Due to the only persistent player state being the state of their ship, anything you encounter will have been placed by a player during the lifetime of that p2p island (player jettisonned cargo or mines), or is part of a PvE set-piece created by the game (USS floating cargo encounters, minefields, mineable asteroids in future). And anything placed by a player likely has a countdown on it to prevent entity overload in the island (see The Great Port Zelada Can Spam incident of spring 3300).
The only sort-of exception to the above may be deployable mining automata, but these will only be there for the original owner to return to (dynamically re-instantiated when the owner returns to collect, and a die roll will determine if an NPC is supposed to have wrecked it in your absence)'
FD have said many times that they aren't going to overlay the PG universe with a database-backed collection of persistent objects that one player can place and another player can encounter.