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Why does Neptune have the fastest winds in the solar system?

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Clouds in Neptune's atmosphere — Neptune A photograph of clouds in Neptune's atmosphere, taken by Voyager 2 in August 1989. The view is from below the planet's equator, and north is up. The Great Dark Spot (center left) is 13,000 km (8,100 miles)—about the diameter of Earth—in its longer dimension. Accompanying it are bright, wispy clouds thought to comprise methane ice crystals. At higher southern latitudes lies a smaller, eye-shaped dark spot with a light core (bottom left). Just above that spot is a bright cloud dubbed Scooter. Each of these cloud features was seen to travel eastward but at a different rate, the Great Dark Spot moving the slowest.

Neptune exhibits the fastest winds in the solar system, reaching speeds as high as 700 meters per second (2,520 km, or 1,570 miles, per hour). While the exact mechanisms driving these extreme atmospheric conditions are not fully understood, scientists believe that the heat liberated from Neptune's interior plays a significant role in the planet's storminess and high wind speeds.12

Neptune emits more than twice the energy that it receives from the Sun, with this additional heat generated within the planet's interior. This internal heat, combined with the high winds, is thought to be responsible for the turbulence observed in Neptune's visible atmosphere. Although Uranus receives more sunlight than Neptune, it has little energy escaping from its interior, which may explain why Neptune's atmosphere is significantly more active.12