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Asteroid Belt Formation and the Origin of Earth's Water (cont)
But it now looks like the asteroid belt never contained objects as massive as an embryo.

The asteroid belt needed to be very massive for
embryos to form.
- But this is inconsistent with the survivability of Vesta
  and small basaltic asteroids.
- There could not have been a lot of mass after 3 Myr.
- But the model requires water to be delivered > 10 Myr.
Embryos did not excite the asteroid belt.
- The eccentricity distribution is too smooth.
- It predicts a thermalized ratio of e and sin(i) of ~2, which is not observed.