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Planet のバックアップ(No.63)


惑星セミナー2018

惑星セミナーは原則として毎週木曜日の14:00から理論部セミナー室で開催しています。
astro-phセミナーは毎週金曜日の12:30から理論部セミナー室で開催しています。

Schedule & History

2017年度 2016年度 2015年度 2014年度

日程発表タイトルRemarks
前期 第1回 5/17 15:00-荻原 正博Formation of the terrestrial planets in the solar system around 1 au via radial concentration of planetesimals15:00
前期 第2回 5/24 15:00-波々伯部 広隆Determination of outer edge of circumplanetary disk in local 3d hydrodynamic simulations15:00
前期 第3回 5/30 14:00-Dimitri VerasThe growing field of post-main-sequence exoplanetary science, with strong connections to the solar systemWednesday@Rinko room
前期 第4回 6/14 14:00-細野 七月Numerical simulations of the giant impact onto the magma ocean
前期 第5回 6/28 14:00-兵頭 龍樹On the origin of Phobos and Deimos
前期 第6回 7/12 14:00-樋口 有理可Inner solar system objects with hyperbolic orbits: Interstellar origin or Oort cloud comets?
前期 第7回 7/19 14:00-中野 龍之介中心星質量による原始惑星系円盤進化の変化
前期 第8回 7/26 14:00-中嶋 彩乃Orbital evolution of Saturn's mid-sized moons and the tidal heating of Enceladus
後期 第1回 9/19 14:00-波々伯部 広隆論文紹介 (Tanigawa et al. 2012, ApJ, Distribution of Accreting Gas and Angular Momentum onto Circumplanetary Disks)
後期 第2回 10/3 14:00-小久保 英一郎Planetesimal Formation by Gravitational Instability of a Porous Dust Disk
後期 第3回 10/24 14:00-瀧 哲朗Chondrule Survivability in the Protosolar disk
後期 第4回 10/31 13:00-Jason Man Yin WooThe curious case of Mars' formation13:00
後期 第5回 11/7 14:00-松本侑士The formation and dynamical evolution of super-Earths through in-situ giant impacts around M dwarfs
後期 第6回 11/14 15:00-Adrien LeleuStability and detectability of co-orbital exoplanets15:00- 院生セミナー室
後期 第7回 11/21 13:00-藤井悠里On the radiation hydrodynamic simulations of formation of circumplanetary disks
後期 第8回 11/29 14:00-長谷川幸彦Reconsideration of Formation Process of Rocky PlanetesimalsThursday
後期 第9回 12/19 14:00-柴田翔Metallicity Enhancement of Gas Giants by Late Accretion of Solids - the Effect of Orbital Evolution
後期 第10回 1/9 10:00-小林浩N body simulation with collisional fragmentation for planet formation in giant impact stages
後期 第11回 2/13 15:00-桑原歩Gas flow around an embedded planet in a protoplanetary disk: the implications for planet formation
5/30 Dimitri Veras, The growing field of post-main-sequence exoplanetary science, with strong connections to the solar system
The quest for identifying the bulk chemical composition of extrasolar planets and robust observational evidence that between 25% and 50% of all Milky Way white dwarfs host currently dynamically-active planetary systems motivate investigations that link their formation and fate. Here I provide a review of our current knowledge of these systems, including an update on the observational and theoretical aspects of the groundbreaking discovery of at least one disintegrating minor planet transiting white dwarf WD 1145+017. I show how this field incorporates several facets of solar system physics and chemistry, and how its interdisciplinary nature requires input from orbital dynamics, stellar evolution, astrochemistry, atmospheric science and surface processes.
10/31 Jason Woo, The curious case of Mars' formation
Dynamical models of planet formation coupled with cosmochemical data from martian meteorites show that Mars' isotopic composition is distinct from that of Earth. Reconciliation of formation models with meteorite data require that Mars grew further from the Sun than its present position. Here, we evaluate this compositional difference in more detail by comparing output from two N-body planet formation models. The first of these planet formation models simulates what is termed the `Classical' case wherein Jupiter and Saturn are kept in their current orbits. We compare these results with another model based on the `Grand Tack', in which Jupiter and Saturn migrate through the primordial asteroid belt. Our estimate of the average fraction of chondrite assembled into Earth and Mars assumes that the initial solid disk consists of only sources of enstatite chondrite composition in the inner region, and ordinary chondrite in the outer region. Results of these analyses show that both models tend to yield Earth and Mars analogues whose accretion zones overlap. The Classical case fares better in forming Mars with its documented composition (29% to 68% enstatite chondrite plus 32% to 67% ordinary chondrite) though the Mars analogues are generally too massive. We also further calculate the isotopic composition of 17O, 50Ti, 54Cr, 142Nd, 64Ni, and 92Mo in the martian mantle from the Grand Tack simulations. We find that it is possible to match the calculated isotopic composition of all the above elements in Mars' mantle with their measured values, but the resulting uncertainties are too large to place good restriction on the early dynamical evolution and birth place of Mars.
11/7 Yuji Matsumoto The formation and dynamical evolution of super-Earths through in-situ giant impacts around M dwarfs
Recently, Earth-sized exoplanets are observed around TRAPPIST-1, which is M8 dwarf and has ~0.08 solar mass. Several on-going missions are targeting planets around M dwarfs. It is expected that more and more such planetary system around M dwarfs would be observed. There are some theoretical studies considering planetary formation around M dwarfs. However, the formation and dynamical evolution of close-in super-Earths have not understood systematically yet. We investigate the formation of close-in super-Earths through N-body simulations around M dwarfs. We use the same disk model with changing the stellar mass. At first, the dynamical evolution of isolation mass protoplanets is studied. As Matsumoto & Kokubo (2017) reported, protoplanets collide with their neighboring protoplanets soon after the orbital crossing around 1 solar mass star. Around M dwarfs, dynamical scattering between protoplanets becomes violent and such tournament-like collisional evolution is not seen. We also perform calculations with the systems that initially have protoplanets and planetesimals around M dwarfs. We find that planetesimals are ejected during some close scattering by protoplanets. The growth of protoplanets would be suppressed due to the ejection of planetesimals.
11/14 Adrien Leleu/ Stability and detectability of co-orbital exoplanets
Despite the existence of co-orbital bodies in the solar system (1:1 Mean-motion resonance), and the prediction of the formation of co-orbital planets by planetary system formation models, no co-orbital exoplanets (also called trojans) have been detected thus far. It can be due to the rarity of the configuration, the degeneracy of the co-orbital signature with other configurations, or the observational biases. After a description of various stable co-orbital configurations for a pair of planet, I will discuss the stability of the lagrangian equilibria (L4 and L5) during the migration in the protoplanetary disc for the variables associated to the resonant angle, but also in the direction of the eccentricities and inclination. Finally I will discuss the signature of co-orbitals exoplanets in Transit Timing Variation, transits, and combination of transit and radial velocity measurements.
12/19 Sho Shibata/ Metallicity Enhancement of Gas Giants by Late Accretion of Solids - the Effect of Orbital Evolution
Recent studies of internal structure of gas giants suggest that their envelope is enriched with heavier elements than hydrogen and helium, relative to their central star composition. It is considered that these enrichment in heavy elements are caused by the capture of planetesimals during the late formation stage of gas giants. Zhou & Lin 2007 and Shiraishi & Ida 2008 performed orbital integrations of planetesimals around a growing protoplanet in a constant protoplanetary disk, and estimated the total captured mass of planetesimals for Jupiter and Saturn. However, they assumed a simple formation models and neglected some physically important effects. In this study, we investigated the effect of a planet migration on the capture of planetesimals, in a single-planetary system and a multi-planetary system, respectively. We find that planetesimals swept by a migrating planet are trapped at the mean-motion resonances (MMRs), which works as a barrier and prevents planetesimals from approaching the planet. Thus, planetary migration itself has little contribution to increasing the amount of captured planetesimals. However, in a multi-planetary system, we find an interesting process that breaks the resonance trap and increases the amount of planetesimals captured by the planets. This effect is important to consider the capture of planetesimals in a multi-planetary system.
2/13 Ayumu Kuwahara/ Gas flow around an embedded planet in a protoplanetary disk: the implications for planet formation
The three-dimensional structure of the gas flow around a planet is thought to influence the accretion of both gas and solid materials. In particular, the outflow in the mid-plane region may prevent the accretion of the solid materials and delay the formation of super-Earths' cores. However, it is not yet understood how the nature of the flow field and outflow speed change as a function of the planetary mass. In this study, we investigate the dependence of gas flow around a planet embedded in a protoplanetary disc on the planetary mass. Assuming an isothermal, inviscid gas disc, we perform three-dimensional hydrodynamical simulations on the spherical polar grid, which has a planet located at its centre. We find that gas enters the Bondi or Hill sphere at high latitudes and exits through the mid-plane region of the disc regardless of the assumed planetary mass. The altitude from where gas predominantly enters the envelope varies with the planetary mass. We also derived the analytic solution of the outflow which is consistent of the results of simulations. The planet-induced gas flow may reduce the accretion of dust and pebbles onto the planet when planetary mass is larger than the square root of Stokes number of the particle. Our results suggest that the flow around proto-cores of super-Earths may delay their growth and, consequently, help them to avoid runaway gas accretion within the lifetime of the gas disc. In this talk, I will also introduce a few latest results of test simulations related to the pebble accretion in the realistic three-dimensional gas flow field.