M. Flock^1,2, S. Fromang^1,2, M. González^2,3 and B. Commerçon⁴

¹CEA, Irfu, SAp Centre de Saclay 91191 Gif-sur-Yvette France
²UMR AIM, CEA-CNRS-Univ. Paris Diderot, Centre de Saclay, 91191 Gif-sur-Yvette, France
³Université Paris Diderot, Sorbonne Paris Cité, AIM, UMR 7158, CEA, CNRS, 91191 Gif-sur-Yvette, France
⁴Laboratoire de radioastronomie, UMR 8112 du CNRS, École normale supérieure et Observatoire de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France

Aims. Our aim is to study the thermal and dynamical evolution of protoplanetary discs in global simulations, including the physics of radiation transfer and magneto-hydrodynamic turbulence caused by the magneto-rotational instability.
Methods. We have developed a radiative transfer method based on the flux-limited diffusion approximation that includes frequency dependent irradiation by the central star. This hybrid scheme is implemented in the PLUTO code. The focus of our implementation is on the performance of the radiative transfer method. Using an optimized Jacobi preconditioned BiCGSTAB solver, the radiative module is three times faster than the magneto-hydrodynamic step for the disc set-up we consider. We obtain weak scaling efficiencies of 70% up to 1024 cores.
Results. We present the first global 3D radiation magneto-hydrodynamic simulations of a stratified protoplanetary disc. The disc model parameters were chosen to approximate those of the system AS 209 in the star-forming region Ophiuchus. Starting the simulation from a disc in radiative and hydrostatic equilibrium, the magneto-rotational instability quickly causes magneto-hydrodynamic turbulence and heating in the disc. We find that the turbulent properties are similar to that of recent locally isothermal global simulations of protoplanetary discs. For example, the rate of angular momentum transport α is a few times 10^-3. For the disc parameters we use, turbulent dissipation heats the disc midplane and raises the temperature by about 15% compared to passive disc models. The vertical temperature profile shows no temperature peak at the midplane as in classical viscous disc models. A roughly flat vertical temperature profile establishes in the optically thick region of the disc close to the midplane. We reproduce the vertical temperature profile with viscous disc models for which the stress tensor vertical profile is flat in the bulk of the disc and vanishes in the disc corona.
Conclusions. The present paper demonstrates for the first time that global radiation magneto-hydrodynamic simulations of turbulent protoplanetary discs are feasible with current computational facilities. This opens up the window to a wide range of studies of the dynamics of the inner parts of protoplanetary discs, for which there are significant observational constraints.

Reference
Flock M, Fromang S, González M and Commerçon B (2013) Radiation magnetohydrodynamics in global simulations of protoplanetary discs. Astronomy & Astrophysics 560:A43.
[doi:10.1051/0004-6361/201322451]
Reproduced with permission © ESO

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Althea V. Moorhead^a, Paul A. Wiegert^b and William J. Cooke^c

^aGeocent LLC, Jacobs ESSSA Group, Marshall Space Flight Center, Huntsville, Alabama 35812
^bDepartment of Physics and Astronomy, The University of Western Ontario, London N6A3K7, Canada
^cNASA Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Alabama 35812

Long-period comet C/2013 A1 (Siding Spring) will experience a close encounter with Mars on 2014 Oct 19. As of 2013 Oct 21, the distance of closest approach between the two is projected to be between 89,000 km and 173,000 km, with a nominal value of 131,000 km. Thus, a collision between the comet and the planet has been ruled out, but the comet’s coma may very well envelop Mars and its man-made satellites. We present a simple analytic model of the dust component of cometary comae that describes the spatial distribution of cometary dust and meteoroids and their size distribution. We find that this model successfully reproduces, to within an order of magnitude, particle fluxes measured by spacecraft Giotto in the coma of 1P/Halley and by spacecraft Stardust in the coma of 81P/Wild 2. We apply our analytic model to C/2013 A1 (Siding Spring) and compute the expected total fluence of potentially damaging particles at Mars at the time of closest approach between the two bodies; we obtain a nominal fluence of 0.15 particles per square meter. We conduct numerical simulations of particle ejection from the comet’s nucleus and compare the resulting spatial distribution with that of our analytic model, and conclude that our spherically symmetric analytic model is adequate for order-of-magnitude fluence estimates.

Reference
Moorhead AV, Wiegert PA andCooke WJ (in press) The meteoroid fluence at Mars due to comet C/2013 A1 (Siding Spring). Icarus
[doi:10.1016/j.icarus.2013.11.028]
Copyright Elsevier

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Emily A. Pringle^1,2, Paul S. Savage¹, Matthew G. Jackson³, Jean-Alix Barrat⁴ and Frédéric Moynier^1,2

¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
²Institut de Physique du Globe de Paris, Université Paris Diderot, 75005 Paris, France
³Department of Earth Science, University of California, Santa Barbara, CA 93109, USA
⁴Université Européenne de Bretagne, Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, F-29280 Plouzané Cedex, France

The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in ²⁹Si/²⁸Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of ²⁹Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

Reference
Pringle EA, Savage PS, Jackson MG, Barrat J-A and Moynier F (in press) Si Isotope Homogeneity of the Solar Nebula. The Astrophysical Journal 779:123
[doi:10.1088/0004-637X/779/2/123]

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Francesca E. DeMeo^a,b,c, Richard P. Binzel^b, Benoit Carry^d,e, David Polishook^b and Nicholas A. Moskovitz^b

^aHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-16, Cambridge, MA, 02138, USA
^bDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
^cHubble Fellow
^dInstitut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, UMR8028 CNRS, 77 av. Denfert-Rochereau 75014 Paris, France
^eEuropean Space Astronomy Centre, ESA, P.O. Box 78, 28691 Villanueva de la Cañada, Madrid, Spain

Very red featureless asteroids (spectroscopic D-types) are expected to have formed in the outer solar system far from the sun. They comprise the majority of asteroids in the Jupiter Trojan population, and are also commonly found in the outer main belt and among Hildas. The first evidence for D-types in the inner and middle parts of the main belt was seen in the Sloan Digital Sky Survey (SDSS). Here we report follow-up observations of SDSS D-type candidates in the near-infrared. Based on follow up observations of 13 SDSS D-type candidates, we find a ∼20% positive confirmation rate. Known inner belt D-types range in diameter from roughly 7 to 30 kilometers. Based on these detections we estimate there are ∼100 inner belt D-types with diameters between 2.5 and 20km. The lower and upper limits for total mass of inner belt D-types is 2×10¹⁶kg to 2×10¹⁷kg which represents 0.01% to 0.1% of the mass of the inner belt. The inner belt D-types have albedos at or above the upper end typical for D-types which raises the question as to whether these inner belt bodies represent only a subset of D-types, they have been altered by external factors such as weathering processes, or if they are compositionally distinct from other D-types. All D-types and candidates have diameters less than 30km, yet there is no obvious parent body in the inner belt. Dynamical models have yet to show how D-types originating from the outer solar system could penetrate into the inner reaches of the Main Belt under current scenarios of planet formation and subsequent Yarkovsky drift.

Reference
DeMeo FE, Binzel RP, Carry B Polishook D and Moskovitz NA (in press) Unexpected D-type Interlopers in the Inner Main Belt. Icarus
[doi:10.1016/j.icarus.2013.11.026]
Copyright Elsevier

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Tobias W. A. Müller and Wilhelm Kley

Institut für Astronomie & Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany

Context. Transitional disks are protoplanetary disks around young stars that display inner holes in the dust distribution within a few au that are accompanied by some gas accretion onto the central star. These cavities could possibly be created by the presence of one or more massive planets that opened a large gap or even cleared the whole inner region.
Aims. If the gap is created by planets and gas is still present in it, then there should be a flow of gas past the planet into the inner region. It is our goal to study in detail the mass accretion rate into this planet-created gap in transitional disks and in particular the dependency on the planet’s mass and the thermodynamic properties of the disk.
Methods. We performed 2D hydrodynamical simulations using the grid-based FARGO code for disks with embedded planets. We added radiative cooling from the disk surfaces, radiative diffusion in the disk midplane, and stellar irradiation to the energy equation to have more realistic models.
Results. The mass flow rate into the gap region depends, for given disk thermodynamics, non-monotonically on the mass of the planet. Generally, more massive planets open wider and deeper gaps which would tend to reduce the mass accretion into the inner cavity. However, for larger mass planets the outer disk becomes eccentric and the mass flow rate is enhanced over the low mass cases. As a result, for the isothermal disks the mass flow is always comparable to the expected mass flow of unperturbed disks Ṁ_d, while for more realistic radiative disks the mass flow is very small for low mass planets (≤4 M_jup) and about 50% of Ṁ_d for larger planet masses. The critical planet mass that allows the disk to become eccentric is much larger for radiative disks than for purely isothermal cases.
Conclusions. Massive embedded planets can reduce the mass flow across the gap considerably, to values of about an order of magnitude smaller than the standard disk accretion rate, and can be responsible for opening large cavities. The remaining mass flow into the central cavity is in good agreement with the observations.

Reference
Müller TWA and Kley W (2013) Modelling accretion in transitional disks. Astronomy & Astrophysics 560:A40.
[doi:10.1051/0004-6361/201322503]
Reproduced with permission © ESO

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