Gliese 12
Gliese 12 is a red dwarf star located away in the constellation Pisces. It has about 24% the mass and 26% the radius of the Sun, and a temperature of about. It is an Stellar [magnetic field#Surface activity|inactive] star and hosts one known exoplanet.
Planetary system
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.Initially its mass was poorly constrained but was determined to be less than 4 times that of Earth. Measurements gathered in 2025 studies provided mass measurements of 0.71 and 0.95 Earth masses. The latter also measured a planetary radius of, and found a density of, higher than the densities of the Solar System's terrestrial planets. This suggests a likely rocky composition, similar to Venus. While this, the former study used the discovery paper's radius and found a lower density that give less constraints on its composition. Scenarios such as an Earth-like composition, volatile-dominated composition, iron-poor, or even a combination are all plausible.
Along with the planets of TRAPPIST-1 and LHS 1140 b, 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 an albedo of zero, is ; if it has an atmosphere, the surface temperature would be greater than this. Assuming an albedo similar to Venus, the equilibrium temperature is.