标题： 富挥发物的熔融超级地球 L 98-59 d 的演化 显示英文标题

标题： Volatile-rich evolution of molten super-Earth L 98-59 d

摘要： 小质量低密度系外行星受到强烈的恒星辐射，但它们的起源尚不清楚。 两种相互竞争的模型是，它们要么形成于岩石内部和氢气-氦气大气层（“气体矮星”），要么形成于以水相为主的整体成分（“水世界”）。 对L 98-59 d的观测揭示了其异常低的密度和光谱特征，为解析其起源提供了窗口。 我们使用一个耦合的大气层-内部建模框架，限制了将L 98-59 d的诞生条件与这些观测结果联系起来的可能演化历史范围。 观测结果可以通过化学还原的地幔和早期显著（>1.8质量%）的硫和氢含量来解释，这与气体矮星和水世界起源模型都不一致。 观测到的光谱特征可以通过在氢背景中就地光化学生成二氧化硫来解释。 L 98-59 d的内部由一个永久的岩浆海洋组成，使其能够在数十亿年的时间尺度上长期保留挥发物，这与调查的开普勒调查趋势一致。 对“宇宙海岸线”的建模表明，早期的挥发物-金属预算是大气保持的关键因素——在这里，我们明确展示了大的初始预算可以解释一些超级地球行星（包括DDT目标）的JWST观测结果。 在打破假设的气体矮星/水世界二分法的同时，我们揭示了一种由高摩尔质量大气层覆盖岩浆海洋定义的演化路径，并邀请对小系外行星进行更细致的分类。 显示英文摘要

摘要： Small low-density exoplanets are sculpted by strong stellar irradiation but their origin is unknown. Two competing scenarios are that they formed either with rocky interiors and H2-He atmospheres (`gas-dwarfs'), or instead with bulk compositions dominated by H2O phases (`water-worlds'). Observations of L 98-59 d have revealed its unusually low density and spectral characteristics, opening a window for disentangling its origin. We constrain the possible range of evolutionary histories linking L 98-59 d's birth conditions to these observations, using a coupled atmosphere-interior modelling framework. Observations are explained by a chemically-reducing mantle and early substantial (>1.8 mass%) sulfur and hydrogen content, inconsistent with both the gas-dwarf and water-world origin scenarios. Observed spectral features are explained by in-situ photochemical production of SO2 in an H2 background. L 98-59 d's interior comprises a permanent magma ocean, allowing long-term retention of volatiles within its interior over billions of years, consistent with surveyed Kepler Survey trends. Modelling of the `cosmic shoreline' suggests that early volatile-metal budget is a determinant of atmospheric retention - here, we explicitly show that large initial budgets can explain JWST observations of some super-Earth planets (including DDT targets). In breaking with the supposed gas-dwarf/water-world dichotomy, we reveal an evolutionary pathway defined by high-molar-mass atmospheres overlying magma oceans, and invite a more nuanced taxonomy of small exoplanets.