meteorites: rocks from space. leonid meteor shower, 1998 european fireball network image meteoroid...
Post on 22-Dec-2015
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Where do meteorites come from?
Well-photographed meteors which have produced meteorites:
Pribram, Czechoslovakia 1959 H5Lost City, Oklahoma 1970 H5Innisfree, Alberta 1977 LL5Peekskill, New York 1992 H6
Tagish Lake, British Columbia 2000 CM1
Tagish Lakefireball
How do meteorites get to the Earth?
(1) Perturbations by Jupiter can put asteroidalmaterial into Earth-crossing orbits(Kirkwood gap clearing).
(2) The Yarkovsky Effect can cause rotatingm-sized objects to spiral inwards to (or outwardsfrom) the sun.
Cosmic-ray exposure (CRE) ages of meteorites(~1 Ma to ~0.5 Ga) give travel time needed form-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# parent
Designation Class & rock types bodies*
Stony chondrites: agglomerate > 13
Stony achondrites: igneous, breccia > 8
Stony-iron pallasite: igneous > 3
Stony-iron mesosiderite: meta-breccia 1 (2)
Iron many groups: igneous 50-80?
* as inferred from chemical & isotopic studies
Meteorites:different types
Designation Type of rock
Chondrite agglomerate-- never melted
(stony)
All else igneous; impact breccias--
(stony, stony- melted at least once
iron, iron)
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)
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
“Chondritic texture”: an agglomeration of chondrules and fine-grained matrix
matrix
chondrules
0.2 mm
Achondrite - any stony meteorite NOT a chondrite - samples of crusts and mantles of differentiated asteroids, the Moon, and Mars
Studies of meteorites provide evidence for:
1) widespread transient, high-T heating events in thesolar 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 systemformation!
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 insolar 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