The New Horizons probe does its flyby of Pluto today.
This is a big deal, technology and a sense of adventure all in one.
I am old enough that I remember knowing about the nine planets, when Pluto was still a planet, and how many moons Jupiter and Saturn had. Voyager 1 and 2 changed the count of the moons, as did subsequent probes, The count of moons around other planets has changed so much, I can’t remember the number of moons I had memorized way back when. It is that realization as a kid that we don’t know it all that grabbed my attention.
A solar system is so huge that it is easy for exploration and travel to reveal new features all the time. Even if everything in a system was mapped, interstellar bodies could be captured, or pass through a system.
If one planned a science fiction campaign limited to one system, there would be plenty of locations for the action.