1. Comets and Life
10 October 2016

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 omens, 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

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

8. 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.

9. 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.

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

12. Comet Collisions
Courtesy: NASA/JPL

13. Kohoutek

14. Comet West

15. Shoemaker-Levy 9

16. Shoemaker-Levy hits Jupiter

17. Hale-Bopp
Ion tail &
Dust tail

18. Halley from Giotto

19. Hyakutake

20. Deep Impact Tempel 1

21. Comet ISON
4 October 2013

22. Comet ISON
10 April 2013

23. Comet ISON
8 October 2013

24. ISON’s path through the sky

25. ISON approaches the Sun

26. ISON is only debris cloud after passing Sun

27. Comet
Hartley
jets

28. Comet McNaught 2007

29. Siding Spring at Mars October 2014

30. MER
PanCam

31. MAVEN
IUVS
Siding Spring

33. Latest Rosetta Images:
Philae Landing, 12 Nov 2014
Perihelion: 13 August 2015
Orbiter Landing: 30 September 2016

34. Rosetta Instruments

36. Rosetta Target: 67P C-G

40. Boulder ‘Cheops’

45. Philae Found!

47. Osiris from
16km

48. 30 September 2016: Rosetta’s last image from 51m

49. Comet Outbursts Are common near perihelion
Studied by JB Vincent (MPS) etal
Published last week in MNRAS
I will show pictures and paper figures from the paper

50. View through Camera 4

53. Approaching Perihelion

54. Outburst in Action

55. Active Pits

60. Location of the outburst node

63. 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

64. Comets and Life Comets are full of organics and water
They supplied and continue to supply these to planet and moon surfaces
Interstellar life could hitch a ride on a comet from another star’s Oort cloud: may have infected Earth with life from space: panspermia
They preserve the material from the early solar system in ‘cold storage’