What is the coldest planet of the solar system?

The solar system is pretty huge place, extending from our sun at the center all the way out to the Kuiper Cliff – a boundary within the Kuiper Belt that is located 50 AU from the sun. As a rule, the farther one ventures from the sun, the colder and more mysterious things get. Whereas temperatures in the inner solar system are enough to burn you alive or melt lead, beyond the "Frost Line", they get cold enough to freeze volatiles like ammonia and methane.