Are you feeling the chilly winds of winter where you live? When the long, dark days of winter begin to drag on and on, it can seem like Earth is the coldest planet in our Solar System. After all, it's not uncommon for many areas to experience below-freezing temperatures or even dips below 0º F on a regular basis.
But is Earth really the coldest planet in the Solar System? Astronomers will quickly tell you it's not even close. In fact, being the third planet from the Sun makes Earth one of the warmer planets, and that's a good thing for us humans. We wouldn't be able to survive some of the coldest temperatures to be found farther out in the Solar System.
Earth sits a comfortable distance away from the Sun, which allows humans and all the life forms on Earth to flourish. As you get farther away from the Sun, though, temperatures drop as the planets receive less and less of the Sun's warming rays.
Using your powers of deduction, you might already have a guess as to which planet in our Solar System is the coldest. If you're an old-school fan of the planets, you probably think Pluto is the coldest planet because it's the furthest from the Sun. And, with temperatures sometimes dipping to -387º F, you would be right, except that Pluto is now classified as a dwarf planet and no longer considered a "real" planet.
So that means the title of coldest planet would go to the "real" planet the farthest from the Sun, right? Well, while that makes sense, you'd only be partially right. It depends upon how you define "coldest."
With Pluto out of the race, the farthest "real" planet from the Sun is Neptune. Neptune and its neighbor, Uranus, are known as the "ice giants," since they are composed of huge amounts of rock and water, ammonia, and methane ice crystals. Uranus is, on average, 1.79 billion miles from the Sun, while Neptune is, on average, 2.8 billion miles from the Sun.
Being more than a billion more miles away from the Sun and receiving only about 40% of the solar radiation received by Uranus, you'd think Neptune would be much colder than Uranus. Scientists have been surprised to learn, though, that Uranus reaches colder temperatures despite the fact that Neptune, on average, is colder than Uranus.
For example, Neptune's average temperature is approximately -350º F. Despite being a billion miles closer to the Sun, the average temperature of Uranus is approximately -325º F. Even though Uranus is usually slightly warmer than Neptune, it does reach the coldest temperatures of any planet. The coldest temperature ever recorded for Uranus was -371º F!
Scientists aren't completely sure why Uranus reaches such cold temperatures despite being so much closer to the Sun than Neptune. Some speculate that it might have something to do with the planet's odd orientation.
Uranus seems to have been knocked on its side, perhaps by a massive impact way back when the Solar System was first forming. Scientists think the strange tilt of Uranus could cause heat from its core to spill out into space. Scientists also suspect that Uranus has a very active atmosphere that causes it to lose heat. By way of comparison, scientists think Neptune's atmosphere helps to retain the heat from its hot core, leading to warmer temperatures than would otherwise be expected.