Elite: Dangerous Horizons is adding an element of gameplay that is exciting for a lot of different people. The Cobra engine is capable of many great feats and the backend procedural generation of the galaxy enables them to render entire planets in amazing realistic detail mostly using that procedural generation backend.
The creation uses what they call Stellar Forge tech to help create these planetary bodies. Stellar Forge uses actual physics principles to determine what kind of star is in a given star system based on available matter and elements, the creation of a star also means a lot of other activity around that star that eventually results in planets, those planets, their composition and even geography are all determined by this complex mathematical model that mirrors real-life. So while Kepler's mission might have found planets supporting life, so too would this system create such planets for us to eventually explore in Elite: Dangerous.
So with this approach in mind, to use procedural generation, they describe the elements that are available (via Stellar Forge) and build the planet from the ground up based on that. They even model tectonic plates, to have real plate activity that can have the planet change over time.
It's really fun to watch them explain how it works and it's incredible that no two planets will be the same. Also, they assure us that the transition will be seamless flying from space to the surface.