Discovery of TOI-2431 b: A New Earth-Sized Exoplanet with an Ultra-Short Orbital Period

In an exciting development for the field of exoplanet research, an international team of astronomers has announced the discovery of a new exoplanet named TOI-2431 b, which orbits a star located just 117 light-years away. The findings, published on July 11, 2025, on the pre-print server arXiv, highlight the capabilities of NASA’s Transiting Exoplanet Survey Satellite (TESS) in identifying potential new worlds beyond our solar system.

TESS, launched in April 2018, has been instrumental in monitoring approximately 200,000 bright stars in our cosmic neighborhood. The satellite detects exoplanets by observing temporary dips in brightness that occur when a planet transits in front of its host star. To date, TESS has identified over 7,600 candidate exoplanets, with 638 of these confirmed, and TOI-2431 b adds to this growing list.

The research, spearheaded by Kaya Han Taş from the University of Amsterdam, confirms that TOI-2431 b is an ultra-short period (USP) planet, with an orbital period of just 5.4 hours. This rapid orbit places the planet extremely close to its host star, at a distance of merely 0.0063 astronomical units (AU). TOI-2431 b boasts a radius of approximately 1.53 times that of Earth and is 6.2 times more massive, resulting in a density of 9.4 g/cm³.

Given its proximity to the star and an estimated equilibrium temperature of around 2,000 K, it is likely that TOI-2431 b has a molten surface. The planet’s unique characteristics also suggest it is tidally deformed, with its shortest axis being about 9 percent shorter than its longest axis. The researchers have calculated a tidal decay timescale of approximately 31 million years, a notably short period compared to other known ultra-short period planets.

The host star, TOI-2431, is a K dwarf, about two-thirds the size and mass of our Sun. Estimated to be around two billion years old, the star has an effective temperature of approximately 4,109 K and a metallicity of -0.02 dex.

The discovery of TOI-2431 b opens up new avenues for exploration, particularly with the James Webb Space Telescope (JWST). The researchers suggest that further observations could provide valuable insights into the planet’s surface composition and potential atmospheric conditions, thus enhancing our understanding of exoplanets similar to Earth.

As the field of exoplanet research continues to expand, findings like those of TOI-2431 b remind us of the vast and diverse worlds beyond our planet, inviting both scientific inquiry and public fascination. The quest to uncover the mysteries of the universe is ongoing, and with each new discovery, we move closer to understanding the possibilities of life beyond Earth.