Constructing the Solar System: A Smashing Success
Asteroids and Meteorites:Our eyes in the early Solar System
Thomas M. Davison
Department of the Geophysical Sciences
Compton Lecture SeriesAutumn 2012
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 1
Compton Lecture Series Schedule
1 10/06/12 A Star is Born
2 10/13/12 Making Planetesimals: The building blocks of planets
3 10/20/12 Guest Lecturer: Mac Cathles
4 10/27/12 Asteroids and Meteorites:10/27/12 Our eyes in the early Solar System
5 11/03/12 Building the Planets
6 11/10/12 When Asteroids Collide
7 11/17/12 Making Things Hot: The thermal effects of collisions
11/24/12 No lecture: Thanksgiving weekend
8 12/01/12 Constructing the Moon
12/08/12 No lecture: Physics with a Bang!
9 12/15/12 Impact Earth: Chicxulub and other terrestrial impacts
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 2
Compton Lecture Series Schedule
1 10/06/12 A Star is Born
2 10/13/12 Making Planetesimals: The building blocks of planets
3 10/20/12 Guest Lecturer: Mac Cathles
4 10/27/12 Asteroids and Meteorites:10/27/12 Our eyes in the early Solar System
5 11/03/12 Building the Planets
6 11/10/12 When Asteroids Collide
7 11/17/12 Making Things Hot: The thermal effects of collisions
11/24/12 No lecture: Thanksgiving weekend
8 12/01/12 Constructing the Moon
12/08/12 No lecture: Physics with a Bang!
9 12/15/12 Impact Earth: Chicxulub and other terrestrial impacts
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 2
Today’s lecture
1 What are asteroids and meteorites?
2 Orbital properties of asteroids
3 How do we classify meteorites?
4 Proposed origins for differentmeteorite classes
How they are linked to asteroidfamilies
5 Evidence of collisions on asteroids
Image courtesy of Ed Sweeney
Image courtesy of Paul Chodas (NASA/JPL)
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 3
Part 1:What are asteroids and meteorites?
Image courtesy of Ed Sweeney
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 4
What are asteroids and comets?
Asteroid
A relatively small, inactive,rocky body orbiting theSun, usually between theorbits of Mars and Jupiter
Comet
A relatively small, at timesactive, object whose icescan vaporize in sunlightforming an atmosphere(and sometimes a tail) ofdust and gas
Vesta: mean diameter = 525 km
Image courtesy ofNASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Comet Hartley 2: 2.25km long
Image courtesy of NASA/JPL-Caltech/UMD
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 5
Asteroids are planetesimals that didn’t grow into planets
Last time, we learnt howplanetesimals wereformed
Small rocky bodies �1–100 km in size
Next week we will learnhow the planets grewfrom planetesimals
Some planetesimals didnot grow into planets
Those that survived nowform the asteroid belt
Examples of some asteroids,compared to the size of Mars
Image courtesy of NASA/JPL/STScI/JHU/APL
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 6
Discovery of Asteroids from 1980 to present
First asteroid, Ceres, discovered in 1801 by Guiseppe Piazzi
By 1980, we knew of �9000 asteroids
Recently, with better observation, we know of half a million!Mercury
Venus
EarthMars
Ceres
Jupiter
Saturn
Uranus
Neptune
Pluto
01020304050607080
Semi-majoraxis[AU]
Titius-BodeActual
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 7
Discovery of Asteroids from 1980 to present
First asteroid, Ceres, discovered in 1801 by Guiseppe Piazzi
By 1980, we knew of �9000 asteroids
Recently, with better observation, we know of half a million!Mercury
Venus
EarthMars
Ceres
Jupiter
Saturn
Uranus
Neptune
Pluto
01020304050607080
Semi-majoraxis[AU]
Titius-BodeActual
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 7
Discovery of Asteroids from 1980 to present
First asteroid, Ceres, discovered in 1801 by Guiseppe Piazzi
By 1980, we knew of �9000 asteroids
Recently, with better observation, we know of half a million!
In the lecture, I showed a movie of asteroid discovery from 1980 tothe present day. You can view that movie in two places online:
On YouTube —http://www.youtube.com/watch?v=XaXcBUFapic
On Scott Manley’s website —http://star.arm.ac.uk/neos/1980-2010/
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 7
Orbits of Asteorids and Comets
Positions of asteroids and comets on October 1, 2008
Image courtesy of Paul Chodas (NASA/JPL)Images courtesy of Paul Chodas (NASA/JPL)
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 8
Orbits of Asteorids and Comets
Positions of asteroids and comets on October 1, 2008
Image courtesy of Paul Chodas (NASA/JPL)
Most asteroids are containedin the main belt betweenMars and Jupiter
Some follow a similar orbitto Jupiter (the Trojans)
Comets tend to have muchlonger orbital periods, andmuch greater eccentricitythan asteroids
Their orbits taken them outto the region of the outerplanets, and beyond
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 8
Orbital eccentricity and inclination
Eccentricity
A planet’s orbital eccentricity, e is ameasure of how elliptical its orbit is
e = 0 means the orbit is circular
0 e 1 for an elliptical orbit
Inclination
The orbital inclination, i is the anglebetween the plane of the orbit of theplanet and the ecliptic — which isthe plane containing Earth’s orbitalpath
Sun
Planet
a
ae
e=0.0 e=0.5 e=0.8
i
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 9
Asteroid families
Some asteroids are groupedbased on where they orbit.For example:
The Hungaria family orbitbetween 1.78 and 2 AUThe Hilda family orbitbetween 3.7 and 4.2 AUThe Jupiter Trojan familyorbit between 5.05 and5.35 AUThe Near-Earth Objectscome within 1.3 AU of theSun on their closestapproach
Why are there gaps where noasteroids orbit?
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 10
Kirkwood gaps
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5Semi-major Axis (AU)
0
50
100
150
200
250
300
350
Ast
eroi
ds (p
er 0
.000
5 A
U b
in)
3:1 5:2 7:3 2:1
Alan Chamberlin (2007, JPL/Caltech)
Mean Motion Resonance( asteroid : Jupiter )
Asteroid Main-Belt DistributionKirkwood Gaps
Image courtesy of Alan Chamberlin (NASA/JPL)
Gaps in the asteroidbelt appear at meanmotion orbitalresonances withJupiter
These gaps are knownas Kirkwood gaps
What is an orbitalresonance?
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 11
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
Orbital resonance
Imagine a child on a swing
If I always give the child a push as theswing is going forward, all those pushes willadd up to make the swing go higher
The velocity increases
The same applies for asteroids in resonancewith Jupiter
A resonance of 3:1 means that the asteroidorbits the Sun 3 times for every orbit thatJupiter makes
So, every third orbit, the asteroid gets asmall push from Jupiter, which speeds it up
It then can either:
Find a new stable orbitFall into a planet-crossing orbit
Planet Formation
We will look more at therole of orbital resonancein the formation of theplanets, next week
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 12
What else can we find out about asteroids?
It is possible to look at the lightreflected from asteroids and tellsomething about their chemistry
Different elements reflect and absorblight at different wavelengths
However, to really understand that data,we need something to compare it to
We do have some sample of asteroids onEarth: these samples are calledmeteorites
Ida
Image courtesy of NASA/JPL
Mathilde
Image courtesy of NASA
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 13
What are meteorites?
Leonid meteor shower, 2009
Image courtesy of Ed Sweeney
Holsinger Meteorite,Meteor Crater, Arizona
Meteoroid
A small particle from a comet orasteroid orbiting the Sun
Meteor
The light phenomena which resultswhen a meteoroid enters the Earth’satmosphere and vaporizes; a shootingstar
Meteorite
A meteoroid that survives its passagethrough the Earth’s atmosphere andlands upon the Earth’s surface
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 14
Meteorites: Falls and Finds
Image courtesy of P. Jenniskens/SETIInstitute
Meteorites can be classified into two typesdepending on how we found them
Falls and Finds
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 15
Meteorites: Falls and Finds
Image courtesy of P. Jenniskens/SETIInstitute
Meteorites can be classified into two typesdepending on how we found them
Falls and Finds
Falls are meteorites that have beenobserved falling to Earth, and arecollected soon after
� 500 meteorites of marble to basketballsize are expected to fall each year andremain intactYet, only � 5–6 are discovered andmade available for scientists
Example: Almahatta Sitta meteorite thatfell in the Nubian Desert in Sudan in 2009
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 15
Meteorites: Falls and Finds
Image courtesy of P. Jenniskens/SETIInstitute
Meteorites can be classified into two typesdepending on how we found them
Falls and Finds
Falls are meteorites that have beenobserved falling to Earth, and arecollected soon after
� 500 meteorites of marble to basketballsize are expected to fall each year andremain intactYet, only � 5–6 are discovered andmade available for scientists
Example: Almahatta Sitta meteorite thatfell in the Nubian Desert in Sudan in 2009
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 15
Meteorites: Falls and Finds
Image courtesy of C. Corrigan/ANSMET
Image courtesy of ANSMET
Meteorites can be classified into two typesdepending on how we found them
Falls and Finds
Finds are meteorites that were notobserved falling to Earth, and are foundlater
Finds are � 30 times more commonBut, sometimes have been weatheredSome areas are better to look thanothers: e.g. deserts or Antarctica
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 15
Meteorites can be separated into two main classesDifferentiated meteorites and Chondritic meteorites
Differentiated meteoritesFormed in planetesimals thatmelted shortly afterSome are metallic (usually anickel-iron alloy)
Core of a melted planetesimal
Some are stony (calledachondrites because they have nochondrules)
Outer layers of a meltedplanetesimal or planetThese include meteorites fromthe Moon, Mars and asteroidssuch as Vesta
Iron meteorite
Image courtesy of H. Raab
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 16
Planetesimals were heated after formation
Differentiated meteorites were melted after their parent planetesimalformed
Most of this heat came from the decay of radioactive material
A major source of this heat is the decay of 26Al to 26Mg
Decays with a half-life of t1{2 � 0.73 Myr
n=64 n= 0
t = 00.00 Myr
n=32 n=32
t = t1/2
0.73 Myr
n=16 n=48
t = 2t1/2
1.46 Myr
n= 8 n=56
t = 3t1/2
2.19 Myr
n= 4 n=60
t = 4t1/2
2.92 Myr
n= 2 n=62
t = 5t1/2
3.65 Myr
n= 1 n=63
t = 6t1/2
4.38 Myr
This heat source is only effective for the first 5 Myr or so
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 17
Radioactive decay is only effective for the first 5 Myr or so
0 1 2 3 4 5 6Time (Ma)
0
2
4
6
8
10
12A
vaila
ble
ener
gy(k
Jg−
1)
26Al60Fe26Al + 60Fe
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 18
Meteorites can be separated into two main classesDifferentiated meteorites and Chondritic meteorites
Chondrites, or primativemeteorites
Chemical compositions thatclosely resemble the SunExcept for volatile elements (e.g.H, He, C, N, O), the abundanceof other elements are within afactor of 2 of the Sun’scompositionThey have not melted since theyaccreted
Chondrite
Image courtesy of H. Raab
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 19
Chondrites can tell us about the early Solar System
Image courtesy of Hawaii Institute ofGeophysics and Planetology
Image courtesy of Alexander Krot, Uni-versity of Hawaii
An important component ofchondrites are calledCalcium-Aluminium-richinclusions (or CAIs)
CAIs are the oldest known objectsto form in the Solar SystemFormed approximately 4567 MyragoFormed at very hightemperatures (¡ 1400 K or2000�F)
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 20
Chondrites can tell us about the early Solar System
Image courtesy of Hawaii Institute ofGeophysics and Planetology
Image courtesy of Alexander Krot, Uni-versity of Hawaii
Chondrites get their names fromone of their main components:Chondrules
Chondrules are small (mm-sized)spheres of silicate rockThey condensed from meltdropletsFormed at lower temperatures( 1000 K or 1350�F)Formed around 2 Myr after CAIsThere are lots of discussionsabout how chondrules formed,and still no consensus from thescientific community
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 20
Chondrites can tell us about the early Solar System
Image courtesy of Hawaii Institute ofGeophysics and Planetology
Image courtesy of Alexander Krot, Uni-versity of Hawaii
In between the chondrules andCAIs is a fine grained matrix
Mostly made up of silicate-richmaterial that formed across arange of Solar System locationsStudying the matrix material cantell us about the heating andcooling histories of the meteoritesPresolar grains that formedelsewhere before our Sun formed
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 20
Chondrites can be classified by their chemical composition
Three main classes are called EnstatiteChondrites, Ordinary Chondrites andCarbonaceous Chondrites
Each of these classes can be furthersubdivided into groups
Enstatite chondrites have 2 groupsOrdinary chondrites have 3 groupsCarbonaceous chondrites have 9 groups
Meteorites with each group have similarphysical properties (e.g. chondrule sizes, mixof different components)
Each group represents materials that weremixed together and accreted at the sametime and placeProbably from the same parent body
Enstatite
Ordinary
Carbonaceous
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 21
Meteorite groups
Meteorites
Chondrites Differentiated
Enstatite Ordinary Carbonaceous Other
EC EH H L LL
CI CM CO CV CK CR CH CBa CBb
R K
Iron Achondrite
. . . Lunar Martian HED . . .
a b
c d
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 22
Differences between chondrite groups
How do we differentiate between enstatite, ordinary andcarbonaceous chondrites?
Enstatite
1 High formationtemperature
2 Low water andoxygen content
3 Little to noaqueous alteration
4 High levels ofheating
Ordinary
1 High formationtemperature
2 Medium watercontent
3 Mild aqueousalteration
4 Medium levels ofheating (¡ 500�C)
Carbonaceous
1 Lower formationtemperature
2 High watercontent
3 Aqueous alterationis common
4 Low levels ofheating ( 200�C)
Likely scenario:
Formed close to the Sun Formed far from the SunÝÑ
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 23
What do we know about where an asteroid formed?
Planetesimals formed in theprotoplanetary disk
Those close to the Sun would havebeen hotter than those far away
Asteroids that formed close to theSun probably wouldn’t have anywater (it not have condensed in thehotter regions near the Sun)
Those far away from the Sun,where the temperature was lower,may contain water (it could havecondensed as ice from the gas)
Ida
Image courtesy of NASA/JPL
Image courtesy of the Lunarand Planetary Institute
Enstatite Ordinary Carbonaceous
Formed close to the Sun Formed far from the SunÝÑ
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 24
Meteorites are samples of asteroids
E-type asteroids are similar incomposition to enstatite chondrites
Hungaria family are E-typeThey orbit at �1.8 AU
S-class (stony) asteroids can be linkedto the ordinary chondrites
They orbit at around 2.1 – 2.8 AU
C-class asteroids are linked to thecarbonaceous chondrites
They orbit at distances of ¡ 2.7 AUThey contain water-bearing minerals
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 25
Meteorites are samples of asteroids
Groups of meteorites are linked toparticular regions of the asteroid belt
However, the regions overlap a littleSo, perhaps they were mixed aftertheir formationWe will talk more about this mixingnext week
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 25
Part 2:Evidence of impacts on asteroids and meteorites
Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 26
All asteroids have one feature in common: Impact Craters
In the lecture, I played a video of Dawn’s virtual flight over Vesta.You can view that video online here:http://www.jpl.nasa.gov/video/index.php?id=1080
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 27
Collisions have long lasting effects
Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
All asteroids show theeffects of collisions ontheir surfaces
Impacts also have effectsthat can be seen inmeteorites
A collision at fast enoughvelocity causes a shockwave to travel throughthe asteroid
The effects of that shockwave can be observed inmeteorites
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 28
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Collisions cause shock waves
Collision between twoasteroids forms acrater on the surface
Inside the asteroid,high pressures areexperienced becauseof the shock wave
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 29
Shock waves alter the minerals in a meteorite
The high pressure created bythe impact event can meltmaterials
In some cases, smallparticles of melt have theeffect of blackening themeteorite
Impacts can also causemetamorphism inmeteorites, e.g.
Planar deformationfeaturesShocked quartz
andtheshock
blacken
edFarmington,an
dfoundthat
whileboth
had
similar
amounts
ofmetal
and
troilite
(theprimaryopaq
uematerials
inordinarychondrites),
inJackalsfontein
theav
erag
eparticlesize
oftheopaq
ues
was
150mm
while
inFarmington
itwas
only
2mm
(Fig.2).The
smaller
particle
size
of
the
opaq
ues
substan
tially
increases
their
effective
cross-section.
Furthermore,the
location
ofthe
opaq
ues
atgrain
boundaries,
whereligh
tnorm
ally
isreflected,increases
theireffect
on
reducingtheam
ountofligh
treturned
from
themineral.Theresult
isthat
shock
blackened
meteoritescan
hav
ean
albedo
comparab
leto
some
carbonaceouschondrites.
Shock
blackened
meteoritesarerelatively
rare;Britt
and
Pieters
(199
1)report
that
only
13:7!
4:5%
of
ordinarychondrite
fallsmeettheiropticaldefinitionofa
black
chondrite.Thus,just
assign
ificantas
thefact
that
shock
events
canturn
ordinarystonymeteoritesblack,
isthefact
that
such
blackeningistheexceptionan
dnot
therule.Asteroidscanbedisassembled,an
dpiecesput
into
Earth-crossingorbits,
withoutblackening85
%of
thematerialaffected.
Theshockstag
eofameteorite
isdetermined
bythe
presence
(orab
undan
ce)ofdam
agein
mineral
crystals
form
edduringthepassage
ofshock
wav
esthrough
arock.Themostcommonly
usedsystem
isthat
ofStoffler
etal.(199
1),which
grad
esmeteoritesinto
sixstag
es,
from
theunshocked
S1through
theheavily
shocked
S6
(see
Tab
le1).
The
criteria
for
shock
stag
einclude
the
optical
extinctionsofthemineral
crystals
(unshocked
minerals
hav
esharp
opticalextinctions,
which
becomeundula-
tory
asshock
dislocates
and
dam
ages
the
crystal
structure);
thepresence
andnature
offracturesin
the
olivine;
theform
ationofmeltpockets;
thepresence
of
opaq
ue
shock
veins;
the
presence
ofshock-induced
mineralssuch
asmaskelyn
ite;
andsolidstaterecrystalli-
zation.
Based
on
laboratory
studies
going
back
several
decad
es(cf.
Fredriksson
etal.,
1963
)estimates
hav
ebeenmad
eforthetotaltemperature
andpeakpressure
excursion
each
shock
stag
erepresents.Though
recent
resultshav
ecalled
into
questionsomeofthesecalibra-
tions(cf.
Xie
etal.,
2001
),thesystem
stillserves
toindicatetherelative
orderingofshock
featuresan
dgives
atleastarough
guideas
tothelevelofshock
pressure
and
temperature
that
agiven
meteorite
must
hav
eexperienced.
Most,butnotall,
shock
blacken
edmeteoritesfor
whichastag
ehas
beendetermined
areS4orhigher,as
mightbeexpected.However,notallS5orS6meteorites
are
black,an
dGrady
(200
0)lists
atleast
one
S2
meteorite
(May
day
)an
dtw
oS3meteorites(G
ladstone
andOrvinio)whichnonethelessareshock
blacken
ed.
Likew
ise,
the
correlation
between
shock
state
and
porosity
isnotnearlyas
strongas
onemightsuspect.
Whiletheless-shocked
meteoritestendonav
erag
eto
be
slightlymore
porous,thiscorrelationisweak,especially
ART
ICLE
INPR
ESS
Fig.1.Theconstrastbetweenunshocked
ordinarychondriteFarmville
(above)an
dthe
shocked
ordinary
chondrite
Farmington
(below)
showshowshock
canturn
essentially
identicalm
aterialfrom
ligh
tgray
toblack.
Fig.2.
High
resolution
SEM
image
ofFarmington,showing
the
distributionofthesubmicronmetallicblebsresponsible
foritsblack
coloring.
Guy
Consolm
agno
S.J.,D.T.Britt/Planetary
andSpace
Science
52(2004)
1119
–1128
1121
Image courtesy of Consolmagno & Britt(2004)
Image courtesy of USGS
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 30
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Impacts can also break apart asteroids
In space, there is constant backgroundradiation, called galactic cosmic rays
These rays provide enough energy toform some short-lived radioactiveisotopes, which decay quickly
But, they can only do this in the upperfew inches of the asteroid or meteoroid
Since we know the half lives of theseisotopes, we can determine how longthe material has been exposed in space
A short cosmic ray exposure agemeans the asteroid was only recentlydisrupted
Collision Processes
We well look at collisionsin more detail in a coupleof weeks time
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 31
Low density asteroids are evidence of breakup events
Macroporosity, %
1E + 22
1E + 20
Mas
s in
Kilo
gram
s (lo
g sc
ale)
1E + 18
1E + 16
1E + 14
1 Ceres (G)
87 Sylvia (P)
Average S
243 Ida (S)
Phobos
Average C253 Mathilde (C)
90 Antiope (C)
45 Eugenia (C)22 Kalliope (M)
16 Psyche (M)
Deimos433 Eros (S)
20 Massalia (S)
4 Vesta (V)2 Pallas (B)
762 Pulcova (F)
11 Parthenope (S)
0 10 20
121 Hermione (C)
30 8070605040
Coherent Asteroids
Fractured Asteroids
Loosely Consolidated (Rubble-pile)
Asteroids
Adapted from Britt et al. (2002) in Asteroids III
Some asteroids have high porosity (low density)Impacts should have crushed some of that pore space out
They have a macroporosity, because they have been brokenapart and reformed
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 32
Summary of today’s lecture
Meteorites are samples of asteroidsand planets
They can tell us about theconditions under which asteroidsformed
They also record the collisionalhistory of asteroids
They are one of our best sources ofinformation about the early SolarSystem
Next week: Building the Planets
Image courtesy of H. Raab
Image courtesy of NASA
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 33
Thank you
Questions?
T. M. Davison Constructing the Solar System Compton Lectures – Autumn 2012 34