In the wikipedia articles for 2000 CR105 and 90377 Sedna they say that astronomers do not know why those objects have such highly eccentric orbits.  It even goes on to say(exact wording from 2000 CR105 article): One theory states that they were pulled from their original positions by a passing star or a very distant and undiscovered giant planet.  If this planet side is true then we would therefore have to add this gaint object as a planet it found to orbit the Sun.  This therefore says that there is a possibility of large planets in the outer reaches of the solar system. Daniel Schibuk