As the planets in our Solar System get further away from the Sun, they generally get colder. So what is the coldest planet of our Solar System. That would be Neptune, the 8th and final planet in the Solar System. If Pluto was still a planet, it would be colder, but now it's Neptune.May 28, 2010
Neptune is located 4.5 billion km from the Sun, on average, and it receives a fraction of the sunlight that the other planets receive. In fact, even though it’s only a little further from the Sun than Uranus, it sees only 40% of the solar radiation received by Uranus.