V. M. Rivilla, ²P. Caselli, ^2,3A. Vasyunin, ⁴A. Palau
The Astrophysical Journal Letters 822,L30 Link to Article [http://dx.doi.org/10.3847/2041-8205/822/2/L30]
¹INAF-Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, I-50125 Firenze, Italy
²Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse, D-85748 Garching, Germany
³Ural Federal University, Ekaterinburg, Russia
⁴Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090 Morelia, Michoacán, México

Phosphorus is a crucial element for the development of life, but so far P-bearing molecules have been detected only in a few astrophysical objects; hence, its interstellar chemistry is almost totally unknown. Here, we show new detections of phosphorus nitride (PN) in a sample of dense cores in different evolutionary stages of the intermediate- and high-mass star formation process: starless, with protostellar objects, and with ultracompact H ii regions. All detected PN line widths are smaller than sime5 km s−1, and they arise from regions associated with kinetic temperatures smaller than 100 K. Because the few previous detections reported in the literature are associated with warmer and more turbulent sources, the results of this work show that PN can arise from relatively quiescent and cold gas. This information is challenging for theoretical models that invoke either high desorption temperatures or grain sputtering from shocks to release phosphorus into the gas phase. Derived column densities are of the order of 1011–12 cm−2, marginally lower than the values derived in the few high-mass star-forming regions detected so far. New constraints on the abundance of phosphorus monoxide, the fundamental unit of biologically relevant molecules, are also given.

¹S. De Angelis, ¹P. Manzari, ¹M.C. De Sanctis, ^1,2E. Ammannito, ^1,3T. Di Iorio
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.07.002]
¹Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Rome, Italy
²University of California Los Angeles, Earth Planetary and Space Sciences, Los Angeles, CA-90095, USA
³ENEA SSPT-PROTER-OAC, Roma, Italy
Copyright Elsevier

Carbonates and clay minerals are present in Solar System bodies such as Mars and asteroid (1) Ceres. Brucite has been proposed in the recent past to fit absorption features in spectra of Ceres. In this study Visible-Near Infrared reflectance spectroscopic measurements have been performed on brucite-carbonate-clay minerals mixtures, in the 0.2-5.1 μm spectral range. Different sets of three- and two-components mixtures have been prepared using these three fine powdered endmembers, by varying the relative proportions of carbonate, clay and brucite. Spectra have been acquired on the endmembers components separately and on the mixtures. Absorption features diagnostic of the carbonate, clay and brucite phases have been analyzed and band parameters (position, depth, area, width) determined. Several trends and correlations with mineral phase content in each mixture have been investigated, with the aim to determining how endmember components influence the mixture spectra and their minimum detectability threshold. Our results indicate that brucite is detectable in mineral mixtures with carbonates and clays, based on its main absorption features at 0.95, 2.45-2.47 and 3.05 μm. While the 0.95 and 3.05-μm features are only discernible for very high brucite contents in the mixtures, the ∼2.45-μm band turns out to be highly diagnostic, also for very small amounts of brucite (of the order of 10 wt%). These experiments, together with DAWN observations of Ceres, substantially rule out the presence of great amounts of brucite globally distributed on the surface of Ceres.

¹Yoshihiro NAKAMUTA, ²Fumio KITAJIMA, ²Kazuhiko SHIMADA
Journal of Mineralogical and Petrological Sciences Article ID: 150906 Link to Article [doi.org/10.2465/jmps.150906]
¹University Museum, Kyushu University, Hakozaki, Fukuoka 812–8581, Japan
²Faculty of Science, Kyushu University, Motooka, Fukuoka 819–0395, Japan

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^1,2Adrien Denoeud et al. (>10)*
Proceedings of the National Academy of Sciences 113, 7745-7749 Link to Article [doi:10.1073/pnas.1512127113]
¹Laboratoire d’Utilisation de Lasers Intenses – CNRS, Ecole Polytechnique, Commissariat à l’Energie Atomique et aux Energies Alternatives, Université Paris-Saclay, F-91128 Palaiseau Cedex, France;
²Sorbonne Universités, Université Pierre et Marie Curie Paris 6, CNRS, Laboratoire d’Utilisation des Lasers Intenses, place Jussieu, 75252 Paris Cedex 05, France
*Find the extensive, full author and affiliation list on the publishers website

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.

¹Suniti Karunatillake, ²James J. Wray, ^3,4Olivier Gasnault, ⁵Scott M. McLennan, ⁵A. Deanne Rogers, ⁶Steven W. Squyres, ⁷William V. Boynton, ⁸J. R. Skok, ¹Nicole E. Button, ¹Lujendra Ojha
Journal of Geophysical Research (Planets) (in Press) Link to Article [DOI: 10.1002/2016JE005016]
¹Geology and Geophysics, Louisiana State University, Baton Rouge, LA, USA
²Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
³Université de Toulouse [UPS; OMP; IRAP], Toulouse, France
⁴CNRS [UMR 5277], Institut de Recherche en Astrophysique et Planétologie, BP, Toulouse Cedex 4, France
⁵Department of Geosciences, Stony Brook University, Stony Brook, New York, USA
⁶Department of Astronomy, Cornell University, Ithaca, New York, USA
⁷Department of Planetary Sciences, University of Arizona, AZ, USA
⁸SETI institute, CA, USA
⁹Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Published by arrangement with John Wiley & Sons

Midlatitudinal hydrated sulfates on Mars may influence brine pH, atmospheric humidity, and collectively water activity. These factors affect the habitability of the planetary subsurface and the preservation of relict biomolecules. Regolith at grain sizes smaller than gravel, constituting the bulk of the martian subsurface at regional scales, may be a primary repository of chemical alteration, mechanical alteration, and biosignatures. The Mars Odyssey Gamma Ray Spectrometer with hundreds of kilometers of lateral resolution and compositional sensitivity to decimeter depth provides unique insight into this component of the regolith, which we call soil. Advancing the globally compelling association between H2O and S established by our previous work [Karunatillake et al., 2014], we characterize latitudinal variations in the association between H and S, as well as in the hydration state of soil. Represented by H2O:S molar ratios, the hydration state of candidate sulfates increases with latitude in the northern hemisphere. In contrast, hydration states generally decrease with latitude in the south. Furthermore, we observe that H2O concentration may affect the degree of sulfate hydration more than S concentration. Limited H2O availability in soil-atmosphere exchange and in subsurface recharge could explain such control exerted by H2O on salt hydration. Differences in soil thickness, ground ice table depths, atmospheric circulation, and insolation may contribute to hemispheric differences in the progression of hydration with latitude. Our observations support chemical association of H2O with S in the southern hemisphere as suggested by Karunatillake et al. [2014], including the possibility of Fe-sulfates as a key mineral group.

¹Alessandro Maturilli, ¹Jörn Helbert, ¹Sabrina Ferrari, ²Björn Davidsson, ¹Mario D’Amore
Earth, Planets and Space 68, 113 Link to Article [DOI: 10.1186/s40623-016-0489-y]
¹Institute of Planetary Research, German Aerospace Center DLR
²Department of Physics and Astronomy, Uppsala University

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¹Romy D. Hanna,²Victoria E. Hamilton, ²Nathaniel E. Putzig
Journal of Geophysical Research (Planets) Link to Article [DOI: 10.1002/2015JE004924]
¹Jackson School of Geological Sciences, University of Texas, Austin, TX
²Department of Space Studies, Southwest Research Institute, Boulder, C
Published by arrangement with John Wiley & Sons

We examine four olivine-bearing regions at a variety of spatial scales with TIR, VNIR, and visible imagery data to investigate the hypothesis that the relationship between olivine abundance and thermal inertia (i.e., effective particle size) can be used to infer the occurrence of olivine chemical alteration during sediment production on Mars. As in previous work, Nili Fossae and Isidis Planitia show a positive correlation between thermal inertia and olivine abundance in TES and THEMIS data, which could be interpreted as indicating olivine chemical weathering. However, geomorphological analysis reveals that relatively olivine-poor sediments are not derived from adjacent olivine-rich materials, and therefore chemical weathering cannot be inferred based on the olivine-thermal inertia relationship alone. We identify two areas (Terra Cimmeria and Argyre Planitia) with significant olivine abundance and thermal inertias consistent with sand, but no adjacent rocky (parent) units having even greater olivine abundances. More broadly, global analysis with TES reveals that the most typical olivine abundance on Mars is ~5-7% and that olivine-bearing (5-25%) materials have a wide range of thermal inertias, commonly 25-600 J · m-2 · K-1 · s-1/2. TES also indicates that the majority of olivine-rich (>25%) materials have apparent thermal inertias less than 400 J · m-2 · K-1 · s-1/2. In summary, we find that the relationship between thermal inertia and olivine abundance alone cannot be used in infer olivine weathering in the examined areas, that olivine-bearing materials have a large range of thermal intertias, and therefore, that a complex relationship between olivine abundance and thermal inertia exists on Mars.