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Webb finds new evidence for planet, a gas giant orbiting Alpha Centauri A, our closest solar twin

Astronomers using the NASA/ESA/CSA James Webb Space Telescope have found strong evidence of a giant planet orbiting a star in the stellar system closest to our own Sun. At just 4 light-years away from Earth, the Alpha Centauri triple star system has long been a compelling target in the search for worlds beyond our solar system.

Illustration of a large spherical object that looks like a gas giant planet. The object appears to have bands of tan, orange, and dark red horizontal lines forming patterns similar to those in the atmosphere of Jupiter. The background is filled with thousands of distant stars that form a Milky Way-like band running from left to right. The host star, Alpha Centauri A, appears as a glowing white circle to the upper left of the planet. Further off in the distance above and to the right of the planet is a smaller glowing circle, nearby Alpha Centauri B. The words “Artist’s Concept” are in the lower left corner. — This artist’s concept shows what the gas giant orbiting Alpha Centauri A could look like. Observations of the triple star system Alpha Centauri using the NASA/ESA/CSA James Webb Space Telescope indicate the potential gas giant, about the mass of Saturn, orbiting the star by about two times the distance between the Sun and Earth.
In this concept, Alpha Centauri A is depicted at the upper left of the planet, while the other Sun-like star in the system, Alpha Centauri B, is at the upper right. Our Sun is shown as a small dot of light between those two stars.
Credit: NASA, ESA, CSA, STScI, R. Hurt (Caltech/IPAC)

Visible only from Earth’s Southern hemisphere, it’s made up of the binary Alpha Centauri A and Alpha Centauri B, both Sun-like stars, and the faint red dwarf star Proxima Centauri. Alpha Centauri A is the third brightest star in the night sky. While there are three confirmed planets orbiting Proxima Centauri, the presence of other worlds surrounding Alpha Centauri A and Alpha Centauri B has proved challenging to confirm.

Now, Webb’s observations from its Mid-Infrared Instrument (MIRI) are providing the strongest evidence to date of a gas giant orbiting Alpha Centauri A. The results have been accepted in a series of two papers in The Astrophysical Journal Letters.

Three panels, each showing a different view of the binary star system Alpha Centauri. The panel on the left is a Digitized Sky Survey image showing a single bright blue point source at the center of a black image with small stars scattered throughout. The very center of this bright source is outlined with a vertical box, tilted slightly to the left, with two diagonal lines leading to the second panel. The second panel is a Hubble Space Telescope image that shows two white stars with 4 diffraction spikes each against a black background. The top star is labeled Alpha Cen B and the bottom Alpha Cen A. Alpha Cen A is outlined with a white square with two diagonal lines leading to the third panel at the furthest right, which shows a James Webb Space Telescope image of the star. An orange star icon and central black circle outlined in white marks the location of Alpha Cen A. A large white circle outlines a blurry red-toned field that surrounds the location of the star. A bright orange blob at 9 o’clock in relation to the star is labeled “S1” and circled — This image shows the Alpha Centauri star system from several different ground- and space-based observatories: the Digitized Sky Survey (DSS), the NASA/ESA Hubble Space Telescope, and the NASA/ESA/CSA James Webb Space Telescope. Alpha Centauri A is the third brightest star in the night sky, and the closest Sun-like star to Earth.
The ground-based image from DSS shows the triple system as a single source of light, while Hubble resolves the two Sun-like stars in the system, Alpha Centauri A and Alpha Centauri B.
The image from Webb’s MIRI (Mid-Infrared Instrument), which uses a coronagraphic mask to block the bright glare from Alpha Centauri A, reveals a potential planet orbiting the star.
Credit: NASA, ESA, CSA, STScI, DSS, A. Sanghi (Caltech), C. Beichman (JPL), D. Mawet (Caltech), J. DePasquale (STScI)

If confirmed, the planet would be the closest to Earth that orbits in the habitable zone of a Sun-like star. However, because the planet candidate is a gas giant, scientists say it would not support life as we know it.

“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. Yet, these are incredibly challenging observations to make, even with the world’s most powerful space telescope, because these stars are so bright, close, and move across the sky quickly,” said Charles Beichman, NASA’s Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech’s IPAC astronomy center, co-first author on the new papers. “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 come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly.”

Several rounds of meticulously planned observations by Webb, careful analysis by the research team, and extensive computer modeling helped determine that the source seen in Webb’s image is likely to be a planet, and not a background object (like a galaxy), foreground object (a passing asteroid), or other detector or image artifact.

The first observations of the system took place in August 2024, using the coronagraphic mask aboard MIRI to block Alpha Centauri A’s light. While extra brightness from the nearby companion star Alpha Centauri B complicated the analysis, the team was able to subtract out the light from both stars to reveal an object over 10,000 times fainter than Alpha Centauri A, separated from the star by about two times the distance between the Sun and Earth.

While the initial detection was exciting, the research team needed more data to come to a firm conclusion. However, additional observations of the system in February 2025 and April 2025 (using Director’s Discretionary Time) did not reveal any objects like the one identified in August 2024.

“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 PhD student Aniket Sanghi of the California Institute of Technology in Pasadena, California. Sanghi is a co-first author on the two papers covering the team’s research.

In these simulations, the team took into account both the 2019 sighting of a potential exoplanet candidate by the European Southern Observatory’s Very Large Telescope, the new data from Webb, and considered orbits that would be gravitationally stable in the presence of Alpha Centauri B, meaning the planet wouldn’t get flung out of the system.

Three panels, each showing a different view of the binary star system Alpha Centauri from the Webb. The left panel shows a rectangular image tilted at a 45 degree angle outlined in white on a grey background. The image is a blown-out bright source at the center, with 8, double columned reddish white diffraction spikes. The center of this bright source is outlined with a vertical box, tilted slightly to the left, with two diagonal lines leading to the second panel. This shows a view of both Alpha Centauri A at the bottom and Alpha Centauri B at the top, both with orange star icons over each star. The star icons are surrounded by mottled red and white blotches. The bottom star is outlined with a white square with two diagonal lines leading to the third panel. Within a large white circle there is a blurry red-toned field with an orange star icon and central black circle outlined in white marking the location of Alpha Cen A. A bright orange blob at 9 o’clock in relation to the star is labeled “S1” and circled. — This 3-panel image captures the NASA/ESA/CSA James Webb Space Telescope’s observational search for a planet around the nearest Sun-like star, Alpha Centauri A. The initial image shows the bright glare of Alpha Centauri A and Alpha Centauri B, then the middle panel shows the system with a coronagraphic mask placed over Alpha Centauri A to block its bright glare. However, the way the light bends around the edges of the coronagraph creates ripples of light in the surrounding space. The telescope’s optics (its mirrors and support structures) cause some light to interfere with itself, producing circular and spoke-like patterns. These complex light patterns, along with light from the nearby Alpha Centauri B, make it incredibly difficult to spot faint planets. In the panel at the right, astronomers have subtracted the known patterns (using reference images and algorithms) to clean up the image and reveal faint sources like the candidate planet.
Credit: NASA, ESA, CSA, STScI, A. Sanghi (Caltech), C. Beichman (JPL), D. Mawet (Caltech), J. DePasquale (STScI)

Researchers say a non-detection in the second and third round of observations with Webb isn’t surprising.

“We found that in half of the possible orbits simulated, the planet moved too close to the star and wouldn’t have been visible to Webb in both February and April 2025,” said Sanghi.

Based on the brightness of the planet in the mid-infrared observations and the orbit simulations, researchers say it could be a gas giant approximately the mass of Saturn orbiting Alpha Centauri A in an elliptical path varying between 1 to 2 times the distance between Sun and Earth.

“These are some of the most demanding observations we’ve done so far with MIRI’s coronagraph,” said Pierre-Olivier Lagage, of CEA, France, who is a co-author on the papers and was the French lead for the development of MIRI. “When we were developing the instrument we were eager to see what we might find around Alpha Centauri, and I’m looking forward to what it will reveal to us next!”

“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts,” Sanghi says. “Of all the directly imaged planets, this would be the closest to its star seen so far. It’s also the most similar in temperature and age to the giant planets in our solar system, and nearest to our home, Earth,” he says. “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.”

If confirmed by additional observations, the team’s results could transform the future of exoplanet science.

“This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterization by Webb and other observatories,” said Beichman.

Press release from ESA Webb.

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