The early stages of planet formation are still not well understood. Coagulation models have revealed numerous obstacles to the dust growth, such as the bouncing, fragmentation and radial drift barriers. We study the interplay between dust coagulation and drift in order to determine the conditions in protoplanetary disk that support the formation of planetesimals. We focus on planetesimal formation via sweep-up and investigate whether it can take place in a realistic protoplanetary disk. We have developed a new numerical model that resolves spatial distribution of dust in the radial and vertical dimension. The model uses representative particles approach to follow the dust evolution in protoplanetary disk. The coagulation and fragmentation of solids is taken into account using Monte Carlo method. A collision model adopting the mass transfer effect, that can occur for different-sized dust aggregate collisions, is implemented. We focus on a protoplanetary disk including a pressure bump caused by a steep decline of turbulent viscosity around the snow line. Our results show that sufficient resolution of the vertical disk structure in dust coagulation codes is necessary to obtain adequately short growth timescales, especially in the case of a low turbulence region. We find that a sharp radial variation of the turbulence strength at the inner edge of dead zone promotes planetesimal formation in several ways. It provides a pressure bump that efficiently prevents the dust from drifting inwards. It also causes a radial variation in the size of aggregates at which growth barriers occur, favoring the growth of large aggregates via sweeping up of small particles. In our model, by employing an ad hoc alpha viscosity change near the snow line, it is possible to grow planetesimals by incremental growth on timescales of approximately 10^5 years.
Extended gaps in the debris disks of both Vega and Fomalhaut have been observed. These structures have been attributed to tidal perturbations by multiple super-Jupiter gas giant planets. Within the current observational limits, however, no such massive planets have been detected. Here we propose a less stringent `lone-planet' scenario to account for the observed structure with a single eccentric gas giant and suggest that clearing of these wide gaps is induced by its sweeping secular resonance. During the depletion of the disk gas, the planet's secular resonance propagates inward and clears a …
Chondrules are silicate spheroids found in meteorites, serving as important fossil records of the early solar system. In order to form chondrules, chondrule precursors must be heated to temperatures much higher than the typical conditions in the current asteroid belt. One proposed mechanism for chondrule heating is the passage through bow shocks of highly eccentric planetesimals in the protoplanetary disk in the early solar system. However, it is difficult for planetesimals to gain and maintain such high eccentricities. In this paper, we present a new scenario in which planetesimals in the ast…
Planet formation at the inner edge of the dead zone II. Outbursts, rings, vortices, and suppression of planetesimal formation
Ludwig-Maximilians-Universität München（慕尼黑大学）；Universitäts-Sternwarte（大学天文台）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Exzellenzcluster ORIGINS（ORIGINS 卓越集群）
The inner solar system possesses a unique orbital structure in which there are no planets inside the Mercury orbit and the mass is concentrated around the Venus and Earth orbits. The origins of these features still remain unclear. We propose a novel concept that the building blocks of the inner solar system formed at the dead-zone inner edge in the early phase of the protosolar disk evolution, where the disk is effectively heated by the disk accretion. First, we compute the dust evolution in a gas disk with a dead zone and obtain the spatial distribution of rocky planetesimals. The disk is all…
The streaming instability is a promising mechanism to drive the formation of planetesimals in protoplanetary disks. To trigger this process, it has been argued that sedimentation of solids onto the mid-plane needs to be efficient and therefore that a quiescent gaseous environment is required. It is often suggested that dead-zone or disk-wind structure created by non-ideal magnetohydrodynamical (MHD) effects meets this requirement. However, simulations have shown that the midplane of a dead zone is not completely quiescent. In order to examine the concentration of solids in such an environment,…
The formation of planetesimals is an unsolved problem in planet formation theory. A prominent scenario for overcoming dust growth barriers in dead zones is the gravitational collapse of locally over-dense regions, shown to robustly produce $\sim$100 km sized objects. Still, the conditions under which planetesimal formation occurs remain unclear. For collapse to proceed, the self-gravity of an overdensity must overcome stellar tidal disruption on large scales and turbulent diffusion on small scales. Here, we relate the scales of streaming and Kelvin-Helmholtz instability, which both regulate pa…
Forming planetesimals from pebbles is a major challenge in our current understanding of planet formation. In a protoplanetary disk, pebbles drift inward near the disk midplane via gas drag and they may enter a dead zone. In this context, we identified that the backreaction of the drag of pebbles onto the gas could lead to a runaway pile-up of pebbles, the so-called no-drift mechanism. We improve upon the previous study of the no-drift mechanism by investigating the nature and characteristics of the resultant planetesimal belt. We performed 1D diffusion-advection simulations of drifting pebbles…
Recent high precision meteoritic data improve constraints on the formation timescale and bulk composition of the terrestrial planets. High resolution N-body simulations allow direct comparison of embryo growth timescale and accretion zones to these constraints. In this paper, we present results of high resolution simulations for embryo formation from a disc of up to 41,000 fully-self gravitating planetesimals with the GPU-based N-body code GENGA. Our results indicate that the growth of embryos are highly dependent on the initial conditions. More massive initial planetesimals, a shorter gas dis…
On the dynamics of planetesimals embedded in turbulent protoplanetary discs
原行星盘中的角动量输运和吸积通常被认为是由MHD湍流通过磁旋转不稳定性（MRI）驱动的。嵌入这些圆盘中的固体（尘埃颗粒、巨石、微行星和行星）的动力学可能受到湍流的强烈影响，因此行星系的形成路径部分取决于湍流的强度和空间分布。我们使用三维MHD模拟研究了嵌入湍流原行星盘中的半径在1米至10公里之间的微行星的动力学。微行星受到气体阻力和随机引力的作用，这是由于湍流盘造成的。在这项研究中，我们使用并比较了局部剪切箱模拟和全球模型的结果。这项工作的主要目的是检查：的增长，和可能的饱和度，嵌入式微行星的速度色散作为其大小和光盘参数的函数;微行星的径向迁移和扩散的速率;剪切盒和全球模拟结果一致的条件下。当使用尺寸为4 H x 16 H x 2 H的剪切盒（H为局部尺度高度）时，我们发现局部和全局模拟之间存在良好的一致性。由于螺旋密度波的激发和传播，所获得的密度波动的幅度对盒子的尺寸敏感。这影响了微行星所经历的随机强迫。[...]我们的模型表明，充分发展的MHD湍流在原行星盘将嵌入星子的破坏性影响。相对较低的湍流水平需要的星子吸积的传统模型的运作，这是一致的存在一个死区的原行星盘。
Content: For up to a few millions of years, pebbles must provide a quasi-steady inflow of solids from the outer parts of protoplanetary disks to their inner regions. Aims: We wish to understand how a significant fraction of the pebbles grows into planetesimals instead of being lost to the host star. Methods:We examined analytically how the inward flow of pebbles is affected by the snow line and under which conditions dust-rich (rocky) planetesimals form. When calculating the inward drift of solids that is due to gas drag, we included the back-reaction of the gas to the motion of the solids. Re…
Episodic planetesimal disruptions triggered by dissipation of gas disk
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University（教育部现代天文与天体物理重点实验室，南京大学）；State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University（南京大学地球科学与工程学院关键地球物质循环与矿床国家重点实验室及月球与行星科学研究所）；CAS Center for Excellence in Comparative Planetology（中国科学院比较行星学卓越创新中心）
Inside-Out Planet Formation (IOPF) is a theory addressing the origin of Systems of Tightly-Packed Inner Planets (STIPs) via {\it in situ} formation and growth of the planets. It predicts that a pebble ring is established at the pressure maximum associated with the dead zone inner boundary (DZIB) with an inner disk magnetorotational instability (MRI)-active region. Using direct $N$-body simulations, we study the collisional evolution of planetesimals formed from such a pebble ring, in particular examining whether a single dominant planet emerges. We consider a variety of models, including some …
A notable challenge of planet formation is to find a path to directly form planetesimals from small particles. We aim to understand how drifting pebbles pile up in a protoplanetary disk with a non-uniform turbulence structure. We consider a disk structure in which the midplane turbulence viscosity is increasing with radius in protoplanetary disks as in the outer region of a dead zone. We perform 1D diffusion-advection simulations of pebbles that include back-reaction (the inertia) to radial drift and vertical/radial diffusion of pebbles for a given pebble-to-gas mass flux. We report a new mech…
We explore planet formation in the HL Tau disk and possible origins of the prominent gaps and rings observed by ALMA. We investigate whether dust gaps are caused by dynamically trapped planetary embryos at the ice lines of abundant volatiles. The global properties of the HL Tau disk (total mass, size) at its current age are used to constrain an evolving analytic disk model describing its temperature and density profiles. By performing a detailed analysis of the planet-disk interaction for a planet near the water ice line including a rigorous treatment of the dust opacity, we confirm that water…
In the classical core-accretion planet formation scenario, rapid inward migration and accretion timescales of kilometer size planetesimals may not favor the formation of massive cores of giant planets before the dissipation of protoplanetary disks. On the other hand, the existence of pressure maxima in the disk could act as migration traps and locations for solid material accumulation, favoring the formation of massive cores. We aim to study the radial drift of pebbles and planetesimals and planet migration at pressure maxima in a protoplanetary disk and their implications for the formation of…
We investigate the formation and evolution of "primordial" dusty rings occurring in the inner regions of protoplanetary discs, with the help of long-term, coupled dust-gas, magnetohydrodynamic simulations. The simulations are global and start from the collapse phase of the parent cloud core, while the dead zone is calculated via an adaptive $α$ formulation by taking into account the local ionization balance. The evolution of the dusty component includes its growth and back reaction on to the gas. Previously, using simulations with only a gas component, we showed that dynamical rings form at th…
Excitation of Rossby wave instability and development of a large-scale vortex at the outer dead zone edge of protoplanetary discs is one of the leading theories that explains horseshoe-like brightness distribution in transition discs. Formation of such vortices requires a relatively sharp viscosity transition. Detailed modelling, however, indicates that viscosity transitions at the outer edge of the dead zone is relatively smooth. In this study, we present 2D global, non-isothermal, gas-dust coupled hydrodynamic simulations to investigate the possibility of vortex excitation at smooth viscosit…
The collisional evolution of solid material in protoplanetary disks is a crucial step in the formation of planetesimals, comets, and planets. Although dense protoplanetary environments favor fast dust coagulation, there are several factors that limit the straightforward pathway from interstellar micron-size grains to pebble-size aggregates. Apart from the grain bouncing, fragmentation, and fast drift to the central star, a notable limiting factor is the electrostatic repulsion of like-charged grains. In this study we aim at theoretical modeling of the dust coagulation coupled with the dust cha…
In dead zones of protoplanetary discs, it is assumed that micrometre-sized particles grow Brownian, sediment to the midplane and drift radially inward. When collisional compaction sets in, the growing aggregates collect slower and therefore dynamically smaller particles. This sedimentation and growth phase of highly porous ice and dust aggregates is simulated with laboratory experiments in which we obtained mm- to cm-sized ice aggregates with a porosity of 90\% as well as cm-sized dust agglomerates with a porosity of 85\%. We modelled the growth process during sedimentation in an analytical ca…
