TOI-1231 b is an exoplanet orbiting the star TOI-1231, located 89.7 light-years (27.5 parsecs) from the Solar System; it was announced in 2021.
The star TOI-1231 has an apparent magnitude of 12.3 and an absolute magnitude of 10.1.
This star has 0.5 times the mass of the Sun, a radius of 0.5 times that of the Sun, a surface temperature of 3562 K, and a spectral type of M3V.
The planet TOI-1231 b orbits the star TOI-1231 with an orbital period of 24.2 days and a semi-major axis of 0.13 astronomical units (19,268,205.7 km).
TOI-1231b was discovered by TESS.
Its host star, TOI-1231, is classified as an M-type main-sequence star. Stars smaller than G-type main-sequence stars—the category to which the Sun belongs—are classified as M-type main-sequence stars, and TOI-1231 is only about half the size of the Sun. Due to its apparent magnitude of 12.3 and its location in the constellation Cygnus, it cannot be seen from most regions of Japan.
This article focuses on TOI-1231b, the only planet discovered so far.
Previously, it was predicted that using TESS, only a single planet—rock-free and no larger than Neptune—would be found in the habitable zone of an M-type dwarf star. TOI-1231b is attracting attention as the first planet to meet these criteria.
One of the characteristics of TOI-1231b is that its surface temperature is approximately 330 K (about 57°C).
Future research is anticipated to determine whether liquid water exists and if there is a possibility of life.
（文責：藤井）
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