Is it possible there is a planet lurking in the wings only four light-years from home, orbiting the nearest sun-like star? The James Webb Space Telescope (JWST) has raised tantalizing suggestions that yes, it is possible, and the secret to unravelling the discovery lies in the most potent starlight-quenching technology ever launched into space.
Astronomers aimed JWST’s Mid-Infrared Instrument (MIRI) at Alpha Centauri A in August 2024, a star scientists and science fiction writers have long dreamed about. The challenge: The light of Alpha Centauri A easily overpowers any dim planetary companions, just as it’s hopeless to see a firefly close to a searchlight. To meet this challenge, the team deployed MIRI’s coronagraphic mask, a precision-engineered device that blocks out the star’s intense glare, revealing objects as much as 10,000 times fainter than Alpha Centauri A itself. This breakthrough enabled the detection of a potential gas giant orbiting at about two astronomical units from its host—twice the distance between Earth and the Sun, and within the star’s habitable zone.
This new potential planet, if confirmed, would not only be the closest exoplanet to its star ever directly imaged, but the first of its kind revolving around a star with this temperature and Sun-like age. “With this system being so close to us, any exoplanets found would offer our best opportunity to collect data on planetary systems other than our own,” said Charles Beichman, executive director of the NASA Exoplanet Science Institute at Caltech and senior scientist at NASA’s Jet Propulsion Laboratory.
The accomplishment is an endorsement of JWST’s MIRI engineering spanning 4.9 to 27.9 microns wavelengths and featuring classical Lyot and four-quadrant phase mask (4QPM) coronagraphs. The masks, combined with optimized filters and Lyot stop optimizations, provide raw contrasts better than 10⁻³ at separations within 1 arcsecond and, upon reference star subtraction, can approach detector noise, as observed on-sky. The four-quadrant phase mask, a first-generation space telescope technology, allows astronomers to peer inward closer to the star than ever before, with sensitivity to hand to spot faint planet companions in mid-infrared light.
But that’s only the beginning of the story in one image. Subsequent JWST follow-up observations in early 2025 failed to recover the planet, and it was likely that its orbit took it too near the A star Alpha Centauri A to be detectable. “We are faced with the case of a disappearing planet! To investigate this mystery, we used computer models to simulate millions of potential orbits, incorporating the knowledge gained when we saw the planet, as well as when we did not,” said Aniket Sanghi, a graduate student at Caltech and co-author of the paper. The simulations show that in half of the orbits available, the planet would have been occulted in the follow-up measurements, and this highlights the need for additional data.
The consequences of the existence of such a planet are enormous. Alpha Centauri is a triple-star system, and a gas giant in the habitable zone would be a challenge to existing models of formation and survival of such planets in dynamically active systems. In binary and multiple star systems, the gravitational “eggbeater” effect can increase collision speeds among planetesimals, usually destroying them before they have a chance to accrete. But recent simulations indicate that gas drag and disk gravity might create dynamically quiet regions where planetesimals might survive and accrete even with an accompanying stellar companion close by. This means that the potential for planet formation in Alpha Centauri-type systems, once deemed unlikely, could be more common than thought.
And while the candidate itself is a gas giant—contrast with the one to support life of its own—it is located in the habitable zone, with room for moons to have even more life-conducive conditions. “It likely has moons,” speculated Charles Beichman, taking the science fiction beauty of Pandora in the “Avatar” films. Exomoons remain the target but the potential brings a new dimension of intrigue to the discovery.
To the future, the soon-to-launched Nancy Grace Roman Space Telescope, launched by May 2027, will again push the boundaries of direct exoplanet imaging. Roman’s Coronagraph Instrument will be the first to fly active coronagraph with onboard deformable mirrors that have the capability of on-the-fly optical error correction. This technology will be capable of monitoring planets 100 million times fainter than their stars, an improvement of up to 1,000 times more powerful than with existing space-based coronagraphs. Roman will complement the infrared observations of JWST with visible-light observations, giving a better look at exoplanetary atmospheres and surfaces.
As it is, the possible planet of Alpha Centauri A is a beacon of promise of what can be done with existing astronomical technology and for the mysteries that lie just within our reach. As Beichman states, “This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterization by Webb and other observatories.”
