Thank you for your comments! I received many feedback on the wording and meaning of upgrades. I will be careful on this topic in my next projects. Cards are the upgrades after you destroy a celestial body. However, I know it was not a very creative way to implement the special object. Also, the visuals on the cards were not enough to distinguish them from any other UI element. So I get your point.
I thought about a levels screen or a progress bar but since it is a clicker, I wanted to create "when will it end?" "what will be the next celestial body?" mystery.