美国科罗拉多大学Ardila David R.课题组在研究中取得进展。他们报道了氢从一对比海王星小的系外行星中逃逸。相关论文于2025年2月12日发表在《自然》杂志上。

研究人员表示，系外行星调查显示，在近100天的轨道上有大量比海王星小的系外行星。这些行星形成了两个种群，在大约1.8 R⊕的地方被称为radithem valley的自然分界线隔开。目前尚不确定这些种群是来自不同的干旱和富水形成渠道，还是由于长期的大气损失而分开进化，或者是这两种因素的结合。

小组报告了对两颗兄弟行星TOI-776 b（1.85±0.13 R⊕）和TOI-776 c（2.02±0.14 R⊕）的持续氢损失的观测，这两颗行星在半径谷附近的大小和成熟的（1-4 Gyr）年龄，使得对于研究它们所属的分裂星系群的起源很有价值。

在这些行星的凌日过程中，吸收出现在宿主恒星的莱曼α发射上，与氢逃逸相容，其速率分别相当于每颗行星每十亿年总质量的0.03-0.6%和0.1-0.9%。外行星TOI-776 c的观测结果与分离蒸汽的流出不相容，这表明它和它的内部兄弟都是在干燥的环境中形成的。这些观测结果支持了氢损失在近轨道亚海王星演化中的重要作用。

附：英文原文

Title: Hydrogen escaping from a pair of exoplanets smaller than Neptune

Author: Loyd, R. O. Parke, Schreyer, Ethan, Owen, James E., Rogers, James G., Broome, Madelyn I., Shkolnik, Evgenya L., Murray-Clay, Ruth, Wilson, David J., Peacock, Sarah, Teske, Johanna, Schlichting, Hilke E., Duvvuri, Girish M., Youngblood, Allison, Schneider, P. Christian, France, Kevin, Giacalone, Steven, Batalha, Natasha E., Schneider, Adam C., Longo, Isabella, Barman, Travis, Ardila, David R.

Issue&Volume: 2025-02-12

Abstract: Exoplanet surveys have shown a class of abundant exoplanets smaller than Neptune on close, <100-day orbits1,2,3,4. These planets form two populations separated by a natural division at about 1.8 R⊕ termed the radius valley. It is uncertain whether these populations arose from separate dry versus water-rich formation channels, evolved apart because of long-term atmospheric loss or a combination of both5,6,7,8,9,10,11,12,13,14. Here we report observations of ongoing hydrogen loss from two sibling planets, TOI-776 b (1.85±0.13 R⊕) and TOI-776 c (2.02±0.14 R⊕), the sizes of which near the radius valley and mature (1–4Gyr) age make them valuable for investigating the origins of the divided population of which they are a part. During the transits of these planets, absorption appeared against the Lyman-α emission of the host star, compatible with hydrogen escape at rates equivalent to 0.03–0.6% and 0.1–0.9% of the total mass per billion years of each planet, respectively. Observations of the outer planet, TOI-776 c, are incompatible with an outflow of dissociated steam, suggesting both it and its inner sibling formed in a dry environment. These observations support the strong role of hydrogen loss in the evolution of close-orbiting sub-Neptunes5,6,7,8,15,16.

DOI: 10.1038/s41586-024-08490-x

Source: https://www.nature.com/articles/s41586-024-08490-x