Cyrena Anne Goodrich^1,2,*, Allan H. Treiman³, Justin Filiberto⁴, Juliane Gross⁵, Michael Jercinovic²

¹Planetary Science Institute, Tucson, Arizona, USA
²Department of Geosciences, University of Massachusetts, Amherst, Massachusetts, USA
³Lunar and Planetary Institute, Houston, Texas, USA
⁴Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
⁵Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA

We used new analytical and theoretical methods to determine the major and minor element compositions of the primary trapped liquid (PTLs) represented by melt inclusions in olivine and augite in the Martian clinopyroxenite, Nakhla, for comparison with previously proposed compositions for the Nakhla (or nakhlite) parent magma. We particularly focused on obtaining accurate K₂O contents, and on testing whether high K₂O contents and K₂O/Na₂O ratios obtained in previous studies of melt inclusions in olivine in Nakhla could have been due to unrepresentative sampling, systematic errors arising from electron microprobe techniques, late alteration of the inclusions, and/or boundary layer effects. Based on analyses of 35 melt inclusions in olivine cores, the PTL in olivine, PTL_oliv, contained (by wt) approximately 47% SiO₂, 6.3% Al₂O₃, 9.6% CaO, 1.8% K₂O, and 0.9% Na₂O, with K₂O/Na₂O = 2.0. We infer that the high K₂O content of PTL_oliv is not due to boundary layer effects and represents a real property of the melt from which the host olivine crystallized. This melt was cosaturated with olivine and augite. Its mg# is model-dependent and is constrained only to be ≥19 (equilibrium Fo = 40). Based on analyses of 91 melt inclusions in augite cores, the PTL in augite, PTL_aug, contained (by wt) 53–54% SiO₂, 7–8% Al₂O₃, 0.8–1.1% K₂O, and 1.1–1.4% Na₂O, with K₂O/Na₂O = 0.7–0.8. This K₂O content and K₂O/Na₂O ratio are significantly higher than inferred in studies of melt inclusions in augite in Nakhla by experimental rehomogenization. PTL_aug was saturated only with augite, and in equilibrium with augite cores of mg# 62. PTL_augrepresents the Nakhla parent magma, and does not evolve to PTL_oliv by fractional crystallization. We therefore conclude that olivine cores in Nakhla (and, by extension, other nakhlites) are xenocrystic. We propose that PTL_oliv and PTL_aug were generated from the same source region. PTL_oliv was generated first and emplaced to form olivine-rich cumulate rocks. Shortly thereafter, PTL_aug was generated and ascended through these olivine-rich cumulates, incorporating fragments of wallrock that became the xenocrystic olivine cores in Nakhla. The Nakhla (nakhlite) mantle source region was pyroxenitic with some olivine, and could have become enriched in K relative to Na via metasomatism. A high degree of melting of this source produced the silica-poor, alkali-rich magma PTL_oliv. Further ascension and decompression of the source led to generation of the silica-rich, relatively alkali-poor magma PTL_aug. Potassium-rich magmas like those involved in the formation of the nakhlites represent an important part of the diversity of Martian igneous rocks.

Reference
Goodrich CA, Treiman AH, Filiberto J, Gross J and Jercinovic M (2013) K2O-rich trapped melt in olivine in the Nakhla meteorite: Implications for petrogenesis of nakhlites and evolution of the Martian mantle. Meteoritics & Planetary Science 48:2371–2405.
[doi:10.1111/maps.12226]
Published by arrangement with John Wiley & Sons

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M. Ali-Dib¹, O. Mousis¹, G. S. Pekmezci², J. I. Lunine³, N. Madhusudhan⁴ and J.-M. Petit<sup>1

1</sup>Université de Franche-Comté, Institut UTINAM, CNRS/INSU, UMR 6213, Besançon Cedex, France
²Dipartimento di Astronomia, Universitá di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
³Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853, USA
⁴Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511, USA

Context. The observation of carbon-rich disks have motivated several studies questioning the influence of the C/O ratio on their gas phase composition in order to establish the connection between the metallicity of hot-Jupiters and that of their parent stars.
Aims. We propose a method that allows the characterization of the adopted C/O ratio in protoplanetary disks independently from the determination of the host star composition. Titanium and vanadium chemistries are investigated because they are strong optical absorbers and also because their oxides are known to be sensitive to the C/O ratio in some exoplanet atmospheres.
Methods. We use a commercial package based on the Gibbs energy minimization technique to compute the titanium and vanadium equilibrium chemistries in protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations are performed for pressures in the 10^-6–10^-2 bar domain, and for temperatures ranging from 50 K to 2000 K.
Results. We find that the vanadium nitride/vanadium oxide and titanium hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the hot parts of disks (T ≥ 1000 K). Our calculations suggest that, in these regions, these ratios can be used as tracers of the C/O value in protoplanetary disks.

Reference
Ali-Dib M, Mousis O, Pekmezci GS, Lunine JI, Madhusudhan N and Petit J-M (2014) Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks. Astronomy & Astrophysics 561:A60.
[doi:10.1051/0004-6361/201321780]
Reproduced with permission © ESO

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V. Alí-Lagoa^1,2, L. Lionni³, M. Delbo⁴, B. Gundlach⁵, J. Blum⁵ and J. Licandro^1,2

¹Instituto de Astrofísica de Canarias (IAC), c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³University Paris VII – Diderot, 5 rue Thomas Mann, 75013 Paris, France
⁴UNS-CNRS-Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
⁵Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany

Aims. We derive the thermal inertia of 2008 EV₅, the baseline target for the Marco Polo-R mission proposal, and infer information about the size of the particles on its surface.
Methods. Values of thermal inertia were obtained by fitting an asteroid thermophysical model to NASA’s Wide-field Infrared Survey Explorer (WISE) infrared data. Grain size was derived from the constrained thermal inertia and a model of heat conductivity that accounts for different values of the packing fraction (a measure of the degree of compaction of the regolith particles).
Results. We obtain an effective diameter D = 370 ± 6   m, geometric visible albedo p_V = 0.13 ± 0.05 (assuming H = 20.0 ± 0.4), and thermal inertia Γ = 450 ± 60 J m^-2 s^−1/2 K^-1 at the 1σ level of significance for its retrograde spin-pole solution. The regolith particles radius is r = 6.6^+1.3_-1.3 mm for low degrees of compaction and r = 12.5^+2.7_-2.6 mm for the highest packing densities.

Reference
Alí-Lagoa V, Lionni L, Delbo M, Gundlach B, Blum J and Licandro J (2014) Thermophysical properties of near-Earth asteroid (341843) 2008 EV₅ from WISE data. Astronomy & Astrophysics 561:A45.
[doi:10.1051/0004-6361/201322215]
Reproduced with permission © ESO

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Álvaro Ribas^1,2,3, Bruno Merín⁴, Hervé Bouy² and Luke T. Maud⁵

¹European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada Madrid Spain
²Centro de Astrobiología, INTA-CSIC, PO Box-Apdo. de correos 78, 28691 Villanueva de la Cañada Madrid, Spain
³Ingeniería y Servicios Aeroespaciales-ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴Herschel Science Centre, ESAC-ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁵School of Physics & Astronomy, EC Stoner Building, University of Leeds, Leeds LS2 9JT, UK

Aims. We study the evolution of circumstellar disks in 22 young (1 to 100 Myr) nearby (within 500 pc) associations over the entire mass spectrum using photometry covering from the optical to the mid-infrared.
Methods. We compiled a catalog of 2340 spectroscopically-confirmed members of these nearby associations. We analyzed their spectral energy distributions and searched for excess related to the presence of protoplanetary disks. The dataset has been analyzed in a homogeneous and consistent way, allowing for meaningful inter-comparison of results obtained for individual regions. Special attention was given to the sensitivity limits and spatial completeness of the observations.
Results. We derive disk fractions as probed by mid-infrared excess in the 22 regions. The unprecedented size of our sample allows us to confirm the timescale of disk decay reported in the literature and to find new trends. The fraction of excess sources increases systematically if measured at longer wavelengths. Disk percentages derived using different wavelength ranges should therefore be compared with caution. The dust probed at 22–24 μm evolves slower than that probed at shorter wavelengths (3.4–12 μm). Assuming an exponential decay, we derive a timescale τ = 4.2 − 5.8 Myr at 22–24 μm for primordial disks, compared to 2 ~ 3 Myr at shorter wavelengths (3.4–12 μm). Primordial disks disappear around 10 ~ 20 Myr. Their decline matches in time a brief increase of the number of “evolved” disks (defined here as including transitional and debris disks). There is more dispersion in the fraction of excess sources with age when measured at 22–24 μm in comparison to shorter wavelengths.
Conclusions. The increase in timescale of excess decay at longer wavelength is compatible with inside-out disk clearing scenarios. The increased timescale of decay and larger dispersion in the distribution of disk fractions at 22–24 μm suggest that the inner (terrestrial-planet forming) and outer (giant-planet forming) zones evolve differently, the latter potentially following a variety of evolutionary paths. The drop of primordial disks and the coincident rise of evolved disks at 10 Myr are compatible with planet formation theories suggesting that the disappearance of the gas is immediately followed by the dynamical stirring of the disk.

Reference
Ribas A, Merín B, Bouy H and Maud LT (2014) Disk evolution in the solar neighbourhood – I. Disk frequencies from 1 to 100 Myr. Astronomy & Astrophysics 561:A54.
[doi:10.1051/0004-6361/201322597]
Reproduced with permission © ESO

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Kevin R. Grazier^a, Julie.C. Castillo-Rogez^a and Philip W. Sharp^b

^aJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
^bDepartment of Mathematics, University of Auckland, New Zealand

We quantify the relative contribution of volatiles supplied from outer Solar System planetesimal reservoirs to large wet asteroids during the first few My after the beginning of the Solar System. To that end, we simulate the fate of planetesimals originating within different regions of the Solar System–and thus characterized by different chemical inventories–using a highly accurate integrator tuned to handle close planet/planetesimal encounters. The fraction of icy planetesimals crossing the Asteroid Belt was relatively significant, and our simulations show that planetesimals originating from the Jupiter/Saturn region were orders of magnitude more abundant than those stemming from the Uranus and Neptune regions when the planets were just embryos. As the planets reached their full masses the Jupiter/ Saturn and Saturn/Uranus regions contributed similar fractions of planetesimals for any material remaining in these reservoirs late in the stage of planetary formation. This implies that large asteroids like Ceres accreted very little material enriched in low-eutectic volatiles (e.g., methanol, nitrogen and methane ices, etc.) and clathrate hydrates expected to condense at the very low temperatures predicted for beyond Saturn’s orbit in current early Solar nebula models. Further, a large fraction of the content in organics of Ceres and neighboring ice-rich objects originates from the outer Solar System.

Reference
Grazier KR, Castillo-Rogez JC and Sharp PW (in press) Dynamical Delivery of Volatiles to the Outer Main Belt. Icarus 780:154.
[doi:10.1088/0004-637X/780/2/154]
Copyright Elsevier

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Laura Vican¹ and Adam Schneider^2,3

¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
²Department of Physics and Astronomy, University of Georgia, Athens, GA 30602, USA
³Current Address: Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606, USA.

We used chromospheric activity to determine the ages of 2820 field stars. We searched these stars for excess emission at 22 μm with the Wide-Field Infrared Survey Explorer. Such excess emission is indicative of a dusty debris disk around a star. We investigated how disk incidence trends with various stellar parameters, and how these parameters evolve with time. We found 22 μm excesses around 98 stars (a detection rate of 3.5%). Of these 98 excess sources, 74 are presented here for the first time. We also measured the abundance of lithium in eight dusty stars in order to test our stellar age estimates.

Reference
Vican L and Schneider A (2014) The evolution of dusty debris disks around solar type stars. The Astrophysical Journal 780:154.
[doi:10.1088/0004-637X/780/2/154]

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Tilman Birnstiel and Sean M. Andrews

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

The expectation that aerodynamic drag will force the solids in a gas-rich protoplanetary disk to spiral in toward the host star on short timescales is one of the fundamental problems in planet formation theory. The nominal efficiency of this radial drift process is in conflict with observations, suggesting that an empirical calibration of solid transport mechanisms in a disk is highly desirable. However, the fact that both radial drift and grain growth produce a similar particle size segregation in a disk (such that larger particles are preferentially concentrated closer to the star) makes it difficult to disentangle a clear signature of drift alone. We highlight a new approach, by showing that radial drift leaves a distinctive “fingerprint” in the dust surface density profile that is directly accessible to current observational facilities. Using an analytical framework for dust evolution, we demonstrate that the combined effects of drift and (viscous) gas drag naturally produce a sharp outer edge in the dust distribution (or, equivalently, a sharp decrease in the dust-to-gas mass ratio). This edge feature forms during the earliest phase in the evolution of disk solids, before grain growth in the outer disk has made much progress, and is preserved over longer timescales when both growth and transport effects are more substantial. The key features of these analytical models are reproduced in detailed numerical simulations, and are qualitatively consistent with recent millimeter-wave observations that find gas/dust size discrepancies and steep declines in dust continuum emission in the outer regions of protoplanetary disks.

Reference
T Birnstiel and Andrews SM (2014) On the outer edges of protoplanetary dust disks. The Astrophysical Journal 780:153.
[doi:10.1088/0004-637X/780/2/153]

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P. R. Brook^1,5, A. Karastergiou¹, S. Buchner^2,6, S. J. Roberts³, M. J. Keith^4,7, S. Johnston⁴ and R. M. Shannon⁴

¹Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
²Hartebeesthoek Radio Astronomy Observatory, P.O. Box 443, Krugersdorp 1740, South Africa
³Information Engineering, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
⁴CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710, Australia
⁵CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710, Australia
⁶School of Physics, University of Witwatersrand, Johannesburg, South Africa
⁷Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar’s magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738–4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk.

Reference
Brook PR, Karastergiou A, Buchner S, Roberts SJ, Keith MJ, Johnston S and Shannon RM (2014) Evidence of an Asteroid Encountering a Pulsar. The Astrophysical Journal – Letters 780:L31.
[doi:10.1088/2041-8205/780/2/L31]

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H. Jay Melosh^1,*, David J. Stevenson², Robin Canup³

¹EAPS, Purdue University, West Lafayette, IN 47907, USA.
²Department of Planetary Science, California Institute of Technology, Pasadena, CA 91125-2100, USA.
³Planetary Science Directorate, Southwest Research Institute Boulder, CO 80302, USA.

This is a short letter without abstract.

Reference
Melosh HJ, Stevenson DJ and Robin Canup R (2013) Credit for Impact Theory. Science 342:1445-1446.
[doi:10.1126/science.342.6165.1445-b]
Reprinted with permission from AAAS

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E. Mazzotta Epifani¹, D. Perna², L. Di Fabrizio³, M. Dall’Ora¹, P. Palumbo⁴, C. Snodgrass⁵, J. Licandro^6,7, V. Della Corte⁴ and G. P. Tozzi⁸

¹INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
²LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France 
³Fundación Galileo Galilei – INAF, Rambla José Ana Fernández Pérez 7, 38712 Breña Baja, TF, Spain
⁴Universitá Parthenope, Dip. Scienze Applicate, Centro Direzionale Isola C4, 80143 Napoli, Italy
⁵Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
⁶Instituto de Astrofísica de Canarias, c/vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
⁷Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁸INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy

Context. With this work we start a systematic analysis of the distant activity of several long-period comets in order to investigate the evolution of activity throughout the solar system and explore differences between comets that pass their perihelion at far or very close distances from the Sun.
Aims. We present observational data for eight long-period comets, observed for the first time beyond r = 5 AU. Three targets have been characterised on their inward orbital branch. The others have passed their perihelion at quite large heliocentric distances (r_q from 4.5 to 7.5 AU).
Methods. We analyse multicolour broadband images (V,R, and I filters) taken at the Telescopio Nazionale Galileo to characterise the dust coma of the comets and investigate their morphology, photometry, colours, and dust production.
Results. The morphological analysis shows many differences among the sample, from the large twisted structure present in the coma of comet C/2005 L3 to the regular coma envelope of C/2010 R1. The colour of the dust coma of all the comets is redder than the Sun. The Afρ value (measured in a reference aperture of radius ρ = 10⁴ km) ranges from 114 ± 2 (C/2005 S4) to 5091 ± 47 (C/2005 L3) cm, depicting a scenario of bodies from moderately to very active. This is confirmed by the first-order quantitative estimate of the dust mass-loss rate for the comets that was obtained from the photometric data: assuming a grain velocity of v = 20 m/s, the dust production rate is comparable with, or even significantly larger than, that measured for many short-period (“old”) comets at much smaller heliocentric distances.

Reference
Epifani, EM, Perna D, Di Fabrizio L, Dall’Ora M, Palumbo P, Snodgrass C, Licandro J, Corte VD and Tozzi GP (2014) Observational results for eight long-period comets observed far from the Sun. Astronomy & Astrophysics 561:A6.
[doi:10.1051/0004-6361/201321290]
Reproduced with permission © ESO

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