FRED ANSWERS YOUR QUESTIONS

Q: In Diamonds are a world’s best friend (AG 145), you say planets were formed by electrostatic attraction of dust and subsequent collisions of protoplanets. If so, how are the layers and molten core of Earth explained? Arnav Mathur, Concord, NSW

A: I should have clarified: electrostatic attraction just starts off the process; the main agent of planet formation is gravity. As the mass of a protoplanet increases, so does its temperature, due to the energy of the colliding objects. As it becomes molten, heavier materials, such as iron, sink to the centre due to their own gravity. On Earth, residual heat (assisted by nuclear fission) keeps the outer core molten, while the inner core is solid due to the enormous pressure it is under.