
Very Basic Planetary Classification System
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Obviously not the absolute in technical sophistication...  :-)
 
   Solar Companion: Not technically a world but not the main star
      or even a part of the close-binary pair.
   Brown Dwarf: A failed star which either didn't achieve enough
      mass to ignite its nuclear fires, or if it did ignite, it
      maintain fusion for very long. This "body" emits a good deal
      of infrared radiation but nothing in the visible spectrum.
   Gas Giant: Fairly obvious. Great for wilderness refueling if
      you use hydrogen to get around.
   Magma Ball: Ouch, this place is hot. This planet is either
      very close to the primary or is on its way to becoming a
      primordial world. It is possible that such a world is
      tidally locked to its sun. Then, one half would be a
      sea of lava, and the other half would be frozen.
   Primordial: A very young world. Atmosphere poisonous (usually
      reducing, being composed primally of nitrogen and carbon
      dioxide with variable amounts of water vapor, ammonia,
      methane, carbon monoxide and hydrogen sulfide).
      Geologically instable. Lots of volcanos and magma seas.
   Asteroid Belt: Not a planet at all, but rather a ring of
      debris most likely caused by a gravitational disturbance
      during a planet's early formation.
   Planetoid: A large chuck of rock which isn't part of an
      asteroid belt. Not necessarily round. Could be a
      captured planet.
   Vacuum Ball: Like the moon, essentially. Lots of rock. No
      atmosphere. Too big to be called a planetoid.
   Snow Ball: Like a planetoid, but composed primarily of ice.
      Usually found only beyond the star's biozone.
   Ice Planet: May have a breathable atmosphere so long as there
      is the ecosystem to support it. More likely a dead planet
      without a breathable atmosphere.
   Shallow World: Has some atmosphere, but it's not something
      you'd want in your lungs even assuming there was enough of
      it to breathe, which there isn't. This place will require
      gobs of terraforming if you really want to live here, and
      it probably won't be worth the effort when you're done.
      Mars might be an example.
   Barren World: Generally a non-breathable atmosphere, but there
      will probably be water tied up as ice crystals in the
      soil. Oxygen will probably reside in oxidizing compounds
      such as ferric oxide or in various nitrates. World may be
      volcanically active. Probably on its way to becoming a
      shallow world. No life beyond bacteria.
   Garden World: Earth is a prime example. Not only can you
      breath the atmosphere without mechanical aid, but life,
      either native or transplanted, thrives in abundance. Not
      all Garden Worlds need be natural... many may be the result
      of terraforming projects.
   Water World: Over 95% covered by water and ice. Possibly a
      breathable atmosphere along with a teaming native ecosystem
      which got evolutionarily stuck due to the total lack of any
      freestanding continents.
   Desert World: This world isn't entirely desert, but the
      hydrographic percentage is relatively low. Most likely, the
      atmosphere is somewhat thin, and the change in temperature
      from day to night is fairly extreme. Assuming an ecosystem
      is present, however, the atmosphere may be breathable.
   Marginal World: Complex lifeforms either never evolved on this
      planet or went extinct sometime within the past couple
      million years. Perhaps the sun flared and knocked out the
      entire ecosystem, or maybe a slew of meteors struck,
      churning up enough dust that the sun was blotted out for
      several decades. Regardless, this world is ripe for
      colonization. Some terraforming will be required, however,
      if the world is to remain habitable over the long term.
      Mars might have been a good example eons ago.
   Belch Ball: Lifeless terrestrial planet with a poisonous,
      toxic, or possibly even borderline-corrosive atmosphere.
   Greenhouse: A world gone to hell because of too much
      greenhouse gases (ala Venus).
   Exotic World: This planet has life, but not as we know it.
      The atmosphere is poisonous to humans and may even contain
      lethal micro-organisms. The temperature, however, is
      probably moderate enough that an individual can walk around
      unscathed by the environment so long as she has a self-
      contained oxygen supply. Many alien homeworlds will
      be exotics.
   Liquid World: Surface predominantly covered by ammonia or
      liquid methane. In the former case, the world may contain
      a teaming alien ecosystem. In the latter, alien life is
      less likely. Of course, other (non-water) liquids are also
      possible.
   Gas Core: This world was once a gas giant, but due to some
      catastrophic incident in the past (most probably the death
      throws of what was formerly the system's primary), was
      cooked quite hot and thereby stripped of most of its
      atmosphere, leaving behind a huge (super-terrestrial)
      core surrounded by heavier gasses. Such a world is quite
      large, with a high gravity and a poisonous, possibly even
      corrosive, atmosphere.
   Special: This world cannot be placed in any of the previously
      defined categories. It may be an artificial planet or
      perhaps a fluke of nature. GM's discretion advised.
 
