A Space Mission to the Earth's Core

A space mission to the Earth's Core is a project worth considering, argues David Stevenson of Caltech. Space, in this case, is not empty vacuum but dense rock, and the "spacecraft" is not of the Voyager class, but something like a grapefruit-sized seismic detector. It might work like this: With an explosive device of some kind, a downward going crack in the Earth would be initiated. Into this crack would be pored a large supply of molten iron containing the probe. The metal-filled crack would "fall" downward owing to gravity with a speed of about 5 m/sec and would close up behind as it went. As Stevenson points out, cracks in the Earth regularly relay magma from the lower depths to the surface. The probe, made of a high-melting-point alloy, would essentially communicate with the surface by sending out seismic waves. Stevenson advances the whole idea of directly probing the Earth's core not as a well formulated plan but as a provocation to scientific thinking. The mission, he allows, might cost as much as the unmanned space program but the scientific rewards could be high: learning more about energy sources (such as radioactivity) at great depths or the origin of hot spots (responsible, say, for creating the Hawaiian islands), and other material properties of the terrestrial core. (Nature, 15 May 2003; see website)