Solar System Structure and Origin

Key Concepts:

  1. What are the key characteristics of our Solar System?
  2. What do they tell us about the origin of our Solar System?
  3. How do astronomers discover other solar systems?

Four Major Characteristics of the Solar System

  1. Large bodies in the solar system have orderly motions.

  2. Planets fall into two main categories:

  3. Terrestrial Planets

    • smaller size and mass
    • higher density (rocks and metal)
    • solid surface
    • few moons and rings
    • closer to the Sun

    Jovian Planets

    • larger size and mass
    • lower density (hydrogen, helium)
    • no solid surface
    • rings and many moons
    • farther from the Sun
  4. Swarms of asteroids and comets populate the solar system.
  5. Notable exceptions to these trends stand out (unusual rotation axis tilts, large moons, unusual orbits).

Formation of Solar Systems

Solar Nebular Theory

  1. Cloud Collapse:

  2. Formation of Protoplanetary disk:

  3. Growth of planets:

Observational Clues

Stars are born in the dusty gas clouds. Driven by gravity, denser parts of the cloud collapses further to form "cores". The picture shown on the left is a false color HST image of a Galactic nebula called M16.
As the gas core collapses on itself due to its own weight, a disk of gas and dust is formed. Gas and dust falls in so quickly with so much energy that sometimes a jet of material is seen being shot out. (Pictures shown on the left are false color HST images of nearby young stellar systems.)
Sometimes strong winds and shocks from the nearby young stars can "blow out" the dusty cover of the young solar systems and reveal the remnants of the forming solar system. (Pictures shown on the left are false color HST images of young stellar systems being revealed by the ionizing radiation of the luminous neighboring young stars in Orion Nebula.)
When the solar system is finally formed and dust has cleared, remnants of the formation process and outlying material in the solar systems (such as "Kuiper belt objects" and "Oort clouds") can be found surrounding the systems. (Picture shown on the left is a false color image of a dusty disk seen around a nearby star named Fomalhaut, imaged in submm/infrared light at James Clark Maxwell Telescope on Mauna Kea, Hawaii.)
Remnants of the solar system formation can also be seen in visible or infrared light around some of the nearest stars when the bright light from the central star can be blocked out. (Picture shown on the left is a false color image of a dusty disk (rocks and ice chunks?) seen around a nearby star named beta Pictoris, imaged at European Southern Observatory.)

Planetary Diversity

Should all planetary systems be like our?

What variations should one expect?

Detecting Planets in Other Solar Systems ("Extrasolar Planets")