近日，美国空间望远镜科学研究所及其研究团队取得一项新进展。经过不懈努力，他们成功探测到系外行星WASP-39 b上的非均匀明暗交界。相关研究成果已于2024年7月15日在国际权威学术期刊《自然》上发表。

该研究团队在假设WASP-39 b轨道参数精确的前提下，利用JWST探测到了WASP-39 b的非均匀明暗交界，从而获得了WASP-39 b近红外(25 μm)的早晨/傍晚透射光谱。研究人员在傍晚观测到更大的凌日深度，平均比早晨大405±88 ppm，也具有比早晨更大的定性特征。该光谱最好的解释是，在该模型中，傍晚结束点比早晨结束点热177⁺⁶⁵_-57K，两个结束点的C/O比值与太阳一致。大气环流模式(GCMs)预测的温差与上述值大致一致，并指向多云的早晨明暗交界和更晴朗的傍晚明暗交界。

据悉，在过去的二十年里，透射光谱学一直是限制系外行星大气物理和化学性质的主要技术。它的一个经典关键假设是，它探测的大气部分——明暗交界区——是均匀的。然而，在过去的十年中，有几项工作对高辐射、高温(T_eq 1000 K)气体巨行星的经验和三维建模提出了质疑。虽然模型预测了傍晚(日-夜)和早晨(夜-日)明暗交界之间的明显差异，但迄今为止还没有报道过系外行星在宽波长范围内的早晨/傍晚直接透射光谱。

附：英文原文

Title: Inhomogeneous terminators on the exoplanet WASP-39 b

Author: Espinoza, Nstor, Steinrueck, Maria E., Kirk, James, MacDonald, Ryan J., Savel, Arjun B., Arnold, Kenneth, Kempton, Eliza M.-R., Murphy, Matthew M., Carone, Ludmila, Zamyatina, Maria, Lewis, David A., Samra, Dominic, Kiefer, Sven, Rauscher, Emily, Christie, Duncan, Mayne, Nathan, Helling, Christiane, Rustamkulov, Zafar, Parmentier, Vivien, May, Erin M., Carter, Aarynn L., Zhang, Xi, Lpez-Morales, Mercedes, Allen, Natalie, Blecic, Jasmina, Decin, Leen, Mancini, Luigi, Molaverdikhani, Karan, Rackham, Benjamin V., Palle, Enric, Tsai, Shang-Min, Ahrer, Eva-Maria, Bean, Jacob L., Crossfield, Ian J. M., Haegele, David, Hbrard, Eric, Kreidberg, Laura, Powell, Diana, Schneider, Aaron D., Welbanks, Luis, Wheatley, Peter, Brahm, Rafael, Crouzet, Nicolas

Issue&Volume: 2024-07-15

Abstract: Transmission spectroscopy has been a workhorse technique over the past two decades to constrain the physical and chemical properties of exoplanet atmospheres. One of its classical key assumptions is that the portion of the atmosphere it probes — the terminator region — is homogeneous. Several works in the past decade, however, have put this into question for highly irradiated, hot (T_eq 1000 K) gas giant exoplanets both empirically and via 3-dimensional modelling. While models predict clear differences between the evening (day-to-night) and morning (night-to-day) terminators, direct morning/evening transmission spectra in a wide wavelength range has not been reported for an exoplanet to date. Under the assumption of precise and accurate orbital parameters on WASP-39 b, here we report the detection of inhomogeneous terminators on the exoplanet WASP-39 b, which allows us to retrieve its morning and evening transmission spectra in the near-infrared (2 5 μm) using JWST. We observe larger transit depths in the evening which are, on average, 405±88 ppm larger than the morning ones, also having qualitatively larger features than the morning spectrum. The spectra are best explained by models in which the evening terminator is hotter than the morning terminator by 177⁺⁶⁵_-57 K with both terminators having C/O ratios consistent with solar. General circulation models (GCMs) predict temperature differences broadly consistent with the above value and point towards a cloudy morning terminator and a clearer evening terminator.

DOI: 10.1038/s41586-024-07768-4

Source: https://www.nature.com/articles/s41586-024-07768-4