Constraints on Conditions in the Solar Nebula from the Laboratory Study of Presolar Grains

Gary R. HussHawai’i Institute of Geophysics and Planetology

University of Hawai’i at Manoa

Silicon Carbide Hibonite (CaAl12O19)

Young stellar systems in Orion

Chondritic Meteorites preserve material from the Solar Nebula

Types of Presolar GrainsName Composition Size AbundanceDiamond C 1-2 nm 1500 ppmSilicon Carbide SiC 0.1-10 m 10-15 ppmGraphite C 0.1-20 m 5-10 ppmTiC, MoC, ZrC, RuC, FeC, Fe-Ni

Inside other materials

1-25 nm n.d.

Si3N4 Si3N4 1-5 m 1-20 ppbForsterite Mg2SiO4 0.2-0.5 m 10-1800 ppmEnstatite MgSiO3 0.2-0.5 mAmorphous Silicate variable 0.2-0.5 m 20-3600 ppmSpinel MgAl2O4 0.1-20 m 1.2 ppmCorundum Al2O3 0.2-3 m 100 ppbHibonite CaAl12O19 1-5 m 20 ppbTiO2 TiO2 n.d. <10 ppbD-rich organics HCNO n.d. n.d.

CI Chondrites: Representative Samples of Molecular Cloud?

• Chemical composition matches Sun

• High abundances of presolar grains

• Severely altered on parent body

CI

(ppm) Diamond SiC Graphite Spinel Al2O3 Silicate (%) Presolar

C 34500 1400 4.2 10 4*

Mg 98900 0.21 2000 2

Al 8680 0.46 0.059 6e-3

Si 106400 9.8 1295 1.2

Ca 9280 1e-4 1e-6

Fe 190400 543 0.3

Fraction of Primitive Chondritic MaterialDirectly Traceable to Molecular Cloud

*Plus unknown amount of interstellar organic compounds.

Constraints on Presolar Carbon in CI from Diamond Abundance

• Hard lower limit: ISM carbon is 20% diamond (Allamandola et al., 1993)

• Reasonable LL: ISM carbon is 4-5% diamond

• Upper limit: major fraction of MC organic material destroyed; other elements unfractionated

5432100

20

40

60

80

100

Percentage of Diamond in CI Carbon

How much of CI chondrites came directly from molecular cloud material?

• Bulk composition implies little chemical fraction-ation and little addition of fractionated material– Evidence for small addition of high-T material (≤5%)

• High abundances of most presolar grains• High percentage of carbon may be presolar

– Large fraction may have been destroyed• High percentage of other elements also presolar

– Complete evaporation and recondensation destroys presolar grains

~90% of CI material from molecular cloud.

Presolar Materials as Tracers of Nebular and Parent Body Processing

Component Thermal Stability Chemical Resistance

Diamond P3 Low High

Diamond HL High High

Diamond P6 Very High High

Silicon Carbide Moderate High

Graphite Low Moderate

Al2O3, Spinel Very High High

Silicates Low to High Low to Moderate

Effects of Metamorphism on Abundances of Presolar Materials

• Abundances of all types decrease with increasing metamorphic grade

• Rate of decrease related to chemical and thermal resistance of materials

All started with the same mixture

LL Chondrites

• Lithophile elements more refractory than Na are unfractionated

• Volatile elements depleted• Refractory presolar components unfractionated• Thermally sensitive presolar components depleted

LL3 Chondrites

1

3

0.1

1

10

Ave LL3 Semarkona (LL3.0)

Decreasing Volatility

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs

CO Chondrites

• Elements more refractory than Au unfractionated (except for addition of CAIs)

• Volatile elements depleted• Presolar components fractionated• Resistant components enriched relative to CI

0.1 0.01

0.1

1

CO3 Chondrites

1

ALHA 77307 (CO3.0)

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs

Decreasing Volatility

CR Chondrites

• Elements more refractory than Cr unfractionated• Volatile elements depleted• Presolar components more steeply fractionated• Resistant components enriched relative to CI

0.1 0.01

1

0.1

1

CR2 Chondrites

Ave CR2Renazzo

Decreasing Volatility

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs

LL3 Chondrites

1

3

0.1

1

10

Ave LL3 Semarkona (LL3.0)

Decreasing Volatility

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs0.1 0.01

0.1

1

CO3 Chondrites

1

ALHA 77307 (CO3.0)

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs

Decreasing Volatility0.1 0.01

1

0.1

1

CR2 Chondrites

Ave CR2Renazzo

Decreasing Volatility

ZnSe

BrSb

NaGa

KAs

MnAu

CrFe

MgCo

NiV

CaLa

SmEu

YbLu

RuIr

AlOs

Crystalline Silicates: Astronomical Observations

• Crystalline silicates are rare in the interstellar medium.

• Crystalline silicates are more abundant in protostellar disks.

• Abundance of crystalline silicates higher near protostar.

Crystalline silicates form in protostellar disks.

Matrix of ALHA 77307

From Brearley 1993, GCA 57, 1521

• Molecular cloud material survives in chondrites

• Its survival depends on structure and composition

• Presolar grains are keys to understanding early solar system processes