page_title: Climate of Uranus
section_title: Circulation models
hierarchical_section_title: Climate of Uranus / Circulation models
caption_attribution_description: English: The greenish color of Uranus' atmosphere is due to methane and high-altitude photochemical smog. Voyager 2 acquired this view of the seventh planet while departing the Uranian system in late January 1986. This image looks at the planet approximately along its rotational pole.
context_page_description: The climate of Uranus is heavily influenced by both its lack of internal heat, which limits atmospheric activity, and by its extreme axial tilt, which induces intense seasonal variation. Uranus' atmosphere is remarkably bland in comparison to the other giant planets which it otherwise closely resembles. When Voyager 2 flew by Uranus in 1986, it observed a total of ten cloud features across the entire planet. Later observations from the ground or by the Hubble Space Telescope made in the 1990s and the 2000s revealed bright clouds in the northern hemisphere. In 2006 a dark spot similar to the Great Dark Spot on Neptune was detected.
context_section_description: Several solutions have been proposed to explain the calm weather on Uranus. One proposed explanation for this dearth of cloud features is that Uranus's internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low internal thermal flux. Why Uranus's heat flux is so low is still not understood. Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun. Uranus, by contrast, radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere. In fact, Uranus's heat flux is only 0.042 ± 0.047 W/m², which is lower than the internal heat flux of Earth of about 0.075 W/m². The lowest temperature recorded in Uranus's tropopause is 49 K (−224 °C), making Uranus the coldest planet in the Solar System, colder than Neptune.
  Another hypothesis states that when Uranus was "knocked over" by the supermassive impactor which caused its extreme axial tilt, the event also caused it to expel most of its primordial heat, leaving it with a depleted core temperature. Another hypothesis is that some form of barrier exists in Uranus's upper layers which prevents the core's heat from reaching the surface. For example, convection may take place in a set of compositionally different layers, which may inhibit the upward heat transport.
caption: The greenish color of Uranus's atmosphere is due to methane and high-altitude photochemical smog. Voyager 2 acquired this view of the seventh planet while departing the Uranian system in late January 1986. This image looks at Uranus approximately along its rotational pole.
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