  Recent analyses have shown that distant orbits within the scattered disk
population of the Kuiper belt exhibit an unexpected clustering in their
respective arguments of perihelion. While several hypotheses have been put
forward to explain this alignment, to date, a theoretical model that can
successfully account for the observations remains elusive. In this work we show
that the orbits of distant Kuiper belt objects cluster not only in argument of
perihelion, but also in physical space. We demonstrate that the perihelion
positions and orbital planes of the objects are tightly confined and that such
a clustering has only a probability of 0.007% to be due to chance, thus
requiring a dynamical origin. We find that the observed orbital alignment can
be maintained by a distant eccentric planet with mass greater than ~10 Earth
masses, whose orbit lies in approximately the same plane as those of the
distant Kuiper belt objects, but whose perihelion is 180 degrees away from the
perihelia of the minor bodies. In addition to accounting for the observed
orbital alignment, the existence of such a planet naturally explains the
presence of high perihelion Sedna-like objects, as well as the known collection
of high semimajor axis objects with inclinations between 60 and 150 degrees
whose origin was previously unclear. Continued analysis of both distant and
highly inclined outer solar system objects provides the opportunity for testing
our hypothesis as well as further constraining the orbital elements and mass of
the distant planet.
