C. T. Adcock¹, E. M. Hausrath¹ and P. M. Forster²

¹Department of Geoscience, University of Nevada Las Vegas, 4505 S. Maryland Pkwy., Las Vegas, Nevada 89154, USA
²Department of Chemistry, University of Nevada Las Vegas, 4505 S. Maryland Pkwy., Las Vegas, Nevada 89154, USA

We currently seek a copyright agreement with Nature Geoscience to display abstracts of their cosmochemistry related publications.

Reference
Adcock CT, Hausrath EM and Forster PM  (2013) Readily available phosphate from minerals in early aqueous environments on Mars. Nature Geoscience 6:824–827.
[doi:10.1038/ngeo1923]

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Arkaprabha Sarangi and Isabelle Cherchneff

We study the formation of molecules and dust clusters in the ejecta of solar metallicity, Type II-P supernovae (SNe) using a chemical kinetic approach. We follow the evolution of molecules and small dust cluster masses from day 100 to day 1500 after explosion. We consider stellar progenitors with initial masses of 12, 15, 19, and 25 M_☉ that explode as SNe with stratified ejecta. The molecular precursors to dust grains comprise molecular chains, rings and small clusters of silica, silicates, metal oxides, sulfides and carbides, pure metals, and carbon, where the nucleation of silicate clusters is described by a two-step process of metal and oxygen addition. We study the impact of the ⁵⁶Ni mass on the type and amount of synthesized dust. We predict that large masses of molecules including CO, SiO, SiS, O₂, and SO form in the ejecta. We show that the discrepancy between the small dust masses detected at infrared wavelengths some 500 days post-explosion and the larger amounts of dust recently detected with Herschel in SN remnants can be explained by the non-equilibrium chemistry linked to the formation of molecules and dust clusters in the ejected material. Dust gradually builds up from small (~10−5 M_☉) to large masses (~5 × 10−2 M_☉) over a 5 yr period after explosion. Subsequent dust formation and/or growth is hampered by the shortage of chemical agents participating in the dust nucleation and the long timescale for accretion. The results highlight the dependence of the dust chemical composition and mass on the amount of ⁵⁶Ni synthesized during the explosion. This dependence may partly explain the diversity of epochs at which dust forms in SNe. More generally, our results indicate that Type II-P SNe are efficient but moderate dust producers with an upper limit on the mass of synthesized dust ranging from ~0.03 to 0.09 M_☉. Other dust sources must then operate at high redshift to explain the large quantities of dust present in young galaxies in the early universe.

Reference
Sarangi A and Cherchneff I (in press) The Chemically Controlled Synthesis of Dust in Type II-P Supernovae. The Astrophysical Journal
[doi:10.1088/0004-637X/776/2/107]

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A. Pommerol^1,*, N. Thomas¹, B. Jost¹, P. Beck², C. Okubo³, A. S. McEwen⁴

¹Physikalisches Institut, Universität Bern, Bern, Switzerland
²Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, CNRS/Université Grenoble I, Grenoble, France
³U.S. Geological Survey, Astrogeology Research Center Survey, Flagstaff, Arizona, USA
⁴Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

We have measured the bidirectional reflectance of analogs of dry, wet, and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their microtexture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward-scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries.

Reference
Pommerol A, Thomas N, Jost B, Beck P, Okubo C and McEwen AS (in press) Photometric properties of Mars soils analogs. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20158]
Published by arrangement with John Wiley & Sons

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C. P. Haynes¹ and C. Millet²

¹UMR 7600, CNRS/Université Pierre et Marie Curie, Paris, France
²CEA, DAM, DIF, Arpajon, France

We perform a multicomponent sensitivity analysis of how the physical and dynamical parameters that characterize a meteor (in-fall) affect the ground overpressure and period of a plausible emitted N-wave signal. The nonlinear propagation model used throughout is based upon Whitham’s nonlinearization method which is modified to take into account a stratified atmosphere. We use sensitivity indices, derived using a Fourier Amplitude Sensitivity Test, to measure how the meteor parameters’ uncertainties affect the uncertainty in the overpressure and period of an emitted N-wave. The investigated parameters include the azimuth, entry angle, diameter, drag coefficient, density, and initial velocity of the meteor, as well as the atmosphere. The method is used to re-examine the crater-forming meteorite fall near Carancas, Peru (2007). We obtain good agreement between the simulated signals and observed waveforms. It is shown that ground overpressure uncertainty depends on the atmospheric uncertainties that are strongly correlated with the unknown trajectory, whereas the period is governed by the diameter uncertainties. Finally, we consider new waveform parameters that help characterize the meteor.

Reference
Haynes CP and Millet C (in press) A sensitivity analysis of meteoric infrasound. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20116]
Published by arrangement with John Wiley & Sons

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Lorin S. Matthews¹, Babak Shotorban², and Truell W. Hyde¹

The coagulation of cosmic dust grains is a fundamental process which takes place in astrophysical environments, such as presolar nebulae and circumstellar and protoplanetary disks. Cosmic dust grains can become charged through interaction with their plasma environment or other processes, and the resultant electrostatic force between dust grains can strongly affect their coagulation rate. Since ions and electrons are collected on the surface of the dust grain at random time intervals, the electrical charge of a dust grain experiences stochastic fluctuations. In this study, a set of stochastic differential equations is developed to model these fluctuations over the surface of an irregularly shaped aggregate. Then, employing the data produced, the influence of the charge fluctuations on the coagulation process and the physical characteristics of the aggregates formed is examined. It is shown that dust with small charges (due to the small size of the dust grains or a tenuous plasma environment) is affected most strongly.

Reference
Matthews LS, Shotorban B and Hyde TW (in press) Cosmic Dust Aggregation with Stochastic Charging. The Astrophysical Journal
[doi:10.1088/0004-637X/776/2/103]

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Christian Klimczak^1,*, Carolyn M. Ernst², Paul K. Byrne¹, Sean C. Solomon^1,3, Thomas R. Watters⁴, Scott L. Murchie², Frank Preusker⁵, Jeffrey A. Balcerski⁶

¹Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C., USA
²The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
³Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
⁴Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, D.C., USA
⁵German Aerospace Center, Institute of Planetary Research, Berlin, Germany
⁶Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio, USA

The volcanic plains that fill the Caloris basin, the largest recognized impact basin on Mercury, are deformed by many graben and wrinkle ridges, among which the multitude of radial graben of Pantheon Fossae allow us to resolve variations in the depth extent of associated faulting. Displacement profiles and displacement-to-length scaling both indicate that faults near the basin center are confined to a ~ 4-km-thick mechanical layer, whereas faults far from the center penetrate more deeply. The fault scaling also indicates that the graben formed in mechanically strong material, which we identify with dry basalt-like plains. These plains were also affected by changes in long-wavelength topography, including undulations with wavelengths of up to 1300 km and amplitudes of 2.5 to 3 km. Geographic correlation of the depth extent of faulting with topographic variations allows a first-order interpretation of the subsurface structure and mechanical stratigraphy in the basin. Further, crosscutting and superposition relationships among plains, faults, craters, and topography indicate that development of long-wavelength topographic variations followed plains emplacement, faulting, and much of the cratering within the Caloris basin. As several examples of these topographic undulations are also found outside the basin, our results on the scale, structural style, and relative timing of the topographic changes have regional applicability and may be the surface expression of global-scale interior processes on Mercury.

Reference
Klimczak C, Ernst CM, Byrne PK, Solomon SC, Watters TR, Murchie SL, Preusker F and Balcerski JA (in press) Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long-wavelength topography. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20157]
Published by arrangement with John Wiley & Sons

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A. C. Boley^1,4, M. A. Morris², and S. J. Desch³

A fundamental, unsolved problem in solar system formation is explaining the melting and crystallization of chondrules found in chondritic meteorites. Theoretical models of chondrule melting in nebular shocks have been shown to be consistent with many aspects of thermal histories inferred for chondrules from laboratory experiments; but, the mechanism driving these shocks is unknown. Planetesimals and planetary embryos on eccentric orbits can produce bow shocks as they move supersonically through the disk gas, and are one possible source of chondrule-melting shocks. We investigate chondrule formation in bow shocks around planetoids through three-dimensional radiation hydrodynamics simulations. A new radiation transport algorithm that combines elements of flux-limited diffusion and Monte Carlo methods is used to capture the complexity of radiative transport around bow shocks. An equation of state that includes the rotational, vibrational, and dissociation modes of H₂ is also used. Solids are followed directly in the simulations and their thermal histories are recorded. Adiabatic expansion creates rapid cooling of the gas, and tail shocks behind the embryo can cause secondary heating events. Radiative transport is efficient, and bow shocks around planetoids can have luminosities ~few× 10⁻⁸ L_☉. While barred and radial chondrule textures could be produced in the radiative shocks explored here, porphyritic chondrules may only be possible in the adiabatic limit. We present a series of predicted cooling curves that merit investigation in laboratory experiments to determine whether the solids produced by bow shocks are represented in the meteoritic record by chondrules or other solids.

Reference
Boley AC, Morris MA and Desch SJ (in press) High-temperature Processing of Solids through Solar Nebular Bow Shocks: 3D Radiation Hydrodynamics Simulations with Particles. The Astrophysical Journal
[doi:10.1088/0004-637X/776/2/101]

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Christoph Duermann, Gerhard Wurm and Markus Kuepper

Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany

In optically thin parts of protoplanetary disks photophoresis is a significant force not just for dust grains, but also for macroscopic bodies. The absolute strength on the supposedly highly porous objects is not known in detail as yet. We set up a low pressure torsion balance and studied photophoretic forces down to 100 nN on plates at a light flux of 100 W/m². We investigated the dependence on plate dimensions and on ambient pressure and considered the influence of channels through the plates. As samples for full (no channel) plates we used tissue with 2 mm thickness and circular shape with diameters of 10 mm, 30 mm and 50 mm. The influence of channels was probed on rectangular-shaped circuit boards of 35 mm × 35 mm area and 1.5 mm thickness. The number of channels was 169 and 352. The pressure was varied over three decades between 0.001 and 1 mbar. At low pressure, the absolute photophoretic force is proportional to the cross section of the plates. At high pressure, gas flow through the channels enhances the photophoretic force. The pressure dependence of the radiative force can (formally) be calculated by photophoresis on particles with a characteristic length. We derived two characteristic length scales l depending on the plate radius r₁, the channel radius r₂, and the thickness of the plate, which equals the length of the channel d asl = r^0.35 × d^0.65. The highest force is found at a pressure p_max = 15 × l^-1 Pa mm. In total, the photophoretic force on a plate with channels can be well described by a superposition of the two components: photophoresis due to the overall size and cross section of the plate and photophoresis due to the channels, both with their characteristic pressure dependencies. We applied these results to the transport of large solids in protoplanetary disks and found that the influence of porosity on the photophoretic force can reverse the inward drift of large solids, for instance meter-sized bodies, and push them outward within the optically thin parts of the disk.

Reference
Duermann C, Wurm G and Kuepper M (in press) Radiative forces on macroscopic porous bodies in protoplanetary disks: laboratory experiments. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321365]
Reproduced with permission © ESO

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B. J. Buratti^1,*, P. A. Dalba¹, M. D. Hicks¹, V. Reddy², M. V. Sykes², T. B. McCord³, D. P. O’Brien², C. M. Pieters⁴, T. H. Prettyman², L. A. McFadden⁵, Andreas Nathues⁶, Lucille Le Corre⁶, S. Marchi⁷, Carol Raymond¹, Chris Russell⁸

¹California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California, USA
²Planetary Science Institute, Tucson,Arizona, USA
³Bear Fight Institute, Winthrop, Washington, USA
⁴Department of Geological Sciences, Brown University, Providence, RI, USA
⁵NASA Goddard Space Flight Center, Greenbelt, MD
⁶Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
⁷NASA Lunar Science Institute, Boulder, Colorado, USA
⁸Department of Earth and Space Sciences and the Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA

The Framing Camera (FC) on the Dawn spacecraft provided the first view of 4 Vesta at sufficiently high spatial resolution to enable a detailed correlation of the asteroid’s spectral properties with geologic features and with the vestoid (V-type) asteroids and the Howardite-Eucrite-Diogenite (HED) class of meteorites, both of which are believed to originate on Vesta. We combine a spectral analysis of the basin with visible and near-IR spectroscopy of vestoids and with archived data over the same spectral range for HED meteorites. The vestoids are only slightly more akin to the Rheasilvia basin than to Vesta as a whole, suggesting that the crustal material ejected is a well-mixed collection of eucritic and diogenitic materials. The basin itself is more diogenitic, implying Vesta is differentiated and the impact that created Rheasilvia uncovered a mineralogically distinct layer. The Rheasilvia basin exhibits a larger range in pyroxene band strengths than Vesta as a whole, further implying that the basin offers a view into a complex, differentiated protoplanet. The discrepancy between the spectral properties of the HED meteorites and Vesta, in particular the meteorites’ deeper pyroxene absorption band and the redder color of the vestoids, can be explained by the abundance of smaller particles on Vesta and by the addition of low-albedo exogenous particles to its surface, which in turn are due to its larger gravity and longer exposure time to impact processing. Solar phase effects are slight and do not explain the spectral discrepancies between the HEDs, Vesta, and the vestoids.

Reference
Buratti BJ, Dalba PA, Hicks MD, Reddy V, Sykes MV, McCord TB, O’Brien DP, Pieters CM, Prettyman TH, McFadden LA, Nathues A, Le Corre L, Marchi S, Raymond C, Russell C (in press) Vesta, vestoids, and the HED meteorites: Interconnections and differences based on Dawn Framing Camera observations. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20152]
Published by arrangement with John Wiley & Sons

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A. P. Jones^1,2, L. Fanciullo^1,2, M. Köhler^1,2, L. Verstraete^1,2, V. Guillet^1,2, M. Bocchio^1,2 and N. Ysard^1,2

¹CNRS, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France
²Université Paris Sud, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France

Context. The evolution of amorphous hydrocarbon materials, a-C(:H), principally resulting from ultraviolet (UV) photon absorption-induced processing, are likely at the heart of the variations in the observed properties of dust in the interstellar medium.
Aims. The consequences of the size-dependent and compositional variations in a-C(:H), from aliphatic-rich a-C:H to aromatic-rich a-C, are studied within the context of the interstellar dust extinction and emission.
Methods. Newly-derived optical property data for a-C(:H) materials, combined with that for an amorphous forsterite-type silicate with iron nano-particle inclusions, a-Sil_Fe, are used to explore dust evolution in the interstellar medium.
Results. We present a new dust model that consists of a power-law distribution of small a-C grains and log-normal distributions of large a-Sil_Fe and a-C(:H) grains. The model, which is firmly anchored by laboratory-data, is shown to quite naturally explain the variations in the infrared (IR) to far-ultraviolet (FUV) extinction, the 217 nm UV bump, the IR absorption and emission bands and the IR-mm dust emission.
Conclusions. The major strengths of the new model are its inherent simplicity and built-in capacity to follow dust evolution in interstellar media. We show that mantle accretion in molecular clouds and UV photo-processing in photo-dominated regions are likely the major drivers of dust evolution.

Reference
Jones AP, Fanciullo L, Köhler M, Verstraete L, Guillet V, Bocchio M and Ysard N (in press) The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321686]
Reproduced with permission © ESO

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