The seventh planet from the sun, Uranus has the coldest atmosphere of any of the planets in the solar system, even though it is not the most distant. Despite the fact that its equator faces away from the sun, the temperature distribution on Uranus is much like other planets, with a warmer equator and cooler poles.
An icy atmosphere
Uranus is composed predominantly of hydrogen, helium and methane. Most of the lighter gases are found in the layered atmosphere. Temperature and pressure increase farther from the insubstantial surface (like most gas giants, the surface of Uranus is set where the pressure of the gas is equal to the pressure at sea level on Earth).
The dense troposphere, which contains the planet's clouds, is frigid at minus 243 degrees Fahrenheit (minus 153 degrees Celsius) to minus 370 F (minus 218 C), making it the coldest atmosphere in the solar system. Warmed by the sun and radiation from space, the troposphere has slightly higher temperatures of minus 370 F (minus 218 C) to minus 243 F (minus 153 C). The outer layer can get was hot as 1,070 F (577 C).
Tipped on its side
Unlike most planets in the solar system, which have their equators pointed in the direction of the sun, Uranus is tipped on its side. The planet faces one pole at a time toward the sun, gradually spinning over the course of its orbit until the other pole receives light instead of darkness. The strange orientation of the planet was likely caused by a collision soon after its formation.
The off-kilter tilt should mean that temperatures at one pole would be higher than at the equator, and significantly higher than at the dark pole. The higher temperatures should drive the planet's weather, as the rising warm air travels to the other pole and falls.
But weather on Uranus functions much as it does on other gas giants. Like Jupiter and Saturn, the planet has bands of zones and belts that orbit parallel to the equator, which is warmer than the poles. The warm temperatures that drive the planet's weather come from the interior of the planet, rather than from the sun. The significant distance to Uranus from the sun may play a role in why the planet's interior heat overpowers the faint light from the star.
A cool interior
Despite the fact that it powers the planet's weather, the internal temperature of Uranus is lower than other planets. Very little excess heat is radiated into space.
Unlike other gas giants, Uranus most likely boasts a rocky core rather than a gaseous one. Temperatures inside it may reach 8,540 F (4,727 C), which sounds warm but is cooler than other planets — Jupiter's core may reach 43,000 F (24,000 C).
— Nola Taylor Redd, SPACE.com Contributor
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