I'm also interested in this as a mechanic. If not for the Kerbol system, at least for other solar systems. IRL we don't really have any pictures of any planets in other star systems, so it makes sense that we wouldn't know much about what orbits other stars.
I suggest that we start out knowing where all the stars of these systems are and what the statistics of those stars are, but we have to perform some activity to be able to catalouge the planets and objects around that star.
Obviously as we play the game more, when we start a new save we'll be able to find all the objects with ease and be super prepared, but the first time playing and discovering planets and systems ought to be really cool.