The game lacks UX. Would be nice to have a different sound for buttons when they have an effect or don't. Also, you can grey out inaccessible buttons
The game loop is broken for such an idle genre. You can heat the sun enough to a super nova and reset the system; you don't need planets at all for this. Matter needed less and accumulated faster than heat.
I would recommend making the progress loop more focused on planet buildings because it has some potential for visually interesting growth of your system.
Also consider adding some randomness to colors, planet sizes, and so on, so the system can look different each time you reset it.