Scattered Disc - Comets

Comets

The Kuiper belt was initially believed to be the source of the Solar System's ecliptic comets. However, studies of the region since 1992 have revealed that the orbits within the Kuiper belt are relatively stable, and that these comets originate from the more dynamic scattered disc.

Comets can loosely be divided into two categories: short-period and long-period—the latter being believed to originate in the Oort cloud. There are two major categories of short-period comets: Jupiter-family comets and Halley-family comets. The latter group, which is named for its prototype, Halley's Comet, are believed to have emerged from the Oort cloud but to have been drawn into the inner Solar System by the gravity of the giant planets. The former type, the Jupiter family, are believed to have originated from the scattered disc. The centaurs are thought to be a dynamically intermediate stage between the scattered disc and the Jupiter family.

There are many differences between SDOs and Jupiter-family comets, even though many of the latter may have originated in the scattered disc. Although the centaurs share a reddish or neutral coloration with many SDOs, their nuclei are bluer, indicating a fundamental chemical or physical difference. One hypothesis is that comet nuclei are resurfaced as they approach the Sun by subsurface materials which subsequently bury the older material.