Core Issues

10/28 - 11/3
by C. Zaitz

I look up a lot, but right now my mind is on core issues, like what is at the core of our home planet. There has been conflict about this very question in the past. In the 17th century, the famous comet hunter Edmund Halley had a theory that the earth was actually hollow, and thought the core was luminous and filled with gas. Where did he get such a bright idea? From none other than his contemporary scientist, Isaac Newton. Newton had calculated the density of the earth, and had found that the center of the earth must be at least twice as dense as the surface. But he also calculated the density of the moon, and mistakenly found it much denser than the earth. Since there was no reason to suggest that the moon was made so much differently than the earth, Edmund Halley sought to explain the difference by suggesting that four-ninths of the earth was empty. He imagined the inner sphere inhabited by throngs of beings, as were all the planets of the solar system. He even had a portrait painted of himself as Astronomer Royal with a diagram of his hollow- shelled earth, forever immortalized. Luckily his comet became so famous that for the most part people have forgotten this aspect of his work. Some folks, however, took the idea of the hollow earth and elaborated, so vestiges of the theory still haunt society today.

Rather than being hollow at its core, Earth is actually quite dense. It is a rocky conglomeration, like the other inner planets, very close in nature to its sister, Venus. Earth and Venus are like twins, separated at birth. Venus has a different disposition than her sister. She’s very hot, with an atmosphere that would crush and melt any visiting earthlings. Earth is more subdued, and more gracious to the living beings that inhabit her outer skin.

Underneath the harsh exterior, Venus has a dense metallic core, similar to earth, with perhaps a liquid outer core surrounding it. On earth, this rotating liquid core generates our strong magnetic field, allowing us to navigate with compasses and protecting us from killing radiation from the sun. Venus seems to be lacking a magnetic field, though her makeup is similar to the earth. The difference may lie in the fact that Venus rotates slowly, and retrograde to the rest of the solar system. The slow rotation may not provide enough energy to generate a magnetic field.

So how do we know about the cores of the planets? On earth, no one has been more than 7.5 miles down. That’s not very far, considering that it would be a journey of 4,000 miles to reach the center. Most of what we know about the interior of the earth comes from seismic data. We can measure how fast earthquake shock waves travel through different materials, and estimate the depth and make-up of earth’s layers. That is how we found out about the liquid outer core of the earth. Seismic data doesn’t tell us everything, but it does rule out a society of folks living in a hollow earth.

As you ponder life at the center of a planet, you can spy Venus by looking toward the sunrise. She’ll be winking at you from the south eastern morning sky.

Until next week, my friends, enjoy the view.