1. COMETS Kristine Drew August 16 th, 2003

2. What is a comet? Comets are a part of the Solar System. Comets are a part of the Solar System. Comets are sometimes called dirty snowballs. They are a mixture of ices (both water and frozen gases) and dust. Comets are sometimes called dirty snowballs. They are a mixture of ices (both water and frozen gases) and dust.

3. Parts of a Comet nucleus: (Solid core) mostly ice and gas with a small amount of dust and other solids; nucleus: (Solid core) mostly ice and gas with a small amount of dust and other solids; coma: dense cloud of water, carbon dioxide and other neutral gases (surrounds the core); coma: dense cloud of water, carbon dioxide and other neutral gases (surrounds the core); dust tail: up to 10 million km long composed of dust particles; this is the most prominent part of a comet to the unaided eye; dust tail: up to 10 million km long composed of dust particles; this is the most prominent part of a comet to the unaided eye; ion tail: as much as several hundred million km long composed of ionized gas. ion tail: as much as several hundred million km long composed of ionized gas.

4. Comets are invisible except when they are near the Sun. Comets are invisible except when they are near the Sun. Most comets are never bright enough to be seen by eye. Most comets are never bright enough to be seen by eye. The comet’s coma and tails are only present when near the sun! The comet’s coma and tails are only present when near the sun!

5. Two tails????

6. Where do comets come from?

8. Each time a comet passes through the inner solar system, it loses millions of tonnes of gas and dust. Each time a comet passes through the inner solar system, it loses millions of tonnes of gas and dust. The debris that is lost from the comet, spreads out through the entire orbit of the comet. The debris that is lost from the comet, spreads out through the entire orbit of the comet. The result: a kind of tube of orbiting debris. The result: a kind of tube of orbiting debris.

10. A little history… Since ancient times people have observed comets. Since ancient times people have observed comets. Comets have often inspired fear in people. Comets have often inspired fear in people. Because of their tails, comets resemble a sword, a portent of death and war. Because of their tails, comets resemble a sword, a portent of death and war. People have blamed comets for everything from earthquakes, illnesses, deaths… basically anything bad! People have blamed comets for everything from earthquakes, illnesses, deaths… basically anything bad!

11. From: Cometagraphia... by: Johannes Hevelius 1668

12. The Blazing Star Threatening the world with Famine, Plague and War: To Princes, Death! To Kingdoms, many Crosses; To all Estates, inevitable Losses! To Herdsmen, Rot; to Plowmen, hapless Seasons; To Sailors, Storms; To Cities, Civil Treasons! From: De cometis: or, A Discourse touching the Nature and Effects of Comets, &c. by John Gadbury; London, 1665.

13. Today, we know that comets were not responsible for any of these terrible events. Today, we know that comets were not responsible for any of these terrible events. There is no need to fear comets anymore! There is no need to fear comets anymore!

14. The most famous comet… Halley’s!

15. Halley’s comet has been observed for over 2000 years. Halley’s comet has been observed for over 2000 years. Confirmed sightings go back 240 B.C. Confirmed sightings go back 240 B.C. Even Halley’s comet had a bad reputation: Even Halley’s comet had a bad reputation: 1456 it caused mass panic in Europe and was blamed for an earthquake! 1456 it caused mass panic in Europe and was blamed for an earthquake!

16. Bayeux Tapestry

18. Chronology… 1705 Edmund Halley figured out the orbit of a comet and predicted it’s return in 1758. 1705 Edmund Halley figured out the orbit of a comet and predicted it’s return in 1758. Of course, as predicted, the comet returned on schedule. Of course, as predicted, the comet returned on schedule. Unfortunately for Halley, he died in 1742. Unfortunately for Halley, he died in 1742.

19. Halley’s nucleus

20. With each pass through the inner solar system, Halley’s comet loses about 6 meters of ice and dust from its nucleus. With each pass through the inner solar system, Halley’s comet loses about 6 meters of ice and dust from its nucleus. Meteor shower caused by debris in Halley’s orbit: Orionids (October) Meteor shower caused by debris in Halley’s orbit: Orionids (October)

21. What are comets made of? Comets are rich in the elements H, C, N, O Comets are rich in the elements H, C, N, O water: H 2 O water: H 2 O Carbon Dioxide CO 2 Carbon Dioxide CO 2 Methane CH 4 Methane CH 4 Ammonia NH 3 Ammonia NH 3 also: some organic material. also: some organic material.

22. Quick Review On average 2-5km in diameter On average 2-5km in diameter Made of C, H, N, and O. Made of C, H, N, and O. Have two visible tails when near the sun. Have two visible tails when near the sun. Highly ellongated orbits, only come by every once in a while. Highly ellongated orbits, only come by every once in a while. Used to cause much grief and fear Used to cause much grief and fear

23. Making a comet! Dry Ice CAUTION: Dry ice is -79 degrees C (-110 degrees F). Any more than brief exposure will cause "burns” Water Ammonia Dirt Organic material The dry ice is frozen carbon dioxide. Water, ammonia, organic (carbon based) molecules, and silicates are all present on comet nuclei. They have been identified through spectral measurements of comet tails and the collection of tiny ice particles by very high flying research aircraft.