Presentation #100.02 in the session Comet and TNO Dynamics.
The sednoids are a sub-population of the detached TNOs (which are currently weakly coupled to the scattering induced by the four giant planets). Depending on which orbital cuts (which are not standard in the literature) are used, there are about 3 to 10 sednoids, with Sedna itself (with a~500 au,q~75 au, and i~12 deg) being the most discussed member. How these objects reached their large perihelia is a question of major cosmogonic interest, as any dynamics related solely to the past history of just the four giant planets fails to make them with any reasonable efficiency. Hypotheses include passing stellar encounters, implantation from other star systems, and additional planets (either now-gone or still-present) in our solar system.
Gladman and Chan (2006) pointed out that orbits like Sedna’s arose naturally if the early solar system contained, temporarily, additional ‘rogue’ planets of the scale of Earth mass. This hypothesis has the advantages of a natural time scale for the dynamics (set by the disposal time scale of the rogues to be ejected by Neptune), and produces the observed declining inclination trend with rising semimajor axis of the detached objects. One must, however, worry about the issue of how the cold classical Kuiper belt (semimajor axes roughly 42-48 au) managed to maintain its low dynamical excitation and whether the orbital distribution of the detached TNOs make sense in a rogue planet scenario.
We present further analytical and numerical explorations of rogue planet scenarios, exploring the strengths and weaknesses of the concept. The known TNOs provide interesting constraints on the mass, orbital history, and duration of the rogue planet in the outer Solar System.