1. Why do we have a satellite?
Origin
Why do we have a satellite?
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2. Historically Earth formed at the same time as the Moon
in the same place as we now find them
from the same raw materials
simplest theory
Problems
Earth is iron rich (large core)
Moon is iron poor (small or no core)
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3. Earth is rich in volatiles Moon is poor in volatiles Conclusions
water
Moon is poor in volatiles
no water
Conclusions
Theory cannot work
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4. Second theory Earth formed first rotating very fast a bulge developed
and a large piece of the Earth was thrown out and became the Moon
whole was the Pacific Ocean
idea of George Darwin (son of Charles D)
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5. Problems Theory cannot work Pacific Ocean is not permanent
not enough angular momentum (Earth should be spinning much faster than it is)
unlikely that the debris would form a satellite around Earth
Theory cannot work
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6. Third theory Moon formed elsewhere in solar system
Earth captured Moon as it passed
could explain the difference in chemistry
Problems
M and E are similar isotopically
not enough angular momentum
difficult to capture a large object
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7. Results after Apollo No explanation of how the Moon could have formed
Therefore, the Moon cannot exist (joke)
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8. More recent ideas Earth formed by itself
very large impact of another body
debris is mix of Earth and this other body
debris is very hot (no volatiles left)
debris is poor in iron (iron already in the core)
accretion takes place to form the Moon
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9. numerical simulations show that it could work
Sounds bizarre but
numerical simulations show that it could work
due to Hartmann and Davis, 1973
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