What makes Earth’s core hot? Why isn’t it just a cold blob made up of metal and minerals?
In: Earth Science
It’s hard for non-hot things to lose heat in the vacuum of space. Even with the so-very-cold 3 K deep space background. Because only radiation (glowing) works, not convection (not much there to move) or conduction (not much there to touch). And glow brightness, radiative loss, goes as the *forth* power of temperature. Half the temperature means 16 times less loss (2⁴). So cooling spacesuits is a challenge, because people generate heat, that needs to be gotten rid of, but not like a glowing red-hot temperature, that would radiate quickly away (suits boil off water instead). One non-realism in The Expanse is spacecraft not having *bloody giant* radiators to cool off their fusion engines.
The crust and mantle insulate the core, keeping Earth’s surface non-hot, keeping radiative loss low. If you exposed the core to space, it would initially cool down 10000x faster, being 10x hotter. Earth is cooling faster lately, because of more tectonics and thinner crust, since the breakup of supercontinent Pangaea. Like a mantle degree per 10 million years.
The heat loss to space is partially compensated for by new heat from radioactive decay of big atomic nuclei assembled in exploding star(s?) before the solar system formed. Before radioactivity was discovered, people were puzzled why the initially molten Earth hadn’t frozen yet, and so thought the Earth must not be very old. Earth was initially molten because slamming together big rocks makes for white-hot splashing – thus burnt-toast dinosaurs. With 4.5 billion years of half lives past, radioactive heating isn’t what it used to be.
The Sun will expand and melt the Earth again, before it has time to freeze solid. And then it will vaporize it.
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