Gliese 12 (GJ 12) is a red dwarf star located 39.7lk=onNaNlk=on away in the constellation Pisces. It has about 24% the mass and 26% the radius of the Sun, and a temperature of about 3296K. It is an inactive star and hosts one known exoplanet.
The transiting exoplanet Gliese 12 b was discovered by TESS, and two independent studies confirming it as a planet were published in May 2024. Gliese 12 b is similar in size to Earth and Venus, and completes an orbit around its star every 12.8 days. Its mass is poorly constrained but is known to be less than 4 times that of Earth.
Along with the planets of TRAPPIST-1, Gliese 12 b is one of the nearest known relatively temperate transiting exoplanets, and so is a promising target for the James Webb Space Telescope to determine whether it has retained an atmosphere. Gliese 12 b orbits slightly closer than the inner edge of its star's habitable zone, with an insolation between those of Earth and Venus. Its equilibrium temperature, assuming zero albedo, is 315K; if it has an atmosphere, the surface temperature would be greater than this.