So Near, and Yet So Far
We can directly observe the composition of the rings of Saturn - 850 million miles away - but we still can't figure out what lies at the center of our Earth - a mere 4,000 miles away! Traditional theory suggests it is a solid core of nickel-iron, surrounded by a liquid region of iron, nickel, and a mix of sulfur, oxygen and silicon. A more avant-garde postulate claims a literal nuclear reactor core of uranium and plutonium, surrounded by a molten core of iron, sulfur and silicon. Both dynamo models account handily for the Earth's magnetic field - including the cyclic variations. The greatest hole ever drilled, on Russia's Kola Peninsula, is only 7.5 miles deep, or less than 0.2% of the way to the center. In geophysicist Herndon's words, "That's roughly comparable to learning about Alaska by driving from St. Petersburg, FL to Tampa."