A scientist proposes sending a grapefruit-size communication device into the heart of the Earth by blasting a crack in the surface and pouring in a huge quantity of molten iron. The weight of the liquid metal would crack the Earth for more than 1,800 miles (3,000 kilometers), carrying the probe to the planet's core in about a week.
The probe would measure temperature, electrical conductivity, and chemical composition, and would beam back data as encoded sound waves to a surface detector.
David J. Stevenson of the California Institute of Technology in Pasadena outlines the plan in the May 16 issue of the scientific journal Nature.
"Planetary missions have enhanced our understanding of the solar system and how planets work, but no comparable exploratory effort has been directed towards the Earth's interior, where equally fascinating scientific issues are waiting to be investigated," Stevenson said in his paper. "I propose a scheme for a mission to the Earth's core, in which a small communication probe would be conveyed in a huge volume of liquid-iron alloy migrating down to the core along a crack that is propagating under the action of gravity."
The proposal might sound ambitious, but it's modest in comparison with the demands of space exploration, Stevenson said.
"We live on the Earth's surface, which divides what is above from what is below. The part above us, the rest of the universe, is mostly empty, mostly unknown The part below is crammed with interesting stuff and is also mostly unknown, despite its much greater proximity to us."
Stevenson calculated that the energy required to create the crack to launch the probe would be equivalent to a few megatons of TNT, an earthquake of magnitude 7 on the Richter scale, or a nuclear device such as those already possessed by many nations.
It may also be feasible to make use of existing favorable stress environments in the Earth and to avoid the use of nuclear devices, Stevenson said in his paper. "The technological challenge of initiating the crack should be less than that posed by the Manhattan Project," he said, referring to the code name for America's first atomic bomb.
According to Stevenson's calculations, it should be possible to send a probe all the way to Earth's core by combining several proven technologies with a few well-grounded scientific assumptions about the workings of the planet.
"We've spent more than [U.S.] $10 billion in unmanned missions to the planets," said Stevenson, who is the Van Osdol Professor of Planetary Science at Caltech. "But we've only been down about ten kilometers [6 miles] into our own planet."
The benefits to science would be significant, Stevenson said, because so little has been directly observed about the inner workings of the Earth. Scientists do not know, for example, the exact composition or even the temperature of the core, and what they do know is based on inferences about seismic data accumulated during earthquakes.
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