Note the word "pure" qualifying most of the
planet types---probably
the
silicate planet is meant to be pure
silicate of some average kind.
Such pure planet types probably
do not exist.
However, the pure planet types are
extreme limits of actual known/hypothesized
planet types that are rich
in the various materials.
Not all planet types are represented by
their extreme-limit avatar in the image.
For all currently known/hypothesized, see
Wikipedia: List of planet types.
The shown extreme-limit planet types
correspond to the following known/hypothesized
planet types:
- Iron planet: Where
Iron Man would feel at home.
- Rocky planet (AKA silicate planet):
Like our own fair planet Earth.
- Carbon planet:
These
planets/exoplanets
have more or maybe much more
carbon than
oxygen which is unlike the
rocky planets.
- Ocean planet (AKA waterworld):
These planets are probably NOT
mostly water, but have
a deep (maybe hundreds of kilometers deep)
planetwide ocean.
- Pure carbon monoxide (CO)
planet:
These planets may NOT
be the extreme limits
of any known/hypothesized
planet types.
- Pure hydrogen
planet: The extreme limit of
Gas giant planets.