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Curious Kids: Why don’t the planets closest to the Sun melt or burn up?

While Mercury is indeed very hot, it is not hot enough to melt. NASA/JPL-Caltech, CC BY

Curious Kids: Why don’t the planets closest to the Sun melt or burn up?

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!


Can you tell me why the planets closest to the sun don’t melt or burn up, please? – Sophie, aged 6, Brisbane.

Hi Sophie. That’s a good question.

The planets closer to the Sun than the Earth are indeed hotter than the Earth is. But that still doesn’t make them hot enough to melt the rocks that they are made from!

Mercury is the small, rocky planet nearest the Sun. The side that faces the Sun has a temperature of around 430℃. Remembering that 100℃ is the temperature at which water boils, that make 430℃ very hot indeed. In fact, it’s hot enough to melt some types of metal, like lead.

However, Mercury is not made of lead. It is made of rocky materials that have melting points above about 600℃.

So while Mercury is indeed very hot, it is not hot enough to melt. And certainly not hot enough to boil or turn into gas.


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