Meteorites:Meteorites:

Rocks from Rocks from spacespace

Leonid meteorshower, 1998 European Fireball Networkimage

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 1959 H5Lost City, Oklahoma 1970 H5Innisfree, Alberta 1977 LL5Peekskill, New York 1992 H6

Tagish Lake, British Columbia 2000 CM1

Tagish Lakefireball

Meteoroid orbits:aphelia between Mars& Jupiter (asteroid belt)

Jupiter

Mars

Spectralreflectanceof variousmeteorites & asteroids

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 All other rocks

Undifferentiatedmeteorites: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

“Chondritic texture”: an agglomeration of chondrules and fine-grained matrix

matrix

chondrules

0.2 mm

CAIs

contains CAIs andpre-solar grains

CAIs

Carbonaceouschondrite

chondrules

Image: J.A. Wood

Contains pre-bioticorganic material

Carbonaceous vs.Ordinary Chondrites

Shocked chondrite:the 1992 Peekskill Fireball meteorite

Differentiatedmeteorites

DAG 485 (urelilite)

Gibeon (IVA iron) Millbillillie (eucrite)

Achondrite - any stony meteorite NOT a chondrite - samples of crusts and mantles of differentiated asteroids, the Moon, and Mars

Big! iron meteorite

Irons - samples of the cores of differentiated asteroids

Iron meteorite:slow-cooling ina metallic core

Mesosideriteorigin:

collision of astripped metalcore & anotherdifferentiatedasteroid?

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