Detached object

[1][2] In this way, detached objects differ substantially from most other known TNOs, which form a loosely defined set of populations that have been perturbed to varying degrees onto their current orbit by gravitational encounters with the giant planets, predominantly Neptune.

Instead, a number of explanations have been put forward, including an encounter with a passing star[10] or a distant planet-sized object,[4] or Neptune migration (which may once have had a much more eccentric orbit, from which it could have tugged the objects to their current orbit)[11][12][13][14][15] or ejected rogue planets (present in the early Solar System that were ejected).

[2] Although Sedna is officially considered a scattered-disc object by the MPC, its discoverer Michael E. Brown has suggested that because its perihelion distance of 76 AU is too distant to be affected by the gravitational attraction of the outer planets it should be considered an inner-Oort-cloud object rather than a member of the scattered disc.

[25] One of the problems with defining this extended category is that weak resonances may exist and would be difficult to prove due to chaotic planetary perturbations and the current lack of knowledge of the orbits of these distant objects.

Due to their great distance and slow movement against background stars, it may be decades before most of these distant orbits are determined well enough to confidently confirm or rule out a resonance.

Further improvement in the orbit and potential resonance of these objects will help to understand the migration of the giant planets and the formation of the Solar System.

[27] Carlos de la Fuente Marcos and Ralph de la Fuente Marcos have calculated that some of the statistically significant commensurabilities are compatible with the Planet Nine hypothesis; in particular, a number of objects[a] which are called extreme trans-Neptunian object (ETNOs)[29] may be trapped in the 5:3 and 3:1 mean-motion resonances with a putative Planet Nine with a semimajor axis ~700 AU.