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By European Space Agency
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.
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This artist’s concept shows what a gas giant orbiting Alpha Centauri A could look like. Observations of the triple star system Alpha Centauri using NASA’s 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. Full illustration and caption shown below. Credits:
Artwork: NASA, ESA, CSA, STScI, R. Hurt (Caltech/IPAC) Astronomers using NASA’s 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.
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.
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.”
Image A: Alpha Centauri 3 Panel (DSS, Hubble, Webb)
This image shows the Alpha Centauri star system from several different ground- and space-based observatories: the Digitized Sky Survey (DSS), NASA’s Hubble Space Telescope, and NASA’s 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. Science: NASA, ESA, CSA, STScI, DSS, A. Sanghi (Caltech), C. Beichman (NExScI, NASA/JPL-Caltech), D. Mawet (Caltech); Image Processing: J. DePasquale (STScI) 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.
Image B: Alpha Centauri 3 Panel (Webb MIRI Image Detail)
This three-panel image captures NASA’s 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, and the middle panel then 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. Science: NASA, ESA, CSA, STScI, A. Sanghi (Caltech), C. Beichman (NExScI, NASA/JPL-Caltech), D. Mawet (Caltech); Image Processing: J. DePasquale (STScI) 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 Caltech 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 a 2019 sighting of the 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.
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.
Image C: Alpha Centauri A Planet Candidate (Artist’s Concept)
This artist’s concept shows what a gas giant orbiting Alpha Centauri A could look like. Observations of the triple star system Alpha Centauri using NASA’s 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. Artwork: NASA, ESA, CSA, STScI, R. Hurt (Caltech/IPAC) 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.
“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.
For example, NASA’s Nancy Grace Roman Space Telescope, set to launch by May 2027 and potentially as early as fall 2026, is equipped with dedicated hardware that will test new technologies to observe binary systems like Alpha Centauri in search of other worlds. Roman’s visible light data would complement Webb’s infrared observations, yielding unique insights on the size and reflectivity of the planet.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
To learn more about Webb, visit:
https://science.nasa.gov/webb
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Last Updated Aug 07, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
James Webb Space Telescope (JWST) View the full article
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By NASA
KEY POINTS
Jupiter, Saturn, and Neptune each emit more energy than they receive from the Sun, meaning they have comparatively warm interiors. NASA’s Uranus flyby with Voyager 2 in 1986 found the planet colder than expected, which challenged ideas of how planets formed and evolved. However, with advanced computer modeling and a new look at old data, scientists think the planet may actually be warmer than previously expected. For millennia, astronomers thought Uranus was no more than a distant star. It wasn’t until the late 18th century that Uranus was universally accepted as a planet. To this day, the ringed, blue world subverts scientists’ expectations, but new NASA research helps puzzle out some of the world’s mystique.
This zoomed-in image of Uranus, captured by the Near-Infrared Camera on NASA’s James Webb Space Telescope on Feb. 6, 2023, reveals stunning views of Uranus’ rings. Credits: NASA, ESA, CSA, STScI Uranus is unlike any other planet in our solar system. It spins on its side, which means each pole directly faces the Sun for a continuous 42-year “summer.” Uranus also rotates in the opposite direction of all planets except Venus. Data from NASA’s Voyager 2 Uranus flyby in 1986 also suggested the planet is unusually cold inside, challenging scientists to reconsider fundamental theories of how planets formed and evolved throughout our solar system.
“Since Voyager 2’s flyby, everybody has said Uranus has no internal heat,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But it’s been really hard to explain why that is, especially when compared with the other giant planets.”
These Uranus projections came from only one up-close measurement of the planet’s emitted heat made by Voyager 2: “Everything hinges on that one data point,” said Simon. “That is part of the problem.”
Now, using an advanced computer modeling technique and revisiting decades of data, Simon and a team of scientists have found that Uranus does in fact generate some heat, as they reported on May 16 in the Monthly Notices of the Royal Astronomical Society journal.
A planet’s internal heat can be calculated by comparing the amount of energy it receives from the Sun to the amount it of energy it releases into space in the form of reflected light and emitted heat. The solar system’s other giant planets — Saturn, Jupiter, and Neptune — emit more heat than they receive, which means the extra heat is coming from inside, much of it left over from the high-energy processes that formed the planets 4.5 billion years ago. The amount of heat a planet exudes could be an indication of its age: the less heat released relative to the heat absorbed from the Sun, the older the planet is.
Uranus stood out from the other planets because it appeared to give off as much heat as it received, implying it had none of its own. This puzzled scientists. Some hypothesized that perhaps the planet is much older than all the others and has cooled off completely. Others proposed that a giant collision — the same one that may have knocked the planet on its side — blasted out all of Uranus’ heat. But none of these hypotheses satisfied scientists, motivating them to solve Uranus’ cold case.
“We thought, ‘Could it really be that there is no internal heat at Uranus?’” said Patrick Irwin, the paper’s lead author and professor of planetary physics at the University of Oxford in England. “We did many calculations to see how much sunshine is reflected by Uranus and we realized that it is actually more reflective than people had estimated.”
The researchers set out to determine Uranus’ full energy budget: how much energy it receives from the Sun compared to how much it reflects as sunlight and how much it emits as heat. To do this, they needed to estimate the total amount of light reflected from the planet at all angles. “You need to see the light that’s scattered off to the sides, not just coming straight back at you,” Simon said.
To get the most accurate estimate of Uranus’ energy budget yet, Oxford researchers developed a computer model that brought together everything known about Uranus’ atmosphere from decades of observations from ground- and space-based telescopes, including NASA’s Hubble Space Telescope and NASA’s Infrared Telescope Facility in Hawaii. The model included information about the planet’s hazes, clouds, and seasonal changes, all of which affect how sunlight is reflected and how heat escapes.
These side-by-side images of Uranus, taken eight years apart by NASA’s Hubble Space Telescope, show seasonal changes in the planet’s reflectivity. The left image shows the planet seven years after its northern spring equinox when the Sun was shining just above its equator. The second photo, taken six years before the planet’s summer solstice, portrays a bright and large northern polar cap. Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI) The researchers found that Uranus releases about 15% more energy than it receives from the Sun, a figure that is similar to another recent estimate from a separate study funded in part by NASA that was published July 14 in Geophysical Research Letters. These studies suggest Uranus it has its own heat, though still far less than its neighbor Neptune, which emits more than twice the energy it receives.
“Now we have to understand what that remnant amount of heat at Uranus means, as well as get better measurements of it,” Simon said.
Unraveling Uranus’ past is useful not only for mapping the timeline of when solar system planets formed and migrated to their current orbits, but it also helps scientists better understand many of the planets discovered outside the solar system, called exoplanets, a majority of which are the same size as Uranus.
By Emma Friedman
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Jul 17, 2025 Editor Lonnie Shekhtman Contact Lonnie Shekhtman lonnie.shekhtman@nasa.gov Location NASA Goddard Space Flight Center Related Terms
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