Sachiko Amari^1,*, Jun-ichi Matsuda², Rhonda M. Stroud³, and Matthew F. Chisholm⁴

¹McDonnell Center for the Space Sciences and the Physics Department, Washington University, St. Louis, MO 63130, USA
²Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan
³Code 6360, Naval Research Laboratory, Washington, DC 20375, USA
⁴Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

The majority of heavy noble gases (Ar, Kr, and Xe) in primitive meteorites are stored in a poorly understood phase called Q. Although Q is thought to be carbonaceous, the full identity of the phase has remained elusive for almost four decades. In order to better characterize phase Q and, in turn, the early solar nebula, we separated carbon-rich fractions from the Saratov (L4) meteorite. We chose this meteorite because Q is most resistant in thermal alteration among carbonaceous noble gas carriers in meteorites and we hoped that, in this highly metamorphosed meteorite, Q would be present but not diamond: these two phases are very difficult to separate from each other. One of the fractions, AJ, has the highest ¹³²Xe concentration of 2.1 × 10^–6 cm³ STP g^–1, exceeding any Q-rich fractions that have yet been analyzed. Transmission electron microscopy studies of the fraction AJ and a less Q-rich fraction AI indicate that they both are primarily porous carbon that consists of domains with short-range graphene orders, with variable packing in three dimensions, but no long-range graphitic order. The relative abundance of Xe and C atoms (6:10⁹) in the separates indicates that individual noble gas atoms are associated with only a minor component of the porous carbon, possibly one or more specific arrangements of the nanoparticulate graphene.

Reference
Amari S, Matsuda J-I, Stroud RM and Chisholm MF (2013) Highly Concentrated Nebular Noble Gases in Porous Nanocarbon Separates from the Saratov (L4) Meteorite. The Astrophysical Journal 778:37.
[doi:10.1088/0004-637X/778/1/37]

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S. Richard¹, P. Barge¹ and S. Le Dizès²

¹Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
²Aix-Marseille Université, CNRS, Centrale Marseille, IRPHE (Institut de Recherche sur les Phénomènes Hors Equilibre), UMR 7342, 49 rue F. Joliot Curie, 13013 Marseille, France

Context. Large-scale persistent vortices could play a key role in the evolution of protoplanetary disks, particularly in the dead zone where no turbulence associated with a magnetic field is expected. These vortices are known to form easily in 2D disks via the Rossby wave or the baroclinic instability. In three dimensions, however, their formation and stability is a complex problem and still a matter of debate.
Aims. We study the formation of vortices by the Rossby wave instability in a stratified inviscid disk and describe their 3D structure, stability, and long-term evolution.
Methods. Numerical simulations were performed using a fully compressible hydrodynamical code based on a second-order finite volume method. We assumed a perfect-gas law and a non-homentropic adiabatic flow.
Results. The Rossby wave instability is found to proceed in 3D in a similar way as in 2D. Vortices produced by the instability look like columns of vorticity in the whole disk thickness; the weak vertical motions are related to the weak inclination of the vortex axis that appears during the development of the RWI. Vortices with aspect ratios higher than 6 are unaffected by the elliptical instability. They relax into a quasi-steady columnar structure that survives hundreds of rotations while slowly migrating inward toward the star at a rate that reduces with the vortex aspect ratio. Vortices with a lower aspect ratio are by contrast affected by the elliptic instability. Short aspect ratio vortices (χ < 4) are completely destroyed in a few orbital periods. Vortices with an intermediate aspect ratio (4 < χ < 6) are partially destroyed by the elliptical instability in a region away from the midplane where the disk stratification is sufficiently strong.
Conclusions. Elongated Rossby vortices can survive many orbital periods in protoplanetary disks in the form of vorticity columns. They could play a significant role in the evolution of the gas and the gathering of solid particles to form planetesimals or planetary cores, a possibility that receives a renewed interest with the recent discovery of a particle trap in the disk of Oph IRS 48.

Reference
Richard S, Barge P and Le Dizès S (2013) Structure, stability, and evolution of 3D Rossby vortices in protoplanetary disks. Astronomy & Astrophysics 559:A30.
[doi:10.1051/0004-6361/201322175]
Reproduced with permission © ESO

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