Water
- There are many reasons to believe that embryos at 1AU were dry.
- Water came from near or beyond the snow-line.
- Convenient to divide this into three sources:
- Comets (~%50 ice) during Oort cloud formation. (Levison et al. 2001)
- Asteroids (Carbonaceous chondrites contain ~ 10% water).
. Most of our systems have big gaps between terrestrial and giant planets
..... 
asteroid belts.
- Planetary embryo(s) from asteroid belt (Morbidelli et al. 2000).
- Not all tp's are wet due to small number statistics. May explain Venus.
Extremes from our systems:
-
This system is dry.
Outer regions cleared before terrestrial planets form.
-
The blue planet is very wet.
- Indeed, this planet accreted 10 Oceans of water from comets alone!
Habitable?
