1. Comets 30 October 2015

2. Introduction The history of comet watching dates back to 1000 BC from the Chinese records and Chaldea, a place in present Iraq. Comets have been regarded as omen, even as recently as 1986. –Battle of Hastings – 1066 – Bayeau Tapestry Today Astronomers study Comets from scientific perspectives, and our understanding of these fascinating objects have grown tremendously.

3. Dirty Snowballs Comets are dusty chunk of ice During each orbit around the sun they partially vaporize Have elliptical Orbits Courtesy: Calvin J. Hamilton

6. Orbits of Comets Elliptical in Shape Randomly oriented Sun Comet Earth Perihelion distance Aphelion distance

7. Comet Hunters Comet are named by International Astronomical Union (IAU) after the person who first discovers them. Many comets are discovered by amateur astronomers. Charles Messier, E. E. Bernard, Shoemaker and Levy, Hale and Bopp, Ikeya, Seki and Hayakutake are popular comet hunters.

8. Origins of Comets Comets are thought to be the left over debris from during the time of formation of the solar system. The elliptical orbits of comets suggest that they underwent gravitational pull from the giant planets. This all lead us to infer two possible locations where comets could start their journey towards the sun: Oort Cloud for long period comets; Kuiper Belt for short period.

9. Comets Tails Ludwig Biermann propose the idea of solar wind to explain comet tails. Mariner 2 spacecraft captured the one such event in 1962.

11. Comet Collisions Courtesy: NASA/JPL

12. Kohoutek

13. Comet West

14. Shoemaker-Levy 9

15. Shoemaker-Levy hits Jupiter

16. Hale-Bopp Ion tail & Dust tail

17. Halley from Giotto

18. Hyakutake

19. Deep Impact Tempel 1

20. Comet ISON 4 October 2013

21. 10 April 2013 Comet ISON

22. 8 October 2013

23. ISON’s path through the sky

24. ISON approaches the Sun

25. ISON is only debris cloud after passing Sun

26. Comet Hartley jets

27. Comet McNaught 2007

28. Siding Spring at Mars October 2014

29. MER PanCam

30. MAVEN IUVS Siding Spring

31. Latest Rosetta Images: Landing, 12 Nov 2014 Perihelion: 13 August 2015

32. Rosetta Target: 67P C-G

36. Boulder ‘Cheops’

43. Approaching Perihelion

44. Outburst in Action

45. View through Camera 4

46. P67 Rotation and Regions

47. Active Pits

49. Key Concepts Kuiper Belt, exterior to Neptune is the primary source of short period (P<200yr) comets Oort Cloud, 10,000 AU from Sun, reservoir of long period comets, stored there billions of years Small objects much more abundant Cometary activity is triggered by sunlight Comet tails: dust, shaped by solar radiation; ion or plasma tail shaped by solar wind Comet grains: CHON + refractory matter Comet nucleus: dirty snowball