Hydrogen escaping from a pair of exoplanets smaller than Neptune

• 成果类型: Article
• 署名作者: 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.
• 署名单位: Eureka Scientific; Imperial College London; University of Cambridge; University of California System; University of California Santa Cruz; Arizona State University; Arizona State University-Tempe; University of Colorado System; University of Colorado Boulder; University System of Maryland; University of Maryland Baltimore County; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; Carnegie Institution for Science; Carnegie Institution for Science; University of California System; University of California Los Angeles; Vanderbilt University; University of Colorado System; University of Colorado Boulder; University of Hamburg; University of Colorado System; University of Colorado Boulder; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; University of Arizona; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL)
• 刊物名称: Nature
• ISSN/ISSBN: 0028-2943
• DOI: 10.1038/s41586-024-08490-x
• 发表日期: 2025-02-20
• 关键词: powered mass-loss; radius distribution; evaporation; planetary; wind; fractionation; atmosphere; DYNAMICS; transit; models

摘要

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 circle plus 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 circle plus) and TOI-776 c (2.02 +/- 0.14 R circle plus), the sizes of which near the radius valley and mature (1-4 Gyr) 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-alpha 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-Neptunes(5, 6, 7-8,15,16).