1. CometsComets l Small dusty/icy chunk of material few kms size (often characterized as “dirty snowball”) l Originally condensed out of Solar nebula and still orbit Sun - primitive material l Orbits often elliptical, large aphelion l Partially vaporized when close to Sun - material (gases) then pushed by sunlight makes long tail (gases) then pushed by sunlight makes long tail l Gas tail always points away from Sun l Also dust tail along orbit

2. COMET IKEYA-SEKI

3. COMET WEST

4. COMET HALE-BOPP

5. PARTS of a COMET Pushed by Sun Dust along comet’s orbit

6. COMET TAIL ORIENTATION Ion trail Dust trail Comet Hale-bop Dust trail Ion trail

7. RECIPE for a COMET l Ingredients ä Frozen methane ä Frozen water ä Frozen ammonia ä Dust grains (dirt) ä Traces of organic compounds and other chemicals l Directions ä Mix into a ball about 10 km across containing 100,000,000,000,000, (10 14 ) kg of this mixture About the mass of Mt. Baker

8. COMET HALLEY

9. COMET HALLEY’S ORBIT

10. COMET HALLEY’S PATH 1910 and 1986 1910 1986

12. Returns to Perihelion of Halley’s Comet 239 BCMarch 30989September 9 163 BCOctober 51066March 23 86 BCAugust 21145April 22 11 BCOctober 51222October 1 AD 66January 261301October 23 141March 201378November 9 218May 111456June 9 295April 201531August 25 274February 161607October 27 451June 241682September 15 530September 251759March 13 760May 221835November 16 837February 271910April 20 912July 91986February

13. BAYEUX TAPESTRY

14. Giotto-Adoration of the Magi

15. ORIGIN of LONG PERIOD COMETS Originate in Oort Cloud -a huge reservoir ancient Solar System material far from Sun -likely produced by planetesimals ejected by Jupiter and Saturn Early on from inner Solar System. Passing star perturbes Cloud sends lumps inward - see as comets when near Sun.

16. KUIPER BELT Planetesimals ejected from inner Solar System by strong gravitational fields of Giant Planets - some interact Jupiter and Saturn flung far out to Oort Cloud, interactions Uranus and Neptune pushed them out to Kuiper Belt Kuiper Belt

17. KUIPER BELT OBJECT

18. KUIPER BELT OBJECTS Sedna e =0.86 Perihelion 76 A U Aphelion 975 AU! P =12,000 years Pluto + 3 Moons

19. METEORS AND METEORITES Meteors are parts of comets that pass through Earth’s orbit - burn up in Earth’s atmosphere Meteorites are ground up pieces of asteroids - off orbit - enter Earth’s atmosphere and survive passage

20. Meteor Shower Comet breakup near perihelion Material spread out along orbit If Earth passes through comet debris - shower

21. A METEOR STORM 1833 Wood Cut Leonid Shower

22. LEONID METEOR SHOWER Long Exposure

23. Dates Some Meteor Showers

24. ANTARCTIC METEORITE Easiest to find meteorites against snow. Most found in Arctic or Antarctic Primitive material - planetesimals - useful for dating Solar System Many varieties - stony, metallic, often contain organic material