Asked by Jonathan Richardson
Rogue planets – worlds that don’t orbit a star but instead move around the galaxy directly – may have formed in a planetary system similarly to how the planets in our very own Solar System did before being cast out by their parent system.
Alternatively, they may never have been bound to a parent star or brown dwarf in the first place. Worlds taking on a mass typical of a planet, that’s having enough gravity to take on a rounded appearance but not so much that it can sustain fusion in its core like a star would, might have formed in a similar way to stars leaving astronomers to name them as sub- brown dwarfs where they formed through the collapse of a gigantic gas cloud.
Image Credit: ESO