What is the Coldest Planet in the Solar System? A Chilling Surprise!

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Indeed, even our own cosmic backyard, the solar system is full of surprises! In fact, if you read our article, What is the Hottest Planet?, you likely received a truly unexpected answer. Well, then what is the coldest planet?

Simply put,Neptune is, by far the most distant planet form the Sun, isn’t it? And, the further a planet lies from the Sun, the cooler the weather, right? Actually, no, because the coldest planet in the solar system is Uranus! But, how could Uranus be colder than Neptune, which lies a whopping one billion miles further from the Sun?

Why is Uranus the coldest planet? It’s all in the atmosphere.

Coldest Planet in the Solar System Uranus on its Side

Photo: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

First of all, both Neptune and Uranus hold the title ice giants in our solar system. So, no matter what, both host truly frigid environments. Yet, Uranus remains the crowned record-holder, experiencing temps as low as -371º F! But, why is Uranus the coldest planet?

Actually, both planets host nearly identical atmospheres. Furthermore, both planets have substantial amounts of methane in their atmosphere, which is among the most potent greenhouse gases. In other words, methane loves to trap in heat trying to enter a planet’s atmosphere.

However, Neptune holds ever so slightly higher amounts of methane. Technically, around 3% versus Uranus’ 2%. Therefore, this slight increase in methane causes more heat entering Neptune’s atmosphere. As a result, Neptune stays consistently around 6 degrees warmer than Uranus!

Is Uranus the coldest planet because of an ancient collision?

Another possible explanation for Uranus’ record-breaking temperature comes from its distant past.

Long ago, it’s believed that Uranus suffered a wild collision with another space object. Unfortunately, astronomers are completely unsure as to what struck the ice giant. However, the collision ultimately left Uranus mysteriously flipped on its side.

Ultimately, Uranus’ core was violently disturbed during the impact. As a result, heat wildly spilled out into space. Now, without powerful internal heat being generated, Uranus host the record-breaking low temperatures we know today!