Rendez-vous with massive interstellar objects, as triggers of destabilization.

We study how close passages of interstellar objects of planetary and substellar masses may affect the immediate and long-term dynamics of the Solar system. We consider two nominal approach orbits, namely the orbits of actual interstellar objects 1I/'Oumuamua and 2I/Borisov, assuming them to be typical or representative for interstellar swarms of matter. Thus, the nominal orbits of the interloper in our models cross the inner part of the Solar system. Series of massive numerical experiments are performed, in which the interloper's mass is varied with a small step over a broad range. We find that, even if a Jovian-mass interloper does not experience close encounters with the Solar system planets (and this holds for our nominal orbits), our planetary system can be destabilized on time-scales as short as several million years. In what concerns substellar-mass interlopers (free-floating brown dwarfs), an immediate (on a time-scale of ∼10–100 yr) consequence of such a massive interstellar object (MISO) flyby is a sharp increase in the orbital eccentricities and inclinations of the outer planets. On an intermediate time-scale (∼103 to 105 yr after the MISO flyby), Uranus or Neptune can be ejected from the system, as a result of their mutual close encounters and encounters with Saturn. On a secular time-scale (∼106 to 107 yr after the MISO flyby), the perturbation wave formed by secular planetary interactions propagates from the outer Solar system to its inner zone. [ABSTRACT FROM AUTHOR]