Why do we have a satellite? Origin Why do we have a satellite? 4/9/02

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) 4/9/02

Earth is rich in volatiles Moon is poor in volatiles Conclusions water Moon is poor in volatiles no water Conclusions Theory cannot work 4/9/02

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) 4/9/02

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 4/9/02

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 4/9/02

Results after Apollo No explanation of how the Moon could have formed Therefore, the Moon cannot exist (joke) 4/9/02

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 4/9/02

numerical simulations show that it could work Sounds bizarre but numerical simulations show that it could work http://www.psi.edu/projects/moon/moon.html due to Hartmann and Davis, 1973 4/9/02