Article

An Earth-sized planet on a 5.4 h orbit around a nearby K dwarf

Kaya Han TaşAnton Pannekoek Institute for Astronomy, University of AmsterdamGuðmundur StefánssonAnton Pannekoek Institute for Astronomy, University of AmsterdamGudmundur StefanssonUniversity of AmsterdamSyarief N. M. FarizAnton Pannekoek Institute for Astronomy, University of AmsterdamEsha GargAnton Pannekoek Institute for Astronomy, University of AmsterdamJuan I. Espinoza-RetamalUniversity of AmsterdamElise KooUniversity of AmsterdamDavid BruijneAnton Pannekoek Institute for Astronomy, University of AmsterdamJacob K. LuhnJet Propulsion Laboratory, California Institute of TechnologyEric B. FordDepartment of Astronomy & Astrophysics, 525 Davey Laboratory, The Pennsylvania State UniversitySuvrath MahadevanDepartment of Astronomy & Astrophysics, 525 Davey Laboratory, The Pennsylvania State UniversitySarah E. LogsdonU.S. National Science Foundation National Optical-Infrared Astronomy Research LaboratoryCaleb I. CanasNASA Goddard Space Flight CenterCaleb I. CañasNASA Goddard Space Flight CenterTe HanDepartment of Physics & Astronomy, The University of California, IrvineMark E. EverettU.S. National Science Foundation National Optical-Infrared Astronomy Research LaboratoryJaime A. Alvarado-MontesAstrophysics and Space Technologies Research Centre, Macquarie UniversityCullen H. BlakeDepartment of Physics and Astronomy, University of PennsylvaniaW. D. CochranMcDonald Observatory and Center for Planetary Systems Habitability, The University of Texas at AustinWilliam D. CochranMcDonald Observatory and Center for Planetary Systems Habitability, The University of Texas at AustinJiayin DongCenter for Computational Astrophysics, Flatiron InstituteRachel B. FernandesCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State UniversityMark R. GiovinazziDepartment of Physics and Astronomy, Amherst CollegeSamuel HalversonJet Propulsion Laboratory, California Institute of TechnologyShubham KanodiaEarth and Planets Laboratory, Carnegie Institution for ScienceDaniel KrolikowskiSteward Observatory, University of ArizonaDaniel M. KrolikowskiSteward Observatory, University of ArizonaMichael McElwainNASA Goddard Space Flight CenterMichael W. McElwainNASA Goddard Space Flight CenterJoe NinanDepartment of Astronomy and Astrophysics, Tata Institute of Fundamental ResearchJoe P. NinanDepartment of Astronomy and Astrophysics, Tata Institute of Fundamental ResearchLeonardo A. ParedesSteward Observatory, University of ArizonaPaul RobertsonDepartment of Physics & Astronomy, The University of California, IrvineChristian SchwabSchool of Mathematical and Physical Sciences, Macquarie University

Astronomy and Astrophysicsjournal2026en

ABI

Abstract

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.

Topics

Stellar, planetary, and galactic studies Astronomy and Astrophysical Research Astrophysics and Star Formation Studies

Identifiers

DOI: 10.1051/0004-6361/202556365

Citations and references

Cited by 091 references

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