Planet 9

Science Daily: Was Planet 9 once an exoplanet, stolen by our sun?

summary - Astronomers show that it is highly likely that the so-called Planet 9 is an exoplanet. This would make it the first exoplanet to be discovered inside our own solar system. The theory is that our sun, in its youth some 4.5 billion years ago, stole Planet 9 from its original star.