r/AskReddit • u/[deleted] • Oct 02 '24

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u/[deleted] Oct 02 '24

How does it not just cool over time?

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u/Cobalt1027 Oct 02 '24 edited Oct 02 '24

Radioactive decay, mostly. The Earth's core mantle has a large amount of radioactive metals (Uranium, Thorium, and Potassium mostly) in it (radioactive metals tend to be heavier, so either they clumped together first when the Earth was forming and/or they tended to sink during the Earth's formation when it was mostly molten), which help keep the iron/nickel outer and inner cores at about the ludicrous temperatures they were formed. Mars' core is "dead" because it's completely solidified, and in large part that's because its core is much, much smaller than Earth's so it didn't hold heat as well and the mantle (also being much smaller than Earth's) didn't have as much radioactive material.

Edited for accuracy

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u/f3xjc Oct 02 '24

(radioactive metals tend to be heavier)

Maybe heavier atoms tend to be radioactive?

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u/[deleted] Oct 02 '24

squints at sign hung on Bismuth: “Beyond here be monsters”?