AI 中文总结
通过三维多流体模拟揭示嵌入原行星盘的行星完全对流包层中尘埃分布的两种主导 regime，解释了不同轨道行星包层成分多样性与迷你海王星大气多样性的关联。
AI 中文摘要
我们开展了气体与尘埃的三维多流体模拟，以量化对流如何重塑嵌入原行星盘的行星包层内尘埃颗粒的空间分布。在本系列第一篇论文（研究了对流稳定包层）的基础上，本文考虑由吸积光度维持对流的包层。行星包层内的尘埃气比主要由其与周围原行星盘的动力学隔离程度决定。当对流延伸至邦迪半径之外时，包层仍与盘流相连，并通过持续的物质交换维持富尘埃状态；反之，当内部对流层与外部再循环层分离时，再循环流会过滤入射固体。此时对流层内的尘埃分布由对流搅拌与重力沉降的竞争关系控制，形成两种 regime：沉降主导 regime（大颗粒通常 s≳0.1 cm 以终端速度下落，包层尘埃耗尽）与对流主导 regime（小颗粒被对流环流捕获，包层保留尘埃）。吸积固体在包层升华前沿的挥发物释放，结合对流混合效率，决定该物质在行星核与包层间的分配。研究结果表明，位于雪线内的超级地球与迷你海王星具有挥发物耗尽的核和富挥发物的包层，而轨道更远的行星则拥有从耗尽到富集的多样包层成分，这种多样性与观测到的迷你海王星大气成分的高度多样性一致。
英文摘要
We perform 3D multifluid simulations of gas and dust to quantify how convection reshapes the spatial distribution of dust grains inside the envelopes of disk-embedded planets. Building on the first paper of this series, which explored convectively stable envelopes, we here consider envelopes in which convection is sustained by the accretion luminosity. The dust-to-gas ratio inside the planetary envelope is set primarily by the degree of dynamical isolation from the surrounding disk. When convection extends beyond the Bondi radius, the envelope remains connected to the disk flow and maintains a dust-rich state through continuous material exchange. Conversely, when an inner convective layer is separated from an outer recycling layer, the recycling flow filters incoming solids. The dust distribution inside the convective layer is then controlled by the competition between convective stirring and gravitational settling. This yields two regimes: a settling-dominated regime, in which large grains (typically $s\gtrsim0.1$ cm) fall at the terminal velocity and the envelope becomes dust depleted, and a convection-dominated regime, in which smaller grains are trapped in convective circulation and the envelope retains its dust. The delivery and release of volatile species from accreting solids at the envelope sublimation front, together with the efficiency of convective mixing, determine how this material is distributed between the core and envelope. Our findings imply that super-Earths and mini-Neptunes inside the water snowline have volatile-depleted cores and volatile-rich envelopes, while planets at wider orbits can have a wide diversity of envelope compositions from depleted to enriched. This compositional diversity for planetary envelopes appears to be consistent with the large diversity in observed atmospheric compositions of mini-Neptunes.
CommentsAccepted for publication in Astronomy and Astrophysics (A&A)
