Which is the coldest planet?

You might expect Neptune, the most distant planet, to be the coldest, but that title goes to Uranus. Its upper atmosphere has been measured at about −224°C (roughly 49 kelvin), the lowest temperature recorded on any planet in the solar system. The likely reason is that Uranus gives off very little internal heat, while Neptune radiates more than twice the energy it receives from the Sun. Uranus is also tipped over on its side, with an axial tilt of about 98 degrees, possibly after a giant collision long ago. Only one spacecraft, Voyager 2, has ever visited it, flying past in January 1986.