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arXiv 2102.00203astro-ph.EP
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超地球π介子的重分子量大气

A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c

A. García Muñoz, L. Fossati, A. Youngblood, N. Nettelmann, D. Gandolfi, J. Cabrera, H. Rauer

摘要:

强烈辐射的系外行星形成了扩展的大气层,可以用来探测更深的行星层。这种联系在小型系外行星的研究中特别有用,因为它们的大气层很难直接表征。在这里,我们报告的3.4σ检测的C II离子在一个单一的过境的超级地球π Men c在其太阳类主恒星的前面。凌日深度和多普勒速度与充满行星洛希瓣的离子一致,并优先远离恒星,这表明它们正在逃离行星。我们认为,π Men c拥有丰富的重挥发物($>=$ 50{\%}的大气质量),但不一定是富碳的厚大气。我们的推理依赖于累积的证据,从报告的C II检测,H I原子在过去的过境,建模的行星的内部,并假设大气,幸存下来的最活跃的阶段,其太阳类主恒星,将生存另一个0.2-2 Gyr。根据目前的大气质量,π Men c仍然可能转变为裸露的岩石核心。我们的发现证实了小型系外行星的假设成分多样性,并代表了通过调查其扩展大气层来了解行星形成和演化路径的里程碑。

英文摘要:

Strongly irradiated exoplanets develop extended atmospheres that can be utilized to probe the deeper planet layers. This connection is particularly useful in the study of small exoplanets, whose bulk atmospheres are challenging to characterize directly. Here, we report the 3.4σ detection of C II ions during a single transit of the super-Earth π Men c in front of its Sun-like host star. The transit depth and Doppler velocities are consistent with the ions filling the planet's Roche lobe and moving preferentially away from the star, an indication that they are escaping the planet. We argue that π Men c possesses a thick atmosphere with abundant heavy volatiles ($>=$ 50{\%} by mass of atmosphere) but that needs not be carbon rich. Our reasoning relies upon cumulative evidence from the reported C II detection, the nondetection of H I atoms in a past transit, modeling of the planet's interior, and the assumption that the atmosphere, having survived the most active phases of its Sun-like host star, will survive another 0.2-2 Gyr. Depending on the current mass of atmosphere, π Men c may still transition into a bare rocky core. Our findings confirm the hypothesized compositional diversity of small exoplanets, and represent a milestone toward understanding the planets' formation and evolution paths through the investigation of their extended atmospheres.

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