pannonian75: I still have yet to find a mod, that alters the textures of the planet terrain from a distance and up close. So I took the liberty and looked into the files. I messed around with some, with my limited modding experience (Skyrim, Oblivion, Fallout 3), and did some testing.
First noticed, the textures are very low resolution (by 2016 standards...or even 2008).
Second, I noticed, the textures controlling the LOD (level of detail) is even smaller.
People noticing strange "artifacts" aren't artifacts, but just bad seams between texture files, as the world generator is patching together a planet's surface from multiple textures, that may or may not go well together.
After spending 4 hours of my time, modifying some textures and see the results, I gave up.
I either got very same looking planets or got no results whatsoever - meaning I couldn't change a damn thing, no matter if I replaced all textures I have found.
This may be the reason of the lack of planet texture mods (not the objects on planets, those are easy), because the way the game draws the textures makes it almost impossible to just edit files and see results.
It needs a good tool to edit planets, which gives a WYSIWYG (what you see is what you get) visual editor, but I'm afraid, that will have to wait for a very talented modding tool maker or Hello Games releasing a workshop. I'm betting on the first one to happen sooner.