~ 4.6 billion years ago huge cloud of gas and dust started collapsing gravitationally
• As it collapsed it spun faster (conservation of angular momentum)
• No (or little) spin in the perpendicular plane
• Local clusters of dust and gas condensed - protosun formed first
• As material cooled, it condensed but never stopped rotating (rotates still since there’s nothing to stop it)
• Cores probably formed first, then attracted neighboring materials to form: planetesimal, protoplanet
• Probably not a unique system - there is increasing evidence for the existence of many other planetary systems
• Still an evolving theory
• All planets revolve around the sun in the same direction, but 3 have different directions of rotation (relative to the rest and to the direction of solar system motion) - Uranus, Venus, (Pluto)
The Terrestrial Planets: Mercury, Venus, Earth, and Mars
Relative Characteristics:
Planet Distance Period Radius Mass
Mercury 0.4 0.24 0.38 0.055
Venus 0.7 0.62 0.95 0.82
Earth 1 1 1 1
Mars 1.5 1.88 0.53 0.11
The Jovian Planets (gas giants)
Jupiter 5.2 11.9 11.2 318
Saturn 9.5 29.5 9.3 95
Uranus 19 84 4.0 14.6
Neptune 30 165 3.9 17.2
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