Alpha Centauri Ab
The candidate planet imaged by JWST (third picture, circled with the label "S1") | |
| Discovery[1] | |
|---|---|
| Discovered by | K. Wagner, et al. |
| Discovery date | 2021 |
| Direct imaging | |
| Designations | |
| Alpha Centauri Ab, Rigil Kentaurus b, C1 | |
| Orbital characteristics | |
| 1.1 AU | |
| Eccentricity | 0.4[2] |
| 2 to 3 years | |
| Inclination | ~15, ~165[2] |
| Star | Alpha Centauri A |
| Physical characteristics[2] | |
| 1.0–1.1 RJ | |
| Mass | 90–150 M🜨 |
| Temperature | 225 K |
Alpha Centauri Ab (also known as Rigil Kentaurus b, or originally as Candidate 1) is a candidate exoplanet directly imaged around Alpha Centauri A in February 2021. If confirmed as an exoplanet, it would orbit at approximately 1.1 AU away from Alpha Centauri A with a period of about a year and would have a mass between that of Neptune and one-half that of Saturn and would therefore likely be a giant planet.[1] The planet candidate is yet to be confirmed as an exoplanetary signal with additional observations needed to confirm its true nature.
History
Astronomers from the Breakthrough Watch Initiative directly imaged the habitable zone candidate using a newly developed system for mid-infrared exoplanet imaging.[3] Previous observations from years before ruled out the possibility of it being a background star. The team presented the discovery of the exoplanet candidate in a publication in Nature Communications titled “Imaging low-mass planets within the habitable zone of Alpha Centauri.”[4] However, the observation arc, being only 100 hours long, is not enough to determine whether a signal is planetary in nature, and it may be zodiacal dust or an instrumental artifact.
Physical characteristics
While little is known about the candidate planet, there are some characteristics that may be inferred based on its observations. It would have an orbital inclination of ~70° relative to Earth's point of view, consistent with the inclination of the Alpha Centauri system as a whole. Because of the detection algorithm, it would be somewhere around Neptune's mass, and would be no larger than 7 R🜨 as its mass would exceed the radial-velocity threshold of ~50 M🜨,[5] but no smaller than 3.3 R🜨 as that would not render the signature given in the paper. Due to this large size, it is highly unlikely to be rocky and is probably a Neptune-sized planet. Follow-up observations will be needed to determine whether it is a planet, cloud of dust, or simply an artifact due to its short observation arc.
James Webb Space Telescope observations
A point-like source at a separation of 2 astronomical units was detected by the James Webb Space Telescope in August 2024, which is confirmed to be neither a background or foreground source and is unlikely to be an instrumental artifact. If it is an exoplanet, it is likely the candidate observed in 2021. The object was not recovered and will need more observations to be confirmed.[6][2] Assuming the point source to be a planet, its mass and radius are estimated at 90–150 M🜨 and 1.0–1.1 RJ. The observations and non-detections of this source suggest an orbital period between 2 and 3 years, an orbital eccentricity of 0.4 and an spin-orbit angle relative to the Alpha Centauri AB orbital plane of approximately 50 to 130°.[2]
See also
- Lists of exoplanets
- List of directly imaged exoplanets
- List of largest exoplanets
- List of nearest exoplanets
References
- ^ a b Wagner, K.; Boehle, A.; Pathak, P.; Kasper, M.; Arsenault, R.; Jakob, G.; Käufl, U.; Leveratto, S.; Maire, A.-L.; Pantin, E.; Siebenmorgen, R. (2021-02-10). "Imaging low-mass planets within the habitable zone of α Centauri". Nature Communications. 12 (1): 922. doi:10.1038/s41467-021-21176-6. ISSN 2041-1723. PMC 7876126. PMID 33568657.
- ^ a b c d e Beichman, Charles; et al. (August 2025). "Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits". The Astrophysical Journal Letters. arXiv:2508.03814.
- ^ "Astronomers' hopes raised by glimpse of possible new planet". the Guardian. 2021-02-10. Retrieved 2021-02-12.
- ^ Gough, Evan (2021-02-11). "Possible Super-Earth in the Habitable Zone at Alpha Centauri". Universe Today. Retrieved 2021-02-12.
- ^ Zhao, L.; Fischer, D.; Brewer, J.; Giguere, M.; Rojas-Ayala, B. (January 2018). "Planet Detectability in the Alpha Centauri System". Astronomical Journal. 155 (1): 12. arXiv:1711.06320. Bibcode:2018AJ....155...24Z. doi:10.3847/1538-3881/aa9bea. S2CID 118994786. Retrieved 29 December 2017.
- ^ Sanghi, Aniket; et al. (August 2025). "Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis". The Astrophysical Journal Letters. arXiv:2508.03812.