The Faintest Exoplanet Ever Seen from Earth

A team of astronomers have won a decade-long game of cosmic hide-and-seek, discovering a third planet orbiting the star Beta Pictoris — and it is the faintest exoplanet ever directly imaged from Earth.

The new world, named Beta Pictoris d, is a gas giant located 63 light-years away. It is 100 times fainter than its sibling Beta Pictoris b, the first planet discovered in this famous system. With a mass of about 2.4 Jupiters, it is also among the lightest exoplanets ever captured in a direct image from a ground-based telescope.

A Serendipitous Discovery

The team, co-led by Ben Sutlieff of the University of Edinburgh and Markus Bonse of the European Southern Observatory (ESO), was originally studying Beta Pictoris b when they noticed something else in their data.

"This was a serendipitous discovery," Sutlieff said. "We initially wanted to look more at a known planet in the system to see how it changed over time."

When they analyzed the images taken with ESO's Very Large Telescope (VLT) using the ERIS instrument, they saw a second faint dot near Beta Pictoris b. Diving into 11 years of archival observations, the planet appeared in multiple images — it had been hiding in plain sight all along.

"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!'," said Jayne Birkby of the University of Oxford.

Confirmed by JWST

Independently, a team led by Aidan Gibbs at the University of California also discovered the same planet using the James Webb Space Telescope (JWST). Both results are published today in The Astrophysical Journal Letters.

Beta Pictoris is now only the second system — after HR 8799 — where more than two planets have been directly imaged. The discovery also solves a mystery about the system's debris disc: Beta Pictoris d has exactly the right mass and orbital position to explain the disc's unusual shape.

What's Next

The discovery demonstrates that even faint planets may be hiding in existing data. With ESO's upcoming Extremely Large Telescope (ELT), astronomers expect to find even more lower-mass planets in directly imaged systems.

"Planets seem to have friends," said Beth Biller of the University of Edinburgh. "Many famous directly imaged exoplanet systems seem to have multiple giant planets, and likely there are even more lower-mass planets hiding in these systems."

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Sources - ESO press release via EurekAlert - Space.com - The Astrophysical Journal Letters

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