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

2. 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. 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. Halley’s comet was the first comet discovered to be periodic. The European spacecraft Giotto took this image of comet Halley during a flyby. You can see the jets of expanding gas and dust.

5. 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. Meteoroids Meteors There are two basic types of meteors: random, shower The random kind which can be observed on any clear night (few per hour) are probably left over interplanetary debris. The shower kind come from comet tails.

7. Comets leave a dusty trail behind them and if their orbits intercept the Earth’s then we 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 sand or gravel and burn up in the atmosphere. It takes a fist sized object to reach the ground.

9. Some do hit the ground

10. Two basic types of meteorites a) stony, b) iron

11. The formation process The solar nebular begins 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. We can see disks of material around other stars. Beta Pictoris

13. As the nebula continues to contract smaller clumps begin to grow by accumulation and accretion to form the planets.

14. Because the planets form at different distances form 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. 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.

16. Detecting other planetary systems by Doppler effect .

17. Detecting other planetary systems by transit.

18. How currently detected planets relate to those in our solar system.

19. Can any of these planets sustain life?