meteorites: what we know, andweb.pdx.edu/~ruzickaa/meteorites/meteorites-psucourse.pdf ·...

Meteorites:

What we know, and

don’t know

Outline:

Meteorites

Meteorite parent bodies

Meteorite diversity

Organic synthesis

Pre-solar grains

Fiery rain

Short-lived nuclides

Rock swapping

© A.Ruzicka

Meteorites

What is a meteorite?

• On Earth, all extraterrestrial rocks

• Any rock that did not form on the

body which it is found

• Mostly 4.56 b.y. old (exceptions)

<< Unclassified

meteorite from

Northwest Africa

Leonid meteor shower,

1998 (European Fireball

Network Image)

Meteoroid

Meteor

(fireball)

Meteorite

Meteorites© A.Ruzicka

1992 Peekskill fireball video clips

(How to turn a $300 car into one worth $10,000.)

Meteorites© A.Ruzicka

Meteorites

What we know – Parent bodies

Most meteorites were derived from parent bodies in the

asteroid belt.

Meteoroid orbits

Meteorite parent bodies© A.Ruzicka

Asteroids as the main source of meteorites


How do meteorites get from asteroids to the Earth?

(1) Gravitational perturbations by Jupiter & Mars can put

asteroidal material into asteroid-crossing orbits.

(2) Collisions between asteroids fragment material into

smaller pieces.

(3) 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


4-Vesta: probable parent body of HED meteorites

giant south

polar basin

diameter = 540 km

albedo = 0.38

Prot = 5.3 hr

spectral class = V

(nearly unique

match to HED

meteorites)

density = 3.4 g/cm3

a = 2.36 AU

howardite

(NWA 2060)

H = howardite, E = eucrite, D = diogenite


What we don’t know:

1. Which asteroids (besides Vesta) supplied our

meteorites?

2. Did they form there, or move in from elsewhere?

3. How were materials assembled and processed in

small bodies?


Was collisional

disruption common?

Break-up Reassembly

Rubble pile


What we know – Diversity

Meteorites are highly variable in their properties.

• Include both melted & unmelted types

• Unmelted meteorites (chondrites) formed in unique

environment: the solar nebula

• Melted meteorites formed in differentiated bodies

Meteorite diversity© A.Ruzicka

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)


Chondrite formation setting:

protoplanetary disks (proplyds)

around young stellar objects (YSOs)

W.K. Hartmann

solar nebula: our proplyd© A.Ruzicka

Chondrites

have “solar

composition”

for most

elements

note light elements—

variable amounts

in different chondrites

© A.Ruzicka

Different chondrite groups

16 chondrite

groups recognized


DAG 485 (ureilite)

Gibeon (IVA iron) Millbillillie (eucrite)Melted

(differentiated)

meteorites

• achondrites

• irons

• stony irons


What we don’t know

What is the exact relationship between chondrites and melted

(igneous) meteorites?

It’s assumed that igneous meteorites were derived from

chondritic parent bodies that were melted

However, dating suggests that some chondrites formed after

igneous meteorites

How were different chondrites and igneous meteorites

produced?


What we know – Organics

Pre-biotic organic synthesis occurred in solar

system building blocks.

• Organic compounds found in interstellar medium (ISM)--

molecular clouds-- and in carbonaceous chondrite meteorites

• Solar system formed by collapse of molecular cloud;

chondrites formed in the early solar system

Organic synthesis© A.Ruzicka

Molecular cloudscold, dense areas in

interstellar medium (ISM)

Horsehead Nebula

Mainly molecular H2,

also dust, T ~ 10s of K


Carbonaceous chondrite—

Rich in organic material


Many organic compounds in carbonaceous chondrites

Include: macromolecular (kerogen-like) carbon, carboxylic acids,

dicarboxylic acids, amino acids, lower alkanes, higher alkanes, aromatic

hydrocarbons, N-compounds

Synthesis possible in different ways, environments:

• in molecular clouds

• in our solar system-- within parent bodies, maybe in dispersed

grains within the solar nebula



1. How much and what type of pre-biotic organic synthesis

occurred via different mechanisms?

2. Were these pre-biotic compounds used to help jump-start

life on Earth?


What we know – Pre solar grains

Pre-solar grains were incorporated & preserved

in chondritic meteorites.

<< contains

microscopic

pre-solar grains,

found by acid

dissolution, gas

extraction, or

isotope

mapping

Pre-solar grains© A.Ruzicka

material suggested astrophysical site

Ne-E exploding nova

S-Xe Red Giant or Supergiant

Xe-HL supernovae

Macromolecular C low-T ISM

SiC C-rich AGB stars, supernovae

Corundum AGB stars

Nanodiamond supernovae

Graphite, Si3N4 supernovae

Pre-solar material in meteorites

These materials are released into the ISM when stars die.


Supernova remnants

Note: planetary nebula have nothing to do with planets!

Planetary

nebulas



1. How many different pre-solar stars contributed

matter to our solar system?

2. Besides contributing matter, did shock waves from

dying stars help trigger the formation of our solar

system?


What we know – Fiery rain

A substantial amount of dust in the early

solar system was processed by intense heating

events to make chondrules & CAIs

(Ca-Al-rich inclusions).

• Chondrules formed as free-floating melt droplets

(“fiery rain”) in early solar system, accreted to form

chondrites. Chondrites accreted to form other bodies

(including planets).

• CAIs formed by an approach to equilibrium at high

temperatures, either as vaporization residues or

condensates. Most were molten.

Fiery rain© A.Ruzicka

Chondrule textures in thin-section

<< barred olivine, almost completely remelted

radial pyroxene & microporphyritic

pyroxene , completely or partly remelted >>

<< microporphyritic olivine >>

mostly remelted



1. What was the nature of the heating events that formed

chondrules and CAIs?

Many possibilities.

2. How did these heating events chemically and isotopically

modify the objects?

3. What is the relationship of chondrules & CAIs to one

another & to other meteorite components?

4. What do these components have to tell us about the

evolution of the solar nebula & how planets formed?


What we know - Short lived nuclides

The decay of short-lived radioactive nuclides was an

important heat source in the early solar system.

• Evidence for many short-lived nuclides found in various

meteorites, can be used as relative chronometers

• Many meteorite parent bodies melted, and short-lived

radioactive decay most promising heat source

Short-lived nuclides© A.Ruzicka

Radionuclide Half-life (Ma) Daughter Ratio measured

26Al 0.73 26Mg 26Mg/24Mg60Fe 1.5 60Ni 60Ni/58Ni53Mn 3.7 53Cr 53Cr/52Cr129I 15.7 129Xe 129Xe/130Xe

+ others

Short-lived nuclides

slope proportional

to 53Mn/55Mn

HED meteorite

parent body

melted &

differentiated while53Mn present

Hutchison (2004)

Proportional to 53Cr/52Cr

© A.Ruzicka


1. What were the most important heat sources for

asteroidal differentiation? (leading candidate: 26Al)

2. Can various short-lived decay schemes be reconciled

to give a coherent timescale of early solar system

evolution?

3. What do short-lived chronometers tell us about how

long it took to form the solar system?

Short-lived nuclides© A.Ruzicka

What we know - Rock swapping

Planetary rock-swapping has occurred throughout solar system

history.

• ~150 martian meteorites, ~150 lunar meteorites (as of 2019)

recognized on Earth; younger than 4.56 b.y.

• Impact-blasted off surfaces; brought to Earth in last ~0.1-10 m.y.

probably many more at earlier times

• Now finding meteorites on the Moon and Mars

<< Iron meteorite

Meridiani Planum

(MER Opportunity

image, sol 339)

Rock swapping© A.Ruzicka

Ancient terrain

on farside of

Moon—

Impact

battered


<< Mars meteorite

found in Northwest

Africa

Rock swapping

Lunar meteorite >>

found in Northwest

Africa

NWA 773

© A

.Ru

zic

ka

Rock swapping

<< Mars meteorite EETA 79001

Log number molecules isotope ratios in 2 meteorites

C1, C2, C3 =

EETA79001 glass

A, B = Zagami

glass

Normal = Zagami

Hutchison (2004)

© A.Ruzicka


1. How much swapping occurred in early solar system?

2. Did Earth receive samples from planets other than Mars?

3. Could life have been transplanted?


Summary

Meteorites present

major interdisciplinary

problems

for progress, will

require increased

collaboration from

scientists from

different fields--

geology

chemistry

biology

astronomy

astrophysics

© A.Ruzicka

meteorites: what we know, andweb.pdx.edu/~ruzickaa/meteorites/meteorites-psucourse.pdf ·...

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