Tamara Goldin

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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.

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

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Editorial

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

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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]
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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]
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J.R. Neeley^a,b, B.E. Clark^a, M.E. Ockert-Bell^a, M.K. Shepard^c, J. Conklin^d, E.A. Cloutis^e, S. Fornasier^f and S.J. Bus^g

^aDepartment of Physics, Ithaca College, Ithaca, NY 14850
^bDepartment of Physics, Iowa State University, Ames, IA 50011
^cDepartment of Geography and Geosciences, Bloomsburg University, Bloomsburg, PA 17815
^dDepartment of Mathematics, Ithaca College, Ithaca, NY 14850
^eDepartment of Geography, University of Winnipeg, Winnipeg, MB, R3B 2E9
^fLESIA, Observatoire de Paris, 5 Place Jules Janssen, F-92195 Meudon Principal Cedex, France
^gInstitute for Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96822

This work updates and expands on results of our long-term radar-driven observational campaign of main-belt asteroids (MBAs) focused on Bus-DeMeo Xc- and Xk-type objects (Tholen X and M class asteroids) using the Arecibo radar and NASA Infrared Telescope Facilities (Ockert-Bell et al., 2008, Ockert-Bell et al., 2010,Shepard et al., 2008a, Shepard et al., 2008b and Shepard et al., 2010). Eighteen of our targets were near-simultaneously observed with radar and those observations are described in Shepard et al. (2010). We combine our near-infrared data with available visible wavelength data for a more complete compositional analysis of our targets. Compositional evidence is derived from our target asteroid spectra using two different methods, a χ² search for spectral matches in the RELAB database and parametric comparisons with meteorites. We present four new methods of parametric comparison, including discriminant analysis. Discriminant analysis identifies meteorite type with 85% accuracy. This paper synthesizes the results of these two analog search algorithms and reconciles those results with analogs suggested from radar data (Shepard et al. 2010). We have observed 29 asteroids, 18 in conjunction with radar observations. For eighteen out of twenty-nine objects observed (62%) our compositional predictions are consistent over two or more methods applied. We find that for our Xc and Xk targets the best fit is an iron meteorite for 34% of the samples. Enstatite Chondrites were best fits for 6 of our targets (21%). Stony-iron meteorites were best fits for 2 of our targets (7%). A discriminant analysis suggests that asteroids with no absorption band can be compared to iron meteorites and asteroids with both a 0.9 and 1.9 μm absorption band can be compared to stony-iron meteorites.

Reference
Neeley JR, Clark BE, Ockert-Bell ME, Shepard MK, Conklin J, Cloutis EA, Fornasier S and Bus SJ  (in press) The composition of M-type asteroids II: Synthesis of spectroscopic and radar observations. Icarus
[doi:10.1016/j.icarus.2014.05.008]
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David P. O’Brien^a, Kevin J. Walsh^b, Alessandro Morbidelli^c, Sean N. Raymond^d,e and Avi M. Mandell^f

^aPlanetary Science Institute, 1700 E. Ft. Lowell, Suite 106, Tucson, AZ 85719, USA
^bDepartment of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA
^cUniversité de Nice — Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
^dUniversité de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 Rue de l’Observatoire, BP 89, F-33270 Floirac Cedex, France
^eCNRS, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 Rue de l’Observatoire, BP 89, F-33270 Floirac Cedex, France
^fNASA Goddard Space Flight Center, Code 693, Greenbelt, MD 20771, USA

A new model for terrestrial planet formation (Hansen, 2009 and Walsh et al., 2011) has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al., 2011 tested a possible mechanism to truncate the disk—a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies—the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as ‘primitive’ bodies).
One implication of the truncation mechanism proposed in Walsh et al. (2011) is the scattering of primitive planetesimals onto planet crossing orbits during the formation of the planets. We find here that the planets will accrete on order 1–2% of their total mass from these bodies. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. The radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system. However, we find that a truncated disk leads to formation timescales more rapid than suggested by radiometric chronometers. In particular the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. This is at odds with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event. However, 5 of the 27 planets larger than half an Earth mass formed in all simulations do experience large late impacts and subsequent accretion consistent with those constraints.

Reference
O’Brien DP, Walsh KJ, Morbidelli A, Raymond SN and Mandell AM (in press) Water Delivery and Giant Impacts in the ‘Grand Tack’ Scenario. Icarus
[doi:10.1016/j.icarus.2014.05.009]
Copyright Elsevier

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