AST101H1 Chapter 8: Chapter 8_ The formation and age of the solar system
8.1 The Search for Origins
Four Criteria for a Successful Solar System Formation Theory (must explain the following)
1. _atterns of motion
2. Why planets fall into two major categories: small, rocky terrestrial planets near Sun and large,
hydrogen-rich jovian planets farther out
3. The existence of huge numbers of asteroids and comets and why these objects reside primarily in
regions called asteroid belt, Kuiper belt, and Oort cloud
4. General patterns while at the same time, making allowances for exceptions to general rules (e.g.
odd axis tilt of Uranus and existence of Earth’s large moon)
Nebular Hypothesis (now Nebular Theory)
Our solar system formed from the gravitational collapse of an interstellar cloud of gas called solar nebula
- Offered natural explanations for all four features of solar system
- Claims planets a natural outgrowth of star formation process, thus predicting that other planetary
systems ought to be common (which we know is true)
Origin
- Gas making up of solar nebula a product of billions of years of galactic recycling that occured
before Sun and planets were born
- Big Bang produced only two elements: hydrogen and helium
- Heavier elements produced by massive stars and released into space upon star death
- Then mixed with other interstellar gas forming new stars
- Only 2% of solar nebula, other 98% hydrogen and helium
Orion Nebula
- Interstellar cloud in which new stars are forming
- Contains protoplanetary disks named proplyds: disks of material from which planets form
Close Encounter Hypothesis
Planets represent debris from a near-collision between the Sun and another star
- Planets formed in blobs of gas gravitationally pulled out of Sun during near-collision
- Now discarded → could not account for either observed orbital motions of planets or near
divison of planets into two major categories
8.2 Explaining the Major Features of the Solar System
- Solar nebula collapse triggered by a cataclysmic event (e.g. impact of a shock wave from
explosion of a nearby star → supernova)
- Gravity continued collapse, strength increased as diameter of cloud decreased (inverse
square law with distance)
As solar nebula shrank, three important processes altered its density, temperature and shape
1. Heating: temperature increased as solar nebula collapsed → gravitational potential energy
converted to the kinetic energy of individual gas particles falling inward → collision of
particles led to thermal energy
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Document Summary
Our solar system formed from the gravitational collapse of an interstellar cloud of gas called solar nebula. Offered natural explanations for all four features of solar system. Claims planets a natural outgrowth of star formation process, thus predicting that other planetary systems ought to be common (which we know is true) Gas making up of solar nebula a product of billions of years of galactic recycling that occured before sun and planets were born. Big bang produced only two elements: hydrogen and helium. Heavier elements produced by massive stars and released into space upon star death. Then mixed with other interstellar gas forming new stars. Only 2% of solar nebula, other 98% hydrogen and helium. Interstellar cloud in which new stars are forming. Contains protoplanetary disks named proplyds: disks of material from which planets form. Planets represent debris from a near-collision between the sun and another star. Planets formed in blobs of gas gravitationally pulled out of sun during near-collision.
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