Neptune is over 1 billion miles (1.6 billion km) farther away from the Sun than Uranus, but the two planets are close in temperature: –365°F (-220°C) on Neptune; –355°F (-214°C) on Uranus.
This results from Neptune’s interior, which is not as solid as Uranus’s.
A partially fluid core will experience more movement than a solid core, and movement, friction, creates heat.
While Neptune is not hotter than Uranus, it is much warmer than expected, given its distance from the Sun.
