Origin

1
Origin

• Why do we have a satellite?

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)

3

• Earth is rich in volatiles
• water
• Moon is poor in volatiles
• no water
• Conclusions
• Theory cannot work

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)

5

• Problems
• 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

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

7
Results after Apollo

• No explanation of how the Moon could have formed
• Therefore, the Moon cannot exist (joke)

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

9

• Sounds bizarre but
• numerical simulations show that it could work
• http//www.psi.edu/projects/moon/moon.html
• due to Hartmann and Davis, 1973