Planetary body


A planetary body or planetary object is any secondary body in the Solar System that is geologically differentiated or in hydrostatic equilibrium and thus has a planet-like geology: a planet, dwarf planet, or planetary-mass moon.
In 2002, planetary scientists Alan Stern and Harold Levison proposed the following algorithm to determine whether an object in space satisfies the definition for a planetary body. The body must:
  1. Be low enough in mass that at no time can it generate energy in its interior due to any self-sustaining nuclear fusion chain reaction.
  2. Be large enough that its shape becomes determined primarily by gravity rather than mechanical strength or other factors in less than a Hubble time, so that the body would on this timescale or shorter reach a state of hydrostatic equilibrium in its interior.
This definition excludes brown dwarfs and stars, as well as small bodies such as planetesimals.