Proxima Centauri B [EN]

Proxima Centauri B (or Proxima b), sometimes referred to as Alpha Centauri Cb, is an exoplanet orbiting within the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of the larger triple star system Alpha Centauri. It is about 4.2 light-years (1.3 parsecs) from Earth in the constellation Centaurus, making it and Proxima d, along with the currently disputed Proxima c, the closest known exoplanets to the Solar System.

Proxima Centauri b orbits its parent star at a distance of roughly 0.04856 AU (7.264 million km; 4.514 million mi) with an orbital period of approximately 11.2 Earth days. Its other properties are only poorly understood, but it is believed to be a potentially Earth-like planet with a minimum mass of at least 1.07 M🜨 and only a slightly larger radius than that of Earth. The planet orbits within the habitable zone of its parent star; but it is not known whether it has an atmosphere. Proxima Centauri is a flare star with intense emission of electromagnetic radiation that could strip an atmosphere off the planet. The planet's proximity to Earth offers an opportunity for robotic space exploration, for example, with the Breakthrough Starshot project.

Announced on 24 August 2016 by the European Southern Observatory (ESO), Proxima Centauri b was confirmed via several years of using the method of studying the radial velocity of its parent star. Furthermore, the discovery of Proxima Centauri b, a planet at habitable distances from the closest star to the Solar System, was a major discovery in planetology and has drawn interest to the Alpha Centauri star system as a whole, of which Proxima itself is a member. As of 2023, Proxima Centauri b is believed to be the best-known exoplanet to the general public.

Proxima Centauri had become a target for exoplanet searches already before the discovery of Proxima Centauri b, but initial studies in 2008 and 2009 ruled out the existence of larger-than-Earth exoplanets in the habitable zone. Planets are very common around dwarf stars, with on average 1–2 planets per star, and about 20–40% of all red dwarfs have one in the habitable zone. Additionally, red dwarfs are by far the most common type of stars.

Before 2016, observations with instruments at the European Southern Observatory in Chile had identified anomalies in Proxima Centauri which could not be satisfactorily explained by flares or chromospheric activity of the star. This suggested that Proxima Centauri may be orbited by a planet. In January 2016, a team of astronomers launched the Pale Red Dot project to confirm this hypothetical planet's existence. On 24 August 2016, the team led by Anglada-Escudé proposed that a terrestrial exoplanet in the habitable zone of Proxima Centauri could explain these anomalies and announced Proxima Centauri b's discovery. In 2022, another planet named Proxima Centauri d, which orbits even closer to the star, was confirmed. Another planet candidate named Proxima Centauri c was reported in 2020, but its existence has since been disputed, while the claimed existence of a dust belt around Proxima Centauri remains unconfirmed.