Where does the Solar System end? Good question.
Some say it ends at Neptune, the most distant planet. But that doesn't make sense, because we know of many objects much farther out than Neptune, even farther away than Pluto. In fact, about two light years from the Sun is a swarm of comets called the Oort Cloud. These objects are gravitationally bound to the Sun, so are part of the Solar System.
However the planets, and even icy objects beyond Pluto, are in a sort of bubble called the
heliosphere which is maintained by the
solar wind of particles given out by the Sun. Leaving the heliosphere would take you into the truly unknown, into space not dominated by the Sun. So, in a sense, this is leaving the Solar System. This is crossing into
interstellar space, the space between the stars.
One human creation has crossed that boundary between the Solar System and the rest of the Galaxy.
Voyager 1 – the First Starship Has Voyager 1 finally left the Solar System? No, that won't happen for tens of thousands of years. But it has left the bubble that the solar wind makes in space. The spacecraft is in the space between the stars, moving through a plasma made from ancient supernova explosions.