JWST Finds Hidden Exoplanet in Beta Pictoris System Using Spectroscopy, Not Imaging
Astronomers using the James Webb Space Telescope have discovered a third planet in the Beta Pictoris system by detecting its chemical fingerprint in spectroscopic data, a technique that could reveal worlds too faint or close to their star for direct imaging.
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Astronomers have uncovered a third planet in the Beta Pictoris system using the James Webb Space Telescope (JWST), but they did not see it directly. Instead, they detected the world—designated Beta Pictoris d—by reading its atmospheric chemical signature in spectroscopic data originally collected to study another planet.
The finding, published in Astrophysical Journal Letters on July 15, 2026, adds a new member to a system already known for its two directly imaged giant planets, Beta Pictoris b and c. The star Beta Pictoris lies 63 light-years from Earth and is about 23 million years old, a relatively young age that makes its prominent debris disk a prime target for planet formation studies.
Beta Pictoris d has a mass at least twice that of Jupiter, making it the least massive of the trio. Its orbit spans roughly 30 astronomical units (AU)—comparable to Neptune's distance from the Sun—and is the widest among the known planets, sitting just inside the inner edge of the debris disk.
The discovery came while lead author Aidan Gibbs, a postdoctoral researcher at UC San Diego, and his team were using JWST's NIRSpec Integral Field Unit to study the atmosphere of Beta Pictoris b. In the spectral data, they noticed absorption lines from carbon monoxide—a distinctive "barcode" pattern—that indicated an unexpected object. By extracting the radial velocity from the spectrum, they calculated the planet's speed and position, confirming it orbits Beta Pictoris in alignment with the debris disk.
Follow-up observations with JWST's MIRI instrument, obtained through Director's Discretionary Time, detected water vapor and methane, solidifying the object's identity as a planet. "We weren't looking for a new planet. We were trying to understand one we already knew existed. Then, this telltale signal appeared in the data where we didn't expect it," said Gibbs.
Jean-Baptiste Ruffio, a research scientist at UC San Diego and principal investigator of the original Webb observations, noted the power of the technique. "A spectrum contains an incredible amount of information. You don't just learn that something is a planet; you immediately begin learning about its temperature, chemistry, and motion," he said.
The detection demonstrates that atmospheric spectroscopy can uncover planets too faint or too close to their star for direct imaging, potentially opening a new avenue for finding worlds in other systems.