The solar system is a collection of celestial bodies centered on the sun and constrained by the sun's gravity. It includes eight planets (from near to far from the sun: Mercury, Venus, earth, Mars, Jupiter, Saturn, Uranus and Neptune), at least 173 known satellites, five identified dwarf planets and hundreds of millions of small celestial bodies in the solar system.
The eight planets in the solar system are all in nearly circular orbits on the same plane and revolve around the sun in the same direction. Except Venus, other planets rotate in the same direction as the revolution. Comets revolve around the sun in the same direction, mostly in elliptical orbits, and generally have a long revolution period.