According to Mike Brown, our Warrior Princess planet is NOT an interloper from another solar system. It's part of the Kuiper Belt. I asked him about the very point, wondering if it could have been extracted from another solar system (which still would not have changed its status as a planet anymore than the origin of a star changes its status as a star). Brown told me the 10th planet, like other Kuiper Belt objects recently announced, reaches at the closest point in its orbit about 36 AU from the sun. The reason is they had gravational encounters with Neptune, which is about 30 AU from the sun. Neptune tossed these critters into strange inclinations. That makes sense and doesn't require them to be captured from another star. Now, I'm not certain about Sedna, which is a different sort of object, with an excessively elliptical orbit and a range that takes it to about 1,000 AU, if I remember right. Thanks, Joe