How are rogue planets made?

They’re not part of a planetary system, so how are these wandering worlds made?

Rogue planets are worlds that don't orbit a star

Rogue planets are worlds that don’t orbit a star

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

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