United Press International
PHIL BERARDELLI, UPI Deputy Science and Technology Editor 06/06/2002
Jun 05, 2002 (United Press International via COMTEX) -- Thousands of miles beneath our feet, a giant nuclear reactor seems to be at work deep within Earth's core, and preliminary research suggests it may be the mysterious power source behind the planet's magnetic field and thermal energy, upon which all life on the planet depends for its survival, scientists told United Press International.
New data analyzed by J. Marvin Herndon, geoscientist and president of Transdyne Corporation, of San Diego, Calif., and Daniel F. Hollenback, a nuclear engineer and criticality expert at Oak Ridge National Laboratory, in Oak Ridge, Tenn., show the reactor -- a ball of uranium about five miles in diameter and located at the center of the core -- may have been operating nearly since the formation of the planet.
Herndon told UPI he has been searching for evidence of the deep-Earth reactor for more than a decade. In 1992, he published a series of papers on planet-sized nuclear reactors based on the discovery, 20 years earlier, of the remnants of a large, natural reactor located at the Oklo uranium mine in the Republic of Gabon in western Africa.
French scientists had discovered the Oklo reactor and determined it had operated for tens of thousands of years some two billion years ago, Herndon said, "but at the time of its discovery there were too many pieces missing to know what that really meant."
Nuclear reactors operating inside planetary cores might explain some mysteries that have puzzled scientists for years, Herndon said. For example, since the 1960s, astronomers have known Jupiter radiates nearly twice the energy it receives from the Sun. But up to now, they have not been able to explain the phenomenon in a way that makes sense, he said.
Earth's magnetic field is an even bigger mystery. Some mechanism obviously generates the field, and many scientists think the field is formed from fluid iron in Earth's main outer core acting like a giant electric dynamo, or motor. The geomagnetic field, as it is called, shuts down periodically and sometimes reverses its polarity -- with the North and South poles exchanging their magnetic charges.
The energy sources previously thought to power the dynamo are unable to decrease and then increase again, Herndon explained, so scientists have had to resort to assuming the dynamo mechanism is inherently unstable. But a nuclear reactor can decrease power output -- and even shut itself down -- and come back to life again, increasing to its full operating power, he said.
Current knowledge of the structure of Earth's interior is derived mainly from seismic data and chemical analyses of common meteorites, Herndon continued. Based on that data, scientists estimate about 30 percent of Earth's mass comprises an outer core, he said, which is thought to consist of iron and maybe one or more lighter elements such as sulfur.
The solid inner core is much smaller -- less than 2 percent of Earth's mass.
Still, current popular geophysical models cannot explain, from an energy standpoint, a planet-sized magnetic field that operates like Earth's -- with its varying power levels and periodic shutdowns, Herndon said.
Herndon said he received a major insight when he studied a different type of meteorite. Enstatite chondrite meteorites, as they are called, have chemical compositions similar to Earth's interior. Unlike more common meteorites, enstatite chondrite meteorites contain most of their uranium in the part of the meteorite that corresponds to Earth's core.
It was one of the clues Herndon needed, he said. Uranium is the heaviest natural element. It makes sense that, over time, solid uranium particles would rain out from Earth's fluid core at high temperatures. Because of their high density, they could collect at the very center of the Earth. After enough uranium collected together, a nuclear reaction would begin, and that appears to be what happened very soon after the formation of the planet.
In 1997, Herndon teamed up with Hollenbach at Oak Ridge. The laboratory has unique computer programs that can analyze the performance of different types of nuclear reactors.
"Dan showed me those numerical simulation programs could be applied to a nuclear reactor at the center of the Earth," Herndon said. "We used data about the uranium content from the meteorite discoveries to generate simulations at varying power levels."
A highly persuasive clue arrived in the form of physical evidence of a nuclear reactor at Earth's core. Recently analyzed samples of lava rock from deep-source volcanic "hot spots" in Hawaii and Iceland contained tiny amounts of the isotopes helium-3 and helium-4.
Although scientists have known about the helium-3 for some time, they have thought it was left over from Earth's formation some four-and-a-half billion years ago. But no known physical process could produce helium-3 except for nuclear fission, Herndon said, and the proportion of the two helium isotopes matches the prediction of the Oak Ridge simulation. This is strong evidence that the geo-reactor is at work, he said.
Based on the simulations, and the helium evidence, Herndon and Hollenbach theorize a five-mile-wide ball of uranium has been operating as a nuclear reactor for about 4.5 billion years. Its output is an awesome 4 million megawatts. Much of the energy it produces is heat, and that might be what powers the mechanism that produces the geomagnetic field, Herndon said.
Perhaps more interesting, the Oak Ridge programs suggest the reactor is a breeder -- that is, it actually produces more nuclear fuel than it consumes, which is why it has been able to operate over a time frame that spans nearly the entire existence of the planet. In addition, the reactor's power level varies in intensity over time and it shuts down periodically.
A nuclear reactor continuously produces lighter elements, such as strontium or barium, as the uranium fuel fissions -- or splits apart. Those fission fragments would begin to absorb neutrons -- the subatomic particles naturally emitted by the fissioning uranium and responsible for the chain reaction -- thereby preventing them from splitting other atoms.
"One might imagine instances in which the rate of production of fission products exceeds their rate of removal by gravitationally driven diffusion," Herndon wrote in a recent paper on the subject. If so, he explained, "the power output of the geo-reactor would decrease and the reactor might eventually shut down, thereby diminishing and ultimately shutting down the Earth's magnetic field."
Over time, as the lighter elements moved away from the uranium core, the reactor would restart.
The research is "certainly going to be a major contribution to geophysics," Hatten S. Yoder, Jr., director emeritus of the Geophysical Laboratory of the Carnegie Institution of Washington, D.C., told UPI. "They have developed an explanation for (Earth's) magnetic field and the fact that you can turn it on and off."
One of the most remarkable aspects of the planetary core reactor, Yoder said, is "it only takes a (five-mile) ball of uranium. That's only 65 percent of all the uranium on Earth."
The reactor's existence, if proven, solves the problem of delayed geothermal cooling and explains the observed heat flow, Yoder said. Without a continuing power source, he said, the heat dissipation would have ended long ago. But "if you have a ball of uranium at the center, it would continue to put out heat."
Herndon said he next plans to search lava samples for traces of radioactive elements that might have been produced by the geo-reactor and be light enough to have escaped the core and reach Earth's surface. Lithium, beryllium, boron and neon are possibilities, he said.
"It's not an easy task because both rock data and nuclear data are needed, but it certainly is important," Herndon said.
Yoder agreed. "High-temperature and high-pressure experiments are needed to test the composition and melting characteristics of the core," he said.
By PHIL BERARDELLI, UPI Deputy Science and Technology Editor
Copyright 2002 by United Press International.
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