content: Using a fuel-optimal Hohmann transfer orbit, about 375 years. Granted, this assumes we want to park ourselves in orbit at the new planet. Obviously, we can budget our fuel differently, get there faster, and do a fly-by like we did of Pluto. New Horizons launched nearly ten years ago and passed Jupiter in about a year. Using a Hohmann transfer to Jupiter should take approximately 5.5 years, so maybe we can get there within a human lifespan. Edit: The Hohman transfer to Pluto would take ~250 years, so maybe a 15-20 year mission could do it? I'm really just doing napkin math fueled by Kerbals.