TOI-237 c is a confirmed exoplanet that represents one of the more recent additions to the rapidly expanding catalogue of small, close-in worlds discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS). It orbits a faint, cool M-type dwarf star approximately 38 parsecs from Earth and was formally announced as a confirmed planet in 2026 following detailed transit analysis and follow-up validation work that ruled out common false-positive scenarios such as eclipsing binaries or blended stellar systems.
The planet is classified as a super-Earth, with a measured radius of about 1.2 Earth radii and a mass of roughly 1.9 Earth masses, placing it among the smaller and likely rocky exoplanets detected in short-period orbits. Its orbital period is extremely brief, completing one revolution around its host star in approximately 1.74 days at a distance of only 0.016 astronomical units, which is about 40 times closer than Mercury is to the Sun. This extreme proximity results in a highly irradiated environment, with an estimated equilibrium temperature near 515 K, hot enough to significantly alter surface conditions if the planet is rocky and lacks a substantial atmosphere.
The host star, TOI-237, is a mid-M dwarf with a mass around 0.17–0.18 solar masses and a radius close to 0.21 solar radii, emitting most of its energy in the infrared due to its low effective temperature of roughly 3200 K. Such stars are common targets for transit surveys because their small size enhances the relative depth of planetary transits, making even Earth-sized planets detectable with space-based photometry like that from TESS.
TOI-237 is already known to host at least one additional planet, TOI-237 b, which has a longer orbital period of about 5.4 days and a slightly larger radius. The presence of multiple close-in planets suggests a compact system architecture, which is a recurring pattern among M-dwarf planetary systems observed by TESS. Dynamical analyses indicate that the system is likely stable, and the planets may be near low-order orbital resonances, a configuration that can provide insight into their formation and migration history.
One of the most interesting aspects of TOI-237 c is its role in probing the so-called “radius valley,” a population gap observed in exoplanet size distributions around 1.5–2 Earth radii. With a radius near 1.2 Earth radii, it lies below this gap, strengthening the case that it could be a predominantly rocky planet rather than a volatile-rich mini-Neptune. This makes it particularly valuable for testing theories of atmospheric loss driven by stellar irradiation, especially in the harsh environments around M dwarfs.
Although its current mass and radius suggest a likely rocky composition, no atmospheric characterization has yet been reported. Its high equilibrium temperature and proximity to its star make it an unlikely candidate for habitability as we understand it, but such worlds are scientifically important because they represent the extreme end of terrestrial planet evolution under strong stellar forcing.
TOI-237 c therefore stands as a key example of a modern TESS discovery: a small, ultra-short-period exoplanet in a compact multi-planet system around a nearby low-mass star, offering valuable constraints on planet formation, migration, and atmospheric erosion in environments very different from our own Solar System.
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