arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2510.02201astro-ph.EP
收藏

理解超级蓬松行星的起源：一种与行星演化耦合的新质量损失机制

Understanding the Origins of Super-Puff Planets: A New Mass-Loss Regime Coupled to Planetary Evolution

Yao Tang, Jonathan J. Fortney, Ruth Murray-Clay, Madelyn Broome

备注：
22 pages, 12 figures; in press, ApJ
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

AI总结：

本研究提出热能介导的光蒸发新机制修正了质量损失估算，构建耦合演化模型，发现超级蓬松行星的大半径源于厚对流包层与辐射大气，其形成需中等质量与特定恒星辐照条件。

摘要：

超级蓬松行星是一类低质量、大半径的行星，一直对行星形成与演化模型构成挑战。要解释它们的物理尺寸，推断出的氢/氦质量占比需很高，而这会导致大气快速逃逸，引发了关于其大气能否长期留存的疑问。近期的建模研究表明，由于辐射大气以及岩质/铁质内核的内部加热发挥了重要作用，低质量行星通常只需少50%的氢/氦质量就能匹配观测到的半径。\n本文通过对亚海王星中极紫外（XUV）驱动的逃逸开展新的定量分析，发现既往研究高估了质量损失，因为低重力环境下的标度律与广泛使用的能量限制机制偏差极大。我们定义了一种新机制——热能介导的光蒸发（thermal-energy-mediated photoevaporation, TEMP），该机制中热能转换对质量损失率起决定性作用。这些效应使得超级蓬松行星抵御质量损失的能力强于此前的认知。\n我们构建了一个耦合演化模型，将更新后的热演化框架与一维流体动力学光蒸发模型相结合。将这一全新的联合模型应用于已观测到的超级蓬松行星和年轻低密度行星后，我们发现，无论假设大气是清澈的还是有霾的，这些行星的质量、半径和凌星压强都与预测结果吻合。这表明超级蓬松行星经历了沸腾蒸发与光蒸发质量损失的共同作用，其中沸腾蒸发占主导。\n我们的结果显示，低密度行星通常同时拥有厚对流包层和大量辐射大气，二者共同造就了它们的大半径。要形成这种结构，这些行星的质量必须处于5-10倍地球质量（$M_\oplus$）的中等范围，且接收的恒星辐照度≤30倍地球辐照度（$F_\oplus$），更倾向于环绕FG型恒星而非M型矮星运行。

英文摘要：

Super-puffs are a class of low-mass, large-radius planets that have challenged planet formation and evolution models. Their high inferred H/He mass fractions, required to explain their physical sizes, would lead to rapid atmospheric escape, raising questions about their long-term retention. Recent modeling work indicates that low-mass planets typically require 50\% less H/He mass to match their observed radius, due to significant roles of the radiative atmosphere and interior heating from the rock/iron core. Here, through a new quantitative analysis of XUV-driven escape in sub-Neptunes, we find that previous studies overestimated mass loss, as scaling laws in low-gravity regimes deviate greatly from the widely used energy-limited regime. We define a new regime, thermal-energy-mediated photoevaporation (TEMP), in which thermal energy conversion critically sets the mass-loss rate. These effects make super-puffs more resilient to mass loss than previously thought. We develop a coupled evolution model integrating this updated thermal evolution framework with a 1D hydrodynamic photoevaporation model. Applying this novel, joint model to observed super-puffs and young low-density planets, we find that their masses, radii and transit pressures align with predictions assuming either a clear or hazy atmosphere. This indicates that super-puffs have undergone a combination of boil-off and photoevaporative mass loss, with boil-off dominating the process. Our results indicate that low-density planets typically possess both a thick convective envelope and substantial radiative atmosphere, which contribute to their large radii. For this to occur, these planets must have intermediate masses of 5-10$M_\oplus$ and receive stellar insolation $\lesssim 30F_\oplus$, favoring FG-type stars over M-dwarfs.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑