2500-6-comets
2500-6-comets
2500-6-comets
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Comets:<br />
Messengers from the Cold, Dark Past<br />
Chapter 6<br />
The Nucleus & Atmosphere of ―Comet Borrelly‖<br />
Composite Image Obtained by NASA Deep Space -1 Spacecraft
The Solar System<br />
Komitis<br />
(Greek)<br />
• ―Longhaired‖<br />
• ―Feathered‖<br />
• ―a Comet‖<br />
Figure 22.1
6.1 Comets Through History<br />
• Written Records of Comets Goes Back to 1140 B.C.E.<br />
in the Middle East and China<br />
• Because Comets Were Unpredictable -<br />
They Were Regarded with Apprehension<br />
• Believed to Herald Some Remarkable Event -<br />
Usually Unfavorable<br />
• Medieval Europe Associated Nothing Good with Comets<br />
• Asia Region Considered Them More Like Other ―Normal‖<br />
Celestial Phenomena<br />
• Scientific Study of Comets by Greek and Romans Can Be<br />
Traced Back More Then 2,000 Years
Halley‘s Comet - The Bayeux Tapestry<br />
The Battle of Hastings - 1066<br />
William of Normandy was preparing his invasion of Britain. He is<br />
supposed to have remarked to his courtiers, "A comet like this is<br />
only seen when a kingdom wants a king". The Bayeux Tapestry<br />
shows an ailing Harold on the throne pointing to his eye as his<br />
courtiers gesture towards the comet in terror. The caption reads isti<br />
mirant stella, ‗They wonder at the star‘.
6.1 Comets Through History<br />
Julius Caesar<br />
William<br />
Shakespeare<br />
1564? - 1616<br />
―When beggars die, there are no <strong>comets</strong> seen /<br />
the heavens themselves blaze forth<br />
the death of princes‖<br />
Characterized Satan as a Comet<br />
―from its horrid hair / Shakes pestilence and war‖<br />
John Milton<br />
1608 - 1674
Comet Halley<br />
Seen From Mauna Kea<br />
Spring - 1986<br />
• Like Most Bright<br />
Comets, Appeared as a<br />
Small Nebulous Patch<br />
of Light with a Tail<br />
• Comets Are Outside<br />
Our Atmosphere -<br />
They Are Not Meteors<br />
• Meteors Streak<br />
Across the Sky,<br />
Whereas a Comet‘s<br />
Movements Are Nearly<br />
Imperceptible<br />
• Photo Is a Good<br />
Approximation of a<br />
Naked-Eye View
―Shooting Stars‖ are Meteors That Hit<br />
EARTH‘S Atmosphere and Burn Up as<br />
They Fall to EARTH
Comet Hale-Bopp<br />
Comets Just Seem to Hang in the Sky<br />
You Have to Watch for Hours to Perceive Any Movement
Appearance of a Comet
Tycho Brahe<br />
Extensively Studied the Great<br />
Comet of 1577<br />
• Carefully Measured Its Position<br />
Against a Background of Stars<br />
• Determined That the Viewing<br />
Angle Did Not Shift Back and<br />
Forth As the View Changed with<br />
EARTH‘S Rotation<br />
• Concluded This Comet Was Not<br />
in EARTH‘S Atmosphere;<br />
It Was Well Beyond the Moon
Edmund Halley<br />
(Rhymes with ―Valley‖)<br />
1656 - 1742<br />
Contemporary of Newton<br />
Studied the Great Comets of<br />
1531, 1607 and 1682<br />
First to Realize:<br />
• Cometary Orbits Could Be<br />
Closed Ellipses<br />
• Comets Could Reappear at<br />
Regular Intervals<br />
The Great Comets were<br />
Really the Same Comet –<br />
Predicted It Would Reappear<br />
in 1758<br />
British Astronomer Edmund Halley<br />
Successfully Predicted Return in 1758 of<br />
Comet That Now Bears His Name
Halley‘s Comet<br />
• Mark Twain was born when<br />
Halley‘s Comet came<br />
• He died when Halley‘s Comet<br />
came again 76 years later
Head of Comet Halley Photographed May 8, 1910<br />
EARTH Passed Through the Tail on May 20, 1910<br />
76 Year Orbit<br />
Appeared in 1910 and 1986<br />
During Last Century<br />
Next Appearance in 2061?
Halley‘s Comet 1986<br />
―Disappointing"<br />
Images<br />
3416, 3457, 3475, 3480, 3491,<br />
3496, 3500<br />
Composite Image<br />
Comet Poorly Placed -<br />
When It Was the Closest<br />
to the SUN, and<br />
Therefore the Brightest,<br />
It Was Located in Its<br />
Orbit on the Opposite<br />
Side of the Sun from<br />
EARTH<br />
European Space Agency's Giotto probe returned 2333 images during the Comet Halley encounter of<br />
March 13-14, 1986. All were recorded before the closest approach of 596 km at 00:03:02 UTC on 14<br />
March 1986; the last from a distance of 1180 km, 15 seconds before closest approach. This composite<br />
image highlights details on the nucleus and the dust jets emanating from the sunlit side.<br />
Photo: MPAE, courtesy Dr H.U. Keller.
Comets in the Nineteenth and Twentieth Centuries
Hale-Bopp<br />
Orbits<br />
of<br />
Comets<br />
• Long-Period Comets<br />
> 200 Years<br />
• Intermediate Comets (Halley-Class Comets)<br />
30-200 Years<br />
- Only a Handful Exist<br />
- Same Origin as Long-Period Comets<br />
-We Will Consider Them to Be Part of<br />
the Long-Period Classification<br />
• Short-Period Comets < 30 Years
Long-Period Comets<br />
Trillions in the Oort Cloud and Oort Disk<br />
Oort Cloud<br />
Sphere 20 - 50,000 AU<br />
Around Our Solar System<br />
Oort Disk<br />
2,000 - 20,000 AU Inside
Long-Period Comets<br />
Trillions in the Oort Cloud and Oort Disk<br />
• Extremely Eccentric Orbits<br />
• So Elongated They Are Approximated<br />
by a Parabola<br />
• Sun Is at One Focus<br />
• Period > 1 Million Years<br />
• 90% of 1500 Comets Discovered by 2001<br />
Are Long-Period
Oort Cloud<br />
Way<br />
Outside<br />
Our<br />
Solar<br />
System,<br />
Kuiper Belt<br />
and<br />
Scattered<br />
Disk
• Elliptical Orbits with Aphelia<br />
Near the Orbit of JUPITER<br />
• Sometimes Called JUPITER-<br />
Family Comets<br />
Short Period Comets<br />
Kuiper Belt in Blue<br />
• Originate in the Kuiper Belt<br />
(Kuiper Belt Obects – KBO‘s)<br />
• The Kuiper Belt Is a Life<br />
Saver-Like Disk of Icy Debris<br />
Which Extends from<br />
NEPTUNE‘S Orbit<br />
at 30 AU Outward to 50 AU<br />
• Bodies Beyond 50 AU Out to<br />
2,000 AU are now called<br />
Scattered Disk Objects (SDOs)
Comets in the Nineteenth and Twentieth Centuries<br />
Long Period<br />
Intermediate<br />
Period<br />
Short Period
6.2 The Comet‘s Atmosphere - The Coma
The Coma<br />
• Brightest Area – Recently Ejected Gas and Dust<br />
• Usually Brightest in the Direction of the SUN<br />
• Released Gas Quickly Broken Down by UV Light<br />
• Creates Molecular Fragments of OH, CH, NH<br />
• Sources of Carbon Molecules Such As C 2 , C 3 Still Unknown<br />
• Gas Density About 1 Millionth of EARTH‘S Atmosphere Density<br />
• After 10,000 km Away, Molecules Stop Reacting with Each Other<br />
• Beyond 100,000 km, Gas Molecules Ionized (Plasma) and Is<br />
Swept Away by Solar Wind<br />
Comet Borrelly<br />
Recorded by Deep Space I Spacecraft<br />
- Smaller, More Carefully<br />
Organized Then Halley<br />
- Shows Distinct Jets of Escaping<br />
Gas and Dust
Composition of the Gases<br />
• Water Ice<br />
Some Neutral Water Has Been Detected - BUT<br />
Released from Nucleus Quickly becomes Ionized as H 2 O + (Plasma)<br />
Broken Down by Sunlight to Hydrogen (H) and Hydroxyl (OH)<br />
• Carbon-Containing Gases<br />
C 2 , C 3 , CO, CO 2 , CH 4 (Methane), CH 3 OH (Methanol)<br />
Indicates Ices Other Than Water Present<br />
Both: (1) Compounds Containing Hydrogen and Carbon<br />
(2) Oxides of Carbon Are Present<br />
Unusual to Contain Materials from<br />
Both Reducing and Oxidizing Environments<br />
Confirms Low-Temperature History of Inhibited Chemical Reactions<br />
• Nitrogen Compounds<br />
N 2 , HCN (Hydrogen Cyanide), NH 3 (Ammonia), CH 3 CH
Comet Tails
COMET HALE-BOPP
COMET HALE-BOPP<br />
- Low Density Plasma Tails are Straight<br />
- Hale-Bopp Tail Is 100 million km long<br />
- Ionized Carbon Monoxide<br />
(CO + )<br />
- Fluorescence Due to UV<br />
Light from Sunlight
COMET HALE-BOPP<br />
Dust Tails<br />
- Composed of Dust Particles<br />
- Tail Usually < 10 Million km<br />
- Color Yellow-White from Sunlight<br />
- Move Relatively Slow (Solar Gravity)<br />
- Mark Position at Time of Release<br />
- So – Traces Path of Comet Thru Sky
Comet Hale-Bopp Note Straight Pale Blue Plasma Tail and<br />
Brighter Yellow-White Curved Dust Tail
Comet Tails<br />
Comet Mrkos Photographed During Six Nights in 1957<br />
Solar Wind – 400 km/s, Traverses Entire Comet in 1 Day<br />
Can Produce Large Changes in Plasma Tail Night-to-Night<br />
But, Curved Dust Tail Remains Relatively Unchanged
6.3 The Comet‘s Nucleus<br />
Gasses Must Come from Somewhere, Detected by Radar,<br />
Photographed in 1986 by Spacecraft
Fred Whipple (left),<br />
Originator of the Dirty-<br />
Snowball Model for<br />
Comet Nuclei,<br />
Listening to Rolad<br />
Sagdeyev (right)<br />
Director of the VEGA<br />
Mission to Comet<br />
Halley and of the USSR<br />
Institute for Space<br />
Research, as the Data<br />
from the 1986 Comet<br />
Flyby Were Received<br />
on EARTH<br />
Rock/Ice Ratio Varies<br />
Comets Made in Different<br />
Places with Different Histories<br />
The Dirty Snowball Model<br />
The VEGA Pictures Provided the First<br />
Visual Evidence That Whipple‘s Model,<br />
Conceived 36 Years Earlier,<br />
Was Indeed Correct
• Cometary Activity Begins at About 3 AU from SUN<br />
Water Ice Begins Rapid Evaporation at 210 o K<br />
Comet<br />
Hale-Bopp<br />
• Hale-Bopp Began Activity at 5 AU<br />
Ices of More Volatile Gasses Must Be Present
Physical Nature of the Nucleus<br />
(Predominant Volatile)<br />
(Methyl Alcohol)
Composition<br />
of the<br />
Nucleus<br />
Nucleus of Comet Halley<br />
Beside Volatile Gasses, It Also<br />
Contains Substantial Quantities<br />
of Dark Carbonaceous and<br />
Silicate Dust<br />
Comet Halley<br />
Spacecraft Giotto, March 1986<br />
Composite of 60 Images<br />
Smallest Details 60 m Across<br />
• Carbon and Hydrocarbon Dust<br />
Predominate Over Silicates
Composition of the Nucleus<br />
Nucleus of Comet Borrelly<br />
Extremely Dark Overall Surface<br />
Albedo = 3%<br />
Some Surface Spots<br />
Albedo =1% (Darker Than Coal)<br />
• Comet Is Covered in Carbon – Rich Materials<br />
• Gasses Must Originate Below the Surface<br />
• Possible That Some of the Carbonaceous Material<br />
Pre-Dates the Origin of the Solar System<br />
• Many Suspected Volatiles in Comets Are Identified in ―Molecular<br />
Clouds‖ Throughout the Galaxy by Radio Astronomers<br />
Comets May Actually Transport Molecules Created Out<br />
Among the Stars to Planets and Bodies in the Solar System
Physical Nature of the Nucleus<br />
Use Radar to Penetrate the Obscuring Gas and Dust<br />
• 1980 – Comet Encke Nucleus Oberved<br />
• 1983 – Comet IRAS-Araki-Alcock Nucleus<br />
Diameter Measured at 5 – 10 km
Physical Nature of the Nucleus<br />
1986 - Giotto Spacecraft Pictures of Halley Nucleus<br />
16 x 8 x 8 km Size Dark – Albedo Only 3 – 4%<br />
Schematic Diagram Illustrating the Main Features<br />
Visible on the Halley Nucleus
Physical Nature of the Nucleus<br />
Comet Borrelly<br />
2001 - Comet Borrelly<br />
Deep Space I Fly-by Photograph<br />
• 8 km Long, 3 - 4 km Wide<br />
• Bowling Pin Shaped<br />
• Rough Jumbled Surface<br />
• Very Low Reflectivity Indicates<br />
Primitive, Carbonaceous Material
Cometary Activity<br />
• Ice Evaporation Begins at Surface Temperature Just Over 200 o K<br />
• Full-Scale Atmosphere Developed as It Crosses Orbit of MARS<br />
• Solar Energy Evaporate More-and More, and Heats Surface<br />
the Near It Get to the SUN<br />
• Losses 10 – 100 Million Tons of Gas and Dust Per Orbit<br />
• It Will Exhaust Its Stores After a Few Thousand Passes Through<br />
the Inner Solar System<br />
• If the Solid Component Is Carried Away -<br />
The Comet Will Simply Shrink Down to Nothing<br />
• If a Core of Residual Material Is Left –<br />
Then This Core Would Be Indistinguishable from a<br />
Dark Near-Earth Asteroid<br />
We Don‘t Know Which Hypothesis Is Correct – Probably Both
Nongravitational Forces<br />
Rocket Effect Exerted<br />
by Gases Escaping in<br />
Jets From a Comet‘s<br />
Nucleus<br />
(Newton‘s Third Law)<br />
Warmest Part<br />
of Comet -<br />
Afternoon<br />
Side Facing<br />
SUN<br />
Whipple‘s ―Dirty Snowball Model‖<br />
Explained Nongravitational Forces
Is<br />
Halley‘s Comet<br />
Dead ?<br />
In 1987 a Carmelite Nun named Sister Maria Gabrel claimed that<br />
Halley‘s Comet would suffer an explosion in 1991, and on 12<br />
February 1991 two Belgian astronomers, Olivier Hainant and Alain<br />
Smette of the Southern European Observatory in Chile, discovered<br />
an outburst of Halley‘s Comet, then 1,243 million miles away. It was<br />
surrounded by a cloud of 19,000 miles, where normally it would<br />
occupy only 9 miles, and was 6 magnitudes or 300 times brighter<br />
than normal. They concluded that Halley‘s Comet had collided with<br />
another body and could now have fragmented entirely, unless it has<br />
become two or more smaller <strong>comets</strong>. A scientific forecast society<br />
claimed that Halley‘s Comet‘s orbit had been knocked out of orbit<br />
and was returning to the Sun. Its next return should occur in 2061<br />
but this is now open to some doubt
Comet<br />
Shoemaker-Levy 9<br />
Week of<br />
July 16, 1994<br />
David Levy
Comet S-L 9 as it Appeared Prior to Its Collision with<br />
JUPITER in July 1994<br />
• There Are More Than 20 Fragments Forming a<br />
―String-of-Pearls‖ with the Largest Near the Center<br />
• Backward Calculation of the Orbit Indicated the Comet Had<br />
Passed 35,000 km Above the Clouds of JUPITER - Summer of 1991<br />
• 2-3 km Diameter Nucleus of Loosely Bound Fragments Was<br />
Disrupted, and That Orbit Was Unstable
Shoemaker-Levy 9<br />
Asteroid Impact with Jupiter<br />
Week of July 16, 1994<br />
The First Observed Asteroid Impact
• The Impacts All Took<br />
Place on the Back-Side of<br />
JUPITER, Just Over the<br />
Horizon as Seen from<br />
EARTH<br />
• The Galileo Spacecraft, on<br />
Its Way to JUPITER at the<br />
Time, Got the Only Direct<br />
View of the Impacts on<br />
JUPITER‘S Night Side
Impact of Comet S-L 9<br />
with JUPITER<br />
• Impact Speed = 60 km/s<br />
• Largest Nucleus = 1 km<br />
• Most Fragments a Few<br />
Hundred Meters Across<br />
• In Under 20 Minutes,<br />
Hubble Space Telescope<br />
Observed an Impact Plume<br />
Rise 3500 km Above<br />
JUPITER‘S Horizon and<br />
Then Collapse Back Down
Impact of Comet S-L 9<br />
with JUPITER<br />
• This Bright<br />
Infrared Flare Was<br />
Formed When the<br />
Debris From the<br />
Impact Fell Back<br />
Into the Atmosphere<br />
of JUPITER - About<br />
20 Minutes After<br />
Impact<br />
• Fireball Was About<br />
10,000 km from<br />
Point of Impact
Shoemaker-Levy 9<br />
Asteroid Impact with<br />
Jupiter
Shoemaker-Levy 9<br />
Asteroid Impact with<br />
Jupiter<br />
Images from:<br />
Hubble Telescope<br />
Left – Composite Image<br />
The ACCRETION PROCESS is Still Happening
Fragment D<br />
Fragment G<br />
Hubble Space Telescope Image of JUPITER<br />
• Impacts of Two Fragments of S-L 9 on JUPITER‘S Atmosphere<br />
• Image Was Recorded Less Than 2 Hours After the Impact
6.4 Comet Dust - Meteors & Meteor Showers<br />
• Comet Dust Fills the Inner Solar System<br />
• Most Either Falls Into the SUN or Is Swept<br />
Outward by the Solar Wind<br />
• A Tiny Fraction Strikes EARTH, Burning Up in the<br />
Atmosphere to Produce the Meteors
Comets in the Nineteenth and Twentieth Centuries
6.4 Comet Dust - Comet Biela<br />
• 1826 – Comet Biela Discovered with a 6.8-Year Orbit<br />
• 1846 Comet Biela Split in Two<br />
• 1852 – Both Fragments Were Present at Next Return<br />
• 1852-1866 – Ceased to Exist; Never Seen Again<br />
• 1872 – EARTH Passed Through the Orbit of Comet Biela<br />
- Thousands of Meteors Visible<br />
- Comet Biela Had Been Transformed into a Stream<br />
of Meteoric Particles
6.4 Comet Dust - Meteors & Meteor Showers
6.4 Comet Dust - Leonid Meteors<br />
• The Leonids Occur Every November<br />
• There Is a Particularly Dense Clump That<br />
EARTH Encounters Every 33 Years<br />
• The Most Resent Clump Occurred 1999-2001<br />
• It Was a Meteor Strom of More Than 1,000 Meteors/Hour<br />
• Several Meteors Appeared Simultaneously<br />
(4 at the Same Time During the Peak)
The Nature of Meteoric Material<br />
• Meteors That Strike EARTH‘S Atmosphere Are Associated<br />
with Showers and Meteor Streams in Space<br />
• Many Non-Shower (Sporadic) Meteors Are Also Remnants of<br />
Dispersed Meteor Streams<br />
• Most Known Meteor Streams Are in Turn Associated with Comets<br />
If Meteors Are Cometary Dust<br />
Then Do Meteorites Also Come From Comets?<br />
The Answer Is NO<br />
• No Meteorites Fall to EARTH During a Meteor Shower<br />
• Meteors and Meteorites Are Made of Different Material<br />
- Density of Meteors = < 1gm/cm 3<br />
- Density of Meteorites 3-7 g/cm 3
The Nature of Meteoric Material<br />
• Fragments of Cosmic Dust Are<br />
Strange, Fluffy Bits of Chemically<br />
Primitive Matter<br />
• Many Contain Organic Matter<br />
That Must Have Been Assembled<br />
in the Interstellar Cloud That<br />
Formed the Solar System<br />
• This Is Based Upon Studies of<br />
Nitrogen and Hydrogen Isotopes<br />
in This Material, Which Are<br />
Found to Have Very Different<br />
Proportions from Normal Solar<br />
System Material<br />
Meteoric Dust Particle
The Nature of Meteoric Material<br />
IRAS Infrared Image Showing the First Cometary Dust Trail Ever<br />
Detected Directly - Temple 2 Dust Trail<br />
• Dust Trail is Thin Blue Line<br />
• False Colors Are Used to Accentuate the Faint Dust Trail<br />
Dust Trail
6.5 Origin and Evolution of Comets<br />
Comets Only Last a Few Thousand Orbits Before They Are Totally Evaporated<br />
There Must Be A Source for New Comets<br />
Long-Period<br />
Comets<br />
• Extremely Eccentric Orbits<br />
• So Elongated They Are<br />
Approximated<br />
by a Parabola with an Aphelion at a<br />
Distance of 50,000 AU<br />
• In 1950, Dutch Astronomer Jan Oort<br />
Suggested the Existence of a Distant<br />
Comet Cloud That Was a Reservoir of<br />
Long Period Comets
Oort Cloud<br />
Way<br />
Outside<br />
Our<br />
Solar<br />
System,<br />
Kuiper Belt<br />
and<br />
Scattered<br />
Disk
• The Kuiper Belt Is a Life Saver-<br />
Like Disk of Icy Debris (Icy<br />
Planetesimals – KBO‘s)<br />
Which Extends from<br />
NEPTUNE‘S Orbit at 30 AU<br />
Outward to 50 AU<br />
Short Period<br />
Comets<br />
Kuiper Belt in Blue<br />
• First Proposed by G.P. Kuiper<br />
50 Years Ago<br />
• Bodies Beyond 50 AU Out to<br />
2,000 AU are now called<br />
Scattered Disk Objects (SDOs)<br />
• SDO‘s Were Originally<br />
Proposed to Have Been Scattered<br />
by Pluto – But Pluto Is Now<br />
Known to Not Be Massive Enough
The<br />
Kuiper Belt<br />
• David Jewitt<br />
and<br />
Jane Luu<br />
Discovered the<br />
Kuiper Belt in<br />
1992<br />
• They (and<br />
Others) Have<br />
Now Discovered<br />
>500 KBO‘s<br />
• Pluto Is Just the<br />
Largest KBO
• KBO‘s are Also Known as Trans-<br />
Neptunian Objects<br />
• NEPTUNE Exerts a<br />
Gravitational Influence on the<br />
Kuiper Belt Much Like JUPITER<br />
Does on the Main Asteroid Belt<br />
Short Period<br />
Comets<br />
Kuiper Belt in Blue<br />
• Most KBO‘s Have Orbits That<br />
Cluster Around One of Three<br />
Resonances with the Orbit of<br />
NEPTUNE<br />
• Pluto Has a 3:2 Resonance<br />
• KBO‘s with Pluto-Like<br />
Characteristics Are Termed<br />
―Plutinos‖
Changing Comet Orbits<br />
Collisions in the Kuiper Belt:<br />
- Produces Cometary Dust<br />
- Contributes to Sending KBO‘s into Orbits Toward the SUN<br />
Today‘s KBO Population Is 100 Time Less Than Original<br />
1. Catastrophic Collisions Such As Shoemaker-Levy 9<br />
2. Trapped by JUPITER into a Short-Period Orbit<br />
Around the Sun and Dies as All Volatiles Are Depleted<br />
KBO‘s Formed in the Coldest Portion of the Original Solar Nebula<br />
They Must Be the Most Primitive of the Surviving Icy Planetesimals<br />
Their Study Should Reveal Some of the Original Conditions in the<br />
Outer Solar Nebula – and Perhaps - In the Interstellar Cloud<br />
from Which It Came
Changing<br />
Comet Orbits<br />
• Eccentricity v.s.<br />
Semimajor Axis of<br />
Kuiper Belt Object<br />
(KBOs)<br />
• Clustering at<br />
Resonances with<br />
NEPTUNE‘S<br />
Orbit<br />
• PLUTO is a<br />
member of the<br />
Highly Populated<br />
Group in the<br />
3:2 Resonance
The Fate of Comets<br />
They May Just Circle the Solar System in the Kuiper Belt for<br />
Billions of Years<br />
Life Expectancy Is<br />
Limited in the Inner<br />
Solar System<br />
Figure 22.1<br />
Some Just Fade out Near Perihelion, Others Break-Up , Others Are<br />
Ejected by Near-by Planetary Gravitational Forces
6.5 Origin of the Oort Cloud and Kuiper Belt<br />
\<br />
• Formed in Place?<br />
But Difficult to Imagine Solids<br />
Condensing at Such Far Out, Cold<br />
Distances from the SUN<br />
• Comets Condensed in the Cold<br />
Outer Regions of the Solar System<br />
Near URANUS, NEPTUNE and the<br />
Inner Edge of the Kuiper Belt<br />
• Variety of Cometary Ices Suggest 30-100 o K Corresponding to<br />
This Region of Space<br />
• Then Comets Either Ejected to Oort Cloud or Gravitationally<br />
Dispersed Through Solar System Crashing into Planets and SUN
ATMOSPHERE AND OCEAN ORIGINS<br />
Comets may have delivered water to EARTH, but, isotope samples of long-period,<br />
Oort Cloud <strong>comets</strong> show its water/ice is not compatible with that on EARTH-<br />
(Comets 2X EARTH Proportions)-No Isotope Data for Kuiper Belt Comets Yet<br />
Intense Bombardment<br />
Until 3.8 BYA<br />
Approximately 0.5 BYA<br />
Earth Cool Enough for Oceans to Reach<br />
a Steady State Similar to That of Today<br />
(Water Not Just Boil Off into Atmosphere)
Recover Comet Material<br />
from Space<br />
Stardust Mission<br />
(USA)<br />
Launch - 2/7/1999<br />
Encounter – 1/2/2004<br />
Return – 1/15/2006
Stardust Mission<br />
(USA)<br />
Launch - February 2, 1999
Stardust Mission<br />
(USA)<br />
Launch<br />
February 2, 1999<br />
Encountered Comet Wild 2<br />
January 2, 2004<br />
5 Year Journey
Stardust Mission<br />
(USA)<br />
Encounter with Comet Wild 2<br />
January 2, 2004<br />
AEROGEL Is Like Cotton-Candy<br />
or Soft, Spongy Styrofoam<br />
Captured<br />
Thousands of<br />
Particles in Its<br />
Aerogel Collector<br />
for Return to<br />
EARTH
Stardust Mission<br />
(USA)<br />
(B.)<br />
(A.)<br />
Aerogel<br />
Collector<br />
Deployed<br />
January 2, 2004, Stardust Flew<br />
within 236 kilometers of Comet<br />
Wild 2 and Captured<br />
Thousands of Particles in Its<br />
Aerogel Collector for Return to<br />
EARTH – January 15, 2006
Stardust Mission<br />
(USA)<br />
January 2, 2004, Stardust flew Within<br />
236 kilometers of Comet Wild 2 and<br />
Captured Thousands of Particles in<br />
Its Aerogel Collector for Return to<br />
EARTH – January 15, 2006
Stardust<br />
First Mission to Return Samples from Comet<br />
On January 2, 2004, Stardust flew within 236<br />
kilometers of Comet Wild 2 and Captured<br />
Thousands of Particles in Its Aerogel Collector<br />
for Return to EARTH - January 2006<br />
Particle<br />
Flew 236 kilometers<br />
(about 147 miles) from<br />
Comet Wild 2<br />
Launch - 2/7/1999<br />
Encounter – 1/2/2004<br />
Return – 1/15/2006<br />
Aerogel Wedge
STAR DUST<br />
DATA INTERPRETATION and RESULTS<br />
Comets are not composed entirely of volatile rich materials but rather are a<br />
mixture of materials formed at all temperature ranges, at places very near the<br />
early sun and at places very remote from it<br />
One mineral found in the material brought back by Stardust is olivine, a primary<br />
component of the green sand found on some Hawaiian beaches - It is among the<br />
most common minerals in the universe, but scientists were surprised to find it in<br />
cometary dust<br />
Olivine is a compound of iron, magnesium and other elements. The Stardust<br />
sample is primarily magnesium - Along with olivine, the dust from Wild 2<br />
contains high-temperature minerals rich in calcium, aluminum and titanium<br />
Collection of cometary particles was greater than expected<br />
Data supports a particular model where strong bipolar jets coming out of the early<br />
sun propelled material formed near to the sun outward to the outer reaches of the<br />
solar system
DEEP IMPACT<br />
Stack<br />
Launch<br />
Main Object<br />
Determine Composition of<br />
Surface vs<br />
Interior of Comet<br />
Launched January 12, 2005<br />
Impact - July 3, 2005<br />
1/12/2005
DEEP<br />
IMPACT<br />
Trajectory<br />
Launched<br />
January 12, 2005<br />
Impact<br />
July 3, 2005
Deep Impact Mission<br />
(USA)<br />
July 3, 2005<br />
Orbiter and Impactor Intercept Comet Temple 1
5.5 year orbit<br />
COMET TEMPEL I<br />
Last Picture from Impactor<br />
• Image approximately<br />
5 minutes before<br />
Deep Impact's probe<br />
smashed into surface<br />
• Smooth regions (lower left, upper<br />
right) are probably younger than<br />
rougher areas with circular features
Deep Impact Mission<br />
(USA)<br />
Impactor Released<br />
Impactor Strikes Temple I<br />
Impactor Heads to Target – Tempel I<br />
Stadium-size Hole Left in Tempel I
Deep Impact Mission<br />
(USA)<br />
Orbiter Records<br />
Data from Impact
Initial ejecta<br />
NASA's Deep<br />
Impact probe<br />
collided with<br />
comet Tempel I at<br />
10:52 p.m. Pacific<br />
time, July 3 (1:52<br />
a.m. Eastern<br />
time, July 4)<br />
• Taken by the<br />
spacecraft's highresolution<br />
camera<br />
13 seconds after<br />
impact<br />
• Image has been<br />
digitally<br />
processed to<br />
better show the<br />
comet's nucleus
DEEP IMPACT<br />
DATA INTERPRETATION and RESULTS<br />
• The amount and brightness of the released debris indicates that<br />
beneath the surface of the comet, there is microscopic dust; water<br />
and carbon dioxide ice; and hydrocarbons. Signatures of these<br />
species were seen in spectra immediately after impact<br />
• The impact, while powerful, was not forceful enough to make an<br />
appreciable change in the comet's orbital path around the Sun<br />
• New information since encounter tells us that the forces holding<br />
the comet together are gravitational forces, and the comet is<br />
extremely weak—weaker than snow
ESA's Rosetta Spacecraft - Launched 3/2/2004<br />
First to undertake long-term exploration of comet at close quarters<br />
• It comprises a large orbiter and small lander<br />
designed to operate for a decade at large distances from the Sun<br />
• Large complement of scientific experiments<br />
designed to complete most detailed study of a comet ever attempted<br />
2014 - After entering orbit around Comet 67P/Churyumov-<br />
Gerasimenko (790M km distant) , small lander sent to icy nucleus,<br />
then spends next two years orbiting comet as it heads towards Sun
Comets:<br />
Messengers from the Cold, Dark Past<br />
Chapter 6<br />
The Nucleus & Atmosphere of ―Comet Borrelly‖<br />
Composite Image Obtained by NASA DS-1 Spacecraft