'Mysterious' celestial object blurs line between planets and brown dwarfs

A new celestial object, located nearly 500 light years away from the Sun, has challenged traditional understandings about how planets and stars form.

The object is located near and likely orbiting a very young star about 440 light years away from the Sun, and is leading astrophysicists to believe that there is not an easy-to-define line between what is and is not a planet.

Lead author Thayne Currie, a post-doctoral fellow in U of T's Department of Astronomy and Astrophysics, said that they have very detailed measurements of this object spanning seven years, even a spectrum revealing its gravity, temperature, and molecular composition, and still they can't determine whether it is a planet or a 'brown dwarf,' asserting that depending on what measurement you consider, the answer could be either.

Named ROXs 42Bb for it's proximity to the star ROXs 42B, the object is approximately nine times the mass of Jupiter, below the limit most astronomers use to separate planets from brown dwarfs, which are more massive.

However, it is located 30 times further away from the star than Jupiter is from the Sun.

Currie says that the new object starts to blur this distinction between planets and brown dwarfs, and may lie within and begin to fill the gap.

The study has been published in Astrophysical Journal Letters.