近日，美国加州理工学院的Renyu Hu及其研究团队取得一项新进展。经过不懈努力，他们对岩石系外行星巨蟹座55e上的次生大气进行研究。相关研究成果已于2024年5月8日在国际权威学术期刊《自然》上发表。

本文报道了JWST的NIRCam和MIRI仪器在4 ~ 12 μm范围内获得的行星热发射光谱。测量结果否定了火星是熔岩世界且被蒸发岩石的稀薄大气覆盖的假设，而证实其拥有一个真正的挥发性大气，很可能富含二氧化碳或一氧化碳。这种大气可能源自并持续由岩浆海洋释放和维持。

据悉，描绘岩石系外行星的特征是天文学的核心工作，然而迄今为止，在岩石系外行星上寻找大气的结果要么是大气质量的严格上限，要么是不确定的结果。巨蟹座55e，一个拥有1.95倍地球半径和8.8倍地球质量的岩石行星，其平衡温度高达约2000 K。这颗行星可能覆盖着一层由C、H、O、N、S和P等元素构成的挥发性物质，占其半径的百分之几。经过广泛的透射光谱学观测，其热辐射已在多个光度波段进行了测量。尽管这些观测结果不支持该行星拥有原始的H₂/He主导的大气，但尚无法最终确定是否存在次生大气。

附：英文原文

Title: A secondary atmosphere on the rocky Exoplanet 55 Cancri e

Author: Hu, Renyu, Bello-Arufe, Aaron, Zhang, Michael, Paragas, Kimberly, Zilinskas, Mantas, van Buchem, Christiaan, Bess, Michael, Patel, Jayshil, Ito, Yuichi, Damiano, Mario, Scheucher, Markus, Oza, Apurva V., Knutson, Heather A., Miguel, Yamila, Dragomir, Diana, Brandeker, Alexis, Demory, Brice-Olivier

Issue&Volume: 2024-05-08

Abstract: Characterizing rocky exoplanets is a central endeavor of astronomy, and yet the search for atmospheres on rocky exoplanets has hitherto resulted in either tight upper limits on the atmospheric mass or inconclusive results. The 1.95-R_Earth and 8.8-M_Earth planet 55 Cnc e, with a predominantly rocky composition and an equilibrium temperature of ~2000 K, may have a volatile envelope (containing molecules made from a combination of C, H, O, N, S, and P elements) that accounts for up to a few percent of its radius. The planet has been observed extensively with transmission spectroscopy, and its thermal emission has been measured in broad photometric bands. These observations disfavor a primordial H₂/He-dominated atmosphere but cannot conclusively determine whether the planet has a secondary atmosphere. Here we report a thermal emission spectrum of the planet obtained by JWST’s NIRCam and MIRI instruments from 4 to 12 μm. The measurements rule out the scenario where the planet is a lava world shrouded by a tenuous atmosphere made of vaporized rock, and indicate a bona fide volatile atmosphere likely rich in CO₂ or CO. This atmosphere can be outgassed from and sustained by a magma ocean.

DOI: 10.1038/s41586-024-07432-x

Source: https://www.nature.com/articles/s41586-024-07432-x