at the core of a star is a 
nuclear or sub-nuclear reation 
that creates gravity 
and certain energies
at the core of 
gas planets 
the same type of activity 
occurs with less magnitude

this causes the
region around 
the reaction 
to be a 
dense gas
at lesser magnitudes of 
 reaction 
the gases 
can become so dense 
we interpret them to be 
solidified or "solid"

certain core energies 
and
gases 
can penetrate 
the "solidified" shell
at even lesser magnitudes of the 
nuclear reaction that creates gravity
the gases
and
solidified crust 
are so dense that they contain 
all the energy within

the magnitudes of the 
core nuclear reactions
are probably dependant 
on its intial mass and energy
a planet like earth exists in a 
delicate balance of the 
reaction that creates gravity/energies
dense gases
and a
solidified crust.

beyond this balance is the very 
low density cold of interplanetary space
and the intersteller medium.