Detached object

Detached objects have perihelia much larger than Neptune's aphelion. They often have highly elliptical, very large orbits with semi-major axes of up to a few hundred astronomical units (AU, the radius of Earth's orbit). Such orbits cannot have been created by gravitational scattering by the giant planets, not even Neptune. Instead, a number of explanations have been put forward, including an encounter with a passing star or a distant planet-sized object, or ejected rogue planets (present in the early Solar System that were ejected). The classification suggested by the Deep Ecliptic Survey team introduces a formal distinction between scattered-near objects (which could be scattered by Neptune) and scattered-extended objects (e.g. 90377 Sedna) using a Tisserand's parameter value of 3. == Classification ==

Detached objects are one of four distinct dynamical classes of TNO; the other three classes are classical Kuiper-belt objects, resonant objects, and scattered-disc objects (SDO). Sednoids also belong to detached objects. Detached objects generally have a perihelion distance greater than 40 AU, deterring strong interactions with Neptune, which has an approximately circular orbit about 30 AU from the Sun. The boundary between the scattered and detached regions can be defined using an analytical resonance overlap criterion. The discovery of 90377 Sedna in 2003, together with a few other objects discovered around that time such as and , has motivated discussion of a category of distant objects that may also be inner Oort cloud objects or (more likely) transitional objects between the scattered disc and the inner Oort cloud. This classification of Sedna as a detached object is accepted in recent publications. This line of thinking suggests that the lack of a significant gravitational interaction with the outer planets creates an extended–outer group starting somewhere between Sedna (perihelion 76 AU) and more conventional SDOs like (perihelion 35 AU), which is listed as a scattered–near object by the Deep Ecliptic Survey. Influence of Neptune 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. They have orbital periods of more than 300 years but most have only been observed over an observation arc of less than a decade. Due to their great distance and slow movement against background stars, it may be decades before most of these distant orbits can be 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. For example, simulations by Emelʹyanenko and Kiseleva in 2007 show that many distant objects could be in resonance with Neptune. They show a 10% likelihood that 2000 CR105 is in a 20:1 resonance, a 38% likelihood that 2003 QK91 is in a 10:3 resonance, and an 84% likelihood that is in an 8:3 resonance. appears to have less than a 1% likelihood of being in a 4:1 resonance. 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 which are called extreme trans-Neptunian object (ETNOs) may be trapped in the 5:3 and 3:1 mean-motion resonances with a putative Planet Nine with a semimajor axis ~700 AU. == Possible detached objects ==

This is a list of known objects by discovery date that could not be easily scattered by Neptune's current orbit and therefore are likely to be detached objects, but that lie inside the perihelion gap of ≈50–75 AU that defines the sednoids. Objects listed below have a perihelion of more than 40 AU, and a semi-major axis of more than 47.7 AU (the 1:2 resonance with Neptune, and the approximate outer limit of the Kuiper Belt): The following objects can also be generally thought to be detached objects, although with slightly lower perihelion distances of 38–40 AU. == See also ==