Gliese 12 b, A Temperate Earth-sized Planet at 12 Parsecs Discovered with TESS and CHEOPS

TL;DR

The paper reports the discovery and validation of Gliese 12 b, an Earth-sized, temperate exoplanet orbiting a nearby M-dwarf star, with potential for future mass measurement and habitability studies.

Contribution

It presents the first validation of a temperate, Earth-sized planet around a nearby, low-activity M-dwarf using combined TESS, CHEOPS, and ground-based observations.

Findings

Gliese 12 b has a 12.76-day orbit and a radius of about 1 Earth radius.

The planet's equilibrium temperature is approximately 315K.

It is one of the nearest Earth-sized planets suitable for habitability studies.

Abstract

We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a bright ($V=12.6$ mag, $K=7.8$ mag) metal-poor M4V star only $12.162\pm0.005$ pc away from the Solar System with one of the lowest stellar activity levels known for an M-dwarf. A planet candidate was detected by TESS based on only 3 transits in sectors 42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory, as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of $12.76144\pm0.00006$ days and a radius of $1.0\pm{0.1}$ R$_\oplus$, resulting in an equilibrium temperature of $\sim$315K. Gliese 12 b has excellent future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the Galaxy.