Generally, small bodies found in the Kuiper Belt. The largest Kuiper Belt Object (KBO), Eris, is <3000 km in diameter. Image source: http://en.wikipedia.org/wiki/File:EightTNOs.png Click on Term to Read More (KBOs) with large orbital eccentricities (perihelia between 30 and 48 The astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More, aphelia >60 AU). These objects were probably flung into their current orbits early in The Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. history by gravitational interactions with the giant planets. The current population of the scattered disk is only ~1% of what it was in the early Solar Definable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with. Gravitational interactions with Neptune in particular can eject them from the Solar System. Alternatively, such interactions may pull scattered disk objects further into the Solar System, where they probably become Centaur asteroids for a period of time. There are ~150 scattered disk objects and Centaurs currently known.
Some or all content above used with permission from J. H. Wittke.