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A team of professional astronomers and citizen scientists from the Backyard Worlds: Planet 9 project has discovered a planetary-mass object co-moving with a star called BD+60 1417.

WISE images of the BD+60 1417 system. Image credit: Léopold Gramaize / Backyard Worlds: Planet 9 project.

BD+60 1417, also known as SAO 15880 and TIC 159527171, is a young K0-type star located about 146 light-years away in the constellation of Ursa Major.

“This star had been looked at by more than one campaign searching for exoplanet companions. But previous teams looked really tight, really close to the star,” said Dr. Jackie Faherty, an astronomer at the American Museum of Natural History and co-founder of the Backyard Worlds: Planet 9 project.

“Because citizen scientists really liked the project, they found an object that many of these direct imaging surveys would have loved to have found, but they didn’t look far enough away from its host.”

In 2018, Backyard Worlds participant Jörg Schümann from Germany alerted the project scientists to a new co-moving system: an object that appeared to be moving with a star.

After confirming the system’s motion, the researchers used ground-based telescopes to observe BD+60 1417 and its companion separately and were immediately excited by what they saw.

Named CWISER J124332.12+600126.2 (W1243 for short), the new object has a mass of about 15 times the mass of Jupiter.

This range overlaps with an important cutoff point — 13 times the mass of Jupiter — which is sometimes used to distinguish planets from brown dwarfs.

“We don’t have a very good definition of the word ‘planet’,” Dr. Faherty said.

Another defining feature is how they form: planets form from material gathering in disks around stars, while brown dwarfs are born from the collapse of giant clouds of gas, similar to how stars form.

But the physical properties of W1243 do not provide any clues to its formation.

“There are hints that maybe it’s more like an exoplanet, but there’s nothing conclusive yet. However, it is an outlier,” Dr. Faherty said.

W1243 is very distant from the host star — about 1,662 times farther than the Earth is from the Sun.

“You had an exoplanet community just staring so close to it,” Dr. Faherty said.

“And we just pulled out a little, and we found an object. That makes me excited about what we might be missing in giant planets that might exist around these stars. Sometimes, you need to broaden your scope.”

A paper describing the discovery was published in the Astrophysical Journal.


Jacqueline K. Faherty et al. 2021. A Wide Planetary Mass Companion Discovered through the Citizen Science Project Backyard Worlds: Planet 9. ApJ 923, 48; doi: 10.3847/1538-4357/ac2499


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