Rocky planets are common around other stars, but their atmospheric properties remain largely unconstrained. Thanks to a wealth of recent planet discoveries and upcoming advances in observing capability, we are poised to characterize the atmospheres of dozens of rocky exoplanets in this decade. The theoretical understanding of rocky exoplanet atmospheres has advanced considerably in the last few years, yielding testable predictions of their evolution, chemistry, dynamics, and even possible biosignatures. We review key progress in this field to date and discuss future objectives. Our major conclusions are as follows: ▪ Many rocky planets may form with initial H2–He envelopes that are later lost to space, likely due to a combination of stellar UV/X-ray irradiation and internal heating. ▪ After the early stages of evolution, a wide diversity of atmospheric compositions is expected as a result of variations in host star flux, atmospheric escape rates, interior exchange, and other factors. ▪ Observations have ruled out both the presence of H2-dominated atmospheres on several nearby rocky exoplanets and the presence of any thick atmosphere on one target. A more detailed atmospheric characterization of these planets and others will become possible in the near future. ▪ Exoplanet biosphere searches are an exciting future goal. However, reliable detections for a representative sample of planets will require further advances in observing capability and improvements in our understanding of abiotic planetary processes.

中文翻译：

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岩石系外行星的大气层


岩石行星在其他恒星周围很常见，但它们的大气特性在很大程度上仍然不受约束。由于最近发现的大量行星和观测能力的即将取得进展，我们准备在这十年内描述数十颗岩石系外行星的大气层。在过去几年中，对岩石系外行星大气层的理论理解取得了长足的进步，对它们的演化、化学、动力学甚至可能的生物特征产生了可测试的预测。我们回顾了该领域迄今为止的主要进展，并讨论了未来的目标。我们的主要结论如下：▪许多岩石行星可能形成于最初的 H2-He 包层，这些包层后来消失在太空中，这可能是由于恒星 UV/X 射线照射和内部加热的结合。▪ 在演化的早期阶段之后，由于宿主恒星通量、大气逃逸率、内部交换和其他因素的变化，预计大气成分会有很大的差异。▪ 观测已经排除了附近几颗岩石系外行星上存在以 H2 为主的大气层，以及一个目标上存在任何厚厚的大气层。在不久的将来，将有可能对这些行星和其他行星进行更详细的大气表征。▪ 系外行星生物圈搜索是一个令人兴奋的未来目标。然而，要对具有代表性的行星样本进行可靠检测，需要进一步提高观测能力并提高我们对非生物行星过程的理解。