Trial by Combat, Tempering and Annealing, and the Ice Line

Today I Learned:
1) Trial by combat was a real thing. In many of the Christian germanic tribes of the dark ages, when disputes couldn't be settled in other ways, the disputing parties would fight to the death, and it was expected that God would let the innocent party survive. This probably worked really well as long as everyone believed that it worked, because most guilty parties would rather confess their guilt than enter a trial by combat and, presumably, die.

2) Tempering a metal (when you heat a metal pretty hot and cool it quickly) works by disrupting the crystal structure of the metal. This makes it harder for cracks to propagate through the metal -- if a spreading crack encounters a defect in the crystal structure, the defect can often just absorb the crack without propagating it.

Annealing, on the other hand (when you heat a metal pretty hot and cool it *slowly*) reforms the crystal structure, giving the metal greater strength at the cost of some brittleness.

3) Astronomy seems to be full of critical lines and points and distances. Today I learned that one of these is the ice line, which is an orbital radius (in our solar system, between Mars and Jupiter). The ice line is the minimum distance at which icy bodies can form without being vaporized over geologic timescales by the parent star. This is imporant because a lot of material in early solar systems is ice, so bodies forming outside the ice line can generally collect many more large objects. That's why all of the planets outside the ice line are so much bigger than the ones outside it -- all the juicy ice mass in the inner solar system was melted away before it could form any really big chunks.