What are the models of Planetary Interiors?

MODELS OF PLANETARY INTERIORS 
Astronomers can construct a model of the interior of a planet from the planet's observed physical proper­ties and from theoretical arguments about the phys­ical laws governing its internal structure. What the astronomer needs to know is the planet's mass, den­sity, shape, rotation rate, gravitational- and magnetic­field strengths, surface temperature, and chemical composition. The model would naturally be more accurate if the astronomer had seismic data and rock samples, as we have for the earth and the moon.
Astronomers unfortunately do not have reliable numbers for each of the quantities listed above. Nev­ertheless, it is still possible to make some headway on determining the internal structure. The mean density of a planet-combined with its total mass, shape, and rotation rate - suggests its internal composition and distribution of mass. When constructing a model of a planet's interior, astronomers start by making the fol­lowing assumptions:

• Since the planet has a stable configuration (it is neither contracting nor expanding), the weight of matter due to gravity's pressing in­ward is balanced by the pressure from more central matter's pushing outward. 
• The pressure exerted by matter in the planet's interior depends on its density and tempera­ture in a more complicated fashion than is true for a simple gas. 
• The flow of heat out of the deep interior de­termines what the decrease in temperature will be out through the body of the planet. 
• Finally the matter in the interior can change from solid to liquid, can deform and flow un­der pressure, and can form different types of mineral compounds. 

Having constructed the model, astronomers can use it to predict how the temperature, pressure, and density vary from the planet's center to the surface. Planetary models essentially show us that, like the earth, the other terrestrial planets possess such lay­ered zones as core, mantle, and crust. Examples of some interior models for the terrestrial planets which should be consulted when reading the following subsections.