That's not the case for Earth though, is it? I had thought it was the tremendous pressures that kept the internal core molten. If it was radiation wouldn't it be enough to destroy us living in such close proximity?
I am barely qualified to call myself even an amateur astronomer, so sorry if I've misinterpreted anything.
edit: re-reading the passage, it sounds like it's a combination of both (bottom of p.245, 246).
> If it was radiation wouldn't it be enough to destroy us living in such close proximity?
Different kinds of radiation differ by how deep they penetrate matter. Simplifying a bit you can imagine that for every atom the radiation passes, there's a probability that it interacts / gets absorbed.
Radiation that passes thousands of kilometres of rock without interaction will have a rather low probability of interacting with a mere metre (or so) of human.
I am barely qualified to call myself even an amateur astronomer, so sorry if I've misinterpreted anything.
edit: re-reading the passage, it sounds like it's a combination of both (bottom of p.245, 246).