section_path: Climate/Internal heating
section_name: Internal heating
paragraph_text: Internal heating
  
  Neptune's more varied weather when compared to Uranus is due in part to its higher internal heating. The upper regions of Neptune's troposphere reach a low temperature of 51.8 K (−221.3 °C). At a depth where the atmospheric pressure equals 1 bar (100 kPa), the temperature is 72.00 K (−201.15 °C). Deeper inside the layers of gas, the temperature rises steadily. As with Uranus, the source of this heating is unknown, but the discrepancy is larger: Uranus only radiates 1.1 times as much energy as it receives from the Sun; whereas Neptune radiates about 2.61 times as much energy as it receives from the Sun.
  
  Neptune is over 50% farther from the Sun than Uranus and receives only ~40% of Uranus's amount of sunlight; however, its internal energy is still enough for the fastest planetary winds in the Solar System. Depending on the thermal properties of its interior, the heat left over from Neptune's formation may be sufficient to explain its current heat flow, though it is harder to explain Uranus's lack of internal heat while preserving the apparent similarity between the two planets.