Detached object

Detached objects are a dynamical class of minor planets in the outer reaches of the Solar System and belong to the broader family of trans-Neptunian objects (TNOs). These objects have orbits whose points of closest approach to the Sun (perihelion) are sufficiently distant from the gravitational influence of Neptune that they are only moderately affected by Neptune and the other known planets: This makes them appear to be "detached" from the rest of the Solar System, except for their attraction to the Sun.^[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. Detached objects have larger perihelia than these other TNO populations, including the objects in orbital resonance with Neptune, such as Pluto, the classical Kuiper belt objects in non-resonant orbits such as Makemake, and the scattered disk objects like Eris.

Detached objects have also been referred to in the scientific literature as extended scattered disc objects (E-SDO),^[3] distant detached objects (DDO),^[4] or scattered–extended, as in the formal classification by the Deep Ecliptic Survey.^[5] This reflects the dynamical gradation that can exist between the orbital parameters of the scattered disk and the detached population.

At least nine such bodies have been securely identified,^[6] of which the largest, most distant, and best known is Sedna. Those with large semi-major axes and high perihelion orbits similar to that of Sedna are termed sednoids. As of 2024, there are three known sednoids: Sedna, 2012 VP₁₁₃, and Leleākūhonua.^[7] These objects exhibit a highly statistically significant asymmetry between the distributions of object pairs with small ascending and descending nodal distances that might be indicative of a response to external perturbations; asymmetries such as this one are sometimes attributed to perturbations induced by unseen planets.^[8][9]