Meteorites:
Rocks from
space
Leonid meteor
shower, 1998
European
Fireball Network
image
Meteoroid
Meteor
(fireball)
Meteorite
1992 Peekskill fireball video clips
(How to turn a $300 car into one worth $10,000.)
Results of ablation: fusion crust, thumbprints, fragmentation
Where do meteorites come from?
Well-photographed meteors which have produced meteorites:
Pribram, Czechoslovakia
Lost City, Oklahoma
Innisfree, Alberta
Peekskill, New York
Tagish Lake, British Columbia
Tagish
Lake
fireball
1959
1970
1977
1992
2000
H5
H5
LL5
H6
CM1
Meteoroid orbits:
aphelia between Mars
& Jupiter (asteroid belt)
Jupiter
Mars
Spectral
reflectance
of various
meteorites
& asteroids
How do meteorites get to the Earth?
(1) Perturbations by Jupiter can put asteroidal
material into Earth-crossing orbits
(Kirkwood gap clearing).
(2) The Yarkovsky Effect can cause rotating
m-sized objects to spiral inwards to (or outwards
from) the sun.
Cosmic-ray exposure (CRE) ages of meteorites
(~1 Ma to ~0.5 Ga) give travel time needed for
m-sized object-- consistent with Yarkovsky Effect
Meteorites:
different types
Designation
Proportion of metal & silicate
Stony
>> 50 % silicate
Stony-iron
~ 50% metal, ~ 50% silicate)
Iron
>> 50% metal alloy
Meteorite types & parent bodies
Designation
Class & rock types
# parent
bodies*
Stony
Stony
chondrites: agglomerate
achondrites: igneous, breccia
> 13
>8
Stony-iron
Stony-iron
pallasite: igneous
mesosiderite: meta-breccia
>3
1 (2)
Iron
many groups: igneous
50-80?
* as inferred from chemical & isotopic studies
Meteorites:
different types
Designation
Type of rock
Chondrite
(stony)
agglomerate-- never melted
All else
(stony, stonyiron, iron)
igneous; impact breccias-melted at least once
Chondrites
All other rocks
Undifferentiated
meteorites:
chondrites
Chondrites
• Meteorite type most often
seen to fall (85.6%)
• Earliest-formed rocks
(ages: ~4.55 b.y.)
• Formed in solar nebula
• Solar-like bulk composition
(planetary building
blocks)
protoplanetary disks
Chondrites
have “solar
composition”
for most
elements
Chondrites
• most contain chondrules
mm to sub-mm-sized objects
formed as melted dispersed objects
• some contain refractory inclusions (CAIs)
mm to cm-sized objects
formed at high temperatures in solar nebula
• some contain pre-solar grains
grains formed around other stars
• some contain pre-biotic organic matter
matrix
chondrules
0.2 mm
“Chondritic texture”: an agglomeration
of chondrules and fine-grained matrix
CAIs
contains CAIs and
pre-solar grains
CAIs
chondrules
Carbonaceous
chondrite
Image: J.A. Wood
Contains pre-biotic
organic material
Carbonaceous vs.
Ordinary Chondrites
Shocked chondrite:
the 1992 Peekskill Fireball meteorite
Gibeon (IVA iron)
Differentiated
meteorites
DAG 485 (urelilite)
Millbillillie (eucrite)
Achondrite - any stony meteorite NOT a chondrite - samples of
crusts and mantles of differentiated asteroids, the Moon, and Mars
Irons - samples of the cores of differentiated asteroids
Big! iron meteorite
Iron meteorite:
slow-cooling in
a metallic core
Mesosiderite
origin:
collision of a
stripped metal
core & another
differentiated
asteroid?
Studies of meteorites provide evidence for:
1) widespread transient, high-T heating events in the
solar nebula
-- to form chondrules, CAIs
2) gas-dust chemical equilibrium in the solar nebula
-- “equilibrium condensation model” valid
3) incomplete mixing & heating of dust in the solar nebula
-- pre-solar material survived solar system
formation!
Studies of meteorites provide evidence for:
4) short-lived heat sources in meteorite parent bodies
-- many asteroids melted & differentiated
-- many asteroids metamorphosed & aqueously
altered
-- short-lived radionuclides, induction heating (?)
were important in early solar system
5) water in many meteorite parent bodies
-- in the form of ice or hydrated materials
-- water in some asteroids too
Studies of meteorites provide evidence for:
6) pre-biotic organic synthesis
-- precursor materials for life formed in space!
7) impact & collision processes
-- collisions important, probably even early in
solar system
-- asteroids may have been disrupted &
reassembled
Studies of meteorites provide evidence for:
8) interplanetary rock-swapping
-- we have martian & lunar meteorites
-- this has implications for life