Coldest Planets In Solar System

Curious Kids: What is the coldest planet in the solar organisation?

(Paradigm credit: NASA images/Shutterstock)

This commodity was originally published at The Conversation. (opens in new tab) The publication contributed the article to Space.com'southward Expert Voices: Op-Ed & Insights .

Brad Gibson (opens in new tab) , Managing director of the Due east.A. Milne Middle for Astrophysics and Head of the Section of Physics and Mathematics, Academy of Hull

What is the coldest planet in the Solar System? — Sejal, aged seven, Bangalore, Bharat

The planets in our solar system are heated by the sun. Here on Earth, we are about 100 1000000 miles away from the sunday — a distance that provides the perfect temperature for life.

Y'all might think, and then, that the coldest planet in the solar system would be Neptune, as it is the furthest away from the sun's warmth. Neptune is an incredible 3 billion miles away from the sun.

Yet, the coldest planet is not Neptune, merely Uranus — fifty-fifty though Uranus is a billion miles closer to the sunday than Neptune. Uranus holds the record for the coldest temperature ever measured in the solar system: a very chilly minus 371 degrees Fahrenheit (minus 224 degrees Celsius), according to NASA (opens in new tab) . The temperature on Neptune is still very cold (opens in new tab), of course — normally around minus 353 degrees F (minus 214 degrees C) — only Uranus beats that.

Related: 25 weird and wild solar system facts

A composite image of Uranus shows both X-ray emissions and infrared emissions against an optical view of the planet. — A Hubble Space Telescope view showing Uranus surrounded by its 4 major rings and 10 of its 17 known satellites. (Epitome credit: X-ray: NASA/CXO/Academy Higher London/Due west. Dunn et al; Optical (HRC): W.Chiliad. Keck Observatory); Optical (VLT/HRC): ESO/VLT/Kirill Feigelman)

Knocked sideways

The reason why Uranus is so cold is cypher to do with its altitude from the dominicus. Billions of years agone, something big crashed into Uranus (opens in new tab) with then much force that it tipped the planet over onto its side. Uranus all the same rolls around the sun on its side today. The impact of the crash likewise let some of the heat that was trapped inside Uranus escape.

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Curious Kids is a serial by The Conversation that gives children the chance to take their questions about the world answered by experts. If you lot accept a question you lot'd like an expert to respond, send it to curiouskids@theconversation.com . We won't be able to answer every question, but nosotros'll practise our very best. (Image credit: The Conversation)

The heat inside planets is left over from when they were formed. Planets are made when smaller chunks of rock smash together, building the full planet piece by piece over many millions of years. Every time these rocks blast together, the planet gains a petty more than heat. If yous clap your hands together for a long time they will outset to experience hot — the same thing happens with planets.

Neptune wasn't hit past a huge asteroid like Uranus was, and so it has been able to hold on to more than of its heat.

You might also exist surprised to acquire that the closest planet to the sun, Mercury, tin also be extremely cold. While the side of Mercury facing the sun is more than than 750 degrees F (400 degrees C), the side facing away from the sun is near minus 328 degrees F (minus 200 degrees C).

The reason for this is that Mercury does non take any temper (opens in new tab), different Earth. An atmosphere like ours acts similar a blanket, holding oestrus in and spreading it all effectually. Because information technology does non have this blanket, the forepart side and the back side of Mercury tin can have very different temperatures.

Measuring temperatures in space

For some nearby planets like Mars, nosotros can send probes to written report the atmosphere directly from the planet'due south surface. Nevertheless, we haven't been able to do this for afar planets such as Neptune and Uranus.

Instead, nosotros have to work out how common cold they are by measuring their temperature from here on Earth. We do this by studying the calorie-free from the planet, which can tell us the types of atoms and molecules which brand up the planet's atmosphere. This information lets us know exactly what the temperature of the planet is: the atoms and molecules act as a kind of temperature "fingerprint" for the planet.

While these planets in our solar system are incredibly cold, there are even chillier places in the universe. The coldest of all is the Boomerang Nebula (opens in new tab), a cloud of dust and gas 30 million billion miles away from us. There, the temperature reaches minus 457 degrees F (minus 272 degrees C).

Zip in the universe tin can exist colder than minus 459 degrees F (minus 273 degrees C), considering at that temperature the tiny particles and atoms that everything is made of basically stop moving, and once that happens it'due south impossible to go colder. This temperature is known as absolute zero (opens in new tab). This means information technology is unlikely that we volition ever find anywhere in the Universe colder than the Boomerang Nebula.

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