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To the Core

15 May 2003 (All day)
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Jules Verne Express. A geophysicist suggests a way to directly observe Earth's mantle and outer core, thousands of kilometers beneath the crust.

Proposals to send an observational mission to Earth's core have been set forth before, most famously by Jules Verne and even in the recent movie The Core. But their suggested methods have had about a snowball's chance of actually succeeding. Now a planetary geophysicist says that with a big bang and about a billion kilograms of molten iron, a probe could journey to the center of the Earth.

The key flaw of past proposals has been that they call for manned missions, says David J. Stevenson of the California Institute of Technology in Pasadena. Stevenson, in what he calls his own modest proposal, argues that an unmanned mission is the solution to surviving unimaginable pressures as a probe descends into the depths.

Stevenson calculates that a detonation of a few megatons of TNT--comparable to a magnitude-7 earthquake--could crack the outer crust just long enough to pour in molten iron. The mass of the metal would force open a crack, about a dozen centimeters wide, that would propagate downward at 5 meters per second. At that pace it would take less than an hour to travel through about 15 kilometers of crust, and then another week or so to pass through the underlying mantle. The trip would require pouring in about 100,000,000 to 10,000,000,000 kilograms of iron--within a week's production capabilities of the world's foundries.

The probe would be grapefruit sized and made of metal alloys with the same melting point as Earth's molten outer core. "It may not survive long once it reaches the core," Stevenson says, but before it expires, he calculates in the 15 May issue of Nature, it could send data back to the surface via sonar waves.

Don't expect the National Science Foundation to pony up right away--the iron alone would cost hundreds of millions of dollars. And even though getting permission to denote a nuclear bomb could be a bit tricky, the plan has its fans. "It would be easy to sneer at this," says Dave Walker, a petrologist at Lamont-Doherty Earth Observatory in Palisades, New York, "but to do so would be a mistake." The molten iron could possibly make it. But, he says, "for me the scientific show-stopper is the probe," which would be difficult to engineer, to both survive the intense conditions and send information back to the surface. Nevertheless, he "heartily endorses" the plan, or something like it, which he says might conceivably provide data on the composition of Earth's insides.

Related sites
David Stevenson's home page
The structure of Earth, from the U.S. Geological Survey
Bad Astronomy's review of The Core

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