永島一秀 , 小林幸雄 , 坂本直哉 , 殿谷梓 , 圦本尚義東工大・地球惑星科学

Presolar Silicates in meteoritesPresolar Silicates in Primitive Chondrites

Mar. 02, 2005

K. Nagashima, S. Kobayashi, N. Sakamoto,

A. Tonotani, and H. Yurimoto

Earth and Planetary Sciences,

Tokyo Institute of Technology

28Si16O

12C, 18O26Al

1µm SiC from Murchison(Amari et al., 1994)

Onion-type structure ofmassive star before supernova

AGB star (source of s-process nuclides)

Supernova ejecta

Stellar outflow

Solar SystemMeteorite

Presolar grains

Silicates are susceptible to aqueous alteration, which transformed silicates into hydrous silicates. This process erases any presolar isotopic signatures.

Difficulties to locate presolar silicates among boundlessly abundant solar system silicates that are major constituents of meteorites.

Presolar grains

ppm

Diamond

SiC

Spinel

Graphite

Corundum

Silicate

Nagashima et al., 2004; Nguyen and Zinner, 2004; Mostefaoui and Hoppe, 2004

It was about a year ago that elusive presolar silicates were first discovered.

0.001 0.01 0.1 1 10 1000 10000100

SIMSSIMS

SCAPS

Isotope MicroscopeIsotope Microscope

SCAPS

Analytical methods • Isotope microscope (Yurimoto et al., 2003)

Secondary Ion Mass Spectrometry: SIMS +

2-D ion detector: SCAPS

ESA MagneticSector

ims-1270

sample

SCAPS10 mm

Spatial resolution of isotope image

Acfer 094

Adelaide

ALHA 77307

Yamato-81025

Murchison

C3-ungrouped

Sample

CM2

CO3.0

CO3.0

C3-ungrouped

altered

pristine

name of chondrite class

17O17O

BSEBSE

18O18O16O16O

Adelaide (ungrouped)

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ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇ…ÇÕïKóvÇ≈Ç∑ÅB

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ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇ…ÇÕïKóvÇ≈Ç∑ÅB

28Si /16O28Si /16OBSEBSE

(‰)

17O17O

(‰)

18O18O

A total of 41 presolar silicates were found.

Oxygen Isotopic Ratios of Presolar Silicates

BSE Images of Presolar Silicates

1µm 1µm

OlivineOlivine PyroxenePyroxene

OlivineOlivine

from Acfer 094 (ungrouped) from Adelaide (ungrouped)

BSE Images of Presolar Silicates

1µmfrom Acfer 094 (ungrouped) 1µmfrom Murchison (CM2)

GEMS? (Glass with Embedded Metal and Sulfide)

Grain size distribution of presolar silicates

Nagashima et al., 2004; Nguyen and Zinner, 2004; Mostefaoui et al., 2004;Messenger et al., 2003; 2004; Floss and Stadermann, 2004; this study

Note that unidentified silicatesare not included.

0

5

10

15

20

0 200 400 600 800 1000

size / nm

nu

mb

er

Origins(after Nittler et al., 1997)

Group 1 O-rich RGB or AGB

Group 2 AGB with Cool Bottom

Processing

Group 3 low-metallicity RGB or AGB

Group 4 still uncertain origin

low-mass AGB?supernovae?

Abundances of presolar silicates in meteorites

meteorite

Acfer 094

Murchison

Yamato-81025

ALHA 77307

Adelaide

class

C3-ungrouped

CM2

CO3

CO3

C3-ungrouped

number of presolar silicates

4

4

20

8

5

abundance(ppm)

10

3

503040

pri

stin

eal

tere

d

Abundances of presolar silicates

Interplanetary Dust Particles (IDPs) 450 ~5500 ppm (Messenger et al., 2003; Floss and Stadermann, 2004)

Aqueously altered chondrites <3 ppm

Most pristine chondrites 10~50 ppm

Destruction of presolar silicates by thermal processing in the solar nebula.

Destruction of presolar silicatesby aqueous alterations on chondrite parent body.

SummaryIn situ isotopic survey of matrix materials in primitive chondrites are conducted.

A total of 41 presolar silicates are identified in 5 chondrites.

The difference of abundances of presolar silicates between IDPs and primitive chondrites could be explained by destruction of presolar silicates by thermal processing in the solar nebula, and aqueous alteration processes on their parent bodies.

Most of presolar silicates are enriched in 17O, suggesting origins in O-rich RGB/AGB stars.

Estimated abundances of presolar silicates in primitive chondrites are 1~50 ppm.

Further studies conducted on different meteorite types will allow us to understand more detailed origins and history of presolar grains, conditions in solar system environments.

Future work

Search for new types of presolar silicate grains such as grains from supernovae.