Proxima Centauri d

Proxima Centauri d
Artistic depiction of Proxima Centauri d, with Proxima Centauri and Alpha Centauri A & B visible in the background
Discovery[1]
Discovery siteVLT-ESPRESSO
Discovery dateFebruary 2022
Radial velocity
Orbital characteristics[2]
0.02881±0.00017 AU
Eccentricity0 (assumed)
5.12338±0.00035 d
Semi-amplitude0.392±0.057 m/s
StarProxima Centauri
Physical characteristics
~0.81±0.08 R🜨[1] (predicted)
Mass≥0.260±0.038 M🜨[2]
Temperature360 K (87 °C; 188 °F)[1]

Proxima Centauri d (also called Proxima d) is a confirmed[2] 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[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.[4] This signal was formally proposed to be a candidate exoplanet by Faria et al. in a follow-up paper published in February 2022,[1] and was independently confirmed in 2025.[2]

Characteristics

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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 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 (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.

Since Proxima d has only been detected by the radial velocity method, only a minimum mass is known; the true mass depends on the orbital inclination. Assuming an inclination of 47°, coplanar with its host star's rotation, its true mass would be 0.357±0.072 M🜨.[2]

Initially, Proxima d was considered a candidate exoplanet because it had not been independently confirmed by more than one observatory,[1] but some astronomers regarded it as confirmed because it could be detected via different methods of measuring the same radial velocity data.[3] As of 2022, Proxima d had 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] Independent confirmation of Proxima d was achieved with the NIRPS spectrograph in work published in July 2025.[2]

See also

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Notes

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  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]

References

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  1. ^ a b c d e f g Faria, J. P.; Suárez Mascareño, A.; et al. (4 January 2022). "A candidate short-period sub-Earth orbiting Proxima Centauri" (PDF). Astronomy & Astrophysics. 658. European Southern Observatory: 17. arXiv:2202.05188. Bibcode:2022A&A...658A.115F. doi:10.1051/0004-6361/202142337.
  2. ^ a b c d e f Suárez Mascareño, Alejandro; Artigau, Étienne; et al. (29 July 2025). "Diving into the planetary system of Proxima with NIRPS: Breaking the metre per second barrier in the infrared". Astronomy & Astrophysics. 700: A11. doi:10.1051/0004-6361/202553728.
  3. ^ a b c Artigau, Étienne; Cadieux, Charles; Cook, Neil J.; Doyon, René; Vandal, Thomas; et al. (September 2022). "Line-by-line Velocity Measurements: an Outlier-resistant Method for Precision Velocimetry". The Astronomical Journal. 164 (3): 18. arXiv:2207.13524. Bibcode:2022AJ....164...84A. doi:10.3847/1538-3881/ac7ce6. 84.
  4. ^ a b Suárez Mascareño, A.; Faria, J. P.; et al. (11 May 2020). "Revisiting Proxima with ESPRESSO". Astronomy & Astrophysics. 639: 24. arXiv:2005.12114. Bibcode:2020A&A...639A..77S. doi:10.1051/0004-6361/202037745. ISSN 0004-6361.
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