Planetary Geology - Introductory lecture - Solar System Formation.

Course mechanics:

Where do the various elements come from?

What do you want in a model for the formation of the Solar System (i.e. what needs to be explained)?

Broad outline for the nebular hypothesis for the formation of the Solar System.

• Formation of nebula (>1000 atoms/cm3) from diffuse gas of previous nova(s).
• Nebula collapse -> rotating and contracting disk, and heat production.
• Development of proto star, T-Tauri phase and associated 'wind'. t=100,000 yrs
• Coeval development of condensates in a particular spatial, temperature-dependent order.
• Gases mostly swept from inner solar system.
• Accretionary development of planets. Significant until 3.6 billion years ago.
• Development of small nebular disks around larger planets and creation of moons.
• Internal differentiation of the planets (ongoing).

Discussion questions for next time:

• Why do the inner and outer planets have different bulk compositions, and describe what differences you might expect in bulk compositions of the inner planets given the scenario for nebular formation of the planets given in your text?
• What determines the bulk composition of the nebular gas cloud?
• Velikovsky in Worlds in Collision proposed that Venus was an interloper, a comet that was captured into its present orbit (yielding the earth some atmosphere and rather wild times on the way). How might this idea be tested if the model for solar system evolution described in your text is anywhere near correct? Put another way - is this idea consistent or inconsistent with the model for solar system evolution given in your text?

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