Growth and Evolution of Planets in protoplanetary Disks

原行星盘中行星的生长和演化

• 批准号: 406707590
• 负责人: Dr. Christoph Schäfer, since 3/2022
• 金额: --
• 依托单位: Observatoire de la Côte dAzur
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/406707590?language=en
• 关键词: Growth; Evolution; Planets; protoplanetary; Disks

As of today over 2600 exoplanetary systems that contain over 3500 planets have been discovered. The debiased observations show that the most abundant planets are Super-Earths (planets with 1-20 Earth masses) with orbital periods shorter than 100 days, followed by giant planets at distances of 1-3 astronomical units (AU) from the parent star. The latter outnumber, by at least a factor of ten, the population of hot-Jupiters (at a distance of about 0.1 AU from the star). The mass distribution of giant planets peaks at about 1-3 Jupiter masses; planets with masses larger than that exist but are quite rare. From a theoretical standpoint, these observations are difficult to understand. Planet migration towards the star can easily explain the existence of close-in super-Earths, but it is a problem to understand why only a minority of giant planets reached orbits less than 1 AU in semi major axis. Also, gas accretion onto planetary cores should be very fast. Thus, it is not understood what prevented super-Earths from becoming giant planets and what limited the growth of giant planets to a few Jupiter masses.This proposal is based on the idea that the difficulties in understanding the extrasolar planets' mass and orbital distributions are due to incorrect assumptions on the protoplanetary disk structure. The classic view of a viscous disk, with viscosity generated by strong turbulence driven by the magneto rotational instability, is challenged by modern magneto-hydrodynamic simulations. Disks are probably much less viscous than previously thought. Nevertheless, disks cannot be inviscid, a minimum viscosity is set for example by the so-called vertical shear instability (VSI). In addition, disk winds remove angular momentum from thin surface layers of the protoplanetary disk, promoting the fast radial transport of gas towards the central star in these layers. Our proposed project is (i) to construct a realistic model of protoplanetary disks accounting for both the VSI and disk winds, and reproducing the observed stellar accretion rates and (ii) to study the accretion of gas and the migration of planets embedded in these disks.

到目前为止，已经发现了2600多个系外行星系统，其中包含3500多颗行星。去偏观测表明，最丰富的行星是轨道周期短于100天的超级地球（1-20个地球质量的行星），其次是距离母星星1-3个天文单位（Au）的巨行星。后者的数量至少是热中子星的十倍（距离星星约0.1 Au）。巨行星的质量分布在木星质量的1-3倍之间，质量大于这个值的行星是存在的，但非常罕见。从理论的角度来看，这些观察是难以理解的。行星向星星迁移可以很容易地解释近距离超级地球的存在，但理解为什么只有少数巨行星到达半长轴小于1 Au的轨道是一个问题。此外，行星核心的气体吸积应该非常快。因此，人们并不了解是什么阻止了超级地球成为巨行星，又是什么限制了巨行星的生长，使其质量只有木星那么小。这一提议基于这样一种观点，即理解太阳系外行星的质量和轨道分布的困难是由于对原行星盘结构的错误假设。经典的观点，粘性盘，与磁旋转不稳定性驱动的强湍流产生的粘性，是由现代磁流体动力学模拟的挑战。彗星的粘性可能比以前认为的要小得多。然而，圆盘不能是无粘性的，例如通过所谓的垂直剪切不稳定性（VSI）来设定最小粘度。此外，盘风从原行星盘的薄表面层中移除角动量，促进这些层中气体向中心星星的快速径向传输。我们建议的项目是（i）构建一个现实的模型，原行星盘占的VSI和磁盘风，并再现所观察到的恒星吸积率和（ii）研究气体的吸积和迁移的行星嵌入在这些磁盘。