This tutorial series contains all the tutorials I have done on the subject of generating a planet in unreal engine. This playlist contains topics ranging from how to generate the planet mesh using geometry script and dynamic mesh to how to add foliage into a planetary landscape. Planet gravity and spaceship system also has been re-used in this system, but they are covered in following playlists.
https://dev.epicgames.com/community/learning/tutorials/dpda/unreal-engine-space-toolkit-planet-generator