The Solar System

• Our local solar system
• Planets
  • Terrestrial planets
  • Jovian planets
  • Our week has 7 days because there are 7 observable moving objects in the sky
    • The Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus
  • Our month is based on how long the Moon takes to complete a trip around the sky
    • Moonth
• Traveling at 230 km/s
• The nearest star to us is Proxima Centauri
• Objects in the solar system formed ~4.5 billion years ago

Mass of Members

• Masses of planets originally measured using Johannes Kepler's laws of planetary motion

Characteristics

• Orderly motion
  • Nearly circular orbits in the same plane
  • Everything is moving counter clockwise
  • Almost all spinning counter clockwise
• Asteroids and comets
  • Asteroid --> more rocky than icy
  • Comet --> more icy than rocky
• Exceptions
  • When astronomers have trouble explaining something, they often assume something hit it
  • Examples
    • Venus upside down
    • Uranus sideways
    • The Moon is relatively huge
      • Largest moon:planet ratio

Formation

• Took ~100 million years
• We have the rules
  • Johannes Kepler's laws
  • Isaac Newton's Laws of Motion
• Forces and interactions
  • Gravity
  • Angular momentum (Kepler's second law)
  • Particles heating up, moving faster, bumping into one another
• Can learn about formation by looking at patterns
  • All the planets lie in nearly the same plane
  • All the planets revolve around the Sun in the same direction
  • The Sun spins in the same direction about its own axis
  • It seems as though the Sun and planets formed together from the solar nebula
• Planet composition
  • Spectroscopic analysis --> which elements are present
  • Sun, Jupiter, Saturn --> similar elements
    • Hydrogen-dominated composition
  • Terrestrial planets and the Moon --> similar elements
    • Deficient in light gases and various ices that form from elements like oxygen, carbon, and nitrogen
    • Rarer heavy elements
  • Inner planets are made of elements that can survive heat
  • Outer solar system is much cooler so ice/gas can exist
  • Planets must form before materials get blown into outer space by solar wind
    • ISM --> interstellar medium

Steps

• Start with a blob or cloud of gas and dust
  • Must have rotation
• Begins to contract because of its own gravity
  • Or could have been hit by a shockwave
• Proto-sun forms
• Disk flattens and rotates faster
  • Accretion disk
    • Rotation slows collapse in the plane of rotation forming a disk
    • Smaller particles run into larger particles forming larger and large chunks
      • Planetesimals
    • Disk also heats up through gravitational contraction
      • Up to hundreds of Kelvin
    • Material near the centre is moving faster so temperature --> higher
• Sun turns 'on'
  • Starts shining
  • Removes gases from inner areas --> leaving dust and debris
• Gas planets can form farther Outer

Space Astronomy