TOI-2431 b


TOI-2431 b is an extrasolar planet orbiting the orange dwarf star TOI-2431. It was initially detected by the transit method in 2019, and with additional observations was confirmed in 2025. The planet is notable for its extremely short orbital period of 5h 22min, one of the shortest known. In about 31 million years, it will enter the Roche lobe of the host star and be torn apart.

Characteristics

TOI-2431 b has around 1.54 times Earth's radius and 6.2 times Earth's mass, resulting in a density of, which is significantly higher than that of Earth and implies a rocky composition.
Its orbital period is extremely short, at just, the sixth-shortest for any known exoplanet, as of 2025. The separation from the host star is, a constant value throughout the orbit, since its eccentricity is zero. The separation is just 30% wider than the Roche lobe of the host star, and is decaying at a rate that implies a remaining lifetime of about 31 million years before the planet enters the star's Roche lobe and is torn apart. This close orbit implies is tidally locked, with one side permanently facing the host star and the other side always facing it. It also implies a high irradiation, and hence a high temperature. Its equilibrium temperature is estimated at, assuming a Bond albedo of 0. The elevated temperature imply its dayside is likely made up from molten lava.
Rocky planets at such orbital periods and high irradiances are expected to have an atmosphere made up from vapors of rock in the side always facing the host star. Such atmosphere can be detected with transmission spectroscopy using powerful telescopes such as the James Webb Space Telescope. Since TOI-2431 has a relatively bright apparent magnitude, TOI-2431 b has a high potential for the detection of such an atmosphere.

Discovery

The planet was initially detected as a candidate in 2019 by the Transiting Exoplanet Survey Satellite and while a candidate, was briefly mentioned in a 2021 HST proposal and a 2022 study about the detection of an evaporating atmosphere made of rock vapor, owing its short orbital period and the feasibility of such a detection. It was confirmed in 2025 by et al, using a joint of Transit photometry from the TESS and Doppler spectroscopy from the NEID and Habitable-zone Planet Finder spectrographs, as well as imaging to secure the accuracy of the observations by ruling out potential artifacts from stars within field of view of the equipments.

Host star

TOI-2431 is a K-type main-sequence star located in the constellation of Cetus. It is somewhat nearby to the Solar System, at a distance of. The star has 0.66 times the mass of the Sun and 0.651 times the Sun's radius. It irradiates 10.9% of the Sun's luminosity from its photosphere at an effective temperature of, giving it an orange hue typical of K-type stars. The spectral type is K7V, the same of 61 Cygni B. Its apparent magnitude of 10.89 is below the threshold for naked eye vision.