An Ancient Stellar Flyby Could Have Put Planet Nine into its Distant Orbit

New observations of a distant exoplanet and its solar system offer proof of a long-standing astronomical theory: passing stars can perturb planetary systems and change planets’ orbits – for better or worse. Depending on how they pass by, stars can nudge planets into more stable orbits or give them a kick that sends out of the system entirely. And new evidence implies that these kinds of encounters may explain the paths of strange objects in our own solar system, like Omuamua or Planet Nine.