I like the material setup and all but I have some suggestions.
Stars over a certain amount of time slowly turn their hydrogen into deuterium then tritium and helium etc. So you can see over a certain amount of time how the stars composition changes ~ Just like real life
Also i think maybe instead of a slider, you can have a dropdown menu of different materials eg nickel and uranium. Once you choose a material, you can have a slider than comes after it. Another thing is that you could have a little plus next to it to add other dropdown menus. I think this'll make a better addition to the already awesome material menu.
Also I think another thing that'll be better is more realistic asteroid impacts. The chicxulub asteroid was only 10km in diameter and yet it almost wiped out life on the planet. But in US2 if you smash a 10km asteroid, it won't do ****. I think that maybe if the impacts are a little revised and made more realistic it'll be cool.
Another thing is regional lights. This goes with the impact thing above. Lets say you smash a 1km asteroid into a planet. Shouldn't lights suddenly turn off in the surrounding area? In US2 all the lights turn off and it's a little unrealistic. I don't like this that much.
Also gamma ray bursts sound like a cool addition to us2. Like maybe a quasar or something has a gamma ray burst and it hits a planet. It would look cool if you could see the atmosphere maybe burn off or something like that.
Also maybe you could add Nuclear Bombs just to see how it effects the atmosphere and kills off planets. Because the tsar bomba blew a hole in the atmosphere where it was dropped and that'd look cool on US2 if we could have that. You could also see how hundreds of nuclear bombs can destroy a planet or redirect an asteroids crashcourse. That kind of thing
I don't know. It's what the community chooses anyway