Earth and Space Science / Unit 9: The Solar System
9.1 Formation and Structure of the Solar System
Notes
The solar system formed about 4.6 billion years ago from a rotating cloud of gas and dust (the solar nebula) that collapsed under gravity.
- Most mass gathered in the center and became the Sun. The rest flattened into a disk.
- Planetesimals collided and grew into planets (accretion).
- Inner planets formed from rock and metal; gas giants formed beyond the frost line, where ice could condense.
- The astronomical unit (AU) is the Earth-Sun distance, about 150 million km. Sunlight takes about 8 minutes to reach Earth.
- Example: Jupiter is about 5.2 AU from the Sun, so about 780 million km ($5.2 \times 150$ million).
Practice
The solar system formed from:
The solar nebula theory.
One astronomical unit is the average distance from:
About 150 million km.
Why are the inner planets rocky?
Ices and gases could not condense close in.
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