JWST Spots Potential Gas Giant Exoplanet Near Alpha Centauri A

NASA's James Webb Space Telescope (JWST) has identified a potential gas giant exoplanet orbiting Alpha Centauri A, one of Earth's nearest Sun-like stars, approximately 4.37 light-years away. This discovery, if confirmed, would mark the closest exoplanet ever directly imaged around a Sun-like star.

In August 2024, JWST's Mid-Infrared Instrument (MIRI), equipped with a coronagraph to block the star's light, detected a point source, designated as "S1," at a separation of about 1.5 arcseconds (approximately 2 astronomical units) from Alpha Centauri A. The detected signal had a flux of approximately 3.5 millijanskys at 15.5 micrometers, corresponding to a contrast ratio of about 5.5 × 10⁻⁵ relative to the star. This suggests that the object could be a gas giant with a temperature around 225 K and a radius between 1 and 1.1 times that of Jupiter. The estimated mass ranges from 90 to 150 Earth masses, placing it between Neptune and Saturn in size.

Subsequent observations in February and April 2025 did not detect the "S1" source. Researchers propose that the object may have moved into a region where JWST's sensitivity is reduced due to its orbital motion. Simulations suggest that if "S1" is on an eccentric orbit with a period between 2 to 3 years and an inclination significantly tilted relative to the Alpha Centauri AB plane, it could have been undetectable during these periods. There is a 52% chance that the object was missed in both follow-up observations due to its orbital position.

If confirmed, this exoplanet would be the closest directly imaged planet orbiting a Sun-like star and would reside within the star's habitable zone, where conditions might allow for liquid water. However, given its size and mass, it is unlikely to be habitable itself but could have moons that might possess conditions suitable for life. This discovery underscores JWST's capability to detect exoplanets in nearby star systems and highlights the importance of continued observations to confirm and characterize such candidates.

The Alpha Centauri system has been a focal point in the search for exoplanets due to its proximity. In 2012, a planet candidate named Alpha Centauri Bb was reported orbiting Alpha Centauri B, but subsequent studies questioned its existence, and it is now considered unconfirmed. Similarly, Proxima Centauri, the third star in the system, has confirmed planets, including Proxima Centauri b, a terrestrial planet in the habitable zone, and Proxima Centauri c, whose existence remains disputed.

Researchers plan to conduct additional JWST observations in 2026 or 2027, when the candidate planet is expected to be in a more favorable position for detection. These follow-up studies aim to confirm the planet's existence and gather more data on its characteristics. Additionally, upcoming missions like NASA's Nancy Grace Roman Space Telescope, set to launch in 2027, will continue the search for exoplanets in nearby star systems, potentially providing further insights into the Alpha Centauri system.

The potential discovery of a gas giant in the habitable zone of Alpha Centauri A has profound implications. It brings us closer to understanding the prevalence and diversity of planetary systems around Sun-like stars. While the candidate planet itself may not be habitable, its presence raises questions about the formation and evolution of planetary systems in our galactic neighborhood. Moreover, this finding fuels public interest and excitement about the possibility of discovering Earth-like planets in nearby systems, potentially harboring life.

As the search for exoplanets continues, the Alpha Centauri system remains a prime target for astronomers. The advancements in telescope technology and observational techniques, exemplified by JWST's capabilities, are paving the way for more detailed studies of our cosmic neighbors. Future observations will be crucial in confirming the existence of this potential exoplanet and understanding its properties, contributing to our broader quest to find habitable worlds beyond our solar system.