1. Comets in the New Millennium
Dr. Erika Gibb
UMSL

2. Comets Through History
Comet as destroyer of the world
1857
Unknown Artist

3. Comets Through History
Comet as destroyer of the world
1857
Unknown Artist
Woodcut showing destructive influence of a 4th century comet
(Stanilaus Lubienietski, Theatrum Cometicum,1668)

4. Comets Through History
They marveled at the star
Halley’s Comet
King Harold being informed of the comet’s appearance
Bayeux Tapestry
Battle of Hastings, 1066

5. Comets Through History
Chinese astronomers documented comets and the disasters attributed to them.
The Mawangdui silk, a surviving record of ancient comets (~300 B.C. )
Believed to include information from back to 1500 B.C.

6. Comets Today Short period (<200 years) Long period (>200 years)
Halley (76 years)
Hale-Bopp (2537 years)
Encke (3.3 years)
Hyakutake (70, ,000 years)

7. Comets Today ~70,000 bigger than 100 km Source of short period comets
(1000 Billion)
Source of long period comets

8. Anatomy of a Comet
Coma
Dust Tail
Ion Tail
Nucleus
Not visible!

9. Why are comets important?
Formed near Jupiter & beyond
(where temperature low enough for water to freeze)
Gravitational interactions flung all over solar system
Impacted early Earth, Sun, were ejected from solar system, formed Oort Cloud
destruction?
source of oceans?
delivery of organics?

10. Why are comets important?
If we know what comets are made of  learn how they affected Earth’s early history
Difficult to study:
Can’t see nucleus from Earth (coma too bright)
Chemistry in coma - how to infer composition of nucleus?
Not predictable
Comets are like cats. They both have tails and do precisely what they want. - David H. Levy

11. Questions that need Answers
What are comets made of?
Where did they form?
What is the internal structure?
Have they been modified since their formation?
Could they have contributed to Earth’s early oceans/organics?

12. Comets are ~ 1/2 ice & 1/2 dust
(But how are these mixed?)
Darker than coal!
Evaporation of ice over only small amount of surface (jets)
Snowy surface just after formation
Dark surface after 4.6 billion years of radiation exposure
If the surface has been modified, how do we measure the original composition?

13. Comets are fragile! Shoemaker-Levy 9 Ganymede: Chain of craters
From a broken comet like SL9?

14. Models of Nucleus
Easily broken implies that comets are made of smaller cometesimals?
Are they made of the same material?
How do we get below the modified surface to test?
Smash a hole in a comet and see if the composition changes!

15. Deep Impact Smash 820 lb probe into comet Tempel 1 at 22,680 miles/hr
Create stadium sized crater
Gets below the surface

16. Deep Impact Image from impactor 90 seconds before impact Smooth area
20-m high scarp
Craters require surface tension
Impact site
Rough spots

17. Worldwide Campaign
Many telescopes, including Keck (below) observed Tempel-1 before & after impact
Changes?
Surface Different from Interior?

18. Worldwide Campaign Sample comet spectrum
Every molecule emits at specific positions  what molecules are present
Height  how much of that molecule is in comet
What do we find?
water, methanol, methane, carbon monoxide, ammonia, hydrogen cyanide, acetylene, ethane, etc

19. What are comets made of?
model
after
before

20. What are comets made of?

21. Schwassman-Wachman 3: May 2006
Broke apart in 1995
As of April 10, 19 fragments
Brightest will be studied with Keck in April/May
Why is this a big deal?

22. Schwassman-Wachman 3: May 2006
Why is this a big deal?
A recently broken comet = newly exposed interior!
Several pieces to study = study whether composition is same throughout

23. Stardust Collector Return Pod Comet Wild 2 Launched 1999
Sample Return Jan 15, 2006

24. Stardust Pod recovery, Jan 15, 2006 Image of tracks
Comet dust impacts in aerogel
Want to help?

25. Comets in the Future Rosetta Mission launched Mar 2004 Lander:Philae
island in the Nile
obelisk with a bilingual inscription
Enabled Champollion to decipher Rosetta Stone
Land on Churyumov- Gerasimenko in 2015