Orbit of Eris

The outer Solar System with orbit of Eris.

The scattered disc (or scattered disk) is a distant region of the Solar System, thinly populated by icy minor planets known as scattered disc objects (SDOs), a subset of the broader family of trans-Neptunian objects (TNOs). The innermost portion of the scattered disc overlaps with the Kuiper belt, but its outer limits extend much farther away from the Sun and farther above and below the ecliptic than the belt proper.

The scattered disk is still poorly understood, although prevailing astronomical opinion suggests it was formed when Kuiper belt objects (KBOs) were "scattered" by gravitational interactions with the outer planets, principally Neptune, into highly eccentric and inclined orbits. While the Kuiper belt is a relatively "round" and "flat" doughnut of space extending from about 30 AU to 47 AU with its member-objects locked in autonomously circular orbits (cubewanos) or mildly-elliptical resonant orbits (plutinos and twotinos), the scattered disc is by comparison a much more erratic milieu. SDOs can often, as in the case of Eris, travel almost as great a "vertical" distance as they do relative to what has come to be defined as "horizontal". Orbital simulations show SDO orbits may well be erratic and unstable and that the ultimate fate of these objects is to be permanently ejected from the core of the solar system into the Oort cloud or beyond.