担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP Sciences  

Context. Planetesimal formation is still mysterious. One of the ways to form planetesimals is to invoke a gas pressure bump in a protoplanetary disc. In our previous paper, we proposed a new scenario in which the piled-up dust at a gas pressure bump created by a migrating planet forms planetesimals by streaming instability in a wide region of the disc as the planet migrates inwards.

Aims. In the present work, we consider the global time evolution of dust and investigate the detailed conditions and results of the planetesimal formation in our scenario.

Methods. We used a 1D grid single-sized dust evolution model, which can follow the growth of the particles in terms of their mutual collision and their radial drift and diffusion. We calculated the time-evolution of the radial distribution of the peak mass and surface density of the dust in a gas disc perturbed by an embedded migrating planet and investigated whether or not the dust satisfies the condition for planetesimal formation.

Results. We find that planetesimals form in a belt-like region between the snowline and the position where the planet reaches its pebble-isolation mass when the strength of turbulence is 10⁻⁴ ≤ α ≤ 10⁻³, which is broadly consistent with the observed value of α. Whether the mechanism of the formation is streaming instability or mutual collision depends on the timescale of the streaming instability. The total mass of planetesimals formed in this scenario also depends on α; it is about 30–100 M_E if the planetary core already exists at the beginning of the simulation and grows by gas accretion, but decreases as the timing of the formation of the planetary core gets later. We also provide simple approximate expressions for the surface density and total mass of the planetesimals and find that the total planetesimal mass strongly depends on the dust mass.

Conclusions. We show that planetesimals form in a belt-like region by a combination of dust pile-up at the gas pressure bump formed by a planet and its inward migration.

DOI： 10.1051/0004-6361/202346126

Web of Science

担当区分：筆頭著者   記述言語：英語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

ABSTRACT

It has been considered that large satellites around gas planets form in situ circumplanetary discs (CPDs). However, dust particles supplied into CPDs drift toward the central planets before they grow into satellitesimals, building blocks of the satellites. We investigate the dust growth in laminar CPDs with magnetic wind-driven accretion. In such laminar discs, dust particles can settle on to the mid-plane and grow large by mutual collision more efficient than in classical turbulent CPDs. First, we carry out 3D local MHD simulations of a CPD including all the non-ideal MHD effects (Ohmic resistivity, Hall effect, and ambipolar diffusion). We investigate if the disc accretion can be governed by magnetic wind-driven accretion and how laminar the disc can be, in a situation where the magnetic disc wind can be launched from the disc. Secondly, we model 1D steady CPDs consistent with the results of the MHD simulations and calculate the steady radial distributions of the dust profiles in the modelled discs, taking account of the collisional growth, radial drift, fragmentation, and vertical stirring by the Kelvin–Helmholtz instability. We show that satellitesimals can form in such CPDs if the dust-to-gas mass ratio of the inflow to the discs is larger than 0.02, which is 50 times smaller than the critical value in turbulent CPDs. This condition can be satisfied when enough amount of dust piles up at the gas pressure bump created by the planets. This result shows that satellitesimals would form in laminar CPDs with magnetic wind-driven accretion.

DOI： 10.1093/mnras/stac3428

Web of Science

その他リンク： https://academic.oup.com/mnras/article-pdf/518/4/5444/47820350/stac3428.pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP Sciences  

Context. Cometary materials are thought to be the reservoir of the primitive materials of the Solar System. The recent detection of glycine and CH₃NH₂ by the ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that amino acids and their precursors may have formed in an early evolutionary phase of the Solar System.

Aims. We aim to investigate the evolution of the interior of comets considering the evaporation process of water followed by the concentration of nonvolatile species.

Methods. We developed a Simplified Cometary Concentration Model (SCCM) to simulate the evaporation and concentration processes on the cometary surface. We use 67P/Churyumov-Gerasimenko as the benchmark of the SCCM. We investigated the depth of the layer where nonvolatile species concentrate after the numerous passages of perihelion after the formation of the Solar System.

Results. We find that the SCCM explains the observed production rates of water and CH₃NH₂ at 100 comet years. Results from the SCCM suggest that the nonvolatile species would concentrate in the top 100 cm of the comet surface within 10 comet years. Our results also suggest that the nonvolatile species would concentrate several meters beneath the surface before it hit the early Earth. This specific mass of nonvolatile species may provide unique chemical conditions for the volcanic hot spring pools.

DOI： 10.1051/0004-6361/202038491

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP Sciences  

Context. Many scenarios have been proposed to avoid known difficulties in planetesimal formation such as drift or fragmentation barriers. However, in these scenarios planetesimals in general only form at some specific locations in protoplanetary discs. On the other hand, it is generally assumed in planet formation models and population synthesis models that planetesimals are broadly distributed in the protoplanetary disc.

Aims. We propose a new scenario in which planetesimals can form in broad areas of these discs. Planetesimals form at the gas pressure bump formed by a first-generation planet (e.g. formed by pebble accretion) and the formation region spreads inward in the disc as the planet migrates.

Methods. We used a simple 1D Lagrangian particle model to calculate the radial distribution of pebbles in the gas disc perturbed by a migrating embedded planet. We consider that planetesimals form by streaming instability at the points where the pebble-to-gas density ratio on the mid-plane becomes larger than unity. In this work, we fixed the Stokes number of pebbles and the mass of the planet to study the basic characteristics of this new scenario. We also studied the effect of some key parameters, such as the gas disc model, the pebble mass flux, the migration speed of the planet, and the strength of turbulence.

Results. We find that planetesimals form in wide areas of protoplanetary discs provided the flux of pebbles is typical and the turbulence is not too strong. The planetesimal surface density depends on the pebble mass flux and the migration speed of the planet. The total mass of the planetesimals and the orbital position of the formation area strongly depend on the pebble mass flux. We also find that the profile of the planetesimal surface density and its slope can be estimated by very simple equations.

Conclusions. We show that our new scenario can explain the formation of planetesimals in broad areas. The simple estimates we provide for the planetesimal surface density profile can be used as initial conditions for population synthesis models.

DOI： 10.1051/0004-6361/202039086

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

Abstract

It is generally accepted that the four major (Galilean) satellites formed out of the gas disk that accompanied Jupiter’s formation. However, understanding the specifics of the formation process is challenging, as both small particles (pebbles) and the satellites are subject to fast migration processes. Here we hypothesize a new scenario for the origin of the Galilean system, based on the capture of several planetesimal seeds and subsequent slow accretion of pebbles. To halt migration, we invoke an inner disk truncation radius, and other parameters are tuned for the model to match physical, dynamical, compositional, and structural constraints. In our scenario it is natural that Ganymede’s mass is determined by pebble isolation. Our slow pebble accretion scenario then reproduces the following characteristics: (1) the mass of all the Galilean satellites; (2) the orbits of Io, Europa, and Ganymede captured in mutual 2:1 mean motion resonances; (3) the ice mass fractions of all the Galilean satellites; and (4) the unique ice-rock partially differentiated Callisto and the complete differentiation of the other satellites. Our scenario is unique to simultaneously reproduce these disparate properties.

DOI： 10.3847/1538-4357/ab46a7

Web of Science

その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ab46a7

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP Sciences  

Jupiter has four large regular satellites called the Galilean satellites: Io, Europa, Ganymede, and Callisto. The inner three of the Galilean satellites orbit in a 4:2:1 mean motion resonance; therefore their orbital configuration may originate from the stopping of the migration of Io near the bump in the surface density distribution and following resonant trapping of Europa and Ganymede. The formation mechanism of the bump near the orbit of the innermost satellite, Io, is not yet understood, however. Here, we show that photophoresis in the circumjovian disk could be the cause of the bump using analytic calculations of steady-state accretion disks. We propose that photophoresis in the circumjovian disk could stop the inward migration of dust particles near the orbit of Io. The resulting dust-depleted inner region would have a higher ionization fraction, and thus admit increased magnetorotational-instability-driven accretion stress in comparison to the outer region. The increase of the accretion stress at the photophoretic dust barrier would form a bump in the surface density distribution, halting the migration of Io.

DOI： 10.1051/0004-6361/201936202

Web of Science

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.14909/yuseijin.28.4_313

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aae837

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa8454

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.icarus.2015.10.023

Scopus

開催年月日： 2019年4月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催年月日： 2019年2月

記述言語：英語  

種別：学会・研究会等 

種別：査読等 

種別：査読等 

種別：査読等