IAU:s definition of planetary systems

The International Astronomical Union (IAU) is the international astronomical organisation that brings together about 13 000 astronomers from many countries worldwide. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU also serves as the internationally recognised authority for assigning designations to celestial bodies and the surface features on them. Founded in 1919, the IAU is the world's largest professional body for astronomers.

  • A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
  • A 'dwarf planet' is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
  • All other objects, except satellites, orbiting the Sun shall be referred to collectively as 'Small Solar System Bodies.'"

So according to IAU, there are eight planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. And there are five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.

According to my new definition of planetary systems, there are ten known planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and Eris. The planets can then be divided into four groups: Dwarf, Standard, Giant and Super Giant.

According to IAU, there are currently 285 moons (it might have changed) in the Solar System the planets according to IAU.

According to this new definition of planetary systems, there are 23 moons in the Solar System and 63 Moonoids. The rest I call Pebbles as they are quite small and you need to draw the line somewhere. I have not yet set a minimum size limit for the Pebbles yet but that will be needed.