期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 884, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.3847/2041-8213/ab498d
关键词
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资金
- DFG [SPP 1992, GA 2557/1-1, SCHN 1382/2-1]
- DLR [50OR1901]
Atmospheric escape is key to explaining the long-term evolution of planets in our solar system and beyond, and in the interpretation of atmospheric measurements. Hydrodynamic escape is generally thought to be driven by the flux of extreme-ultraviolet photons that the planet receives from its host star. Here, we show that the escape from planets orbiting hot stars proceeds through a different yet complementary process: drawing its energy from the intense near-ultraviolet emission of the star that is deposited within an optically thin, high-altitude atmospheric layer of hydrogen excited into the lower state of the Balmer series. The ultra-hot exoplanet KELT-9b likely represents the first known instance of this Balmer-driven escape. In this regime of hydrodynamic escape, the near-ultraviolet emission from the star is more important at determining the planet mass loss than the extreme-ultraviolet emission, and uncertainties in the latter become less critical. Further, we predict that gas exoplanets around hot stars may experience catastrophic mass loss when they are less massive than 1-2 Jupiter masses and closer in than KELT-9b, thereby challenging the paradigm that all large exoplanets are stable to atmospheric escape. We argue that extreme escape will affect the demographics of close-in exoplanets orbiting hot stars.
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