The Origin of the Solar System

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The Origin of the Solar System

• Chapter 6

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Observational Constraints

• Motion
• all planets orbit Sun
• same direction same plane
• most rotate in same direction
• Chemical
• Jupiter Saturn
• same composition as Sun
• Other planets
• systematic decrease in density as distance
  increases

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Solar Nebula

• Start with rotating cloud of gas and dust
• Collapses because of gravity
• spins faster
• flattens into disk-shape
• gets hotter
• Sun forms in center
• Temperature decreases outward
• As nebula cools, gas condenses
• Forms solid particles (dust grains)

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Forming Planets

• Dust grains stick together
• form rocks
• Grow into planetesimals
• some still survive today
• asteroids
• comets
• Larger planetesimals attract smaller ones
  (gravity)
• Planetesimals accrete
• form protoplanets / planet cores
• initially cold
• Collisions become violent
• heating melts protoplanet
• differentiation occurs

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Forming Jovian Planets

• Snow line
• Location beyond which ices form
• Building blocks (solids)
• both silicates and ices
• Protoplanets / planet core
• grew larger
• gravity captured hydrogen helium
• composition similar to Sun
• gaseous accretion disk forms around planet
• Moons form in disk around planet

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Evolution of the Solar System

• Collisions dominate early-on
• produces early heavy bombardment
• comets collide with terrestrial planets
• Deposit volatiles that form atmosphere(water,
  carbon dioxide, etc.)
• Planets sweep up / throw out remaining
  planetesimals
• Ones thrown out
• Oort cloud
• Ones that remain
• Comets (Kuiper belt)
• Asteroids (asteroid belt)

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Planetary Evolution - Geological

• Internal heating leads to geologic activity
• volcanism, tectonics
• active worlds
• As core cools solidifies, activity slows,
  eventually stops
• e.g. Moon
• Earth, Venus large enough to still be active

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Planetary Evolution - Atmosphere

• Atmosphere formed by
• gases escaping from interior
• impacts of comets (volatile-rich debris)
• Fate of water depended on temperature (distance
  from Sun)
• Atmospheres changed chemically over time
• Life on Earth substantially changed the atmosphere