How close an orbit could you get to Earth with a planet-sized object/ship without severely disrupting Earth's orbit?

My idea involves an alien spaceship inside a roughly Earth to Mars sized/massed planet, but the whole planet is displaced when the drive is activated. If you wanted to travel back to our solar system but didn't want to destroy Earth or send it out of orbit, is there a temporary orbital path that wouldn't throw our solar system's orbital mechanics out of whack? A general idea would be sufficient. Ideally, it would:

1. Be close enough that 23rd century ships (specs to be decided but not super-tech) could fly back and forth in a time-frame of a few months.
2. Allow communication back and forth that was in hours or less (at least initially).
3. The closer and better matched the orbit, the shorter the duration of the orbit would need to be. (if we have to get weird and exotic, we could probably do a rendezvous between planets at the front end, then again after a year to 6 months.
4. We can have almost perfect control of the starting position of the planet as well as direction and velocity. However,it would be very hard to alter the trajectory of the planet once it arrived.
5. Once the story goal is achieved, the planet would be displaced to elsewhere and solar mechanics would need to be able to resume something close to normal orbits.

posted over 4 years ago

DWKraus‭

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