Astronomers have confirmed a third giant planet orbiting Beta Pictoris, a young star 63 light-years away that has been one of the most closely watched planetary systems in the sky for nearly four decades. The planet, designated Beta Pictoris d, had been sitting in telescope archives for more than eleven years before two independent research teams — one using the European Southern Observatory's Very Large Telescope (VLT) in Chile, the other using NASA's James Webb Space Telescope — separately tracked it down and confirmed it was real.
The new planet is roughly 2.4 times the mass of Jupiter and follows an orbit wider than its two known siblings, Beta Pictoris b and c. It is also extraordinarily faint: about 100 times dimmer than Beta Pictoris b, which makes it, by the researchers' account, the faintest planet ever directly imaged from the ground. The VLT team, led by Ben Sutlieff of the University of Edinburgh and Markus Bonse of ESO, spotted it with the telescope's ERIS instrument, then combed back through SPHERE instrument archives to find earlier, fainter traces of it. A separate team led by Aidan Gibbs of the University of California San Diego picked up its chemical signature — including carbon monoxide, methane and water — in Webb spectroscopy data. Both papers were accepted for publication in The Astrophysical Journal Letters.
A system known for hiding planets
Beta Pictoris has been a proving ground for direct-imaging techniques since the 1980s, when astronomers first photographed its edge-on debris disk — a flattened ring of dust and rock left over from planet formation. Planet b was confirmed in 2008 and planet c in 2019, both found through the painstaking work of subtracting out the glare of the central star to reveal faint companions hidden in its light. Planet d's existence had been suspected for years because of subtle gaps and asymmetries in the debris disk that a hidden planet's gravity could explain, but no one had been able to pin it down directly until now.
"This was a serendipitous discovery," said Ben Sutlieff, an astronomer at the University of Edinburgh and co-lead of the VLT study. "We initially wanted to look more at a known planet in the system, Beta Pictoris b, to see how it changed over time."
Planet d, it seems, has been playing a game of hide-and-seek with us for over a decade and only now can we say "found you!"
— Jayne Birkby, astronomer, University of Oxford
Beth Biller, a co-author on the VLT paper at the University of Edinburgh, said systems like this one suggest giant planets tend not to form alone: "Planets seem to have friends." Beta Pictoris is now only the second system, after HR 8799, in which more than two planets have been directly imaged and confirmed around the same star.
Both teams say the discovery, rather than closing the book on the system, gives them a new target for follow-up observations. Confirming the planet's exact orbit will take repeated imaging over the coming years, and researchers want to use Webb's spectroscopy to pin down its atmospheric composition in more detail — data that could help settle long-running questions about how gas giants far from their stars actually form.
