First thing, to have some good details over the planet, the textures should be 2048x2048 instead of 1024x1024. This means the generation will be 4 times slower, or now take 40 seconds.
Worse, this is assuming the planet calculation loop takes 100% of the CPU, which i cannot afford if it has to run in real-time one day (unless i add "dual CPU system" to the minimum requirements?). By dedicating 20% of the CPU (which is still a lot i think), the generation time will be again increased by a factor of 5: now it will take 200 seconds (or more than 3 minutes) to generate a single planet.
Since the goal is to render a full solar system one day, that means travelling from one planet's ground to another one's should not take less than 3 minutes. That's going to be a problem. Fortunately i still have some ideas in mind to improve the performance a bit, but quality will suffer a bit.