Astronomers using the powerful James Webb Space Telescope (JWST), a joint project of NASA, ESA, and CSA, have made an extraordinary discovery that could change our understanding of planetary systems. The strongest evidence to date has been found suggesting the existence of a giant planet orbiting one of the stars in our nearest star system, Alpha Centauri. Located just 4.37 light-years from Earth, this triple star system has been a focus of the scientific community for decades as a primary target in the search for worlds beyond our Solar System.

The Fascinating Alpha Centauri System

The Alpha Centauri system, visible primarily from our planet's Southern Hemisphere, consists of three stars. The two main components, Alpha Centauri A and Alpha Centauri B, form a binary pair. Both stars are very similar to our Sun; Alpha Centauri A is a G2V-type star, identical to the Sun, while Alpha Centauri B is slightly smaller and cooler, a K1V-type. These two stars orbit each other with a period of approximately 80 years. The third, much more distant and fainter member of the system is the red dwarf Proxima Centauri. Although Proxima Centauri is best known for being the closest star to the Sun and for having at least three confirmed planets orbiting it, the search for planets around the brighter stars, Alpha Centauri A and B, has proven to be extremely challenging and has not yet yielded definitive results.

Revolutionary Observations by the James Webb Telescope

The latest observations conducted with Webb's Mid-Infrared Instrument (MIRI) provide the most compelling data to date on the existence of a gas giant orbiting Alpha Centauri A. These revolutionary results, which could fundamentally change our understanding of planetary systems, have been accepted for publication in two scientific papers in the prestigious journal The Astrophysical Journal Letters.

If the existence of this planet is definitively confirmed, it will become the nearest known exoplanet to Earth located within the habitable zone of a Sun-like star. The habitable zone is the region around a star where conditions allow for the existence of liquid water on a planet's surface, which is a key prerequisite for life as we know it. However, scientists emphasize that, given the candidate is a gas giant, it could not support life itself. Nevertheless, an intriguing possibility arises that some of its potential large, rocky moons could have the conditions for the emergence and development of life.

Charles Beichman of NASA's Jet Propulsion Laboratory (JPL) and NASA's Exoplanet Science Institute at Caltech's IPAC astronomical center, one of the lead authors of the papers, highlighted the complexity of this undertaking. "Given that this system is so close to us, any exoplanet found would offer us the best opportunity to gather data on planetary systems beyond our own. However, these are incredibly demanding observations, even for the most powerful space telescope in the world, because these stars are extremely bright, close, and move quickly across the sky," he explained. "Webb was designed and optimized to find the most distant galaxies in the universe. The operations team at the Space Telescope Science Institute had to develop a completely custom observing sequence just for this target, and their extra effort paid off spectacularly."

The Mystery of the Vanishing Planet

To even detect the faint light of a potential planet, the team had to overcome the immense glare of the star Alpha Centauri A. This was achieved by using the coronagraph on the MIRI instrument, a specialized device that blocks the direct light from the star, thus allowing the observation of much fainter objects in its immediate vicinity. The first observations of the system took place in August 2024. The analysis was further complicated by the light from the nearby companion star, Alpha Centauri B. Despite this, the team managed to digitally subtract the light of both stars and detect an object that is more than 10,000 times fainter than Alpha Centauri A, at a distance from the star that is roughly twice the distance of the Earth from the Sun.

Although the initial discovery was extremely exciting, the science team needed more data to draw a firm conclusion. However, additional observations of the system conducted in February and April 2025 (using Director's Discretionary Time) did not reveal an object similar to the one identified in August 2024. "We are faced with a case of a vanishing planet! To investigate this mystery, we used computer models to simulate millions of potential orbits, taking into account the knowledge gained when we saw the planet, as well as when we did not see it," said Aniket Sanghi, a doctoral student at the California Institute of Technology (Caltech) in Pasadena and also one of the lead authors of the papers.

Characteristics of the Potential New World

In their simulations, the team took into account not only the new Webb observations but also an earlier observation of a potential exoplanet candidate from 2019 by the European Southern Observatory's Very Large Telescope (VLT). They considered only those orbits that would be gravitationally stable in the presence of the massive star Alpha Centauri B, meaning the planet would not be ejected from the system due to complex gravitational interactions.

The researchers say that the lack of detection in the second and third rounds of observations with Webb is not surprising. "We found that in half of the simulated possible orbits, the planet moved too close to the star and would not have been visible to Webb in either February or April 2025," Sanghi explained. Based on the planet's brightness in the mid-infrared observations and the orbit simulations, the researchers conclude that it could be a gas giant with a mass approximately that of Saturn, orbiting Alpha Centauri A in an elliptical path, with its distance from the star varying between one and two astronomical units (one astronomical unit is the average distance of the Earth from the Sun).

Implications for Science and Future Research

Pierre-Olivier Lagage from CEA in France, a co-author of the papers and the French lead for the MIRI instrument development, commented on the technical side of the discovery: "These are some of the most challenging observations we have performed so far with MIRI's coronagraph. When we were developing the instrument, we were eager to see what we might find around Alpha Centauri, and I look forward to what it will reveal to us next!"

If confirmed, the potential planet seen in Webb's image of Alpha Centauri A will mark a new milestone in the efforts to directly image exoplanets. "Of all the directly imaged planets, this would be the closest to its star ever seen. It is also the most similar in temperature and age to the giant planets in our Solar System, and the closest to our home, Earth," says Sanghi. "Its very existence in a system of two closely separated stars would challenge our understanding of how planets form, survive, and evolve in chaotic environments." The confirmation of this discovery with additional observations could transform the future of exoplanet science, opening a new chapter in the search for worlds beyond our own.