论文标题

嵌入行星的第一批气氛的回收:依赖核心质量和光学深度

Recycling of the first atmospheres of embedded planets: Dependence on core mass and optical depth

论文作者

Moldenhauer, T. W., Kuiper, R., Kley, W., Ormel, C. W.

论文摘要

最近的观察结果发现,近距离行星,具有丰富的氢气和氦气大量。这些是所谓的超级矿石和迷你纽扣。他们的大气成分表明,它们在杂质磁盘富含气体阶段的早期形成,并能够避免成为热木星。作为一个可能的解释,最近的研究探讨了回收假设,并表明大气 - 磁盘回收能够完全补偿辐射冷却,从而阻止了开尔文 - 赫尔姆霍尔茨的收缩,以防止失控的气体积聚。 为了了解确定大气回收效率的参数,我们通过探索核心质量的影响,室外气体对亚较小轨道(逆风)的影响以及周围气体对回收时间尺度的光学深度来扩展我们的早期研究。此外,我们分析了它们对形成气氛的大小和质量的影响。 对于探索的参数空间,所有模拟最终都达到平衡,由于流体动力回收引起的加热完全补偿了辐射冷却。在这种均衡中,大气与核心质量比率保持在$ 10 \,\%$以下,以防止大气变得自我散发并进入失控的气体积聚。较高的核心质量会导致大气变得湍流,从而进一步增强了回收利用。 即使我们的最高核心质量为$ 10 \,M_ \ Mathrm {Earth} $,大气 - 磁盘回收的效率也足够有效,足以完全补偿辐射冷却并防止大气变得自我散发。因此,热木星的原位形成不太可能,而天然气巨头的迁移是解释其存在所需的关键过程。我们的发现表明,大气 - 磁盘回收是对近距离地球和迷你北极群体流行的最自然的解释。

Recent observations found close-in planets with significant atmospheres of hydrogen and helium in great abundance. These are the so-called super-Earths and mini-Neptunes. Their atmospheric composition suggests that they formed early during the gas-rich phase of the circumstellar disk and were able to avoid becoming hot Jupiters. As a possible explanation, recent studies explored the recycling hypothesis and showed that atmosphere-disk recycling is able to fully compensate for radiative cooling and thereby halt Kelvin-Helmholtz contraction to prevent runaway gas accretion. To understand the parameters that determine the efficiency of atmospheric recycling, we extend our earlier studies by exploring the effects of the core mass, the effect of circumstellar gas on sub-Keplerian orbits (headwind), and the optical depth of the surrounding gas on the recycling timescale. Additionally, we analyze their effects on the size and mass of the forming atmosphere. For the explored parameter space, all simulations eventually reach an equilibrium where heating due to hydrodynamic recycling fully compensates radiative cooling. In this equilibrium, the atmosphere-to-core mass ratio stays well below $10 \, \%$, preventing the atmosphere from becoming self-gravitating and entering runaway gas accretion. Higher core masses cause the atmosphere to become turbulent, which further enhances recycling. Even for our highest core mass of $10 \, M_\mathrm{Earth}$, atmosphere-disk recycling is efficient enough to fully compensate for radiative cooling and prevent the atmosphere from becoming self-gravitating. Hence, in-situ formation of hot Jupiters is very unlikely, and migration of gas giants is a key process required to explain their existence. Our findings imply that atmosphere-disk recycling is the most natural explanation for the prevalence of close-in super-Earths and mini-Neptunes.

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