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Originally Posted by [url=http://www.badastronomy.com/phpBB/viewtopic.php?p=431470#431470
Project Orion[/url]]At about 19 grams per cubic centimeter, it is 1.6 times more dense than lead at the Earth's surface. But deep within our planet density depends only on atomic number and atomic mass. Uranium, having the greatest atomic number and atomic mass, would be the most dense substance in our planet and will ultimately end up at the center of the Earth.
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This is not necessarily true. Chemistry is not just density. If it were, the surface of the Earth would be blanketed by a layer of heavy carbon dioxide, leaving the lighter oxygen way over our heads.
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For twenty years planetary scientists, believing that they had considered and eliminated all possible planetary-scale energy sources, pronounced that the extra energy being radiated was from the original gravitational collapse some 4.5 billion years ago. When I started thinking about the problem around 1990, that explanation did not make sense to me.
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That is an important point.
