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Gas giant may orbit Alpha Centauri [1]
['Rob Beschizza']
Date: 2025-08-12
Alpha Centauri, part of the three-star system closet to our own, is often posed in science fiction as humanity's first hop into the beyond—or perhaps its first meeting of the minds with alien intelligences. For the first time, scientists have strong evidence that Alpha Centauri A has a planet in orbit, a gas giant about twice as far from its star as Earth is from the sun. The observations are from NASA's James Webb Space Telescope.
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."
Here's a quote from Aniket Sanghi of Caltech, co-first author of the papers covering the research:
"If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts. 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."
NASA, ESA, CSA, Aniket Sanghi (Caltech), Chas Beichman (NExScI, NASA/JPL-Caltech), Dimitri Mawet (Caltech)
NASA's Nancy Grace Roman Space Telescope, scheduled to launch next year or 2027, has dedicated hardware for observing exoplanets in visible spectra, hopefully "yielding unique insights on the size and reflectivity of the planet."
Context from Phil Plait:
The star has been a target for planet hunters for a long time (in fact with another astronomer I proposed using STIS, a camera on Hubble, to look for one back in the 90s, but it got turned down as being too speculative, which, fair). In 2021 astronomers announced they found a candidate planet orbiting Alpha Cen A using the Very Large Telescope (or VLT), but the detection wasn't strong enough to make a confident claim.
The closest known exoplanets are those orbiting Proxima Centauri, a red dwarf in the same system. Don't get your hopes up: "Proxima Centauri is a flare star with intense emission of electromagnetic radiation that could strip an atmosphere off the planet."
Previously:
• 'Young' exoplanet may end up a super-Earth
• Watch: history of exoplanet observations as generative music
• Potentially habitable exoplanet: The fine print
• Which is the most boring exoplanet?
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