Vs'Qs
Actually a moon, not a planet. Vs'Qs is a barren, desolate place, devoid of any natural life. Vs'Qs was the place where the body of Optimus Prime happened to land on, having been blasted off into space randomly after his death. The Matrix of Leadership contained within the body was found during the Matrix Quest.
Read more about this topic: List Of Transformers Planets