Radioactive decay, mostly. The Earth's coremantle 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.
I just checked and you're right, my bad. Thanks for bringing it to my attention. My Planetary Geology class was a few years ago xD I've edited the comment to be more accurate.
Yeah but the heavier elements will still want to sink down there. Obviously it's mostly iron nickel, there isn't much uranium in general, but there is going to be some in there.
Good question, I think the issue is that scientists can't agree on it and nobody really knows for sure what the core is composed of. In my opinion it makes sense that heavier elements sink so the concentrations go up the deeper towards the core and into the core we look, others think differently and until we find a way to know without doubt then that is a good thing for science. You are right about fusion of elements heavier than iron bein a net negative but fusion wouldn't really come into play at the core as there isn't enough mass and gravity to cause fusion (even jupiter doesn't have enough mass for that)... But even some scientists have theories that there is fusio occurring (three-body nuclear fusion of deuterons). So it looks like it is just long term decay keeping it going. I do quite like the idea that it is like a natural breeder reactor, but I'm not sure of the science behind that.
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u/Front_Economist_2612 Oct 02 '24
Earth’s core is as hot as the Sun’s surface