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 meteorites Presolar 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

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

SIMS SCAPS Isotope Microscope SCAPS Analytical methods Isotope microscope (Yurimoto et al., 2003) Secondary Ion Mass Spectrometry: SIMS + 2-D ion detector: SCAPS ims-1270 sample SCAPS

Spatial resolution of isotope image

Acfer 094 Adelaide ALHA Yamato Murchison C3-ungrouped Sample CM2 CO3.0 C3-ungrouped altered pristine name of chondriteclass

17 O BSE 18 O 16 O Adelaide (ungrouped)

28 Si / 16 O BSE (‰)  17 O (‰)  18 O

A total of 41 presolar silicates were found. Oxygen Isotopic Ratios of Presolar Silicates

BSE Images of Presolar Silicates 1µm Olivine Pyroxene Olivine from Acfer 094 (ungrouped)from Adelaide (ungrouped)

BSE Images of Presolar Silicates 1µm from Acfer 094 (ungrouped) 1µm from 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 silicates are not included. number

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 ALHA Adelaide class C3-ungrouped CM2 CO3 C3-ungrouped number of presolar silicates abundance (ppm) pristine altered

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 silicates by aqueous alterations on chondrite parent body.

Summary In 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 17 O, 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.