Astronomers this week announced the discovery of an odd object orbiting a star located around 440 light years from our solar system. The object's size and position is now giving scientists trouble in determining what exactly it is.
The object, dubbed ROXs 42Bb, is around nine times the mass of Jupiter, just shy of the mark where astronomers would classify the object as a brown dwarf. However, the object's distance from its sun is also around 30 times further than the distance from Jupiter to our sun, calling into question whether the object can rightfully be called a planet.
"We have very detailed measurements of this object spanning seven years, even a spectrum revealing its gravity, temperature, and molecular composition," said Thayne Currie, lead author of a paper about the finding published in Astrophysical Journal Letters and an astronomer at the University of Toronto. "Still, we can't yet determine whether it is a planet or a failed star – what we call a 'brown dwarf'. Depending on what measurement you consider, the answer could be either."
The question of what to call ROXs 42Bb touches on how astronomers currently think massive gas planets form. While most believe these planets form around a pre-existing core, another hypothesis holds that accreted gas around a new star can collapse into a planet or a brown dwarf.
"It's very hard to understand how this object formed like Jupiter did," said Currie. "However, it's also too low mass to be a typical brown dwarf; disk instability might just work at its distance from the star. It may represent a new class of planets or it may just be a very rare, very low-mass brown dwarf formed like other stars and brown dwarfs: a 'planet mass' brown dwarf."
Image via Thayne Currie/University of Toronto