[论文解读] Planet Formation Theory in the Era of ALMA and Kepler: from Pebbles to Exoplanets

Joanna Drążkowska, Bertram Bitsch+8 more|arXiv (Cornell University)|Mar 18, 2022

Stellar, planetary, and galactic studies被引用 56

一句话总结

本章回顾 ALMA 和 Kepler 观测如何约束尘埃演化、砾粒吸积和行星胚体吸积，以及多样行星系统的人口合成，并将盘子与系外行星联系起来。

ABSTRACT

Our understanding of planet formation has been rapidly evolving in recent years. The classical planet formation theory, developed when the only known planetary system was our own Solar System, has been revised to account for the observed diversity of the exoplanetary systems. At the same time, the increasing observational capabilities of the young stars and their surrounding disks bring new constraints on the planet formation process. In this chapter, we summarize the new information derived from the exoplanets population and the circumstellar disks observations. We present the new developments in planet formation theory, from dust evolution to the growth of planetary cores by accretion of planetesimals, pebbles, and gas. We review the state-of-the-art models for the formation of diverse planetary systems, including the population synthesis approach which is necessary to compare theoretical model outcomes to the exoplanet population. We emphasize that the planet formation process may not be spatially uniform in the disk and there are preferential locations for the formation of planetesimals and planets. Outside of these locations, a significant fraction of solids is not growing past the pebble-sizes. The reservoir of pebbles plays an important role in the growth of planetary cores in the pebble accretion process. The timescale of the emergence of massive planetary cores is an important aspect of the present models and it is likely that the cores within one disk form at different times. In addition, there is growing evidence that the first planetary cores start forming early, during the circumstellar disk buildup process.

研究动机与目标

• 总结系外行星人口统计如何约束行星形成理论。
• 整合来自圆周盘的观测约束，关于早期行星形成阶段。
• 在统一框架内勾勒核心、砾粒和气体吸积模型的发展。

提出的方法

• 讨论来自系外行星统计（超地行星、迷你海王星、巨行星）和盘观测（尘/气质量、尺寸、子结构）的约束。
• 描述砾粒与行星胚体吸积框架及固体的径向重新分布。
• 解释人口合成作为将理论与系外行星群体比较的工具。

实验结果

研究问题

• RQ1 系外行星人口统计对核心和气体吸积的效率与时间尺度有何含义？
• RQ2 盘子子结构与尘埃演化如何告知行星胚体和行星在何时、何地形成？
• RQ3 如何在人口合成框架内调和砾粒吸积与行星胚体吸积，以再现观测到的行星结构？

主要发现

• 系外行星人口统计显示以超地球和迷你海王星为主导的群体，在1 AU内对太阳型恒星的发生率在偏差校正后约为 140–200% 。
• 巨行星在1 AU内相对稀少，在1–10 AU最常见，一些调查在长周期段可以检测到高达25 AU的巨行星，且在约2–3 AU出现转折。
• Kepler 多行星系统通常等间距排列，互倾角较小，且往往不处于共振链。
• 盘观测揭示子结构（缝隙、环、螺旋）表明行星形成在盘组装早期甚至早于盘组装阶段就已在进行，质量预算显示固体/尘质量虽大但不确定。
• 尘埃增长和径向漂移显现，尘盘常比气盘在尘量上更小，子结构可能减缓漂移。
• 盘中的湍流通常较低到中等（α 大约 10^-4 至 3×10^-3），并可能随高度和半径变化，影响行星形成效率。