Scientists have found strong evidence of a giant gas planet orbiting Alpha Centauri A — the closest sun-like star system to Earth, just 4.37 light-years away. While the planet itself is unlikely to support life, its moons could be promising candidates for habitability, potentially becoming our nearest “life-bearing” neighbours beyond the solar system.
This potential gas giant was detected in direct imaging observations made by NASA’s James Webb Space Telescope (JWST), the most powerful space observatory to date. The discovery was first reported in August 2024 but has so far proved elusive in follow-up observations. Astronomers caution that further study is needed to confirm its existence and characterise its environment, but the signs are tantalising.
Dr Carly Howett, associate professor of space instrumentation at the University of Oxford, told the BBC: “This is an incredibly exciting find. Four light years is a long way for us, but in the context of our galaxy, it’s very close — it’s practically in our cosmic backyard. The fact that this planet orbits a star so similar to our Sun, with comparable temperature and brightness, makes it an important target when we think about habitable worlds.”
The newly detected planet orbits roughly two astronomical units (AU) from Alpha Centauri A — near the outer edge of the star’s habitable zone, where temperatures could allow liquid water to exist. Although the planet is a massive gas giant, likely enveloped in a thick cloud of hydrogen and helium much like Jupiter or Saturn, it’s almost certainly inhospitable to life itself.
However, scientists are especially interested in the prospect that this gas giant hosts a system of moons, potentially large and icy worlds similar to Jupiter’s Ganymede or Saturn’s Titan. In our solar system, these moons have environments considered among the most promising for extraterrestrial life.
Ganymede, the largest moon in the solar system, is thought to harbour a vast subsurface ocean beneath its icy crust, while Titan has a dense nitrogen-rich atmosphere and lakes of liquid hydrocarbons on its surface. Both bodies are the focus of intense astrobiological research and upcoming missions, such as NASA’s Europa Clipper and ESA’s JUICE, aiming to investigate their habitability.
The Alpha Centauri gas giant, located close to the habitable zone, could host moons with enough stellar energy to maintain liquid water, either on the surface or in subsurface oceans. Moreover, tidal heating—gravitational interactions between a massive planet and its moons—could provide internal warmth to these moons, even if they orbit far from the star. This heating mechanism sustains subsurface oceans on moons like Europa and Enceladus in our own solar system.
Charles Beichman from NASA’s Jet Propulsion Laboratory, co-first author of the study said: “These observations are pushing the limits of what we can do with the world’s most powerful space telescope. Stars like Alpha Centauri are so bright and move quickly across the sky that it’s incredibly challenging to detect planets orbiting them directly.”
Dr Howett added: “Probably the planet was either behind the star or too close in some follow-ups. Detecting such a world requires an element of luck and perfect timing.”
To confirm and learn more about this planet, astronomers plan to use upcoming instruments like NASA’s Nancy Grace Roman Space Telescope, set to launch in 2027. This next-generation telescope will have advanced capabilities for detecting exoplanets and studying their atmospheres.
Dr Howett said: “By analysing the light spectrum from the planet, we can begin to understand what gases it contains and whether conditions might support life on orbiting moons. It opens a new window on the possibility of habitable environments beyond Earth-like planets themselves.”
The discovery expands the search for life beyond terrestrial planets, emphasising the importance of exomoons—moons orbiting planets outside our solar system—as potential habitats. Large moons around gas giants may be common throughout the galaxy, possibly more numerous and stable habitats than Earth-sized planets.
While direct detection of such moons remains beyond current technology, their potential to sustain life makes them critical targets for future exploration.
In sum, the detection of a gas giant near Alpha Centauri A’s habitable zone brings the prospect of life-bearing moons closer to Earth than ever before. Confirming their presence will be a decades-long challenge, but the scientific payoff could be revolutionary — finding life in our nearest star system, just a cosmic stone’s throw away.
