Working on a bit of a story that includes the ejection of the planet Jupiter from the solar system rather suddenly with all of the planets staying generally within it. I understand this is complicated because the mass of Jupiter compared to that of the rest of the planets.
Much appreciated!
Rogue Planet. Jupiter is far enough away, and isolated enough, that another Jupiter-sized planet (or larger) flung out of it's solar system, which would necessarily be traveling in a straight line, could pass close enough to lift Jupiter out of its orbit.
Note that the straight line could be from any direction; not all systems are oriented to spin in the same direction as ours happens to be spinning. So the rogue can come from "above" or "underneath" the flat plane most of our planets are in (convenient way to avoid collisions with any other planets). If it comes in to close to our own plane of rotation; you would have to worry about any other planets in its path.
As I said, we are not affected by any tides caused by the gravitational pull of Jupiter; Heck we aren't affected if all the other planets are aligned with us. So a rogue planet passing through close to Jupiter won't have any noticeable effect upon us either.
That said, the rogue entering and exiting our Oort Cloud, and our Jupiter exiting, could cause major disturbances there that ultimately result in many tens of thousands of asteroids being deflected into the inner solar system. When those have hit us in the past, most recently about 65 million years ago, they have caused Life on Earth a bit of trouble.
It's possible that a rogue high-to-stellar-mass object passing at high speed through the solar system near Jupiter at a high angle to the ecliptic plane would a) be able to change Jupiter's velocity that it can escape the solar system (most likely at an angle to the ecliptic, and thus minimise its interactions with any other planets), and b) have a sufficiently brief and distant encounter with the rest of the solar system that the other planets are not disturbed much by the object's presence.
This would almost certainly require Jupiter's position to be fairly far from all other planets to minimise the effects of the object's gravity.
Such an object could be anything from a brown dwarf to a normal star to a neutron star; without doing the maths, I couldn't give any parameters (e.g. velocity of the rogue object) as to what would be necessary, but it's certainly plausible. It would need to increase Jupiter's speed by under 50% (from ~13km/s to ~18.5km/s) to achieve solar escape velocity.
As to the "suddenly" part, it would still take a while for Jupiter to actually depart the solar system entirely; at its escape velocity of 18.5km/s, it would still take decades, if not centuries to get as far as Neptune is from the Sun. A higher velocity would decrease the time taken, but it gives you some idea of the timescales involved.
