The coldest planet is

Uranus is recognized as the coldest planet in the Solar System, holding the record for the lowest temperature ever measured at approximately -224°C (49 K) [t2][t7][t10]. Although Neptune is the farthest planet from the Sun, it is not the coldest because it possesses an internal heat source that radiates more energy than it receives [t6][t8]. In contrast, Uranus lacks this significant internal heat, causing its atmosphere to reach lower minimum temperatures than Neptune's average of -214°C [t5][t10]. While Pluto was historically considered the coldest when classified as a planet, its 2006 reclassification as a dwarf planet shifted the title to Uranus [t9]. Therefore, despite being closer to the Sun than Neptune, Uranus's unique atmospheric dynamics and lack of internal heat make it the most frigid planet [t6][t10].