Now, back to the solar system. You all know about gravity, by which any massive body has an attraction for nearby objects which varies as the inverse square of the distance between the objects. This is a very weak force. It only becomes significant when at least one of the bodies is very massive. (Two people have very little gravitational attraction for each other, but each does have a significant attraction to the earth due to its huge mass.) The sun has an immense mass. Most people think of all the planetary movements as simply the effect of the gravitational attraction of the sun. In most people’s thinking, an orbit is stable when the gravitational force pulling toward the sun equals the centrifugal force away from the sun caused by the planet’s speed. They think that there are no other forces involved, or if there are, they are insignificant. Thus they believe that for any given orbital speed and mass, there is a stable orbital distance. However, there are other forces that complicate the issue.

The sun also has an electrostatic charge, as does each planetary body. Electrostatic attraction (called a coulomb interaction) is stronger than gravitational force, and in fact it has had a more significant part to play in the solar system than most people think. Many scientists believe that planetary bodies are electrically neutral, though they are not. But it is not possible to identify the forces of gravity separate from the coulomb forces without knowing the mass of each object. Coulomb forces behave just like gravitational forces, varying by the inverse square of the distance. So if we assume the coulomb force to be zero we can calculate a mass based on observed ‘gravitational’ attraction and everyone is happy. But in fact, everyone is wrong. The coulomb interaction between planetary bodies at this point in history is small – most of the charge has leaked off and there has been little recharging now that we have a benign system – so our mass calculations are close. But at creation and during the catastrophic era the coulomb interactions between planets were huge. Legends of many cultures record bolts of lightning from the planets, especially Jupiter and Mars.

A third force involved is solar wind, which puts a small but constant force on every planet, directly away from the sun. It also imposes a slight drag on each planet, slowing it down. Yes, you heard right, everything is slowing down and wearing out, just as the 2nd law of Thermodynamics promises it would. Forces of gravity also are slowly decaying, due to the loss of mass of the sun as its fuel is burned.

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