Key Observations

• Planets all orbit the Sun in the same direction

• Planets all orbit close to the ecliptic plane

• Sun spins in same direction as the planets orbit

Key Observations

• Small, rocky planets orbit close to the Sun

• Large, gas/liquid planets orbit far from the Sun

Terrestrial Jovian

• Distance from the Sun must affect the formation of the planets

Chemistry of the Solar Neighborhood

• Big Bang only produced H, He, Li, Be• Everything else has been produced in the life cycle of

stars– we’re all star dust!

Formation of Solar System• How might the distance from the Sun affect the formation

of planets?– Temperature

• temperature drops off with distance from the Sun

Temperature Profile

Formation of Solar System• How might the distance from the Sun affect the formation

of planets?– Temperature

• temperature drops off with distance from the Sun

• temperature of a gas is a measure of its average random speed– H & He existed as gas throughout the solar nebula– close to Sun H & He moving too fast (too hot) to be captured by planets– further from Sun H & He are moving slow enough to be captured by

planets– may be another reason why the outer planets are much more massive

than the inner ones– also explains why Jovian planets are made mostly of H & He whereas

the terrestrial planets have almost no H nor He

Formation of Solar System

Orion’s Nebula

Orion’s Nebula

Orion’s Nebula

QuickTime™ and a decompressor

are needed to see this picture.