Futoshi Takahashi, Hideo Tsunakawa, Masaki Matsushima & Hisayoshi Shimizu

Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581, Japan
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan
Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan
Department of Earth and Environmental Sciences, Kumamoto University, Kumamoto 860-8555, Japan

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Reference
Takahashi et al. (2014) Reorientation of the early lunar pole.  Nature Geoscience 7:401.
[doi:10.1038/ngeo2173]

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Katharine L. Robinson & G. Jeffrey Taylor

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii 96822, USA

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

Reference
Robinson KL & Taylor GJ (2014) Heterogeneous distribution of water in the Moon.  Nature Geoscience 7:401.
[doi:10.1038/ngeo2173]

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Tamara Goldin

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

Reference
Goldin T (2014) Planetary science: Water and the lunar dynamo.  Nature Geoscience 7:400.
[doi:10.1038/ngeo2183]

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Long Xiao

Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, 430074, China

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

Reference
Xiao L (2014) China’s touch on the Moon.  Nature Geoscience 7:391.
[doi:10.1038/ngeo2175]

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Editorial

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Reference
Editorial (2014) Volatile lunacy.  Nature Geoscience 7:389.
[doi:10.1038/ngeo2184]

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Johan Vellekoop^a, Appy Sluijs^a, Jan Smit^b, Stefan Schouten^c,d, Johan W. H. Weijers^c, Jaap S. Sinninghe Damsté^c,d, and Henk Brinkhuis^a

^aMarine Palynology, Department of Earth Sciences, Faculty of Geosciences, Laboratory of Palaeobotany and Palynology, Utrecht University, 3584 CD, Utrecht, The Netherlands;
^bEventstratigraphy, Sedimentology, Faculty of Earth- and Life Sciences, VU University Amsterdam, 1081 HV, Amsterdam, The Netherlands;
^cGeochemistry, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands; and
^dDepartment of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute of Sea Research, 1790 AB, Den Burg, Texel, The Netherlands

Here, for the first time (to our knowledge), we are able to demonstrate unambiguously that the impact at the Cretaceous–Paleogene boundary (K–Pg, ∼66 Mya) was followed by a so-called “impact winter.” This impact winter was the result of the injection of large amounts of dust and aerosols into the stratosphere and significantly reduced incoming solar radiation for decades. Therefore, this phase will have been a key contributory element in the extinctions of many biological clades, including the dinosaurs. The K–Pg boundary impact presents a unique event in Earth history because it caused global change at an unparalleled rate. This detailed portrayal of the environmental consequences of the K–Pg impact and aftermath aids in our understanding of truly rapid climate change.

Reference
Vellekoop J, Sluijs A, Smit J, Schouten S, Weijers JWH, Damsté JSS and Brinkhuis H (2014) Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary.  Proceedings of the National Academy of Sciences of the United States of America 111:7537.
[doi:10.1073/pnas.1319253111]

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M. Köhler, A. Jones and N. Ysard

Institut d’Astrophysique Spatiale (IAS), Université Paris-Sud & CNRS, Bât. 121, 91405 Orsay, France

Context. The depletion of iron and sulphur into dust in the interstellar medium and the exact nature of interstellar amorphous silicate grains is still an open question.
Aims. We study the incorporation of iron and sulphur into amorphous silicates of olivine- and pyroxene-types and their effects on the dust spectroscopy and thermal emission.
Methods. We used the Maxwell-Garnett effective-medium theory to construct the optical constants for a mixture of silicates, metallic iron, and iron sulphide. We also studied the effects of iron and iron sulphide in aggregate grains.
Results. Iron sulphide inclusions within amorphous silicates that contain iron metal inclusions show no strong differences in the optical properties of the grains. A mix of amorphous olivine- and pyroxene-type silicate broadens the silicate features. An amorphous carbon mantle with a thickness of 10 nm on the silicate grains leads to an increase in absorption on the short-wavelength side of the 10 μm silicate band.
Conclusions. The assumption of amorphous olivine-type and pyroxene-type silicates and a 10 nm thick amorphous carbon mantle better matches the interstellar silicate band profiles. Including iron nano-particles leads to an increase in the mid-IR extinction, while up to 5 ppm of sulphur can be incorporated as Fe/FeS nano inclusions into silicate grains without leaving a significant trace of its presence.

Reference
Köhler M, Jones A and Ysard N (2014) A hidden reservoir of Fe/FeS in interstellar silicates?.  Astronomy & Astrophysics 565:L9.
[doi:10.1051/0004-6361/201423985]
Reproduced with permission © ESO

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Anton I. Ermakov^a, Maria T. Zuber^a, David E. Smith^a,b, Carol A. Raymond^c, Georges Balmino^d, R.R. Fu^a and B.A. Ivanov^e

^aDepartment of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
^bNASA Goddard Space Flight Center, Greenbelt, MD, USA
^cJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
^dCentre national d’études spatiales (CNES), Toulouse, France
^eInstitute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, Russian Federation

Vesta is a differentiated asteroid as confirmed by gravity and spectroscopy measurements from the Dawn mission. We use the shape and gravity field of Vesta determined from observations of the Dawn spacecraft to develop models of the asteroid’s interior structure. We compute a three-layer interior structure model by minimizing the power of the residual gravity anomaly. The densities of the mantle and crust are based on constraints derived from the Howardite-Eucrite-Diogenite (HED) meteorites.
Vesta’s present-day shape is not in hydrostatic equilibrium. The Rheasilvia and Veneneia impact basins have a large effect on Vesta’s shape and are the main source of deviation from hydrostatic shape. Constraining a pre-giant-impact rotation rate and orientation of the spin axis from an ellipsoidal fit to the parts of Vesta unaffected by the giant impacts, and using the theory of figure, we can constrain the shape of the core.
Our solution for Vesta’s crust-mantle interface reveals a belt of thick crust around Rheasilvia and Veneneia. The thinnest crust is in the floor of the two basins and in the Vestalia Terra region. Our solution does not reveal an uplift of the crust-mantle boundary to the surface in the largest basins. This, together with the lack of olivine detected by the Visible and Infrared Spectrometer (VIR) data in Rheasilvia and Veneneia, indicates that Vesta’s presumed olivine mantle was either not brought to the surface by these large impacts or was covered by ejecta from subsequent impacts.

Reference
Ermakov AI, Zuber MT, Smith DE, Raymond CA, Balmino G, Fu RR and Ivanov BA (in press) Constraints on Vesta’s Interior Structure Using Gravity and Shape Models from the Dawn Mission. Icarus
[doi:10.1016/j.icarus.2014.05.015]
Copyright Elsevier

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Jiao He and Gianfranco Vidali

When dust grains have a higher temperature than they would have in dense clouds, and when H, H2, and O2 have a negligible residence time on grains, the formation of water should still be possible via the hydrogenation of OH and Eley–Rideal-type reactions. We determined that the OH desorption energy from an amorphous silicate surface is at least 143 meV (1656 K). This is 400 K higher than the value previously used in chemical models of the interstellar medium and is possibly as high as 410 meV (4760 K). This extends the temperature range for the efficient formation of water on grains from about 30 K to at least 50 K, and possibly over 100 K. We do not find evidence that water molecules leave the surface upon formation. Instead, through a thermal programmed desorption experiment, we find that water formed on the surface of an amorphous silicate desorbs at around 160 K. We also measured the cross-sections for the reaction of H and D with an O₃ layer on an amorphous silicate surface at 50 K. The values of the cross-sections, σ_H = 1.6 ± 0.27 Ų and σ_D = 0.94 ± 0.09 Ų, respectively, are smaller than the size of an O₃ molecule, suggesting the reaction mechanism is more likely Eley–Rideal than hot-atom. Information obtained through these experiments should help theorists evaluate the relative contribution of water formation on warm grains versus in the gas phase.

Reference
He J and Vidali G (2014) Experiments of water formation on warm silicates. The Astrophysical Journal 788:50.
[doi:10.1088/0004-637X/788/1/50]

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S. Hu^a, Y. Lin^a, J. Zhang^a, J. Hao^a, L. Feng^a, L. Xu^b, Yang^a and J. Yang^a

^aKey Laboratory of the Earth’s Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
^bNational Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, China

We measured the hydrogen isotopes and water contents of melt inclusions and apatite that locate far from shock-induced melt veins in the Martian meteorite GRV 020090, using nano-scale secondary ion mass spectrometry (nanoSIMS). The melt inclusions in olivine show hydration profiles, with both the water contents and the δD values increasing from the cores (2σ) (170±7 ppm and 3386±126 ‰) to the rims (5337±200 ppm and 5519±65 ‰). The extremely high δD values of the melt inclusions relative to a maximum of 4239±81 ‰ of apatite that crystallized from the last residual melt convincingly argue that the observed hydration postdated emplacement of the parent magma of GRV 020090. This is also a robust line of evidence for past-presence of liquid water on Mars. Diffusion simulation of the hydration profiles of both water contents and δD values constrains the duration of liquid water up to 130,000-250,000 years at 0 °C or 700-1,500 years at 40 °C. All analyses of the melt inclusions, including the hydration profiles, show a logarithmic correlation between the water contents and the δD values, plotting within a two-endmember mixing area. The extremely D-enriched endmember represents Martian underground water, with a δD value of 6034±72 ‰ (2σ). This is the highest δD value reported in Martian meteorites and it is consistent with the recent analyses of Martian soils by the Curiosity rover (Leshin et al., 2013), suggestive of more water escaped from Mars than previous estimates.
The analyses of apatite show a distinct positive correlation between the water contents (0.10-0.58 wt%) and the δD values (737-4239 ‰), which can be explained by assimilation of D-rich Martian crustal materials and enhancement of water via fractional crystallization. The observed correlation suggests that the water contents of Martian mantle reservoirs might have been overestimated from D-enriched apatite in previous studies. Our estimation based on the least contaminated apatite grains from GRV 020090 turned out a low water content of the primordial parent magma (380-750 ppm), which was likely derived from a relatively dry Martian mantle reservoir of GRV 020090 (∼38-75 ppm H₂O).

Reference
Hu S, Lin Y, Zhang J, Hao J, Feng L, Xu L, Yang W and Yang J  (in press) NanoSIMS Analyses of Apatite and Melt Inclusions in the GRV 020090 Martian Meteorite: Hydrogen Isotope Evidence for Recent Past Underground Hydrothermal Activity on Mars. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.05.008]
Copyright Elsevier

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