Gliese 12 (GJ 12) is ared dwarf star located 39.7light-years (12.2parsecs) away in the constellationPisces. It has about 24% the mass and 26% the radius of the Sun, and a temperature of about 3,296 K (3,023 °C; 5,473 °F). It is aninactive star and hosts one knownexoplanet.[5]
Thetransiting exoplanet Gliese 12 b was discovered byTESS, and two independent studies confirming it as a planet were published in May 2024.[5][6] Gliese 12 b is similar in size to Earth andVenus, and completes an orbit around its star every 12.8 days.[7]
Initially its mass was poorly constrained but was determined to be less than 4 timesthat of Earth.[5] Measurements gathered in 2025 studies provided mass measurements of 0.71[8] and 0.95Earth masses (ME).[7] The latter also measured a planetary radius of 0.934 R🜨, and found a density of7.0+2.3 −2.1g/cm3, higher than the densities of the Solar System'sterrestrial planets. This suggests a likely rocky composition, similar toVenus.[7] While this, the former study used the discovery paper's radius (0.958 R🜨) 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.[8]
Along with the planets ofTRAPPIST-1 andLHS 1140 b, Gliese 12 b is one of the nearest known relatively temperate transiting exoplanets, and so is a promising target for theJames Webb Space Telescope to determine whether it has retained an atmosphere.[9][7] Gliese 12 b orbits slightly closer than the inner edge of its star'shabitable zone, with aninsolation between those of Earth and Venus.[6] Itsequilibrium temperature, assuming analbedo of zero, is 315 K (42 °C; 107 °F); if it has an atmosphere, the surface temperature would be greater than this.[5] Assuming an albedo similar to Venus, the equilibrium temperature is 218 K (−55 °C; −67 °F).[7]
^abcdefghTurner, Daisy A.; et al. (2025). "The mass of the exo-Venus Gliese 12 b, as revealed by HARPS-N, ESPRESSO, and CARMENES".arXiv:2506.20564 [astro-ph.EP].
^abcdBrady, Madison; Bean, Jacob; Basant, Ritvik; Brown, Nina; Das, Tanya; Nixon, Matthew; Luque, Rafael; Piaulet-Ghorayeb, Caroline; Radica, Michael (2025-06-25). "An Earth-like Density for the Temperate Earth-sized Planet GJ 12b".arXiv:2506.20561 [astro-ph.EP].
