Jayne Birkby said Beta Pictoris d had been hiding in the Beta Pictoris system for over a decade before the team could finally say, “found you!” The new gas giant sits 63 light-years away and is 100 times fainter than Beta Pictoris b.
Ben Sutlieff, the co-leader of the team, said the result came from “a serendipitous discovery,” after researchers looked back through 11 years of archival data. The planet is the faintest exoplanet ever seen from Earth, and it adds a new directly imaged world to a field in which less than 100 of the more than 6,000 worlds in NASA's exoplanet catalog were found that way.
Beta Pictoris b search
Sutlieff said the group first set out to learn more about Beta Pictoris b and how it changed over time. “We initially wanted to look more at a known planet in the system, Beta Pictoris b, to see how it changed over time,” he said. The team was not hunting for a third planet at the start.
That makes the result more than a routine addition to NASA's exoplanet catalog. Beta Pictoris d is farther from its parent star than Beta Pictoris b and Beta Pictoris c, and it is cooler than both. Its mass, about 2.4 times that of Jupiter, is also well below the roughly 10 times the mass of Jupiter for Beta Pictoris b and Beta Pictoris c.
11 years of archival data
The discovery depended on comparing older images against the team’s target rather than waiting for a fresh sighting. By working through 11 years of archival data, the astronomers separated the planet’s dim light from the glare of its star and picked out a signal that had been missed before.
That is the practical lesson for readers following direct-imaging work: the method can turn old observations into new planets when a faint object sits close enough to a bright star to be overlooked. Direct imaging is hard, and this detection shows how a slow search can pay off without a new observing campaign.
Beta Pictoris debris disk
Beta Pictoris d also fits the system in a way the others did not. Its mass and location may help explain the odd shape and location of the system's debris disk, giving researchers a better match between what they see around the star and the planets they have now identified.
Birkby’s description captured the patience behind the find. “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!’” The next step is more study of Beta Pictoris d itself and how it compares with the better-known planets already in the system.
