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<p>Young exoplanets provide vital insights into the early dynamical and atmospheric evolution of planetary systems. Many multi-planet systems younger than 100 Myr exhibit mean-motion resonances, probably established through convergent disk migration. Over time, however, these resonant chains are often disrupted, mirroring the Nice model proposed for the Solar System. Here we present a detailed characterization of the ~200-Myr-old TOI-2076 system, which contains four sub-Neptune planets between 1.4 and 3.5 Earth radii. We demonstrate that its planets are near to but not locked in mean-motion resonances, making the system dynamically fragile. The four planets have comparable core masses but display a monotonic increase in hydrogen and helium (H/He) envelope mass fractions (from stripped to 1%, 5% and 5%) with decreasing stellar insolation. This trend is consistent with atmospheric mass loss due to photoevaporation, which predicts that the envelopes of irradiated planets either erode completely or stabilize at a residual level of ~1% by mass within the first few hundred million years, with more distant, less-irradiated planets retaining most of their primordial envelopes. Additionally, previous detections of metastable helium outflows rule out a pure water-world scenario for the TOI-2076 planets. Our finding provides direct observational evidence that the dynamical and atmospheric reshaping of compact planetary systems begins early and offers an empirical anchor for models of their long-term evolution.</p>

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An adolescent and near-resonant planetary system near the end of photoevaporation

  • 期刊论文

  • 发表日期：

    2026年2月27日

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  • Mu-Tian Wang,
  • Fei Dai,
  • Hui-Gen Liu,
  • Howard Chen,
  • Zhecheng Hu,
  • Erik Petigura,
  • Steven Giacalone,
  • Eve Lee,
  • Max Goldberg,
  • Adrien Leleu,
  • Andrew W. Mann,
  • Madyson G. Barber,
  • Joshua N. Winn,
  • Karen A. Collins,
  • Cristilyn N. Watkins,
  • Richard P. Schwarz,
  • Howard M. Relles,
  • Francis P. Wilkin,
  • Enric Palle,
  • Felipe Murgas,
  • Avi Shporer,
  • Ramotholo Sefako,
  • Keith Horne,
  • Hugh P. Osborn,
  • Yann Alibert,
  • Luca Fossati,
  • Andrea Fortier,
  • Sérgio Sousa,
  • Alexis Brandeker,
  • Pierre Maxted,
  • Alexia Goldenberg

摘要

Young exoplanets provide vital insights into the early dynamical and atmospheric evolution of planetary systems. Many multi-planet systems younger than 100 Myr exhibit mean-motion resonances, probably established through convergent disk migration. Over time, however, these resonant chains are often disrupted, mirroring the Nice model proposed for the Solar System. Here we present a detailed characterization of the ~200-Myr-old TOI-2076 system, which contains four sub-Neptune planets between 1.4 and 3.5 Earth radii. We demonstrate that its planets are near to but not locked in mean-motion resonances, making the system dynamically fragile. The four planets have comparable core masses but display a monotonic increase in hydrogen and helium (H/He) envelope mass fractions (from stripped to 1%, 5% and 5%) with decreasing stellar insolation. This trend is consistent with atmospheric mass loss due to photoevaporation, which predicts that the envelopes of irradiated planets either erode completely or stabilize at a residual level of ~1% by mass within the first few hundred million years, with more distant, less-irradiated planets retaining most of their primordial envelopes. Additionally, previous detections of metastable helium outflows rule out a pure water-world scenario for the TOI-2076 planets. Our finding provides direct observational evidence that the dynamical and atmospheric reshaping of compact planetary systems begins early and offers an empirical anchor for models of their long-term evolution.