Your article neglects the most difficult problem associated with sending a probe to the vicinity of Earth’s core: sending the information back. Even a few feet of earth will stop conventional radio waves. Extra-low-frequency transmissions would do the job, but a transmission could take years.

Augusto Soux
San Diego, Calif.

David J. Stevenson of the California Institute of Technology in Pasadena envisions a probe that sends data via encoded vibrations at low frequencies. Sensitive detectors at Earth’s surface can pick up small seismic waves that would be produced by a 10-watt vibrating source, he notes. Over the course of a mission, the probe would send out about 100 million vibrations–enough to encode sufficient information about the deep-Earth environment .–S. Perkins The liquid iron channels already exist–in the form of active volcanoes.

Allan Morrison
Manitoba, Canada

There is a far more interesting way to get to the core than setting off hydrogen bombs and filling the crack immediately afterwards. A better method would be to drop a 100,000-ton hardened-iron mass shaped like a spear from a great height, like an orbit. This would go through the crust pronto. To get the spear in orbit, you simply go to the moon with a few robots and mine the needed iron. With a little acceleration, the iron is in orbit, and presto, you’re ready for action. Cheers.

Thor Olson
Redmond, Wash.

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