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arXiv 2303.09653astro-ph.EP
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大气作为亚海王星内部的窗口:氢-硅烷-水包层的耦合化学与结构

Atmospheres as windows into sub-Neptune interiors: coupled chemistry and structure of hydrogen-silane-water envelopes

William Misener, Hilke E. Schlichting, Edward D. Young

AI总结:

本文将H、Si、O物种化学平衡与大气结构模型耦合,发现亚海王星内部与大气相互作用产生大量硅烷和水,抑制了对流并形成更厚的非对流区,表明岩浆与氢作用即可产生内源水。

摘要:

亚海王星系外行星通常被假设由富含硅酸盐的岩浆洋和覆盖其上的富氢大气组成。先前关于硅酸盐物质释气的研究表明,这种大气与内部的相互作用会影响大气的整体结构和范围。但这些模型仅考虑了氢气大气中的 SiO,并未考虑它们之间的化学反应。在此,我们将 H、Si 和 O 物种之间的化学平衡计算与大气结构模型相耦合。我们发现,富硅酸盐内部与富氢大气的相互作用会产生大量的硅烷(SiH$_4$)和水(H$_2$O)。这些物质可延伸至大气高层,尽管其丰度在温度最高、最深的区域达到最大。例如,对于一颗质量为 4 $M_\oplus$、平衡温度为 1000 K、底部温度为 5000 K且拥有 0.1 $M_\oplus$ 氢包层的行星,硅物种和水按数量可占大气底部的 30%。由于这种丰度增强,我们发现温度 $\gtrsim 2500$ K 时对流受到抑制。该温度低于以往未考虑大气化学的模型所预测的温度,这意味着由此产生的非对流区域更厚。我们的研究结果表明,仅通过岩浆与氢的相互作用就能产生大量的内源水,而无需吸积富冰物质。我们讨论了大气与内部相互作用特征的可观测性以及未来的工作方向,包括凝结物悬浮和更复杂的化学网络。

英文摘要:

Sub-Neptune exoplanets are commonly hypothesized to consist of a silicate-rich magma ocean topped by a hydrogen-rich atmosphere. Previous work studying the outgassing of silicate material has demonstrated that such atmosphere-interior interactions can affect the atmosphere's overall structure and extent. But these models only considered SiO in an atmosphere of hydrogen gas, without considering chemical reactions between them. Here we couple calculations of the chemical equilibrium between H, Si, and O species with an atmospheric structure model. We find that substantial amounts of silane, SiH$_4$, and water, H$_2$O, are produced by the interaction between the silicate-rich interior and hydrogen-rich atmosphere. These species extend high into the atmosphere, though their abundance is greatest at the hottest, deepest regions. For example, for a 4 $M_\oplus$ planet with an equilibrium temperature of 1000 K, a base temperature of 5000 K, and a 0.1 $M_\oplus$ hydrogen envelope, silicon species and water can comprise 30 percent of the atmosphere by number at the bottom of the atmosphere. Due to this abundance enhancement, we find that convection is inhibited at temperatures $\gtrsim 2500$ K. This temperature is lower, implying that the resultant non-convective region is thicker, than was found in previous models which did not account for atmospheric chemistry. Our findings show that significant endogenous water is produced by magma-hydrogen interactions alone, without the need to accrete ice-rich material. We discuss the observability of the signatures of atmosphere-interior interaction and directions for future work, including condensate lofting and more complex chemical networks.

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