标题： 半径谷中的动力学不稳定性与巨型撞击的故事 显示英文标题

标题： A tale of dynamical instabilities and giant impacts in the radius valley

摘要： 半径在 1 到$4 R_\oplus$之间的行星的大小分布，在接近 1.4 和$2.2R_\oplus$处达到峰值，并在$1.8 R_\oplus$处出现一个凹陷——所谓的“半径谷”。 最近的统计分析表明，位于这个谷中的行星（$1.5 < R < 2R_\oplus$）往往比谷外的行星具有稍高的轨道偏心率。 这种动力学特征的起源仍然不清楚。 我们重新审视了“打破链条”的形成模型，并提出晚发的动力学不稳定性——发生在盘弥散之后——可能解释了在半径谷中观测到的偏心率升高现象。 我们的模拟显示，谷内的行星（$R < 2 R_\oplus$）通常是岩石行星，而谷外的行星（$R > 2 R_\oplus$）通常是富含水的行星。 经历了强烈动力学不稳定性以及大量晚期巨型撞击的岩石行星，其轨道会被激发并且半径增加，最终将其置于半径谷中。 相比之下，谷外更大的富含水的行星经历较弱的不稳定性以及较少的撞击，导致较低的偏心率。 这种对比导致谷内偏心率分布出现峰值。 半径谷中的行星被动态激发的程度在很大程度上取决于轨道不稳定之前的轨道架构。 轨道谷行星的偏心率升高主要出现在以下场景中：在不稳定发生前100天内（通常为$\gtrsim 5$）形成了足够数量的岩石行星，并且还存在外部扰动者（$P > 100$天），这些扰动进一步增强了动力学不稳定性的影响。 显示英文摘要

摘要： The size distribution of planets with radii between 1 and $4 R_\oplus$ peaks near 1.4 and $2.2R_\oplus$, with a dip around $1.8 R_\oplus$ -- the so-called "radius valley." Recent statistical analyses suggest that planets within this valley ($1.5 < R < 2R_\oplus$) tend to have slightly higher orbital eccentricities than those outside it. The origin of this dynamical signature remains unclear. We revisit the "breaking the chains" formation model and propose that late dynamical instabilities -- occurring after disk dispersal -- may account for the elevated eccentricities observed in the radius valley. Our simulations show that sub-valley planets ($R < 2 R_\oplus$) are generally rocky, while those beyond the valley ($R > 2 R_\oplus$) are typically water-rich. Rocky planets that undergo strong dynamical instabilities and numerous late giant impacts have their orbits excited and their radii increased, ultimately placing them into the radius valley. In contrast, the larger, water-rich planets just beyond the valley experience weaker instabilities and fewer impacts, resulting in lower eccentricities. This contrast leads to a peak in the eccentricity distribution within the valley. The extent to which planets in the radius valley are dynamically excited depends sensitively on the orbital architecture before the orbital instability. Elevated eccentricities among radius valley planets arise primarily in scenarios that form a sufficiently large number of rocky planets within 100 days (typically $\gtrsim 5$) prior to instability, and that also host external perturbers ($P > 100$ days), which further amplify the strength of dynamical instabilities.