Proxima Centauri d

Proxima Centauri d is a confirmed exoplanet orbiting the red dwarf star Proxima Centauri, the closest star to the Sun and part of the Alpha Centauri triple star system. Together with one or two other planets in the Proxima Centauri system, it is the closest known exoplanet to the Solar System, located approximately away in the constellation of Centaurus. The first signs of the exoplanet emerged as a weak 5.15-day signal in radial velocity data taken from the Very Large Telescope during a 2020 study on Proxima b's mass. This signal was formally proposed to be a candidate exoplanet by Faria et al. in a follow-up paper published in February 2022, and was independently confirmed in 2025.

Characteristics

Proxima d is a sub-Earth at least one-quarter of the mass of Earth, orbiting at roughly every 5.1 days. It is the least massive and innermost known planet of the Proxima Centauri system. It was the least massive exoplanet detected with the radial velocity method from 2022 until the discovery of Barnard's Star e in 2025. Its proximity to the star and short orbital period of 5.1 days suggest that it is likely tidally locked due to strong tidal forces. Although Proxima d orbits too close to its star to have a habitable equilibrium temperature by the HARPS spectrograph at the La Silla Observatory. Independent confirmation of Proxima d was achieved with the NIRPS spectrograph in work published in July 2025.