Classifying Solid Planetary Bodies

Abstract

Distinct solar system (SS) solid planetary objects are defined in terms of dynamic and solid state characteristics. This includes Keplerian orbits, self gravitation, upper and lower mass limits that effect planet shape, integrity, and equation of state. Criteria are based on parameters that vary with pressure and temperature such as bulk modulus (β), rigidity (μ), density (ρ), within major and dwarf planets and irregular objects (IO). Rotation offsets gravitation pressure effects. In accordance with recent IAU guidelines planetary bodies are divided into cis‐ and trans‐Neptunian major and dwarf planets with solid cores and (smaller) IO. Cis‐Neptunian bodies include terrestrial and large gaseous planets, planetary moons, asteroids, and main‐belt comets within Neptune’s orbit. New classes of objects beyond Neptune (trans‐Neptunian objects or TNOs) similar to Pluto include Kuiper belt and Oort cloud objects, i.e. short and long period comets, and scattered disk objects that are IO if they are not large enough to have a gravitationally (spheroid) dominated shape. There may also be hitherto undetected TNOs such as asteroid parent bodies that may be (sub‐dwarf) proto‐planets. Physical criteria discussed here for defining solid SS planetary bodies are also likely applicable to exoplanets.