1. Chapter 4: The Solar System Comets Comets are described as “dirty” snowballs They are fragile conglomeration of frozen ices and dust When they get close to the sun the ices begin to melt and jets of gasses escape from the nucleus caring dust with it. Comets shine by reflected solar light Finally comets are divided into two large classes of short-term and long term

2. Chapter 4: The Solar System While the nucleus of a comet may be only a few km in size The coma can be over 100,000 km in size and the tail can be up to 1 AU in size

3. Chapter 4: The Solar System Comets usually form two different tails: gas and dust The gas tail points directly away from the Sun while the dust tail tends to follow along the orbit

4. Chapter 4: The Solar System Halley’s comet was the first comet discovered to be periodic.

5. Chapter 4: The Solar System While the Kuiper belt may be the source of short period comets, while the Oort cloud appears to be the source of long-period comets.

6. Chapter 4: The Solar System Meteoroids There are two basic types of meteoroids: random, shower The random kind which can be observed on any clear night (few per hour) are probably left over interplanetary debris.

7. Chapter 4: The Solar System Comets leave a dusty trail behind them and if their orbits intercept the Earth’s then me get meteor showers (dozens per hour) when the Earth slams into them. Meteors enter the Earth’s atmosphere at such high speeds that friction heats them to white-hot temperatures and they burn up. Most meteors are the size of gravel and burn up in the atmosphere. It takes a first sized object to reach the ground.

8. Chapter 4: The Solar System

9. Some do hit the ground

10. Chapter 4: The Solar System Two basic types of meteorites a) stony, b) iron

11. Chapter 4: The Solar System The formation process The solar nebular began to contract. Due to conservation of angular momentum the cloud begins to flatten. The central condensation condenses faster than the rest and eventually reaches densities and temperatures high enough to form a star.

12. Chapter 4: The Solar System We can see disks of material around other stars.

13. Chapter 4: The Solar System As the nebula continues to contract smaller clumps begin to grow by accumulation and accretion to form the planets.

14. Chapter 4: The Solar System Because the planets form at different distances from the sun (and thus different temperatures) the planets are made out of different materials. The hot temperatures of the inner solar system prevented planets from collecting lighter gasses. So the inner planets are made of denser materials (iron and rock) while the outer planets retained mostly hydrogen and helium gases and ices.

15. Chapter 4: The Solar System Finally, when the star is “born” it develops a “wind” that blows away most of the remaining dust to give us a “clean” solar system.