Outer Planets & Debris, Page 14: [Previous Page] [Next Page] [Class Home Page] Textbook pages 272 - 278
  • Everything (Sun, planets, asteroids, comets) were created about 4.5 b.y.a.

  • The material making up the Solar System came from a single mostly homogeneous cloud. This material collapsed due to its own gravitation, via Helmholtz contraction (slowed by the outward pressure created by the contraction heat).

  • The matter rotated in a flattened plane, splayed out in a disk due to conservation of angular momentum.

  • With time, material not falling to the central Sun would either be thrown out of the system or begin to collect and build up planetesimals.

  • At safe relative distances, planetesimals built up to form the planets. Movie
    Why are the planets so different chemically?
    Differing distances (temperatures) from the Sun allowed for the differing chemistries that would go into making the planets. Planets near by were formed in much higher temperatures, boiling off their lighter elements (H, He), and leaving behind rocks of metals and silicates. Very distant planets were formed in such a cold environment to have formed water, ammonia and methane ices (like the distant comets).