2500-6-comets

Comets:
Messengers from the Cold, Dark Past
Chapter 6
The Nucleus & Atmosphere of ―Comet Borrelly‖
Composite Image Obtained by NASA Deep Space -1 Spacecraft

The Solar System
Komitis
(Greek)
• ―Longhaired‖
• ―Feathered‖
• ―a Comet‖
Figure 22.1

6.1 Comets Through History
• Written Records of Comets Goes Back to 1140 B.C.E.
in the Middle East and China
• Because Comets Were Unpredictable -
They Were Regarded with Apprehension
• Believed to Herald Some Remarkable Event -
Usually Unfavorable
• Medieval Europe Associated Nothing Good with Comets
• Asia Region Considered Them More Like Other ―Normal‖
Celestial Phenomena
• Scientific Study of Comets by Greek and Romans Can Be
Traced Back More Then 2,000 Years

Halley‘s Comet - The Bayeux Tapestry
The Battle of Hastings - 1066
William of Normandy was preparing his invasion of Britain. He is
supposed to have remarked to his courtiers, "A comet like this is
only seen when a kingdom wants a king". The Bayeux Tapestry
shows an ailing Harold on the throne pointing to his eye as his
courtiers gesture towards the comet in terror. The caption reads isti
mirant stella, ‗They wonder at the star‘.

6.1 Comets Through History
Julius Caesar
William
Shakespeare
1564? - 1616
―When beggars die, there are no comets seen /
the heavens themselves blaze forth
the death of princes‖
Characterized Satan as a Comet
―from its horrid hair / Shakes pestilence and war‖
John Milton
1608 - 1674

Comet Halley
Seen From Mauna Kea
Spring - 1986
• Like Most Bright
Comets, Appeared as a
Small Nebulous Patch
of Light with a Tail
• Comets Are Outside
Our Atmosphere -
They Are Not Meteors
• Meteors Streak
Across the Sky,
Whereas a Comet‘s
Movements Are Nearly
Imperceptible
• Photo Is a Good
Approximation of a
Naked-Eye View

―Shooting Stars‖ are Meteors That Hit
EARTH‘S Atmosphere and Burn Up as
They Fall to EARTH

Comet Hale-Bopp
Comets Just Seem to Hang in the Sky
You Have to Watch for Hours to Perceive Any Movement

Appearance of a Comet

Tycho Brahe
Extensively Studied the Great
Comet of 1577
• Carefully Measured Its Position
Against a Background of Stars
• Determined That the Viewing
Angle Did Not Shift Back and
Forth As the View Changed with
EARTH‘S Rotation
• Concluded This Comet Was Not
in EARTH‘S Atmosphere;
It Was Well Beyond the Moon

Edmund Halley
(Rhymes with ―Valley‖)
1656 - 1742
Contemporary of Newton
Studied the Great Comets of
1531, 1607 and 1682
First to Realize:
• Cometary Orbits Could Be
Closed Ellipses
• Comets Could Reappear at
Regular Intervals
The Great Comets were
Really the Same Comet –
Predicted It Would Reappear
in 1758
British Astronomer Edmund Halley
Successfully Predicted Return in 1758 of
Comet That Now Bears His Name

Halley‘s Comet
• Mark Twain was born when
Halley‘s Comet came
• He died when Halley‘s Comet
came again 76 years later

Head of Comet Halley Photographed May 8, 1910
EARTH Passed Through the Tail on May 20, 1910
76 Year Orbit
Appeared in 1910 and 1986
During Last Century
Next Appearance in 2061?

Halley‘s Comet 1986
―Disappointing"
Images
3416, 3457, 3475, 3480, 3491,
3496, 3500
Composite Image
Comet Poorly Placed -
When It Was the Closest
to the SUN, and
Therefore the Brightest,
It Was Located in Its
Orbit on the Opposite
Side of the Sun from
EARTH
European Space Agency's Giotto probe returned 2333 images during the Comet Halley encounter of
March 13-14, 1986. All were recorded before the closest approach of 596 km at 00:03:02 UTC on 14
March 1986; the last from a distance of 1180 km, 15 seconds before closest approach. This composite
image highlights details on the nucleus and the dust jets emanating from the sunlit side.
Photo: MPAE, courtesy Dr H.U. Keller.

Comets in the Nineteenth and Twentieth Centuries

Hale-Bopp
Orbits
of
Comets
• Long-Period Comets
> 200 Years
• Intermediate Comets (Halley-Class Comets)
30-200 Years
- Only a Handful Exist
- Same Origin as Long-Period Comets
-We Will Consider Them to Be Part of
the Long-Period Classification
• Short-Period Comets < 30 Years

Long-Period Comets
Trillions in the Oort Cloud and Oort Disk
Oort Cloud
Sphere 20 - 50,000 AU
Around Our Solar System
Oort Disk
2,000 - 20,000 AU Inside

Long-Period Comets
Trillions in the Oort Cloud and Oort Disk
• Extremely Eccentric Orbits
• So Elongated They Are Approximated
by a Parabola
• Sun Is at One Focus
• Period > 1 Million Years
• 90% of 1500 Comets Discovered by 2001
Are Long-Period

Oort Cloud
Way
Outside
Our
Solar
System,
Kuiper Belt
and
Scattered
Disk

• Elliptical Orbits with Aphelia
Near the Orbit of JUPITER
• Sometimes Called JUPITER-
Family Comets
Short Period Comets
Kuiper Belt in Blue
• Originate in the Kuiper Belt
(Kuiper Belt Obects – KBO‘s)
• The Kuiper Belt Is a Life
Saver-Like Disk of Icy Debris
Which Extends from
NEPTUNE‘S Orbit
at 30 AU Outward to 50 AU
• Bodies Beyond 50 AU Out to
2,000 AU are now called
Scattered Disk Objects (SDOs)

Comets in the Nineteenth and Twentieth Centuries
Long Period
Intermediate
Period
Short Period

6.2 The Comet‘s Atmosphere - The Coma

The Coma
• Brightest Area – Recently Ejected Gas and Dust
• Usually Brightest in the Direction of the SUN
• Released Gas Quickly Broken Down by UV Light
• Creates Molecular Fragments of OH, CH, NH
• Sources of Carbon Molecules Such As C 2 , C 3 Still Unknown
• Gas Density About 1 Millionth of EARTH‘S Atmosphere Density
• After 10,000 km Away, Molecules Stop Reacting with Each Other
• Beyond 100,000 km, Gas Molecules Ionized (Plasma) and Is
Swept Away by Solar Wind
Comet Borrelly
Recorded by Deep Space I Spacecraft
- Smaller, More Carefully
Organized Then Halley
- Shows Distinct Jets of Escaping
Gas and Dust

Composition of the Gases
• Water Ice
Some Neutral Water Has Been Detected - BUT
Released from Nucleus Quickly becomes Ionized as H 2 O + (Plasma)
Broken Down by Sunlight to Hydrogen (H) and Hydroxyl (OH)
• Carbon-Containing Gases
C 2 , C 3 , CO, CO 2 , CH 4 (Methane), CH 3 OH (Methanol)
Indicates Ices Other Than Water Present
Both: (1) Compounds Containing Hydrogen and Carbon
(2) Oxides of Carbon Are Present
Unusual to Contain Materials from
Both Reducing and Oxidizing Environments
Confirms Low-Temperature History of Inhibited Chemical Reactions
• Nitrogen Compounds
N 2 , HCN (Hydrogen Cyanide), NH 3 (Ammonia), CH 3 CH

Comet Tails

COMET HALE-BOPP

COMET HALE-BOPP
- Low Density Plasma Tails are Straight
- Hale-Bopp Tail Is 100 million km long
- Ionized Carbon Monoxide
(CO + )
- Fluorescence Due to UV
Light from Sunlight

COMET HALE-BOPP
Dust Tails
- Composed of Dust Particles
- Tail Usually < 10 Million km
- Color Yellow-White from Sunlight
- Move Relatively Slow (Solar Gravity)
- Mark Position at Time of Release
- So – Traces Path of Comet Thru Sky

Comet Hale-Bopp Note Straight Pale Blue Plasma Tail and
Brighter Yellow-White Curved Dust Tail

Comet Tails
Comet Mrkos Photographed During Six Nights in 1957
Solar Wind – 400 km/s, Traverses Entire Comet in 1 Day
Can Produce Large Changes in Plasma Tail Night-to-Night
But, Curved Dust Tail Remains Relatively Unchanged

6.3 The Comet‘s Nucleus
Gasses Must Come from Somewhere, Detected by Radar,
Photographed in 1986 by Spacecraft

Fred Whipple (left),
Originator of the Dirty-
Snowball Model for
Comet Nuclei,
Listening to Rolad
Sagdeyev (right)
Director of the VEGA
Mission to Comet
Halley and of the USSR
Institute for Space
Research, as the Data
from the 1986 Comet
Flyby Were Received
on EARTH
Rock/Ice Ratio Varies
Comets Made in Different
Places with Different Histories
The Dirty Snowball Model
The VEGA Pictures Provided the First
Visual Evidence That Whipple‘s Model,
Conceived 36 Years Earlier,
Was Indeed Correct

• Cometary Activity Begins at About 3 AU from SUN
Water Ice Begins Rapid Evaporation at 210 o K
Comet
Hale-Bopp
• Hale-Bopp Began Activity at 5 AU
Ices of More Volatile Gasses Must Be Present

Physical Nature of the Nucleus
(Predominant Volatile)
(Methyl Alcohol)

Composition
of the
Nucleus
Nucleus of Comet Halley
Beside Volatile Gasses, It Also
Contains Substantial Quantities
of Dark Carbonaceous and
Silicate Dust
Comet Halley
Spacecraft Giotto, March 1986
Composite of 60 Images
Smallest Details 60 m Across
• Carbon and Hydrocarbon Dust
Predominate Over Silicates

Composition of the Nucleus
Nucleus of Comet Borrelly
Extremely Dark Overall Surface
Albedo = 3%
Some Surface Spots
Albedo =1% (Darker Than Coal)
• Comet Is Covered in Carbon – Rich Materials
• Gasses Must Originate Below the Surface
• Possible That Some of the Carbonaceous Material
Pre-Dates the Origin of the Solar System
• Many Suspected Volatiles in Comets Are Identified in ―Molecular
Clouds‖ Throughout the Galaxy by Radio Astronomers
Comets May Actually Transport Molecules Created Out
Among the Stars to Planets and Bodies in the Solar System

Physical Nature of the Nucleus
Use Radar to Penetrate the Obscuring Gas and Dust
• 1980 – Comet Encke Nucleus Oberved
• 1983 – Comet IRAS-Araki-Alcock Nucleus
Diameter Measured at 5 – 10 km

Physical Nature of the Nucleus
1986 - Giotto Spacecraft Pictures of Halley Nucleus
16 x 8 x 8 km Size Dark – Albedo Only 3 – 4%
Schematic Diagram Illustrating the Main Features
Visible on the Halley Nucleus

Physical Nature of the Nucleus
Comet Borrelly
2001 - Comet Borrelly
Deep Space I Fly-by Photograph
• 8 km Long, 3 - 4 km Wide
• Bowling Pin Shaped
• Rough Jumbled Surface
• Very Low Reflectivity Indicates
Primitive, Carbonaceous Material

Cometary Activity
• Ice Evaporation Begins at Surface Temperature Just Over 200 o K
• Full-Scale Atmosphere Developed as It Crosses Orbit of MARS
• Solar Energy Evaporate More-and More, and Heats Surface
the Near It Get to the SUN
• Losses 10 – 100 Million Tons of Gas and Dust Per Orbit
• It Will Exhaust Its Stores After a Few Thousand Passes Through
the Inner Solar System
• If the Solid Component Is Carried Away -
The Comet Will Simply Shrink Down to Nothing
• If a Core of Residual Material Is Left –
Then This Core Would Be Indistinguishable from a
Dark Near-Earth Asteroid
We Don‘t Know Which Hypothesis Is Correct – Probably Both

Nongravitational Forces
Rocket Effect Exerted
by Gases Escaping in
Jets From a Comet‘s
Nucleus
(Newton‘s Third Law)
Warmest Part
of Comet -
Afternoon
Side Facing
SUN
Whipple‘s ―Dirty Snowball Model‖
Explained Nongravitational Forces

Is
Halley‘s Comet
Dead ?
In 1987 a Carmelite Nun named Sister Maria Gabrel claimed that
Halley‘s Comet would suffer an explosion in 1991, and on 12
February 1991 two Belgian astronomers, Olivier Hainant and Alain
Smette of the Southern European Observatory in Chile, discovered
an outburst of Halley‘s Comet, then 1,243 million miles away. It was
surrounded by a cloud of 19,000 miles, where normally it would
occupy only 9 miles, and was 6 magnitudes or 300 times brighter
than normal. They concluded that Halley‘s Comet had collided with
another body and could now have fragmented entirely, unless it has
become two or more smaller comets. A scientific forecast society
claimed that Halley‘s Comet‘s orbit had been knocked out of orbit
and was returning to the Sun. Its next return should occur in 2061
but this is now open to some doubt

Comet
Shoemaker-Levy 9
Week of
July 16, 1994
David Levy

Comet S-L 9 as it Appeared Prior to Its Collision with
JUPITER in July 1994
• There Are More Than 20 Fragments Forming a
―String-of-Pearls‖ with the Largest Near the Center
• Backward Calculation of the Orbit Indicated the Comet Had
Passed 35,000 km Above the Clouds of JUPITER - Summer of 1991
• 2-3 km Diameter Nucleus of Loosely Bound Fragments Was
Disrupted, and That Orbit Was Unstable

Shoemaker-Levy 9
Asteroid Impact with Jupiter
Week of July 16, 1994
The First Observed Asteroid Impact

• The Impacts All Took
Place on the Back-Side of
JUPITER, Just Over the
Horizon as Seen from
EARTH
• The Galileo Spacecraft, on
Its Way to JUPITER at the
Time, Got the Only Direct
View of the Impacts on
JUPITER‘S Night Side

Impact of Comet S-L 9
with JUPITER
• Impact Speed = 60 km/s
• Largest Nucleus = 1 km
• Most Fragments a Few
Hundred Meters Across
• In Under 20 Minutes,
Hubble Space Telescope
Observed an Impact Plume
Rise 3500 km Above
JUPITER‘S Horizon and
Then Collapse Back Down

Impact of Comet S-L 9
with JUPITER
• This Bright
Infrared Flare Was
Formed When the
Debris From the
Impact Fell Back
Into the Atmosphere
of JUPITER - About
20 Minutes After
Impact
• Fireball Was About
10,000 km from
Point of Impact

Shoemaker-Levy 9
Asteroid Impact with
Jupiter

Shoemaker-Levy 9
Asteroid Impact with
Jupiter
Images from:
Hubble Telescope
Left – Composite Image
The ACCRETION PROCESS is Still Happening

Fragment D
Fragment G
Hubble Space Telescope Image of JUPITER
• Impacts of Two Fragments of S-L 9 on JUPITER‘S Atmosphere
• Image Was Recorded Less Than 2 Hours After the Impact

6.4 Comet Dust - Meteors & Meteor Showers
• Comet Dust Fills the Inner Solar System
• Most Either Falls Into the SUN or Is Swept
Outward by the Solar Wind
• A Tiny Fraction Strikes EARTH, Burning Up in the
Atmosphere to Produce the Meteors

Comets in the Nineteenth and Twentieth Centuries

6.4 Comet Dust - Comet Biela
• 1826 – Comet Biela Discovered with a 6.8-Year Orbit
• 1846 Comet Biela Split in Two
• 1852 – Both Fragments Were Present at Next Return
• 1852-1866 – Ceased to Exist; Never Seen Again
• 1872 – EARTH Passed Through the Orbit of Comet Biela
- Thousands of Meteors Visible
- Comet Biela Had Been Transformed into a Stream
of Meteoric Particles

6.4 Comet Dust - Meteors & Meteor Showers

6.4 Comet Dust - Leonid Meteors
• The Leonids Occur Every November
• There Is a Particularly Dense Clump That
EARTH Encounters Every 33 Years
• The Most Resent Clump Occurred 1999-2001
• It Was a Meteor Strom of More Than 1,000 Meteors/Hour
• Several Meteors Appeared Simultaneously
(4 at the Same Time During the Peak)

The Nature of Meteoric Material
• Meteors That Strike EARTH‘S Atmosphere Are Associated
with Showers and Meteor Streams in Space
• Many Non-Shower (Sporadic) Meteors Are Also Remnants of
Dispersed Meteor Streams
• Most Known Meteor Streams Are in Turn Associated with Comets
If Meteors Are Cometary Dust
Then Do Meteorites Also Come From Comets?
The Answer Is NO
• No Meteorites Fall to EARTH During a Meteor Shower
• Meteors and Meteorites Are Made of Different Material
- Density of Meteors = < 1gm/cm 3
- Density of Meteorites 3-7 g/cm 3

The Nature of Meteoric Material
• Fragments of Cosmic Dust Are
Strange, Fluffy Bits of Chemically
Primitive Matter
• Many Contain Organic Matter
That Must Have Been Assembled
in the Interstellar Cloud That
Formed the Solar System
• This Is Based Upon Studies of
Nitrogen and Hydrogen Isotopes
in This Material, Which Are
Found to Have Very Different
Proportions from Normal Solar
System Material
Meteoric Dust Particle

The Nature of Meteoric Material
IRAS Infrared Image Showing the First Cometary Dust Trail Ever
Detected Directly - Temple 2 Dust Trail
• Dust Trail is Thin Blue Line
• False Colors Are Used to Accentuate the Faint Dust Trail
Dust Trail

6.5 Origin and Evolution of Comets
Comets Only Last a Few Thousand Orbits Before They Are Totally Evaporated
There Must Be A Source for New Comets
Long-Period
Comets
• Extremely Eccentric Orbits
• So Elongated They Are
Approximated
by a Parabola with an Aphelion at a
Distance of 50,000 AU
• In 1950, Dutch Astronomer Jan Oort
Suggested the Existence of a Distant
Comet Cloud That Was a Reservoir of
Long Period Comets

Oort Cloud
Way
Outside
Our
Solar
System,
Kuiper Belt
and
Scattered
Disk

• The Kuiper Belt Is a Life Saver-
Like Disk of Icy Debris (Icy
Planetesimals – KBO‘s)
Which Extends from
NEPTUNE‘S Orbit at 30 AU
Outward to 50 AU
Short Period
Comets
Kuiper Belt in Blue
• First Proposed by G.P. Kuiper
50 Years Ago
• Bodies Beyond 50 AU Out to
2,000 AU are now called
Scattered Disk Objects (SDOs)
• SDO‘s Were Originally
Proposed to Have Been Scattered
by Pluto – But Pluto Is Now
Known to Not Be Massive Enough

The
Kuiper Belt
• David Jewitt
and
Jane Luu
Discovered the
Kuiper Belt in
1992
• They (and
Others) Have
Now Discovered
>500 KBO‘s
• Pluto Is Just the
Largest KBO

• KBO‘s are Also Known as Trans-
Neptunian Objects
• NEPTUNE Exerts a
Gravitational Influence on the
Kuiper Belt Much Like JUPITER
Does on the Main Asteroid Belt
Short Period
Comets
Kuiper Belt in Blue
• Most KBO‘s Have Orbits That
Cluster Around One of Three
Resonances with the Orbit of
NEPTUNE
• Pluto Has a 3:2 Resonance
• KBO‘s with Pluto-Like
Characteristics Are Termed
―Plutinos‖

Changing Comet Orbits
Collisions in the Kuiper Belt:
- Produces Cometary Dust
- Contributes to Sending KBO‘s into Orbits Toward the SUN
Today‘s KBO Population Is 100 Time Less Than Original
1. Catastrophic Collisions Such As Shoemaker-Levy 9
2. Trapped by JUPITER into a Short-Period Orbit
Around the Sun and Dies as All Volatiles Are Depleted
KBO‘s Formed in the Coldest Portion of the Original Solar Nebula
They Must Be the Most Primitive of the Surviving Icy Planetesimals
Their Study Should Reveal Some of the Original Conditions in the
Outer Solar Nebula – and Perhaps - In the Interstellar Cloud
from Which It Came

Changing
Comet Orbits
• Eccentricity v.s.
Semimajor Axis of
Kuiper Belt Object
(KBOs)
• Clustering at
Resonances with
NEPTUNE‘S
Orbit
• PLUTO is a
member of the
Highly Populated
Group in the
3:2 Resonance

The Fate of Comets
They May Just Circle the Solar System in the Kuiper Belt for
Billions of Years
Life Expectancy Is
Limited in the Inner
Solar System
Figure 22.1
Some Just Fade out Near Perihelion, Others Break-Up , Others Are
Ejected by Near-by Planetary Gravitational Forces

6.5 Origin of the Oort Cloud and Kuiper Belt
\
• Formed in Place?
But Difficult to Imagine Solids
Condensing at Such Far Out, Cold
Distances from the SUN
• Comets Condensed in the Cold
Outer Regions of the Solar System
Near URANUS, NEPTUNE and the
Inner Edge of the Kuiper Belt
• Variety of Cometary Ices Suggest 30-100 o K Corresponding to
This Region of Space
• Then Comets Either Ejected to Oort Cloud or Gravitationally
Dispersed Through Solar System Crashing into Planets and SUN

ATMOSPHERE AND OCEAN ORIGINS
Comets may have delivered water to EARTH, but, isotope samples of long-period,
Oort Cloud comets show its water/ice is not compatible with that on EARTH-
(Comets 2X EARTH Proportions)-No Isotope Data for Kuiper Belt Comets Yet
Intense Bombardment
Until 3.8 BYA
Approximately 0.5 BYA
Earth Cool Enough for Oceans to Reach
a Steady State Similar to That of Today
(Water Not Just Boil Off into Atmosphere)

Recover Comet Material
from Space
Stardust Mission
(USA)
Launch - 2/7/1999
Encounter – 1/2/2004
Return – 1/15/2006

Stardust Mission
(USA)
Launch - February 2, 1999

Stardust Mission
(USA)
Launch
February 2, 1999
Encountered Comet Wild 2
January 2, 2004
5 Year Journey

Stardust Mission
(USA)
Encounter with Comet Wild 2
January 2, 2004
AEROGEL Is Like Cotton-Candy
or Soft, Spongy Styrofoam
Captured
Thousands of
Particles in Its
Aerogel Collector
for Return to
EARTH

Stardust Mission
(USA)
(B.)
(A.)
Aerogel
Collector
Deployed
January 2, 2004, Stardust Flew
within 236 kilometers of Comet
Wild 2 and Captured
Thousands of Particles in Its
Aerogel Collector for Return to
EARTH – January 15, 2006

Stardust Mission
(USA)
January 2, 2004, Stardust flew Within
236 kilometers of Comet Wild 2 and
Captured Thousands of Particles in
Its Aerogel Collector for Return to
EARTH – January 15, 2006

Stardust
First Mission to Return Samples from Comet
On January 2, 2004, Stardust flew within 236
kilometers of Comet Wild 2 and Captured
Thousands of Particles in Its Aerogel Collector
for Return to EARTH - January 2006
Particle
Flew 236 kilometers
(about 147 miles) from
Comet Wild 2
Launch - 2/7/1999
Encounter – 1/2/2004
Return – 1/15/2006
Aerogel Wedge

STAR DUST
DATA INTERPRETATION and RESULTS
Comets are not composed entirely of volatile rich materials but rather are a
mixture of materials formed at all temperature ranges, at places very near the
early sun and at places very remote from it
One mineral found in the material brought back by Stardust is olivine, a primary
component of the green sand found on some Hawaiian beaches - It is among the
most common minerals in the universe, but scientists were surprised to find it in
cometary dust
Olivine is a compound of iron, magnesium and other elements. The Stardust
sample is primarily magnesium - Along with olivine, the dust from Wild 2
contains high-temperature minerals rich in calcium, aluminum and titanium
Collection of cometary particles was greater than expected
Data supports a particular model where strong bipolar jets coming out of the early
sun propelled material formed near to the sun outward to the outer reaches of the
solar system

DEEP IMPACT
Stack
Launch
Main Object
Determine Composition of
Surface vs
Interior of Comet
Launched January 12, 2005
Impact - July 3, 2005
1/12/2005

DEEP
IMPACT
Trajectory
Launched
January 12, 2005
Impact
July 3, 2005

Deep Impact Mission
(USA)
July 3, 2005
Orbiter and Impactor Intercept Comet Temple 1

5.5 year orbit
COMET TEMPEL I
Last Picture from Impactor
• Image approximately
5 minutes before
Deep Impact's probe
smashed into surface
• Smooth regions (lower left, upper
right) are probably younger than
rougher areas with circular features

Deep Impact Mission
(USA)
Impactor Released
Impactor Strikes Temple I
Impactor Heads to Target – Tempel I
Stadium-size Hole Left in Tempel I

Deep Impact Mission
(USA)
Orbiter Records
Data from Impact

Initial ejecta
NASA's Deep
Impact probe
collided with
comet Tempel I at
10:52 p.m. Pacific
time, July 3 (1:52
a.m. Eastern
time, July 4)
• Taken by the
spacecraft's highresolution
camera
13 seconds after
impact
• Image has been
digitally
processed to
better show the
comet's nucleus

DEEP IMPACT
DATA INTERPRETATION and RESULTS
• The amount and brightness of the released debris indicates that
beneath the surface of the comet, there is microscopic dust; water
and carbon dioxide ice; and hydrocarbons. Signatures of these
species were seen in spectra immediately after impact
• The impact, while powerful, was not forceful enough to make an
appreciable change in the comet's orbital path around the Sun
• New information since encounter tells us that the forces holding
the comet together are gravitational forces, and the comet is
extremely weak—weaker than snow

ESA's Rosetta Spacecraft - Launched 3/2/2004
First to undertake long-term exploration of comet at close quarters
• It comprises a large orbiter and small lander
designed to operate for a decade at large distances from the Sun
• Large complement of scientific experiments
designed to complete most detailed study of a comet ever attempted
2014 - After entering orbit around Comet 67P/Churyumov-
Gerasimenko (790M km distant) , small lander sent to icy nucleus,
then spends next two years orbiting comet as it heads towards Sun

Comets:
Messengers from the Cold, Dark Past
Chapter 6
The Nucleus & Atmosphere of ―Comet Borrelly‖
Composite Image Obtained by NASA DS-1 Spacecraft