Modeling Atmospheric Ion Escape from Kepler-1649 b and c over Time
Abstract Rocky planets orbiting M dwarf stars are prime targets for atmospheric characterization, yet their long-term evolution under intense stellar winds and high-energy radiation remains poorly constrained. The Kepler-1649 system, hosting two terrestrial exoplanets orbiting an M5V star, provides a valuable laboratory for studying atmospheric evolution in the extreme environments typical of M dwarf systems. In this Letter, we show that both planets could have retained atmospheres over gigayear timescales. Using a multispecies magnetohydrodynamic model, we simulate atmospheric ion escape driven by stellar winds and extreme-ultraviolet radiation from 0.8 to 4.0 Gyr. The results reveal a clear decline in total ion escape rates with stellar age, as captured by a nonparametric LOWESS regression, with O + comprising 98.3%–99.9% of the total loss. Escape rates at 4.0 Gyr are 2 to 3 orders of magnitude lower than during early epochs. At 0.8 Gyr, planet b exhibits 3.79× higher O + escape rates than planet c, whereas by 4.0 Gyr its O + escape rates becomes 39.5× lower. This reversal arises from a transition to sub-magnetosonic star–planet interactions, where the fast magnetosonic Mach number, M f , falls below unity. Despite substantial early atmospheric erosion, both planets may have retained significant atmospheres, suggesting potential long-term habitability. These findings offer predictive insight into atmospheric retention in the Kepler-1649 system and inform future JWST observations of similar M dwarf terrestrial exoplanets aimed at refining habitability assessments.
Authors
- Jinlian Ma (ORCID: https://orcid.org/0009-0000-9313-5251)
- Duncan Christie (ORCID: https://orcid.org/0000-0002-4997-0847)
- Haijun Zhou (ORCID: https://orcid.org/0000-0003-1397-0607)
- Nikolaos Georgakarakos (ORCID: https://orcid.org/0000-0002-7071-5437)
- Nathan J. Mayne (ORCID: https://orcid.org/0000-0001-6707-4563)
- Mei Ting Mak (ORCID: https://orcid.org/0000-0002-1624-3360)
- Chuanfei Dong (ORCID: https://orcid.org/0000-0002-8990-094X)
- Zhaojin Rong (ORCID: https://orcid.org/0000-0003-4609-4519)
- Laura Chin (ORCID: https://orcid.org/0009-0006-7877-1835)
- Xiao‐Bo Li (ORCID: https://orcid.org/0000-0003-4585-589X)
- Haitao Li (ORCID: https://orcid.org/0000-0001-6395-1936)
- Yajun Zhu (ORCID: https://orcid.org/0009-0001-0648-1373)
- Hong-Liang Yan (ORCID: https://orcid.org/0000-0002-8609-3599)
- Lianghai Xie (ORCID: https://orcid.org/0000-0001-9635-4644)
- Shi Chen (ORCID: https://orcid.org/0009-0005-6480-7465)
- J. J. Qin (ORCID: https://orcid.org/0009-0000-2934-4067)
- Xinyi He (ORCID: https://orcid.org/0009-0002-8332-9225)
- X.-Q. Wang (ORCID: https://orcid.org/0009-0000-2869-0072)
Institutions
- Boston University (US)
- Chinese Academy of Sciences (CN)
- University of Exeter (GB)
- Beijing Normal University (CN)
- University of Oxford (GB)
- Max Planck Institute for Astronomy (DE)
- National Space Science Center (CN)
- Institute of Geology and Geophysics (CN)
- Institute of High Energy Physics (CN)
- National Astronomical Observatories (CN)
- University of Chinese Academy of Sciences (CN)
- Hebei Normal University (CN)
Publication Details
- Journal
- The Astrophysical Journal Letters
- Published
- 2025-11-26
- DOI
- https://doi.org/10.3847/2041-8213/ae1a65
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- UK Research and Innovation
- National Natural Science Foundation of China
- Chinese Academy of Sciences
- China Scholarship Council
- Youth Innovation Promotion Association of the Chinese Academy of Sciences
- EarthLab, University of Washington
- Youth Innovation Promotion Association