AI 中文总结
本研究通过耦合大气-内部演化模型，提出大气留存由脱气调控的宇宙沙洲和逃逸调控的宇宙海岸线两个边界决定，为行星大气演化及相关观测提供了新框架。
AI 中文摘要
近期詹姆斯·韦布空间望远镜（JWST）的观测从两侧对传统的“宇宙海岸线”理论提出挑战：最炎热的近距“熔岩行星”拥有浓厚的挥发性大气，此处的辐射本应驱动最极端的大气逃逸；而围绕M型矮星的较冷类地行星却拥有裸露的岩石表面，按理论这类行星的大气本应留存。我们采用耦合大气-内部演化模型，证明大气留存并非由单一逃逸边界决定，而是由两个边界调控：受脱气作用调控的高温“宇宙沙洲”，以及受逃逸作用调控的低温“宇宙海岸线”，二者之间的“无大气谷”可能是被剥离的亚海王星核心的“墓地”。沙洲的形成源于多行星系统中长期偏心率激发产生的潮汐加热维持的长寿岩浆洋，该岩浆洋使大部分挥发性物质溶解，仅暴露少量大气储库用于逃逸；而较冷行星则会固化，将挥发性物质封存于深部固体地幔，同时使剩余物质过度暴露于逃逸过程。这种双 regime 结构将单一宇宙海岸线重构为由脱气和逃逸两种不同物理机制设定的两个边界。我们针对G、K、M型恒星，给出了随挥发性物质储量、行星质量、年龄和潮汐加热变化的两个边界的时间演化拟合结果。除非受到极端潮汐或其他内部加热的维持，厚大气的熔岩行星不太可能存在于比K型更冷的恒星周围。该框架将USP熔岩行星的大气留存与宜居带行星关联起来，为TRAPPIST-1系统和JWST DDT表征的目标选择与结果解读提供了依据。
英文摘要
Recent JWST observations challenge the traditional 'cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial planets around M dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated 'cosmic sandbar' and a cooler, escape-regulated 'cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by tidal heating from secular eccentricity excitation in multi-planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M stellar types as a function of volatile inventory, planetary mass, age, and tidal heating. Lava worlds with thick atmospheres are unlikely around stars cooler than K-type unless sustained by extreme tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.
CommentsAccepted for publication in ApJL (The Astrophysical Journal Letters), 2026. 26 pages, 3 figures, 3 tables
Journal refAstrophys. J. Lett. 1008 (2026) L4
