An Earth-Sized Planet in a 5.4h Orbit Around a Nearby K dwarf
Kaya Han Ta\c{s}, Gudmundur Stefansson, Syarief N.M. Fariz, Esha Garg, Juan I. Espinoza-Retamal, Elise Koo, David Bruijne, Jacob Luhn, Eric B. Ford, Suvrath Mahadevan, Sarah E. Logsdon, Caleb I. Ca\~nas, Te Han, Mark E. Everett, Jaime A. Alvarado-Montes, Cullen Blake

TL;DR
This paper reports the discovery of an ultra-short period Earth-sized planet orbiting a nearby K dwarf star, with detailed characterization suggesting a lava-world with potential for atmospheric studies.
Contribution
The study presents the first confirmation and detailed analysis of TOI-2431 b, an ultra-short period planet with a 5.4-hour orbit, using combined space-based and ground-based observations.
Findings
Planet has a 5-hour 22-minute orbit, one of the shortest known.
Planet's radius and mass suggest an Earth-like composition.
High irradiation makes it a prime candidate for atmospheric phase-curve analysis.
Abstract
We present the discovery and confirmation of the ultra-short period (USP) planet TOI-2431 b orbiting a nearby ( pc) late K star ( = ) using observations from the Transiting Exoplanet Survey Satellite (TESS), precise radial velocities with the NEID and the 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 , and a mass of , suggesting it has a density compatible with an Earth-like composition and, due to its high irradiation, is likely a 'lava-world' with a = . We estimate that the current orbital period is only 30% larger than the…
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