Stevenson's tongue-in-cheek idea about sending a probe into the earth includes the use of nuclear weapons to crack the Earth's crust, simultaneously melting and filling the crack with molten iron containing a probe. The iron, by the action of its weight, will propagate a crack into the mantle and would subsequently sink and reach the Earth's core in weeks. Communication with the probe would be achieved with modulated acoustic waves.[1][2] This idea was used in the book Artemis Fowl: The Opal Deception.