Comets in the New Millennium
Dr. Erika Gibb
UMSL
Comets Through History
Comet as destroyer of the
world
1857
Unknown Artist
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)
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
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.
Comets Today
Short period (<200 years)
Halley (76 years)
Encke (3.3 years)
Long period (>200 years)
Hale-Bopp (2537 years)
Hyakutake (70,000114,000 years)
Comets Today
~70,000
bigger than
100 km
Source of
short period
comets
~1012 comets?
(1000 Billion)
Source of
long period
comets
Anatomy of a Comet
Dust Tail
Ion Tail
Coma
Nucleus
Not visible!
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?
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
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?
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?
Comets are fragile!
Shoemaker-Levy 9
Ganymede: Chain of craters
From a broken comet like
SL9?
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!
Deep Impact
Smash 820 lb probe
into comet Tempel 1
at 22,680 miles/hr
Create stadium sized
crater
Gets below the
surface
Deep Impact
Image from impactor
90 seconds before
impact
Smooth area
20-m high scarp
Craters require
surface tension
Impact site
Rough spots
Worldwide Campaign
Many telescopes, including Keck
(below) observed Tempel-1 before &
after impact
Changes?
Surface Different from Interior?
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
What are comets made of?
model
after
before
What are comets made of?
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?
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
Stardust
Collector
Return Pod
Launched 1999
Sample Return Jan 15, 2006
Comet Wild 2
Stardust
Pod recovery, Jan 15, 2006
Image of tracks
Comet dust impacts in aerogel
Want to help?
http://stardustathome.ssl.berkeley.edu/
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 ChuryumovGerasimenko in 2015