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Candidate exoplanet orbiting Alpha Centauri A
Candidate 1
The discovery image of Candidate 1, taken by the NEAR instrument at ESO's Very Large Telescope in 2021.
Candidate 1 (also known as C1 or Alpha Centauri Ab) is an exoplanet candidate 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. 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. 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.” 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.
The possible detection of the planet is extremely preliminary, and the object may not even count as a planetary candidate.
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 ME, 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.
The discovery image of Candidate 1, taken by the NEAR instrument at ESO's Very Large Telescope in 2021.
