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Age dependence of the occurrence and architecture of ultra-short-period planet systems

Nature Astronomy volume 9, pages 995–1006 (2025)Cite this article

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Abstract

Ultra-short-period (USP) planets, with orbital periods shorter than 1 day, represent a unique class of exoplanets whose origin remains puzzling. Determining their age distribution and temporal evolution is vital for uncovering their formation and evolutionary pathways. Using a sample of over 1,000 short-period planets around Sun-like stars, we found that the host stars of USP planets are relatively older and have a higher prevalence in the Galactic thick disk compared to stars hosting other short-period planets. Furthermore, we found that the occurrence of USP planets increases with stellar age, and we uncovered evidence indicating that USP planetary system architectures evolve on gigayear timescales. This includes a distinct dip/pile-up in period distributions around ~1 day and an expansion of orbital spacings with time. In addition, younger USP planet systems are observed to have fewer transiting planets, implying fewer nearby companions or larger mutual orbital inclinations. Our findings indicate that USP planets continuously form through inward migration driven by tidal dissipation over gigayear timescales, and that younger and older USP planets may have originated via different specific tidal migration pathways.

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Fig. 1: Comparison of kinematic properties of hot-planet hosts.
Fig. 2: Comparison of the Galactic velocity distributions and kinematic ages of hot-planet hosts.
Fig. 3: The frequencies of USP planets (fUSP) as a function of average age \(\bar{t}\) from different indicators.
Fig. 4: Comparison of the architecture between the younger and older USP planet systems and HS planet systems.

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Data availability

The datasets generated and analysed in this study are available via Zenodo (https://zenodo.org/records/14221205)59. Other data used in this study are accessible from the public archives of the observatories or survey websites.

Code availability

The KeplerPORTs software package60,61 is publicly available at https://github.com/nasa/KeplerPORTs.

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Acknowledgements

This work is supported by the National Key R&D Program of China (Grant No. 2024YFA1611803) and the National Natural Science Foundation of China (Grant Nos. 12273011, 12150009 and 12403071). We acknowledge funding from the science research grants from the China Manned Space Project (Grant No. CMS-CSST-2021-B12). J.-W.X. acknowledges support from the National Youth Talent Support Program. D.-C.C. acknowledges the Cultivation Project for the LAMOST Scientific Payoff, a Research Achievement of CAMS-CAS and the fellowship of the Chinese Postdoctoral Science Foundation (Grant No. 2022M711566). Funding for LAMOST (www.lamost.org) has been provided by the Chinese NDRC. LAMOST is operated and managed by the National Astronomical Observatories, CAS.

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Authors and Affiliations

  1. School of Astronomy and Space Science, Nanjing University, Nanjing, China

    Pei-Wei Tu, Ji-Wei Xie, Di-Chang Chen & Ji-Lin Zhou

  2. Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education, Nanjing, China

    Pei-Wei Tu, Ji-Wei Xie, Di-Chang Chen & Ji-Lin Zhou

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Contributions

J.-W.X. conceived the project and designed the research. P.-W.T. led the data analyses. P.-W.T., J.-W.X. and D.-C.C. analysed the results and drafted the paper. All authors contributed to discussing the results and editing and revising the paper.

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Correspondence to Ji-Wei Xie.

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Tu, PW., Xie, JW., Chen, DC. et al. Age dependence of the occurrence and architecture of ultra-short-period planet systems. Nat Astron 9, 995–1006 (2025). https://doi.org/10.1038/s41550-025-02539-1

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