N -body simulations of planet formation via pebble accretion II. How various giant planets form
N -body simulations of planet formation via pebble accretion II. How various giant planets form
复制标题
通过卵石吸积进行行星形成的 N 体模拟 II。
DOI：
10.1051/0004-6361/202039210
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发表时间：
2021
影响因子：
6.5
通讯作者：
Matsumura S
中科院分区：
文献类型：
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作者：
Matsumura S
目的行星的初始盘条件与最终的轨道和物理性质之间的联系还不是很清楚。本文用数值方法研究了球体吸积形成行星系统的过程，考察了质量、耗散时间和金属度等圆盘性质对行星形成结果的影响。方法通过考虑新的行星-圆盘相互作用模型和第二类迁移，改进了当时的体代码SYMBA。我们采用‘Two-α’盘模型来模拟标准盘湍流和由磁盘绕驱动的质量吸积的影响。结果我们成功地再现了太阳系外巨行星的半长轴、偏心率和行星质量的总体分布趋势。有两种类型的巨行星形成趋势，这取决于圆盘的消散时间是否与行星形成时间相当。当行星形成速度足够快时，巨大的行星就完全长大了(木星质量或更高)，并广泛分布在整个圆盘上。另一方面，当行星的形成受到圆盘耗散的限制时，圆盘通常会形成低质量的冷木星。我们的模拟也自然地解释了为什么热木星(HJS)往往是孤立的，以及观察到的偏心率-金属丰度趋势是如何产生的。低金属度盘倾向于在原地形成近圆形和共面的HJS，因为行星的形成比高金属度盘慢，因此原行星核在气体吸积之前显著迁移。另一方面，高金属丰度盘在原地或通过偏心轨道的潮汐环流产生HJS。这两条路径通常都涉及到动力不稳定性，因此HJS往往具有较宽的偏心率和倾角分布。当具有非常宽轨道的巨行星(“超冷木星”)是由卵石吸积和散射形成时，我们预测它们属于富金属恒星，具有偏心轨道，并倾向于在轨道内部有(~80%)同伴。
AimsThe connection between initial disc conditions and final orbital and physical properties of planets is not well-understood. In this paper, we numerically study the formation of planetary systems via pebble accretion and investigate the effects of disc properties such as masses, dissipation timescales, and metallicities on planet formation outcomes.MethodsWe improved theN-body code SyMBA that was modified for our Paper I by taking account of new planet–disc interaction models and type II migration. We adopted the ‘two-α’ disc model to mimic the effects of both the standard disc turbulence and the mass accretion driven by the magnetic disc wind.ResultsWe successfully reproduced the overall distribution trends of semi-major axes, eccentricities, and planetary masses of extrasolar giant planets. There are two types of giant planet formation trends, depending on whether or not the disc’s dissipation timescales are comparable to the planet formation timescales. When planet formation happens fast enough, giant planets are fully grown (Jupiter mass or higher) and are distributed widely across the disc. On the other hand, when planet formation is limited by the disc’s dissipation, discs generally form low-mass cold Jupiters. Our simulations also naturally explain why hot Jupiters (HJs) tend to be alone and how the observed eccentricity-metallicity trends arise. The low-metallicity discs tend to form nearly circular and coplanar HJs in situ, because planet formation is slower than high-metallicity discs, and thus protoplanetary cores migrate significantly before gas accretion. The high-metallicity discs, on the other hand, generate HJs in situ or via tidal circularisation of eccentric orbits. Both pathways usually involve dynamical instabilities, and thus HJs tend to have broader eccentricity and inclination distributions. When giant planets with very wide orbits (“super-cold Jupiters”) are formed via pebble accretion followed by scattering, we predict that they belong to metal-rich stars, have eccentric orbits, and tend to have (~80%) companions interior to their orbits.