I have a planetary capital - now what?

So I’ve gotten to a planetary capital - I’ve got some remaining technologies to research . . . but is there a point to them? The last technology to research is a mine? Does something happen when I research the rest? Is there some “ending” or final reward? Or is it just sandbox free play from here?

The (current,) final challenge is to see how much Adamantine you can mine. Note that you will still need your research facilities, so don’t delete them when you complete the technology tree. At the moment Adamantine is simply stored in a construction materials depot, so it is effectively sandbox mode with a suggested goal.