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 Series
Autumn 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
10/27/12
Asteroids and Meteorites:
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
12/01/12
Constructing the Moon
12/08/12
No lecture: Physics with a Bang!
12/15/12
Impact Earth: Chicxulub and other terrestrial impacts
8
9
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
10/27/12
Asteroids and Meteorites:
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
12/01/12
Constructing the Moon
12/08/12
No lecture: Physics with a Bang!
12/15/12
Impact Earth: Chicxulub and other terrestrial impacts
8
9
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 different
meteorite classes
Image courtesy of Ed Sweeney
How they are linked to asteroid
families
5
Evidence of collisions on asteroids
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?
Vesta: mean diameter = 525 km
Asteroid
A relatively small, inactive,
rocky body orbiting the
Sun, usually between the
orbits of Mars and Jupiter
Image courtesy of
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Comet
Comet Hartley 2: 2.25km long
A relatively small, at times
active, object whose ices
can vaporize in sunlight
forming an atmosphere
(and sometimes a tail) of
dust and gas
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 how
planetesimals were
formed
Small rocky bodies
1–100 km in size
Examples of some asteroids,
compared to the size of Mars
Next week we will learn
how the planets grew
from planetesimals
Some planetesimals did
not grow into planets
Those that survived now
form the asteroid belt
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!
Titius-Bode
Actual
70
60
50
40
30
20
T. M. Davison
Plu
t
Me
rcu
ry
0
o
10
Ve
nu
s
Ea
rth
Ma
rs
Ce
res
Jup
ite
r
Sa
tur
n
Ur
anu
s
Ne
ptu
ne
Semi-major axis [AU]
80
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!
Titius-Bode
Actual
70
60
50
40
30
20
T. M. Davison
Plu
Me
rcu
ry
0
to
10
Ve
nu
s
Ea
rth
Ma
rs
Ce
res
Jup
ite
r
Sa
tur
n
Ur
anu
s
Ne
ptu
ne
Semi-major axis [AU]
80
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 to
the 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
Most asteroids are contained
in the main belt between
Mars and Jupiter
Some follow a similar orbit
to Jupiter (the Trojans)
Comets tend to have much
longer orbital periods, and
much greater eccentricity
than asteroids
Image courtesy of Paul Chodas (NASA/JPL)
T. M. Davison
Their orbits taken them out
to the region of the outer
planets, and beyond
Constructing the Solar System
Compton Lectures – Autumn 2012
8
Orbital eccentricity and inclination
Planet
Eccentricity
A planet’s orbital eccentricity, e is a
measure of how elliptical its orbit is
Sun
ae
e = 0 means the orbit is circular
0 e
1 for an elliptical orbit
a
Inclination
The orbital inclination, i is the angle
between the plane of the orbit of the
planet and the ecliptic — which is
the plane containing Earth’s orbital
path
T. M. Davison
Constructing the Solar System
e=0.0
e=0.5
e=0.8
i
Compton Lectures – Autumn 2012
9
Asteroid families
Some asteroids are grouped
based on where they orbit.
For example:
The Hungaria family orbit
between 1.78 and 2 AU
The Hilda family orbit
between 3.7 and 4.2 AU
The Jupiter Trojan family
orbit between 5.05 and
5.35 AU
The Near-Earth Objects
come within 1.3 AU of the
Sun on their closest
approach
Why are there gaps where no
asteroids orbit?
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
10
Kirkwood gaps
Asteroid Main-Belt Distribution
Kirkwood Gaps
Asteroids (per 0.0005 AU bin)
350
Mean Motion Resonance
( asteroid : Jupiter )
3:1
5:2
7:3
Gaps in the asteroid
belt appear at mean
motion orbital
resonances with
Jupiter
2:1
300
250
200
150
These gaps are known
as Kirkwood gaps
100
50
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
Semi-major Axis (AU)
3.1
3.2
3.3
3.4
3.5
What is an orbital
resonance?
Alan Chamberlin (2007, JPL/Caltech)
Image courtesy of Alan Chamberlin (NASA/JPL)
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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall 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 the
swing is going forward, all those pushes will
add up to make the swing go higher
The velocity increases
The same applies for asteroids in resonance
with Jupiter
Planet Formation
We will look more at the
role of orbital resonance
in the formation of the
planets, next week
A resonance of 3:1 means that the asteroid
orbits the Sun 3 times for every orbit that
Jupiter makes
So, every third orbit, the asteroid gets a
small push from Jupiter, which speeds it up
It then can either:
Find a new stable orbit
Fall into a planet-crossing orbit
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
12
What else can we find out about asteroids?
Ida
It is possible to look at the light
reflected from asteroids and tell
something about their chemistry
Different elements reflect and absorb
light at different wavelengths
However, to really understand that data,
we need something to compare it to
Image courtesy of NASA/JPL
Mathilde
We do have some sample of asteroids on
Earth: these samples are called
meteorites
Image courtesy of NASA
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
13
What are meteorites?
Leonid meteor shower, 2009
Meteoroid
A small particle from a comet or
asteroid orbiting the Sun
Meteor
Image courtesy of Ed Sweeney
Holsinger Meteorite,
Meteor Crater, Arizona
The light phenomena which results
when a meteoroid enters the Earth’s
atmosphere and vaporizes; a shooting
star
Meteorite
A meteoroid that survives its passage
through the Earth’s atmosphere and
lands upon the Earth’s surface
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
14
Meteorites: Falls and Finds
Meteorites can be classified into two types
depending on how we found them
Falls and Finds
Image courtesy of P. Jenniskens/SETI
Institute
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
15
Meteorites: Falls and Finds
Meteorites can be classified into two types
depending on how we found them
Falls and Finds
Falls are meteorites that have been
observed falling to Earth, and are
collected soon after
500 meteorites of marble to basketball
size are expected to fall each year and
remain intact
Yet, only 5–6 are discovered and
made available for scientists
Image courtesy of P. Jenniskens/SETI
Institute
T. M. Davison
Example: Almahatta Sitta meteorite that
fell in the Nubian Desert in Sudan in 2009
Constructing the Solar System
Compton Lectures – Autumn 2012
15
Meteorites: Falls and Finds
Meteorites can be classified into two types
depending on how we found them
Falls and Finds
Falls are meteorites that have been
observed falling to Earth, and are
collected soon after
500 meteorites of marble to basketball
size are expected to fall each year and
remain intact
Yet, only 5–6 are discovered and
made available for scientists
Example: Almahatta Sitta meteorite that
fell in the Nubian Desert in Sudan in 2009
Image courtesy of P. Jenniskens/SETI
Institute
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
15
Meteorites: Falls and Finds
Meteorites can be classified into two types
depending on how we found them
Falls and Finds
Image courtesy of C. Corrigan/ANSMET
Finds are meteorites that were not
observed falling to Earth, and are found
later
Finds are 30 times more common
But, sometimes have been weathered
Some areas are better to look than
others: e.g. deserts or Antarctica
Image courtesy of ANSMET
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
15
Meteorites can be separated into two main classes
Differentiated meteorites and Chondritic meteorites
Differentiated meteorites
Formed in planetesimals that
melted shortly after
Some are metallic (usually a
nickel-iron alloy)
Iron meteorite
Core of a melted planetesimal
Some are stony (called
achondrites because they have no
chondrules)
Outer layers of a melted
planetesimal or planet
These include meteorites from
the Moon, Mars and asteroids
such as Vesta
T. M. Davison
Constructing the Solar System
Image courtesy of H. Raab
Compton Lectures – Autumn 2012
16
Planetesimals were heated after formation
Differentiated meteorites were melted after their parent planetesimal
formed
Most of this heat came from the decay of radioactive material
A major source of this heat is the decay of 26 Al to 26 Mg
Decays with a half-life of t1{2
0.73 Myr
n=64 n= 0
n=32 n=32
n=16 n=48
n= 8 n=56
n= 4 n=60
n= 2 n=62
n= 1 n=63
t=0
0.00 Myr
t = t1/2
0.73 Myr
t = 2t1/2
1.46 Myr
t = 3t1/2
2.19 Myr
t = 4t1/2
2.92 Myr
t = 5t1/2
3.65 Myr
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
12
26
Al
Fe
26
Al +
60
Available energy (kJ g−1 )
10
60
Fe
8
6
4
2
0
0
T. M. Davison
1
2
3
Time (Ma)
Constructing the Solar System
4
5
6
Compton Lectures – Autumn 2012
18
Meteorites can be separated into two main classes
Differentiated meteorites and Chondritic meteorites
Chondrites, or primative
meteorites
Chemical compositions that
closely resemble the Sun
Except for volatile elements (e.g.
H, He, C, N, O), the abundance
of other elements are within a
factor of 2 of the Sun’s
composition
They have not melted since they
accreted
T. M. Davison
Constructing the Solar System
Chondrite
Image courtesy of H. Raab
Compton Lectures – Autumn 2012
19
Chondrites can tell us about the early Solar System
An important component of
chondrites are called
Calcium-Aluminium-rich
inclusions (or CAIs)
Image courtesy of Hawaii Institute of
Geophysics and Planetology
CAIs are the oldest known objects
to form in the Solar System
Formed approximately 4567 Myr
ago
Formed at very high
temperatures (¡ 1400 K or
2000 F)
Image courtesy of Alexander Krot, University of Hawaii
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
20
Chondrites can tell us about the early Solar System
Chondrites get their names from
one of their main components:
Chondrules
Image courtesy of Hawaii Institute of
Geophysics and Planetology
Chondrules are small (mm-sized)
spheres of silicate rock
They condensed from melt
droplets
Formed at lower temperatures
( 1000 K or 1350 F)
Formed around 2 Myr after CAIs
There are lots of discussions
about how chondrules formed,
and still no consensus from the
scientific community
Image courtesy of Alexander Krot, University of Hawaii
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
20
Chondrites can tell us about the early Solar System
In between the chondrules and
CAIs is a fine grained matrix
Image courtesy of Hawaii Institute of
Geophysics and Planetology
Mostly made up of silicate-rich
material that formed across a
range of Solar System locations
Studying the matrix material can
tell us about the heating and
cooling histories of the meteorites
Presolar grains that formed
elsewhere before our Sun formed
Image courtesy of Alexander Krot, University of Hawaii
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 Enstatite
Chondrites, Ordinary Chondrites and
Carbonaceous Chondrites
Each of these classes can be further
subdivided into groups
Enstatite chondrites have 2 groups
Ordinary chondrites have 3 groups
Carbonaceous chondrites have 9 groups
Meteorites with each group have similar
physical properties (e.g. chondrule sizes, mix
of different components)
Enstatite
Ordinary
Carbonaceous
Each group represents materials that were
mixed together and accreted at the same
time and place
Probably from the same parent body
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
21
Meteorite groups
a
b
Meteorites
Chondrites
Enstatite
EC
c
CI
Ordinary
EH
CM
T. M. Davison
Differentiated
Carbonaceous
H
L
LL
CO
CV
CK
CR
Other
Iron
R
K
...
CH
CBa
CBb
Constructing the Solar System
Achondrite
Lunar
Martian
HED
...
d
Compton Lectures – Autumn 2012
22
Differences between chondrite groups
How do we differentiate between enstatite, ordinary and
carbonaceous chondrites?
Ordinary
Enstatite
Carbonaceous
1
High formation
temperature
1
High formation
temperature
1
Lower formation
temperature
2
Low water and
oxygen content
2
Medium water
content
2
High water
content
3
Little to no
aqueous alteration
3
Mild aqueous
alteration
3
Aqueous alteration
is common
4
High levels of
heating
4
Medium levels of
heating (¡ 500 C)
4
Low levels of
heating ( 200 C)
Likely scenario:
Formed close to the Sun
T. M. Davison
ÝÑ
Formed far from the Sun
Constructing the Solar System
Compton Lectures – Autumn 2012
23
What do we know about where an asteroid formed?
Planetesimals formed in the
protoplanetary disk
Ida
Those close to the Sun would have
been hotter than those far away
Asteroids that formed close to the
Sun probably wouldn’t have any
water (it not have condensed in the
hotter regions near the Sun)
Those far away from the Sun,
where the temperature was lower,
may contain water (it could have
condensed as ice from the gas)
Enstatite
T. M. Davison
ÝÑ
Image courtesy of the Lunar
and Planetary Institute
Ordinary
Formed close to the Sun
Image courtesy of NASA/JPL
Carbonaceous
Formed far from the Sun
Constructing the Solar System
Compton Lectures – Autumn 2012
24
Meteorites are samples of asteroids
E-type asteroids are similar in
composition to enstatite chondrites
Hungaria family are E-type
They orbit at 1.8 AU
S-class (stony) asteroids can be linked
to the ordinary chondrites
They orbit at around 2.1 – 2.8 AU
C-class asteroids are linked to the
carbonaceous chondrites
They orbit at distances of ¡ 2.7 AU
They 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 to
particular regions of the asteroid belt
However, the regions overlap a little
So, perhaps they were mixed after
their formation
We will talk more about this mixing
next 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
All asteroids show the
effects of collisions on
their surfaces
Impacts also have effects
that can be seen in
meteorites
A collision at fast enough
velocity causes a shock
wave to travel through
the asteroid
Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
T. M. Davison
Constructing the Solar System
The effects of that shock
wave can be observed in
meteorites
Compton Lectures – Autumn 2012
28
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
Collisions cause shock waves
Collision between two
asteroids forms a
crater on the surface
Inside the asteroid,
high pressures are
experienced because
of the shock wave
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
29
The high pressure created by
the impact event can melt
materials
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
and the shock blackened Farmington, and found that
Fig. 1. The constrast between unshocked ordinary chondrite Farmville
(above) and the shocked ordinary chondrite Farmington (below)
shows how shock can turn essentially identical material from light gray
to black.
In some cases, small
particles of melt have the
effect of blackening the
meteorite
Impacts can also cause
metamorphism in
meteorites, e.g.
The shock stag
presence (or abun
formed during th
rock. The most co
et al. (1991), whi
from the unshock
(see Table 1).
The criteria f
extinctions of the
have sharp optic
tory as shock
structure); the pr
olivine; the forma
opaque shock ve
minerals such as
Fig. 2. High resoluti
distribution of the sub
coloring.
Guy Consolmagno S.J., D.T. Britt / Planetary and Space Science 52
ARTICLE IN PRESS
Shock waves alter the minerals in a meteorite
Image courtesy of Consolmagno & Britt
(2004)
Planar deformation
features
Shocked quartz
Image courtesy of USGS
30
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Impacts can also break apart asteroids
In space, there is constant background
radiation, called galactic cosmic rays
These rays provide enough energy to
form some short-lived radioactive
isotopes, which decay quickly
But, they can only do this in the upper
few inches of the asteroid or meteoroid
Since we know the half lives of these
isotopes, we can determine how long
the material has been exposed in space
Collision Processes
We well look at collisions
in more detail in a couple
of weeks time
A short cosmic ray exposure age
means the asteroid was only recently
disrupted
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
31
Low density asteroids are evidence of breakup events
1E + 22
Coherent
Asteroids
Mass in Kilograms (log scale)
1 Ceres (G)
4 Vesta (V)
2 Pallas (B)
1E + 20
87 Sylvia (P)
20 Massalia (S)
762 Pulcova (F)
11 Parthenope (S)
121 Hermione (C)
1E + 18
Average S
253 Mathilde (C)
Phobos
1E + 16
433 Eros (S)
22 Kalliope (M)
90 Antiope (C)
Average C
243 Ida (S)
1E + 14
16 Psyche (M)
45 Eugenia (C)
Loosely
Consolidated
(Rubble-pile)
Asteroids
Deimos
Fractured
Asteroids
0
10
20
30
40
50
Macroporosity, %
60
70
80
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 broken
apart and reformed
T. M. Davison
Constructing the Solar System
Compton Lectures – Autumn 2012
32
Summary of today’s lecture
Meteorites are samples of asteroids
and planets
They can tell us about the
conditions under which asteroids
formed
They also record the collisional
history of asteroids
Image courtesy of H. Raab
They are one of our best sources of
information about the early Solar
System
Next week: Building the Planets
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