It was once thought that planets do not produce significant internal energy; they only absorb energy from sunlight and then re-radiating it into space. Then, in the late 1960s, astronomers discovered that Jupiter, pictured at left, radiates about twice as much energy as it absorbs from sunlight. Later, Saturn and Neptune were also observed to radiate prodigious amounts of internally generated energy.

The explanation proffered for two decades by NASA scientists, that the radiated energy was left over from planetary formation, did not make sense to J. Marvin Herndon, pictured at right, because Jupiter is 98% a mixture of hydrogen and helium, excellent heat transport media, and Neptune is only 5% the mass of Jupiter.

In a flash of inspiration, the pieces all fell into place, the lessons of Oklo began to make sense on a grander, planetary scale. Herndon worked out the physics, using Fermi's nuclear reactor theory, as Kuroda had done, and in 1992 published a scientific article entitled "Feasibility of nuclear fission reactors as energy sources for the giant outer planets" in Naturwissenschaften [1].

Herndon realized that, inside the giant planets, density of an element is a function almost entirely of atomic number and atomic mass, meaning that uranium would be most dense and would tend to concentrate at the planet's center by gravity. Billions of years ago, nuclear fission chain reactions could begin in the concentrated uranium and could continue into the present, as implied by Oklo observations, through fuel breeding reactions. Herndon also realized that, with planetocentric reactors, there is a natural mechanism for removing fission products, which if left in place could shut down neutron chain reactions; the fission products would be roughly half the atomic number and atomic mass as uranium and thus would tend to migrate outward as the uranium tended to migrate inward.

Initially, Herndon considered only thermal neutron reactors moderated by hydrogen for the giant planets, but soon realized that hydrogen was not necessary; planetocentric nuclear fission reactors would function quite well as fast neutron breeder reactors. That insight opened the door to the possibility of nuclear reactors at the centers of non-hydrogenous planets.

New advances often beget further advances. And that was the case here as can be seen by checking out other web-pages on this site: (click here) or (click here), for example, or, see [2-11].

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