Saturn’s Internal structure

Saturn is termed a gas giant, but it is not entirely gaseous. The planet primarily consists of hydrogen, which becomes a non-ideal liquid when the density is above 0.01 g/cm3. This density is reached at a radius containing 99.9% of Saturn's mass. The temperature, pressure and density inside the planet all rise steadily toward the core, which, in the deeper layers of the planet, cause hydrogen to transition into a metal.

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Earth, but more dense.
Examination of the gravitational moment of the planet, in

combination with physical models of the interior, allowed French astronomers Didier Saumon and Tristan Guillot to place constraints on the mass of the planet's core. In 2004, they estimated that the core must be 9–22 times the mass of the Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions into gas with increasing altitude. The outermost layer spans 1,000 km and consists of a gaseous atmosphere.

Saturn has a hot interior, reaching 11,700 °C at the core, and the planet radiates 2.5 times more energy into space than it receives from the Sun. Most of this extra energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression, but this alone may not be sufficient to explain Saturn's heat production. An additional mechanism may be at play whereby Saturn generates some of its heat through the "raining out" of droplets of helium deep in its interior. As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves the outer layers of the planet depleted of helium. These descending droplets may have accumulated into a helium shell surrounding the core.