Small Solar System body

A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other objects, except satellites, orbiting the Sun shall be referred to collectively as 'Small Solar System Bodies' ".^[1]

This encompasses all

Makemake, and Eris and others that may turn out to be dwarf planets

.

Definition

The current definition was included in the 2006 IAU resolution that defined the term

interstellar interlopers 1I/ʻOumuamua and 2I/Borisov

.

It is not presently clear whether a lower size bound will be established as part of the definition of small Solar System bodies in the future, or if it will encompass all material down to the level of meteoroids, the smallest macroscopic bodies in orbit around the Sun. (On a microscopic level there are even smaller objects such as interplanetary dust, particles of solar wind and free particles of hydrogen.)

Except for the largest, which are in

hydrostatic equilibrium, natural satellites (moons) differ from small Solar System bodies not in size, but in their orbits. The orbits of natural satellites are not centered on the Sun, but around other Solar System objects such as planets, dwarf planets

, and small Solar System bodies.

Some of the larger small Solar System bodies may be reclassified in future as dwarf planets, pending further examination to determine whether or not they are in hydrostatic equilibrium.

The orbits of the vast majority of small Solar System bodies are located in two distinct areas, namely the

centaurs, comets, and scattered disc

objects.