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Van Flandern was on Coast this week with his exploding planet hypothesis. The asteroids and the other pieces that we see as meteorites seem to have been part of a planet that broke apart. It's an old idea, except for the part where Mars was a moon of this exploded planet. Perhaps this exploded planet was a gas giant, too, and all that is left is pieces of the rocky core. It's at the distance-from-the-sun junction where rocky planets and gas giants meet.

Perhaps this exploded planet was a gas giant, too, and all that is left is pieces of the rocky core. It's at the distance-from-the-sun junction where rocky planets and gas giants meet.

I think I heard somewhere that the total mass of the asteroid belt is only about 1/4th of a planet, debunking the "exploded planet" theory.

Another interesting theory is Bode's Law, that the orbital distances of the planets are roughly 4+3x2^n where n is the position in the sequence (divide by 10 to get Astronomical Units). Mercury (4)/10 = .4AU (36MM miles), Venus (4+3x2^0)/10 = .7AU (67MM), Earth (4+3x2^1)/10 = 1AU (93MM), Mars (4+3x2^2)/10 = 1.6AU (141MM), Ceres (4+3x2^3)/10 = 2.8AU, Jupiter (4+3x2^4)/10 = 5.2AU (483MM), Saturn (4+3x2^5)/10 = 10AU(886MM), Uranus (4+3x2^6)/10 = 19.6AU(1,783MM). The "law" breaks down after Uranus. The intersting thing is that the asteroid belt fits right where the next planet ought to be.

-PJ

Van Flandern was on Coast this week with his exploding planet hypothesis. The asteroids and the other pieces that we see as meteorites seem to have been part of a planet that broke apart. It's an old idea, except for the part where Mars was a moon of this exploded planet. Perhaps this exploded planet was a gas giant, too, and all that is left is pieces of the rocky core. It's at the distance-from-the-sun junction where rocky planets and gas giants meet.

The asteroid belt has an estimated total combined mass of less than 1 tenth of the Earth’s moon. Jupiter also has a profound effect on the asteroid belt. Since Jupiter has a semimajor axis of 5.2 AU (I AU is the distance from the Sun to the Earth) it has an orbital period of 11.86 years. Since the asteroids are not all at the same distance from the sun, some of them have an orbital period of one half of Jupiter. This puts that asteroid in a 2:1 orbital resonance with Jupiter. The result of this resonance is gaps called Kirkwood’s gaps. So here is the rub; why did not these asteroids form a planet? The reason is the gravitational force of Jupiter. It perturbs the asteroids giving them random velocities relative to each other. Another effect of both Jupiter and the Sun on the asteroid belt is a group of asteroids that both precede and follow Jupiter in its orbit by 60 degrees. These asteroids are known as the Trojans.