¹Richard W. Court, ¹Mark A. Sephton
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College, London, SW7 2AZ, UK

Heating and ablation of micrometeoroids during atmospheric entry yields volatile gases capable of altering atmospheric chemistry, surface climate and habitability. We have subjected powdered samples of the carbonaceous chondrites Orgueil (CI1), ALH 88045 (CM1), Cold Bokkeveld (CM2), Murchison (CM2) and Mokoia (CV3) to stepped pyrolysis-Fourier transform infrared spectroscopy to simulate the atmospheric entry of micrometeoroids and to quantify the yields of water, carbon dioxide and sulphur dioxide at various temperatures, offering insights into the nature of their source phases. We have incorporated these data into the recently-developed E-Belt model of the Late Heavy Bombardment (LHB) to estimate the production of volatiles from infalling micrometeoroids at Earth and Mars around four billion years ago. At the present day, the 4 (±2)×1010 g yr-1 of micrometeoroids arriving at Earth yield around 2.5 (±1.3) ×109 g yr-1 of indigenous water, 4.1 (±2.2) ×109 g yr-1 of total water, 1.9 (±1.0) ×109 g yr-1 of carbon dioxide and about 1.1 (±0.6) ×109 g yr-1 of sulphur dioxide, where “indigenous” water exclude water evolved at the initial pyrolysis step of 250 °C. For Mars, the infall of 6.8×109 g yr-1 of micrometeoroids yields 3.6 (±1.9) ×108 g yr-1 of indigenous water, 6.4 (±3.4) ×108 g yr-1 of total water, 2.4 (±1.3) ×108 g yr-1 of carbon dioxide and 1.5 (±0.8) ×108 g yr-1 of sulphur dioxide. The LHB is associated with micrometeoroidal infall masses of 1.3 (±0.8)×1022 g at Earth and 2.3 (±1.3)×1021 g at Mars. For Earth, this mass is estimated to have produced 8.3 (±4.9)×1020 g of indigenous water, 1.4 (±0.8)×1021 g of total water, 6.3 (±3.7)×1020 g of carbon dioxide and 3.8 (±2.2)×1020 g of sulphur dioxide, with production rates in the peak 50 Myr of the LHB estimated at 5.1 (±3.1) ×1012 g yr-1 of indigenous water, 8.6 (±5.1) ×1012 g yr-1 of total water, 3.9 (±2.3) ×1012 g yr-1 of carbon dioxide and 2.3 (±1.4) ×1012 g yr-1 of sulphur dioxide. For Mars, total 4.1-3.7 Ga production of 1.3 (±0.8) ×1020 g of indigenous water, 2.2 (±1.3) ×1020 g of total water, 9.3 (±5.5) ×1019 g of carbon dioxide and around 5.8 (±3.4) ×1019 g of sulphur dioxide is estimated, with peak 50 Myr rates of 8.2 (±4.8) ×1011 g yr-1 of indigenous water, 1.4 (±0.8) ×1012 g yr-1 of total water, 5.8 (±3.5) ×1011 g yr-1 of carbon dioxide and 3.6 (±2.1) ×1011 g yr-1 of sulphur dioxide. The errors in these estimates for the present-day rates are dominated by ±50% uncertainty in the LDEF figure of 4 (±2)×1010 g yr-1 of micrometeoroids while the errors for the ancient rates are dominated by the similarly large uncertainty regarding the mass ratio of micrometeoroids to asteroids. These errors indicate the need for improved understandings of infall rates and better models of solar system evolution. Current models of climate for early Earth and Mars focus on volcanic outgassing for greenhouse gases and aerosols, but pay less attention to extraterrestrial sources. Our data quantify an additional exogenous source of volatiles that augments the endogenous production.

Reference
Court RW, Sephton MA (2014) New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.09.010]

Copyright Elsevier

^1,2,9Hiroshi Nagaoka, ³Hiroshi Takeda, ⁴Yuzuru Karouji, ⁵Makiko Ohtake,
^6,7Akira Yamaguchi, ⁸Shigekazu Yoneda, ^1,2Nobuyuki Hasebe
¹Research Institute for Science and Engineering, Waseda University, Shinjuku,
Tokyo 169-8555, Japan
²Schools of Advanced Science and Engineering, Waseda University, Shinjuku,
Tokyo 169-8555, Japan
³Department of Earth & Planetary Science, University of Tokyo, Hongo, Tokyo
113-0033, Japan
⁴Institute of Space and Astronautical Science (ISAS), Japan Aerospace
Exploration Agency (JAXA), Sagamihara, Kanagawa 252-5210, Japan
⁵Planetary Science Department, Japan Aerospace Exploration Agency (JAXA),
Sagamihara, Kanagawa 252-5210, Japan
⁶National Institute of Polar Research (NIPR), Tachikawa, Tokyo 190-8518,
Japan
⁷Department of Polar Science, School of Multidisciplinary Science, Graduate
University for Advanced Studies, Tokyo 173-8518, Japan
⁸National Museum of Nature and Science (NMNS), Tsukuba, Ibaraki 305-0005,
Japan
⁹Schools of Advanced Science and Engineering, Waseda
University, Shinjuku, Tokyo 169-8555, Japan

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Reference
Nagaoka H, Takeda H, Karouji Y, Ohtake M, Yamaguchi A, Yoneda S, Hasebe N (2014) Implications for the origins of pure anorthosites found in the feldspathic lunar meteorites, Dhofar 489 Group. Earth, Planets and Space 66:115
Link to Article [doi:10.1186/1880-5981-66-115]

^1,2Léna Le Roy,^1,2Anais Bardyn,¹Christelle Briois,²Hervé Cottin,²Nicolas Fray,²Laurent Thirkell,³Martin Hilchenbach

¹Laboratoire de Physique et Chimie de l’Environnement et de l’Espace(LPC2E), UMR 7328 CNRS–Université d’Orléans, 3A Avenue de la Recherche Scientifique, 45071 Orléans Cedex2, France
²Laboratoire Interuniversitaire des Systèmes Atmosphériques, LISA, UMR CNRS 7583, Université Paris Est Créteil(UPEC) et Université Paris Diderot (UPD), Institut Pierre Simon Laplace, 61 Avenue du Général De Gaulle, 94010 Créteil Cedex, France
³Max Planck Institute for Solar System Research (MPS), Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Le Roya L, Bardyn A, Briois C, Cottin H, Fray N, Thirkell L, Hilchenbach M (2014) COSIMA calibration for the detection and characterisation of the cometary solid organic matter. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.08.015]

O. Ruesch¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹1Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Germany

The magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite, and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR) orbital observations of Vesta’s surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta’s surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe²⁺/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (~<50–60 vol %) is found in 2–5 km wide, morphologically fresh areas. Our global survey reveals a dozen of these areas clustering in the eastern hemisphere of Vesta. The hemispherical coincidence with a widespread, low enrichment in diogenite-like pyroxene suggests the presence of a distinct compositional terrain. On the central mound of the Rheasilvia impact basin, no olivine enrichment was found, suggesting the absence of an olivine-dominated mantle above the basin’s excavation depth or, alternatively, a low amount of olivine homogeneously mixed with diogenite-like pyroxenes. Rare olivine-enriched areas in close proximity to diogenite-like pyroxene are found as part of material ejected by the Rheasilvia impact. Such cooccurrence is reminiscent of local, ultramafic lithologies within the crust. The possible formation of such lithologies on Vesta is supported by some HED meteorites dominated by olivine and orthopyroxene.

Reference
Ruesch O et al. (2014) Detections and geologic context of local enrichments in olivine on Vesta with VIR/Dawn data. Journal of Geophysical Research: Planets

Link to Article [10.1002/2014JE004625]

D. L. Blaney¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

A suite of eight rocks analyzed by the Curiosity Rover while it was stopped at the Rocknest sand ripple shows the greatest chemical divergence of any potentially sedimentary rocks analyzed in the early part of the mission. Relative to average Martian soil and to the stratigraphically lower units encountered as part of the Yellowknife Bay formation, these rocks are significantly depleted in MgO, with a mean of 1.3 wt %, and high in Fe, averaging over 20 wt % FeO_T, with values between 15 and 26 wt % FeO_T. The variable iron and low magnesium and rock texture make it unlikely that these are igneous rocks. Rock surface textures range from rough to smooth, can be pitted or grooved, and show various degrees of wind erosion. Some rocks display poorly defined layering while others seem to show possible fractures. Narrow vertical voids are present in Rocknest 3, one of the rocks showing the strongest layering. Rocks in the vicinity of Rocknest may have undergone some diagenesis similar to other rocks in the Yellowknife Bay Formation as indicated by the presence of soluble calcium phases. The most reasonable scenario is that fine-grained sediments, potentially a mixture of feldspar-rich rocks from Bradbury Rise and normal Martian soil, were lithified together by an iron-rich cement.

Reference
Blaney DL et al. (2014) Chemistry and texture of the rocks at Rocknest, Gale Crater: Evidence for sedimentary origin and diagenetic alteration. Journal of Geophysical Research: Planets

Link to Article [10.1002/2014JE004650]

Micah J. Schaible andRaúl A. Baragiola

Laboratory of Atomic and Surface Physics, University of Virginia, Charlottesville, Virginia, USA

Hydroxyl on the lunar surface revealed by remote measurements has been thought to originate from solar wind hydrogen implantation in the regolith. The hypothesis is tested here through experimental studies of the rate and mechanisms of OH bond formation due to H⁺implantation of amorphous SiO₂ and olivine in ultrahigh vacuum. The samples were implanted with 2–10 keV H⁺, in the range of solar wind energies, and the OH absorption band at ~2.8 µm measured by transmission Fourier transform infrared spectroscopy. For 2 keV protons in SiO₂, the OH band depth saturated at fluences F ~5 × 10¹⁶ H⁺/cm² to a maximum 0.0032 absorption band depth, corresponding to a column density η_s = 1.1 × 10¹⁶ OH/cm². The corresponding values for 5 keV protons in olivine are >2 × 10¹⁷/cm², 0.0067, and 4.0 × 10¹⁶ OH/cm². The initial conversion rate of implanted H⁺ into hydroxyl species was found to be ~90% and decreased exponentially with fluence. There was no evidence for molecular water formation due to proton irradiation. Translating the laboratory measurements in thin plate samples to the granular lunar regolith, it is estimated that the measurements can account for a maximum of 17% relative OH absorption in reflectance spectroscopy of mature soils, consistent with spacecraft observations in the infrared of the Moon.

Reference
Schaible MJ and Baragiola RA (2014) Hydrogen implantation in silicates: The role of solar wind in SiOH bond formation on the surfaces of airless bodies in space. Journal of Geophysical Research: Planets

Link to Article [10.1002/2014JE004650]

P. Senthil Kumar¹, K. J. Prasanna Lakshmi¹, N. Krishna¹, R. Menon¹, U. Sruthi¹, V. Keerthi², A. Senthil Kumar², D. Mysaiah¹, T. Seshunarayana¹ and M. K. Sen¹

¹National Geophysical Research Institute, Council of Scientific and Industrial Research, Hyderabad, India
²National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad, India

Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to kilometer-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed, and elongated with an average edge angle of 100°. The size distribution of cobble- to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures, and faults in the bedrock beneath the crater rim. The fracturing, fragmentation, and fluvial degradation of Lonar Crater have important implications for Mars.

Reference
Kumar SP, Prasanna Lakshmi KJ, Krishna N, Menon R, Sruthi U, Keerthi V, Kumar AS, Mysaiah D, Seshunarayana T and Sen MK (2014) Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt. Journal of Geophysical Research: Planets
Link to Article [10.1002/2013JE004543]

Nicholas P. Ballering, George H. Rieke, and András Gáspár
Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

Observations of debris disks allow for the study of planetary systems, even where planets have not been detected. However, debris disks are often only characterized by unresolved infrared excesses that resemble featureless blackbodies, and the location of the emitting dust is uncertain due to a degeneracy with the dust grain properties. Here, we characterize the Spitzer Infrared Spectrograph spectra of 22 debris disks exhibiting 10 μm silicate emission features. Such features arise from small warm dust grains, and their presence can significantly constrain the orbital location of the emitting debris. We find that these features can be explained by the presence of an additional dust component in the terrestrial zones of the planetary systems, i.e., an exozodiacal belt. Aside from possessing exozodiacal dust, these debris disks are not particularly unique; their minimum grain sizes are consistent with the blowout sizes of their systems, and their brightnesses are comparable to those of featureless warm debris disks. These disks are in systems of a range of ages, though the older systems with features are found only around A-type stars. The features in young systems may be signatures of terrestrial planet formation. Analyzing the spectra of unresolved debris disks with emission features may be one of the simplest and most accessible ways to study the terrestrial regions of planetary systems.

Reference
Ballering NP, Rieke GH, and Gáspár A (2014) Stellar abundances and presolar grains trace the nucleosynthetic origin of molybdenum and Ruthenium. The Astrophysical Journal 793, 57
Link to Article [10.1088/0004-637X/793/1/57]

¹Hansen, C.J., ²Andersen, A.C., ¹Christlieb, N.
¹Landessternwarte, ZAH, Königstuhl 12, 69117 Heidelberg, Germany
²Dark Cosmology centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark

This work presents a large consistent study of molybdenum (Mo) and ruthenium (Ru) abundances in the Milky Way. These two elements are important nucleosynthetic diagnostics. In our sample of 71 Galactic metal-poor field stars, we detect Ru and/or Mo in 52 of these (59 including upper limits). The sample consists of high-resolution, high signal-to-noise spectra covering both dwarfs and giants from [Fe/H] = −0.63 down to −3.16. Thus we provide information on the behaviour of Mo I and Ru I at higher and lower metallicity than is currently known. In this sample we find a wide spread in the Mo and Ru abundances, which is typical of heavy elements. We confirm earlier findings of Mo enhanced stars around [Fe/H] = −1.5 and add ~15 stars both dwarfs and giants with normal (0.5 dex) stars to the currently known stellar sample. This indicates that several formation processes, in addition to high entropy winds, can be responsible for the formation of elements like Mo and Ru. We trace the formation processes by comparing Mo and Ru to elements (Sr, Zr, Pd, Ag, Ba, and Eu) with known formation processes. Based on how tight the two elements correlate with each other, we are able to distinguish if they share a common formation process and how important this contribution is to the element abundance. We find clear indications of contributions from several different formation processes, namely the p-process, and the slow (s-), and rapid (r-) neutron-capture processes. From these correlations we find that Mo is a highly convolved element that receives contributions from both the s-process and the p-process and less from the main and weak r-processes, whereas Ru is mainly formed by the weak r-process as is silver. We also compare our absolute elemental stellar abundances to relative isotopic abundances of presolar grains extracted from meteorites. Their isotopic abundances can be directly linked to the formation process (e.g. r-only isotopes) providing a unique comparison between observationally derived abundances and the nuclear formation process. The comparison to abundances in presolar grains shows that the r-/s-process ratios from the presolar grains match the total elemental chemical composition derived from metal-poor halo stars with [Fe/H] around −1.5 to −1.1 dex. This indicates that both grains and stars around and above [Fe/H] = −1.5 are equally (well) mixed and therefore do not support a heterogeneous presolar nebula. An inhomogeneous interstellar medium (ISM) should only be expected at lower metallicities. Our data, combined with the abundance ratios of presolar grains, could indicate that the AGB yields are less efficiently mixed into stars than into presolar grains. Finally, we detect traces of s-process material at [Fe/H] = −1.5, indicating that this process is at work at this and probably at even lower metallicity.

Reference
Hansen CJ, Andersen AC, Christlieb N (2014) Stellar abundances and presolar grains trace the nucleosynthetic origin of molybdenum and Ruthenium. Astronomy & Astrophysics 568, A47
Link to Article [http://dx.doi.org/10.1051/0004-6361/201423535]

Reproduced with permission (C) ESO

¹Moroz, T.N., ¹Goryainov, S.V., ¹Pokhilenko, N.P., ¹Podgornykh, N.M.
¹Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russian Federation

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Reference
Moroz TN, Goryainov SV, Pokhilenko NP, Podgornykh NM (2014) Crystalline and amorphous matter in the Chelyabinsk meteorite: Evidence from Raman spectroscopy. Doklady Earth Sciences 457, 831-834
Link to Article [DOI: 10.1134/S1028334X14070071]