It is certainly a possibility. Since we haven’t discovered a ninth planet yet we can be reasonably sure that if it exists it is quite distant from the Sun. Recently, astronomers analysed the motions of objects at the furthest edge of the Solar System and noticed something peculiar. The elliptical orbits of many of these objects all seemed to line up in the same direction. This could be explained if there exists a sizeable ninth planet. This as-yet-unproven planet must orbit at least 20 times further away than Neptune and could be 10 times the mass of the Earth.