Thanks a lot! :D
Kind of - it's all generated on-the-fly (procedurally).
- when you scroll around in the Galaxy Map, new "pages" of systems are generated
- when you enter a new system, the planets are generated (using a consistent Noise generator)
- when you land on a planet, the initial surface area is generated
- when you walk around the planet, new "areas" of the surface are generated.
It's all down to using unique numbers to "seed" the random number generation. By seeding the RND() function, you will always get a consistently-random output. So, each system, planet, surface tile will always end up with the same seed (number). It's predictable, therefore you don't ever need to store it, just trust that it'll always come out the same.
Check out some linkson Procedural Generation and you'll disappear down the rabbit-hole for this stuff - it's fascinating (though I've only just started to dabble in it myself). Have fun! :D