Solar System regularities
- Inner, terrestrial planets
- 4 to 5 gm/cm3
- mostly rock, with some Fe Table 20-2
- density decreases away from sun
- Mercury has highest % of Fe, Mars the smallest % Fe
- outer, Jovian, giant planets
- about 1 gm/cm3
- mostly compressed H, He (water would be denser)
Division between terrestrial and giant planets -- the Ice Zone
- Below ~ 150 K, water-vapor condenses to ice
- this happens just inside the orbit of Jupiter fig.TA 45
- now solid ice added to dust composition
- ice 2-3 times the abundance of silicate rock
- planetesimals can grow more effectively
- dust sticks together via collisions
- like dust-bunnies collecting under the bed