What are Scattered Disc Objects?

Scattered disc objects are among the most distant and cold objects in the solar system. They are located between 35 and as much as 1,000 AU from the Sun. With eccentricities as high as 55 degrees, some travel as far "vertical" relative to the plane of the ecliptic as they do "horizontal." Unlike most other objects in the solar system, such as the planets and most asteroids, these objects have highly inclined and eccentric orbits, with circular orbits being the exception rather than the norm.

The largest is Eris, whose discovery in 2003 precipitated the formal defining of the word "planet" and the demotion of Pluto from the planet classification. Eris is classified as a dwarf planet along with Pluto, which it exceeds in size and mass, and Ceres, previously considered the largest asteroid. Scattered disc objects are considered a subset of trans-Neptunian objects, which is an umbrella term used to refer to any body beyond the orbit of Neptune, including Pluto.

Although their origin is not completely understood, it is thought that scattered disc objects were previously members of the Kuiper belt, which got ejected into eccentric, scattered orbits through close encounters with Neptune. They have some of the coldest surfaces in the solar system, with temperatures ranging between 30 K and 55 K. From the surface of one, the Sun would look like little more than an exceptionally bright star.

As Pluto is roughly 32 AU away from the Sun, scattered disc objects range from slightly more distant to over 30 times farther from the Sun than Pluto. There are none closer to the Sun than 35 AU, because in that range, they would fall into the gravitational influence of Neptune and begin to normalize their orbits.