Structure Temperature Pressure

Saturn consists almost entirely of helium and hydrogen. Gas giant planets are thought to have accreted out of the solar nebula through collisions as a core of ice with a small component of rock, up to about 10 Earth masses, at which point the gas of the solar nebula began to be attracted to the protoplanets. Later differentiation may consist mainly of separation of helium and hydrogen.

Knowing that the planet must consist almost entirely of helium and hydrogen based on its density and the abundance of those elements in the solar system, models for the planet's interior can be made based on laboratory physics. The behavior of those elements can be predicted as pressure in the planet increases with depth. In the planet's interior, helium and hydrogen gas gradually become liquid with increasing pressure and depth. At a pressure of about 2.5 million atmospheres (250 GPa), hydrogen changes abruptly into a metallic state. In its metallic state the hydrogen atom's electrons flow freely among the nuclei, creating an electrically conductive region. Beneath the metallic zone probably lies a planet's dense ice-silicate core, thought to make up about one-third of its total mass and reach to about one-quarter of the planet's radius. Saturn's interior is thought to reach a pressure of 45 million atmospheres (4,500 GPa) and a temperature of about 22,000°F (12,000°C). Compare this to the Earth, which reaches only 8,700°F (4,800°C) and 3.5 million atmospheres (360 GPa) in the inner core.

The density of Saturn is low, consisting as it does mainly of helium and hydrogen. The shallow parts of the planet's temperature profile can be measured through stellar occultation: As a star's light is eclipsed behind Saturn, its light is extinguished gradually by the increasing density of Saturn's atmosphere. The rate of extinction of the star's light yields information on the density of the atmosphere, which in turn can be related to temperature (the higher the temperature, the less dense the atmosphere). Spectra obtained from a known constituent in the atmosphere, such as methane, can also give temperature information.

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