Proxima Centauri d

Proxima Centauri d (also called Proxima d) is a candidate^[2][1] 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 two other planets^[a] in the Proxima Centauri system, it is the closest known exoplanet to the Solar System, located approximately 4.2 light-years (1.3 parsecs; 40 trillion kilometres; 25 trillion miles) 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.^[4][1]

Proxima Centauri d

Artistic depiction of Proxima Centauri d, with Proxima Centauri and Alpha Centauri A & B visible in the background
Discovery[1]
Discovery site	VLT-ESPRESSO
Discovery date	2020
Detection method	Radial velocity
Orbital characteristics[1]
Semi-major axis	0.02885+0.00019 −0.00022 AU
Eccentricity	0.04+0.15 −0.04
Orbital period (sidereal)	5.122+0.002 −0.0036 d
Semi-amplitude	0.39±0.07 m/s
Star	Proxima Centauri
Physical characteristics[1]
Mean radius	~0.81±0.08 R🜨 (predicted)
Mass	≥0.26±0.05 M🜨
Temperature	360 K (87 °C; 188 °F)

Characteristics

Proxima d is a sub-Earth at least one-quarter of the mass of Earth (or twice the mass of Mars), orbiting at roughly 0.029 AU (4.3 million km; 2.7 million mi) every 5.1 days.^[4] It is the least massive and innermost known planet of the Proxima Centauri system. It is the least massive exoplanet detected with the radial velocity method as of 2022^[update]. 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 (which likely reaches 360 K (87 °C; 188 °F)^[1] from about 190% of Earth's irradiation—assuming an Earth-like reflectivity, it is theoretically possible that Proxima d possesses polar regions with habitable temperatures.

Proxima d is considered a candidate exoplanet by its discoverers and the NASA Exoplanet Archive, because it has not been independently confirmed by more than one observatory.^[1][2] However, some astronomers regard Proxima d as confirmed because it could be detected via different methods of measuring the same radial velocity data from which Proxima d was discovered.^[3] As of 2022, Proxima d has been detected by the ESPRESSO spectrograph on the Very Large Telescope,^[1]: 9 and also at a 2σ level (which does not constitute confirmation) by the HARPS spectrograph at the La Silla Observatory.^[3]

See also

• List of nearest exoplanets
• Proxima Centauri b
• Proxima Centauri c

Notes

1. Proxima Centauri c's radial velocity signature was disputed in a 2022 study, which instead attributed its detection to potential bias in data processing methods, thereby leaving its existence disputed.^[3]