Solar system chronology WE Heraeus Winterschool “The early phase of planet formation” Bad Honnef 18.2.2008 Articles for this lecture: Trieloff M. and Palme H. (2006) The origin of solids in the early solar system. In: Planet Formation – Theory, Observations, and Experiments (Eds. H. Klahr & W. Brandner), pp.64-89, Cambridge: Cambridge University Press (basic principles of cosmochemistry and chronology for astrophysicists) Trieloff M., Jessberger E.K., Herrwerth I., Hopp J., Fiéni C., Ghélis M., Bourot-Denise M. and Pellas P. (2003). Structure and thermal history of the H-chondrite parent asteroid revealed by thermochronometry. Nature 422, 502-506. Trieloff M., Kunz J., Clague D.A., Harrison D. and Allègre C.J. (2000) The nature of pristine noble gases in mantle plumes. Science 288, 1036-1038. Request offprints from: [email protected]

M. Trieloff

University of Heidelberg, Institute of Mineralogy, Heidelberg, Germany

Immanuel Kant (1724-1804)

Pierre Simon Laplace (1749-1827)

Origin of the solar system:
collapse of an interstellar cloud (gas + dust), planet formation in a rotating accretion disc
nearly circular orbits in the ecliptic plane, low inclinations

Star formation in the Orion nebula:

Mass rich stars first…

Protoplanetary discs in the Orion nebula

Solar mass stars still infant …

Undisturbed discs photographed as silhouettes (McCaughrean and O’Dell, 1996)

IR spectroscopy of protoplanetary disks: Mg silicates olivine+pyroxene – crystalline fraction higher in inner disks (van Boekel et al. 2004)

40 +- 20%

55 +- 25%

95 +- 10%

15 +- 10%

10 +- 5%

40 +- 15%

IR spectroscopy of protoplanetary disks: Mg silicates olivine+pyroxene – crystalline fraction higher in inner disks (van Boekel et al. 2004)

Crystalline fractions in some outer disks considerable, similar to solar system comets (Wooden et al., 2000)


Dust processing in disks and radial mixing into outer disks

Cometary grains from comet Wild-2 returned by the STARDUST mission

Refractory forsterite grain from STARDUST collector

First results: Silicates (Olv, Px, Fs), glass, Fe-Ni sulfides, refractory grains (An,Di,Sp) no phyllosilicates and carbonates in Wild-2 grains

Models taking into account annealing, evaporation, and condensation of Mg silicates reproduce radial mixing of crystalline species into outer disk /comet forming regions (Gail 2003)

Planets in extrasolar systems: exotic (observationally biased), but they exist:
1995-2007: ~250 exoplanets found (radial velocity variations, transitions)
2006: 5.5 Earth mass planet detected by gravitational lensing Mass (Jupiter-masses)

10

1

0,1 0,01

0,1

1

Distance from star [AU] Abstand vom Zentralstern [Erdradien]

Formation of planets in our solar system 4.5 Ga ago? Geoscientists need rocks !
Eyewitnesses of planet formation

Problems:
Earth rocks: available, but young
tectonically active, suffered large scale differentation processes
Other planetary rocks: no sample return (except for Moon)

Oldest rocks:
Isua, Greenland (3.8-3.9 Ga)

Oldest minerals:
Zirkons
Jack Hills, West Australia

U-Pb-Pb age of zirkons, Jack Hills, Australia: 4404± ±4 Ma (Peck et al., 2001; Wilde et al., 2001)

U-Pb-Pb age of zirkons, Jack Hills, Australia: 4404± ±4 Ma (Peck et al., 2001; Wilde et al., 2001)

Formation of planets in our solar system 4.5 Ga ago? Geoscientists need rocks !
Eyewitnesses of planet formation

Problems:
Earth rocks: available, but young (generally < 3.8 Ga, zircons up to 4.4 Ga)
Planetary rocks: no sample return (except for Moon)
Even if rocks from other terrestrial planets are available, most probably they are not remnants of early stages of protoplanet formation, as these did not survive early energetic large scale planetary differentiation processes (core formation, mantle-crust differentiation)

Solution: Meteorites
samples from small planetesimals that escaped energetic planetary formation / differentiation processes

1492: Stony meteorite Ensisheim

1492: Stony meteorite Ensisheim

1492: Stony meteorite Ensisheim

Hans Baldung Grien: The conversion of Saulus (1505)

Albrecht Dürer: Melancolia (1514)

Meteorites: Fragments of small bodies in the solar system, the asteroids between Mars and Jupiter Inferred number of parent bodies is >100 (accretion to full-sized planet inhibited by early Jupiter?!)

Innisfree

Problem: recognition of early processes through secondary effects of collisions and impact cratering (shock metamorphism, reheating, disturbance of radiometric clocks, etc.)

Eros viewed by NEAR

Carbonaceous chondrites (CI, CM, CV, CO, …): (mild thermal/aqueous metamorphism)


undifferentiated, e.g. preaccretional structures preserved

• Chondrules

• Ca,Al-rich inclusions • Fine grained matrix (volatile rich)
undifferentiated, e.g. ‘cosmic’ Fe,Ni abundance

Allende

Variation of oxidation state and metal abundance demonstrates compositional variety of undifferentiated planetary bodies Ordinary chondrites: H: high Fe L: Low Fe LL: Low total, low metallic Fe

Solar total iron 1,0

EH

Carbonaceous chondrites: named after main member CI (Ivuna) CM (Mighei) CV (Vigarano) CO (Ornans)

(Fe metal /Si)CI

0,8

Enstatite chondrites

re du ce d

EL EL 0,6 H

ox idi se d

0,4

CI chondrites match solar 0,0 elemental 0,0 0,2 composition within uncertainties

CV

L

0,2

CR

CO

LL LL

0,4

0,6

(Fe silicate +sulfide /Si)CI

CI/CM

0,8

1,0

Variation of oxygen isotopic composition demonstrates variety of undifferentiated planetary bodies

10 An in hyd cr ea r ou sin s c h g ox ond id at rites io : n st at e

R

5

LL

L

H

n) ti o

CK

A

CV

on s CV

-15

CO

CM

si ti po om C

C

in i ti

al c

-10

CK

CM

CR

l te ra

tria

io nat

E

CR

ne n li

-a

res Ter

-5

ctio l fra

(p re

17

O SMOW

0

δ

Reason of 16O enrichment in carbonaceous chondrite anhydrous minerals: Disk chemistry or presolar oxides?

CI

eo qu

us

a

ra l te

tio

n

CO rie to c fra

s

re ng AIs i C as re c In

-10

-5

0

5 18

δ O SMOW

10

15

20

Carbonaceous chondrites (CI, CM, CV, CO, …): (mild thermal/aqueous metamorphism)
preaccretional structures preserved

4564.7± 0.6 Ma (CR Acfer059; Amelin et al., 2002)

• Chondrules 2-3 Ma age difference supported by 26Al-26Mg chronometry • Ca,Al-rich inclusions 4567.2± 0.6 Ma (U-Pb-Pb, CV Efremovka; Amelin et al., 2002)

Allende

Carbonaceous chondrites (CI, CM, CV, CO, …): (mild thermal/aqueous metamorphism)
preaccretional structures preserved

4564.7± 0.6 Ma (CR Acfer059; Amelin et al., 2002)

• Chondrules

238U

• Ca,Al-rich inclusions 4567.2± 0.6 Ma (U-Pb-Pb, CV Efremovka; Amelin et al., 2002)

235U

Zoned type B1 CAI from Leoville (CV) Fassait (Ti-rich diopside)

Melilite

Anorthite

Fraction CI chondritic composition condensed

Condensation sequence of minerals in a cooling solar nebula: Ca,Al minerals important high temperature condensates

Fe-Ni-metal

Enstatite – MgSiO3 Gehlenite Ca2Al2SiO7

Hibonite CaAl12O19

Forsterite – Mg2SiO4

Spl

Cpx Albite Anorthite

from: Davis & Richter 2005

Ca,Al-rich Inclusions: refractory mineral assemblages, oldest solar system objects
4567.2± 0.6 Ma (Amelin et al., 2002)
contain excess 26Mg from decay of short-lived 26Al

Lee et al. 1976

Ca,Al-rich Inclusions: refractory mineral assemblages, oldest solar system objects
4567.2± 0.6 Ma (Amelin et al., 2002) 26Al-26Mg systematics: Processing within few 0.1 Ma Young et al. 2005

Short-lived nuclides in the early solar system and their half-lives:
26Mg (0.72 Ma) 129I
129Xe (16 Ma) 182Hf
182W (9 Ma) 53Mn
53Cr (3.7 Ma) 244Pu
fission (80 Ma) 10Be
10B (1.5 Ma) 41Ca
41K (0.1 Ma) 60Fe
60Ni (1.5 Ma)

Trapezium (Orion nebula)

26Al

... injected into protoplanetary disks (solar mass)


Radiometric dating


Planetesimal heating … nucleosynthesis in mass-rich stars … or nuclear reactions due to solar irradiation (10Be)

Early formed asteroids: high abundance of 26Al, strongest heating effects
Differentiated meteorites: from metallic cores and silicate mantles and crusts of differentiated asteroids

Hf

W 182Hf

182W

Fast accretion and differentiation
formation of metallic cores contemporaneously with CAIs (182Hf182W; Kleine et al., 2004; Schersten et al. 2004)
formation and cooling of basaltic crust within few Ma (Eucrites, Angrites: Pb-Pb-dating; e.g. Lugmair and Galer, 1992; Baker et al.,. 2005)

Ordinary chondrites (H, L, LL): significant thermal metamorphism by 26Al decay heat

3 4

H4 Chondrite (~650°C) Silikat + Fe-Ni Metall

H6 Chondrite (~850°C)

6 5

Temperatur [K]

Cooling curves in a chondritic asteroid heated by 26Al decay, r=100 km, 26Al/ 27Al=4x 10-6, i.e. 2.5 Ma after Allende CAIs (analytical model after Miyamoto et al., 1981)

1000 800 Closure temperature of U-Pb/Pb in phosphates: 720K

600

Closure temperature of K-Ar / 40Ar- 39Ar in oligoclase: 550K = Retention temperature of 244Pu fission tracks in orthopyroxene

7

400

16

23

35

47

Retention temperature of 244Pu fission tracks in merrillite: 390K

4550

4500

4450

4400

Zeit vor heuteb.p. [Millionen Time [Ma]Jahre]

Guarena (H6) 0,0

budgets of whole rock sample, feldspar separate and also pyroxene separate are all dominated by oligoclase feldspar
No difference in closure temperature
No significant age differences
mean age represents cooling through oligoclase closure temperature of 550 K

log K/Ca [g/g]

K-40Ar

-0,5 -1,0 -1,5

whole rock oligoclase feldspar orthopyroxene

-2,0

~1200-1400°C: degassing of Ca-derived 37Ar from pyroxene

-2,5

4600

Apparent Age [Ma]

Oligoclase feldspar composition (EMPA)

~700-900°C: degassing of K-derived 39Ar and Caderived 37Ar from oligoclase feldspar

4500

4400

4300

mean of three plateau ages: 4454 ± 6 Ma 4200

4100

0

20

40

60

Fractional 39Ar release

80

100

244Pu

–fission track chronometry

(Laboratoire de Minéralogie du Muséum d`Histoire Naturelle de Paris) • Activity of short lived 244Pu (ττ1/2= 80 Ma) in the early solar system produces radiation damage (fission tracks) in phosphates (e.g. merrillite) and adjacent silicates (e.g. orthopyroxene) • Different retention temperatures (MRL: 390 K, OPX: 550 K) result in different fission track densities if cooling sufficiently slow • Typical corrections (in merrillite): cosmic ray tracks