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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12$\begingroup$ 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 KochanskiJun 21, 2019 at 6:28
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$\begingroup$ Oh, okay! I have seen some people say that it's true, so I guess that fulfills part b. $\endgroup$– GoingFTLJun 21, 2019 at 19:07
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$\begingroup$ 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 SherwoodFeb 13, 2020 at 7:12
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2 Answers
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To have an asteroid belt with the mass of a planet, asteroids would have to be much more massive or be much more closer apart from each other. Either of these will likely cause the asteroid belt to become a new planet.
Rocks in Saturn's rings are also very close apart, but they are not forming a new moon because of the Roche limit, and if some chunks of rings happen to merge they will be pulled apart again, while for the asteroid belt it is not true because it is much further from its parent body (the Sun).
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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.
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$\begingroup$ 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. $\endgroup$ Jun 21, 2019 at 13:11
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3$\begingroup$ 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. $\endgroup$ Jun 21, 2019 at 14:40