An Earth-sized planet on a 5.4 h orbit around a nearby K dwarf
We present the discovery and confirmation of the ultrashort period (USP) planet TOI-2431 b orbiting a nearby ( d ~ 36 pc) late K star ( T eff = 4109 ± 28 K) using observations from the Transiting Exoplanet Survey Satellite (TESS), precise radial velocities (RVs) with NEID and Habitable-zone Planet Finder (HPF) spectrographs, as well as ground-based high-contrast imaging from NESSI. TOI-2431 b has a period of 5 hours and 22 minutes, making it one of the shortest-period exoplanets known to date. TOI-2431 b has a radius of 1.534 ± 0.033 R ⊕ and a mass of 6.2 ± 1.6 M ⊕ , where the exact mass precision shows a slight dependence on the choice of prior. This suggests TOI-2431 b has a density compatible with an Earth-like composition and due to its high irradiation, it is likely to be a “lava-world” with a T eq = 2063 ± 30 K. We estimate that the current orbital period is only 30% larger than the Roche-limit orbital period and that it has an expected orbital decay timescale of only ~31 Myr. Finally, due to the brightness of the host star ( V = 10.9, K = 7.6), we find that TOI-2431 b has a high emission spectroscopy metric (ESM) of 27, making it one of the best USP systems for atmospheric phase-curve analyses.
Authors
- Eric B. Ford (ORCID: https://orcid.org/0000-0001-6545-639X)
- Samuel Halverson (ORCID: https://orcid.org/0000-0003-1312-9391)
- Rachel B. Fernandes (ORCID: https://orcid.org/0000-0002-3853-7327)
- Joe P. Ninan (ORCID: https://orcid.org/0000-0001-8720-5612)
- Sarah E. Logsdon (ORCID: https://orcid.org/0000-0002-9632-9382)
- Eunmo Koo (ORCID: https://orcid.org/0000-0001-9943-9694)
- Jacob K. Luhn (ORCID: https://orcid.org/0000-0002-4927-9925)
- Jiayin Dong (ORCID: https://orcid.org/0000-0002-3610-6953)
- Caleb I. Cañas (ORCID: https://orcid.org/0000-0003-4835-0619)
- Michael W. McElwain (ORCID: https://orcid.org/0000-0003-0241-8956)
- Shubham Kanodia (ORCID: https://orcid.org/0000-0001-8401-4300)
- Daniel M. Krolikowski (ORCID: https://orcid.org/0000-0001-9626-0613)
- Mark E. Everett (ORCID: https://orcid.org/0000-0002-0885-7215)
- Te Han (ORCID: https://orcid.org/0000-0002-7127-7643)
- Paul Robertson (ORCID: https://orcid.org/0000-0003-0149-9678)
- Guđmundur Stefánsson (ORCID: https://orcid.org/0000-0001-7409-5688)
- Jaime A. Alvarado-Montes (ORCID: https://orcid.org/0000-0003-0353-9741)
- Mark R. Giovinazzi (ORCID: https://orcid.org/0000-0002-0078-5288)
- W. D. Cochran
- Suvrath Mahadevan (ORCID: https://orcid.org/0000-0001-9596-7983)
- Cullen H. Blake (ORCID: https://orcid.org/0000-0002-5423-5919)
- Juan I. Espinoza-Retamal (ORCID: https://orcid.org/0000-0001-9480-8526)
- Christian Schwab (ORCID: https://orcid.org/0000-0002-0091-7105)
- Leonardo A. Paredes (ORCID: https://orcid.org/0000-0003-1324-0495)
- David Bruijne
- Kaya Han Taş
- Syarief N. M. Fariz
- Esha Garg
Institutions
- Tata Institute of Fundamental Research (IN)
- Goddard Space Flight Center (US)
- Pennsylvania State University (US)
- U.S. National Science Foundation (US)
- Jet Propulsion Laboratory (US)
- University of Arizona (US)
- University of Illinois Urbana-Champaign (US)
- Pontificia Universidad Católica de Chile (CL)
- Amherst College (US)
- Astrakhan Tatischev State University (RU)
- Joint Institute for Nuclear Astrophysics (US)
- Carnegie Institution for Science (US)
- Princeton University (US)
- University of California, Irvine (US)
- Five Colleges (US)
- Australian Astronomical Observatory (AU)
- Millennium Institute of Astrophysics (CL)
- Uzbek State University of World Languages (UZ)
- Planetary Systems (United States) (US)
- Astronomical Institute of the Slovak Academy of Sciences (SK)
- NSF NOIRLab (US)
- Flatiron Health (United States) (US)
- Flatiron Institute (US)
- University of Pennsylvania (US)
- University of Amsterdam (NL)
- Macquarie University (AU)
Publication Details
- Journal
- Astronomy and Astrophysics
- Published
- 2026-01-27
- DOI
- https://doi.org/10.1051/0004-6361/202556365
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00