Obviously as you travel around the planet, you'll find a lot of different structures - observatories, trading posts, mining facilities, mineral storage, and more. However, I've never personally found a crashed ship before first successfully solving the puzzle at a nearby transmission tower.
This begs the question - Is it possible to randomly encounter crashed ships? Or is the transmission tower "pre-quest" required to spawn the crashed ship?
(I suspect solving the transmission tower puzzle is required, since that would explain why the crashed ship you find is always ±1 item slot compared to your current ship... but I don't have any concrete proof.)