In the past, the asteroid belt was thought to be the remains of a shattered planet. Of course, that was all pseudoscience, the mass of the asteroid belt being 4% of the moon. I've been wondering, what would happen if this did occur. What would an asteroid belt with around 50% of the Earth's mass be like? How often would asteroids hit earth? Would it influence Mars?

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    $\begingroup$ A good question! But not really "pseudoscience". Like the Steady State Theory, it was a perfectly good scientific theory, open to test by experiment and observation. It was tested by experiment and observation, and found not to be compatible with them. Theories that turn out not to be true are successes of science, not failures. Pseudoscience is when a theory is (a) untestable, (b) has a continuing "after-life" after being refuted. $\endgroup$ – Martin Kochanski Jun 21 '19 at 6:28
  • $\begingroup$ Oh, okay! I have seen some people say that it's true, so I guess that fulfills part b. $\endgroup$ – GoingFTL Jun 21 '19 at 19:07
  • $\begingroup$ If I understand right, it's believed that the asteroid belt was much more massive, but most of it was flung out of the system by interactions with planets (or fell into planets). $\endgroup$ – Anton Sherwood Feb 13 '20 at 7:12

The mass of a planet? There probably was, billions of years ago, and perhaps still is, but the debris of this planet-in-the-making has been shattered and dispersed by impacts. We know from fragments which have struck the Earth that the planet which was forming there had grown large enough to have a molten interior where the heavy metals, mostly iron and nickel, had sunk to the centre and differentiated from the rocky mantle. A massive impact must have shattered this forming planet about 4 or 5 billion years ago, and the debris has become so dispersed that it is difficult to assess how much there originally was. Some was kicked out of the asteroid belt completely, the rest is still there but much of it so finely shattered and dispersed that we can't see it (the asteroid belt covers an enormous area, much larger than the orbit of the Earth-moon system).

The resulting absence of a body with substantial gravitational field to attract comets & other objects has enabled them to pass on by, perhaps to impact the Earth and inner planets. Bodes Law says here should be a planet there, but whether it would have been a Mars-sized planet or not, nobody knows. The differentiation of nickel-iron from the rocky material becomes hard to explain without a fairly substantial planetesimal there to separate them, and in our solar system at least, Bodes Law seems fairly reliable.

  • $\begingroup$ Certainly some of the material has been part of a larger body. It's not immediately clear if there was ever only one such body or if it was maybe several Moon or Pluto sized bodies. $\endgroup$ – Steve Linton Jun 21 '19 at 13:11
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    $\begingroup$ Since this contradicts the current scientific theories as quoted and referenced in places like Wiki, can you please provide recent, refereed studies which support this proposition. $\endgroup$ – Carl Witthoft Jun 21 '19 at 14:40

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