1. Comets Astronomy 311 Professor Lee Carkner Lecture 22

2. Which of the following is not true about Pluto ? a)Its composition is different from that of any other planet b)Its orbit is highly inclined c)It has several moons d)HST has imaged craters on its surface e)It crosses the orbit of Neptune

3. Which correctly lists TNO regions from closest to the sun to furthest away? a)Centaurs, Kuiper belt, Scattered disk b)Scattered disk, Kuiper belt, Centaurs c)Kuiper belt, Scattered disk, Centaurs d)Kuiper belt, Centaurs, Scattered disk e)Scattered disk, Centaurs, Kuiper belt

4. Upcoming  Quiz #3 on Monday, Nov 5  Covers Gas Giants through The Sun  Final exam Monday Nov 12, 3pm  Covers entire course  Observing project due next Friday, Nov 9

5. Comets Throughout History  People throughout history have observed the passing of comets  “When beggars die, there are no comets seen; The heavens themselves blaze forth the death of princes.” --Julius Caesar, Act II, Scene II

6. Edmund Halley

7. Comet Halley   He used Newton’s new laws to determine its orbit (P=76 years so A=18 AU)   He was the first to realize that comets are solar system objects on highly elliptical orbits  Comet Halley will return again in 2061

8. Finding Comets   Large observatories do not have time to spend looking for them   If you see a faint fuzzy patch in the sky with your telescope, that is a good candidate for a new comet   More and more comets are being found by automated observatories

9. Observing a Comet  When we look at a comet with our eyes (or a small telescope) we see:   Tail: Long streamer of gas and particles that can be more than 100 million km long

10. Structure of a Comet

11. Comet Tails   A comet generally has 2 tails:  Ion Tail (blue)   Always points away from the Sun  Dust Tail (yellow)   Points roughly away from the Sun, but is curved back towards the Sun by gravity

12. The Two Tails of a Comet

13. The Heart of the Comet   This is what the comet looks like far from the Sun and is the source of the tail and the coma   Composed of rock and ice

14. Comet Jets   The heat from the Sun boils off material   Sometimes volatiles boil inside the comet and are released as a jet   Comet orbits cannot be strictly predicted by Newton’s laws

15. Comet Composition  A comet is a mixture of ice and rock  “dirty snowball”  Comets are composed of:  Silicates (rock)  Water (ice)  Carbon Dioxide (“dry ice”)  Ammonia  Organic material  Comets contain many carbon compounds including C 2, CH, CN (cyanogen)

16. Comet Orbits  Comets have highly elliptical orbits that bring them close to the Sun and then back to the Kuiper Belt or Oort Cloud   Short period comet orbits are constantly being altered by Jupiter and Saturn

17. Meteor Showers  As the comet circles the Sun its orbit fills up with lost material   When the Earth passes through this material we get a meteor shower   Meteors are small dust particles and thus burn up before they reach the ground

18. Anatomy of a Meteor Shower

19. The Perseid Meteor Shower  Occur every year around August 12   Get about 50 meteors per hour   Meteors appear to come from the direction of the constellation Perseus  The Perseids are debris from Comet Swift- Tuttle

20. Comet Deliveries   Comets could be a source of volatiles, including water   Could the Earth’s water have come from comets?

21. Death of a Comet  At each passage, the comet loses material   Eventually all the volatiles will boil off   Comets can also hit a planet or be ejected from the solar system in a close encounter

22. Spacecraft Studying Comets  Imaging  Giotto (1985) -- took close-up pictures of Comet Halley in 1986  Gathering   Impacting  Deep Impact (2004) – blasted a 25m deep crater into Comet Temple (2005)  Landing  Rosetta (2004) -- will land a probe on the nucleus of Comet 67P/Churyumov-Gerasimenko (2014) 

23. Next Time  Read Chapter 16

24. Summary  Comets are small (10 km) bodies that have highly elliptical orbits that originate in the Kuiper belt or Oort cloud  The Sun boils off material making the comet visible  Comets can produce meteor showers and large impacts

25. Summary: Comet Structure  Nucleus: small (10km) core that is the source of the comet material  Coma: large (~1 million km) cloud of gas around the nucleus  Tail: comets have two tails, both pointing away from the Sun:  Ion -- pushed by solar wind  Dust -- pushed by solar light pressure  Jets: gas expelled from the nucleus under pressure