Short answers, pulled from the story.
The scattered disc is a distant, sparsely populated region of the outer Solar System containing icy small bodies called scattered-disc objects (SDOs). Their orbits are highly eccentric, reaching eccentricities as high as 0.8, and can tilt up to 40 degrees from the ecliptic. The region extends from roughly 30 AU out to well beyond 100 AU from the Sun.
The first scattered-disc object was identified in 1996 by astronomers at Mauna Kea in Hawaii, with three more found by the same survey in 1999. The discovery was made possible by CCD cameras, which capture about 90% of incoming light compared to roughly 10% for photographic film. Over a thousand trans-Neptunian objects were detected between 1992 and 2006 using this technology.
Jupiter-family comets are thought to originate in the scattered disc. Neptune perturbs scattered-disc objects inward, where they become centaurs orbiting between Jupiter and Neptune, and eventually evolve into Jupiter-family comets as they approach the Sun. Studies since 1992 showed that Kuiper belt orbits are relatively stable, making the scattered disc the more likely source for these short-period comets.
Most classical Kuiper belt objects appear reddish because sunlight converts surface methane into tholins, which absorb blue light. Scattered-disc objects instead appear white or grey. Michael E. Brown proposed that Eris, for example, has methane frozen across its entire surface at its current distance from the Sun, creating a bright white layer of ice a few inches thick.
Sedna is officially classified as a scattered-disc object by the Minor Planet Center, but its discoverer Michael E. Brown argues it belongs to the inner Oort cloud. With a perihelion distance of 76 AU, Sedna is too remote to be influenced by Neptune's gravity, which many researchers consider the defining characteristic of scattered-disc membership.
When Jupiter and Saturn settled into a 2:1 orbital resonance in the early Solar System, their combined gravity destabilized the orbits of Uranus and Neptune, sending Neptune outward through the proto-Kuiper belt. As Neptune migrated, it scattered vast numbers of small bodies into higher, more eccentric orbits. One model estimates that 90% or more of scattered-disc objects were placed in their current orbits by Neptune's resonances during this migration epoch.