"Planet Nine may be even more exotic than astronomers had thought.

The putative world, which some scientists think lurks unseen far beyond Pluto's
orbit, could be a former "rogue planet" that was captured by our solar system at
some point in the past, a new study suggests."

See:

http://www.space.com/35277-planet-ni...exoplanet.html



So, we may already have an "exoplanet" in our own solar system?