Study Findings: An Adolescent and Near-resonant Planetary System Near the End of Photoevaporation

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Credit: Image by Adis Resic from Pixabay

Nature Astronomy abstract of study findings:

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.

Citation: Wang, MT., Dai, F., Liu, HG. et al. An adolescent and near-resonant planetary system near the end of photoevaporation, Nat Astron (2026).

https://doi.org/10.1038/s41550-026-02795-9

Study-related stories:

Florida Tech – “Assessment of Rare Teenage Planetary System Deepens Understanding of Cosmic Evolution”

Universe Today – “Adolescence Is Tumultuous, Even For Exoplanets”

Daily Galaxy – “Scientists Discover ‘Teenage’ Planetary System, Unlocking Secrets of Cosmic Growth”