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Saturn's Temperature: One Cool Planet

With an average temperature of minus 288 degrees Fahrenheit (minus 178 degrees Celsius), Saturn is a pretty cool planet. Although there are some small differences as one travels from the equator to the poles, much of Saturn's temperature variation is horizontal. This is because most of the planet's heat comes from its interior, rather than from the sun.

Cassini Saturn Storm
These red, orange and green clouds (false color) in Saturn's northern hemisphere indicate the tail end of a massive storm that started in December 2010. Even after visible signs of the storm started to fade, infrared measurements continued to reveal powerful effects at work in Saturn's stratosphere.
Credit: NASA/JPL-Caltech/Space Science Institute

Layers of gas

Saturn is mostly made up of hydrogen, with some helium. Gases such as sulfur, methane, ammonia, nitrogen and oxygen lie within the planet's atmosphere, creating colorful bands.

Temperatures in Saturn's atmosphere increase along with pressure the closer one travels to the center. As a giant gas planet, Saturn doesn't have solid ground; scientists set the surface of the planet at the point where pressure is equal to that of sea level on Earth.

Saturn contains three layers of clouds. The upper layers of ammonia ice have temperatures ranging from minus 280 F (minus 173 C) to minus 170 F (113 C). The next layer contains water ice, with temperatures from minus 127 F (minus 88 C) to 26 F (minus 3 C). Temperatures in the lower layers climb as high as 134 F (57 C). Pressures in this region equal those found a few miles under Earth's ocean.

When Voyager 2 traveled to the ringed planet, it found that temperatures near the north pole were about 18 F (10 C) colder than those found at mid-latitudes, a difference that may be seasonal.

Heating sources

Saturn contains a rocky core, 10 to 20 times the mass of Earth, which is surrounded by liquid metallic hydrogen. This massive core was likely the first part of the planet created, and it trapped gas as the planet formed. Moving out from the core, the liquid hydrogen becomes less metallic, gradually shifting into a gas the further one travels from the center of the planet.

The interior may reach temperatures of up to 21,000 F (11,700 C). Because the distance to Saturn from the sun averages 886 million miles (1.4 billion kilometers), most of the planet's heat comes from its core. Saturn radiates more than twice as much heat into space as it receives from the sun. Much of the heat is caused by the gravitational compression of the planet, but scientists theorize that some of it may come from friction created by helium sinking into the planet's interior.

— Nola Taylor Redd, SPACE.com Contributor

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