My knowledge of astrophysics is nearly null but my guess would be based on its size and hypothetical mass scientists would know how massive a celestial body would have to be in order for the rogue planets to be trapped by its gravity and if there aren’t any bodies of that size in the vicinity then they can conclude they are rogue.
This is amazing. But also, how do we know they are not in orbit? Don’t you have to observe something for a long time to know that?
My knowledge of astrophysics is nearly null but my guess would be based on its size and hypothetical mass scientists would know how massive a celestial body would have to be in order for the rogue planets to be trapped by its gravity and if there aren’t any bodies of that size in the vicinity then they can conclude they are rogue.
I could be 100% wrong though.