The solar system is shaped like a disk

• The solar nebula, from which the solar system bodies formed, began as a large, hot ball of gas and dust

• What role did gravity play in shaping the solar system?

• Why is the solar system shaped like a disk, rather than a sphere?

• Most planetary orbits fall into a single plane

• All planets revolve in the same direction (counterclockwise, viewed from the North pole)

• Most planets rotate in the same direction (counterclockwise, viewed from the North pole)
  • Venus   –   backwards!
  • Uranus   –   sideways!
  • Pluto   –   sideways!

• Why do a few of the planets exhibit anomalous orbits?

The obliquity (axial tilt) of the planets. [NASA, Calvin J. Hamilton]

What are planets made of?

• Sugar and spice, and all things nice?

• Gas and dust, and things that rust?

• Do different planets have different composition? Why, or why not?