<P> The scattered disc is a sparsely populated region, overlapping with the Kuiper belt but extending to beyond 100 AU . Scattered disc objects (SDOs) have very elliptical orbits, often also very inclined to the ecliptic . Most models of Solar System formation show both KBOs and SDOs first forming in a primordial belt, with later gravitational interactions, particularly with Neptune, sending the objects outward, some into stable orbits (the KBOs) and some into unstable orbits, the scattered disc . Due to its unstable nature, the scattered disc is suspected to be the point of origin of many of the Solar System's short - period comets . Their dynamic orbits occasionally force them into the inner Solar System, first becoming centaurs, and then short - period comets . </P> <P> According to the Minor Planet Center, which officially catalogues all trans - Neptunian objects, a KBO, strictly speaking, is any object that orbits exclusively within the defined Kuiper belt region regardless of origin or composition . Objects found outside the belt are classed as scattered objects . In some scientific circles the term "Kuiper belt object" has become synonymous with any icy minor planet native to the outer Solar System assumed to have been part of that initial class, even if its orbit during the bulk of Solar System history has been beyond the Kuiper belt (e.g. in the scattered - disc region). They often describe scattered disc objects as "scattered Kuiper belt objects". Eris, which is known to be more massive than Pluto, is often referred to as a KBO, but is technically an SDO . A consensus among astronomers as to the precise definition of the Kuiper belt has yet to be reached, and this issue remains unresolved . </P> <P> The centaurs, which are not normally considered part of the Kuiper belt, are also thought to be scattered objects, the only difference being that they were scattered inward, rather than outward . The Minor Planet Center groups the centaurs and the SDOs together as scattered objects . </P> <P> During its period of migration, Neptune is thought to have captured a large KBO, Triton, which is the only large moon in the Solar System with a retrograde orbit (it orbits opposite to Neptune's rotation). This suggests that, unlike the large moons of Jupiter, Saturn and Uranus, which are thought to have coalesced from rotating discs of material around their young parent planets, Triton was a fully formed body that was captured from surrounding space . Gravitational capture of an object is not easy: it requires some mechanism to slow down the object enough to be caught by the larger object's gravity . A possible explanation is that Triton was part of a binary when it encountered Neptune . (Many KBOs are members of binaries . See below .) Ejection of the other member of the binary by Neptune could then explain Triton's capture . Triton is only 14% larger than Pluto, and spectral analysis of both worlds shows that their surfaces are largely composed of similar materials, such as methane and carbon monoxide . All this points to the conclusion that Triton was once a KBO that was captured by Neptune during its outward migration . </P>

What are the relative positions of the gas giants and the kuiper belt