What if a distant ninth planet shepherds the orbits of Neptune and extreme trans-Neptunian objects like Sedna and 2012 VP113? Batygin and Brown proposed in 2016 that a 5–10 Earth-mass body on a 400–800 AU, highly inclined orbit could explain the clustered orientations of detached objects whose perihelia lie beyond Neptune's gravitational reach. This scenario includes the hypothetical Planet Nine alongside Neptune and the detached bodies whose aligned orbits sparked the search. No direct detection has been made yet, but the orbital clustering remains statistically significant and continues to motivate wide-field sky surveys.