Inventory of the Solar System

• Major Planets
  
  There are, of course eight nine (?) planets in the solar system. Planets seem to come in two varieties; the terrestrial planets which are like Earth with rocky composition and relatively thin atmospheres, and the jovians, which are gas giants like Jupiter. The orbits of the planets seem to follow a relation first reported by Bode, although it was not he who discovered this curious mathematical pattern. In this series of numbers, there seems to be a simple relation between the size of the orbit in astronomical units, and the period of the orbit, in years. Pluto has been demoted to being just one of the objects in the Kuiper Belt.
    In the world of Star Trek there is a rather clever scheme for classifying planets.
  
  
• Minor Planets
  
  These are what non-astronomers call asteroids. There are thousands and thousands of them. Most of them orbit between Mars and Jupiter. It's the ones which cross Earth's orbit which are interesting.
  
  
• Major Moons
  
  These are the things which orbit major planets. We know of at least sixty-six of these things, most of which have had their properties carefully measured. We have one orbiting the Earth. It is called the Moon.
  
  
• Minor Moons
  
  Just recently discovered, these are bodies which are under the influence of certain minor planets. Dactyl is a modest sized rock which orbits the asteroid called Ida. And most recently, astronomers have discovered a satellite orbiting (45) Eugenia.
  
  
• Comets
  
  Are those members of the solar sytem which spend most of their lives outside the orbit of Pluto. They consist almost entirely of volitiles such as frozen water and carbon dioxide. But when they do decide to visit the inner solar system, they can put on quite a show with splendid, long glowing tails.
  
  
  
  
      Visit the Official Nine Planets site.
  
      This very cool NASA site allows you to fly anywhere in the solar system and look at any other object.
  
  
      Make your own Solar System!