The mystery of origin of the Moon has bothered the astronomers for hundreds of years. Big hopes were set on the landing of humans on the Moon. All Apollo missions brought more than half a ton of ground samples. Nowadays, forty years after the first landing on the Moon the answer for the question ‘where did the Moon come from?’ is as far as it was in times of Galileo.
Hypotheses were created and replaced with new ones because in some point they were too incompatible with other results of research.
The recently remaining hypothesis was presented by Robin Canup (SWRI, Boulder) in 1997 at the ‘American Astronomical Society’ conference.
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New Moon Theory
LASP Faculty member Robin Canup presented a new theory on how the moon formed at an American Astronomical Society meeting July 31, 1997. The current theory produced from Harvard University is that an asteroid the size of Mars hit the Earth ejecting mantel material into space which accreted to form our moon. Canup’s calculations however show that before the material could have accreted, quite a bit of it would have fallen back to the Earth. Hence there would not be enough material to form the moon. She figures that an asteroid three times the mass of the Mars sized object would be needed to create enough material to account for the current mass of the moon. But this theory has problems of its own. The angular momentum produced from the impact is far to great compared to the current value. So researchers are finding themselves re-thinking the theory of how the moon was formed.
‘The Daily Camera’; Boulder; July 28, 1997.
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The first problem of this hypothesis is, as we read, the fact that the Earth after such collision would rotate much faster than it does now. Other aspect of the ‘Giant Impact’ hypothesis is the fact that it doesn’t explain anything but contrary – it complicates the problem even more. The question “where did the Moon come from?” is only replaced with the question “where did the Impactor come from?”. If the considerations of Ms. Canup concern an object three times of mass of Mars, then it is one third of Earth’s mass. So we can no longer talk about an asteroid as the above text suggests. It is a medium-sized planet. From where would such a planet come to this point of the Solar System and why on such collision course with Earth, which apparently is needed by the hypothesis of Robin Canup. If it was a planet that was formed in the Solar System then why was it formed on such collision orbit? Why the collision with Earth would have taken place just after formation of this planet? This parts of which it was made should have fallen on Earth and Venus (or Jupiter) before the planet was formed.
If it was an object from the outside of the Solar System then why such similarity in the chemical composition of the Moon and the Earth?
One of the most important arguments against the Giant Impact hypothesis are the today’s parameters of the Earth’s orbit. Either the eccentricity (0.017) or the angle between orbit’s plane round the Sun and the orbits’ planes of other planets (max. 3°) don’t indicate that such catastrophe took place at all.
We do not find answers to all these questions in Robin Canup’s hypothesis.
Tadeusz Tumalski
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