Let’s look inward for a few minutes not at our individual navels, but at the very core of our planet, Earth. And why not? Billions and billions of dollars are spent on exploring the heavens and rather little on understanding what lies beneath our feet.
Enter Dr. David J. Stevenson, the George Van Osdol Professor of Planetary Science at the California Institute of Technology (Caltech) in Pasadena, California. He has published what he calls "a modest proposal" to probe the Earth’s interior. Briefly, he suggests that a small data transmission device could be conveyed in a large volume of molten iron alloy along a crack in the mantle propagated by the action of gravity. When the probe reaches the core, perhaps after a week of travel, it would send high-frequency seismic waves to the surface where they would be sensed by a ground-coupled wave detector.
The science behind his idea is sound. A probe the size of a grapefruit would be sufficient to transmit data. The volume of iron alloy needed to transport a probe is readily available; he estimates a volume equal to between an hour’s and a week’s worth of the world’s foundry production. The density of the liquid iron alloy would be much greater than molten rock, hence gravity would pull it toward the Earth’s centre. Check out his proposal in detail at www.gps.caltech.edu/faculty/stevenson.
As an exercise in pure scientific enquiry, this is brilliant. We at CMJ wanted to know more, and contacted Prof. Stevenson. What, we wondered, could be done with the information gathered by the probe?
"You don’t do it for a practical reason," he responded. "You do it because it is part of being a human being to be fascinated by the world around us. You would learn about Earth composition and deep interior, essential information for understanding how Earth formed and evolved."
Perhaps it is a nave question, but we asked about the possibility of accidentally creating a new volcano when the Earth’s mantle is deliberately cracked.
"Unlikely," said Stevenson, "because the crack closes up behind and is overwhelmingly dominated by a fluid that wants to go down. The negative buoyancy of iron is enormous compared to the positive buoyancy of magma."
So if no immediate practical application for the information that might be learned about the Earth’s core, how serious can Prof. Stevenson be about his "modest proposal"?
"It’s deliberately outrageous with only a small probability of being successful," he allowed. "But the science behind it is sufficiently well-based that I’m hoping some people will think further about it."
So let’s get thinking. Our understanding of how mineral deposits form has been greatly aided by studying plate tectonics and undersea black smokers. These phenomena were virtually unknown 50 years ago. Fifty years from now the mineral industry might well wonder how we ever got along without an understanding of the Earth’s core.