Presolar Silicates in meteorites Presolar Silicates in Primitive Chondrites 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 K. Nagashima, S. Kobayashi, N. Sakamoto, A. Tonotani, and H. Yurimoto Earth and Planetary Sciences, Tokyo Institute of Technology Mar. 02, 2005
Presolar grains Silicates are susceptible to aqueous alteration, which transformed silicates into hydrous silicates. This process erases any presolar isotopic signatures. It was about a year ago that elusive presolar silicates were first discovered. Nagashima et al., 2004; Nguyen and Zinner, 2004; Mostefaoui and Hoppe, 2004 Difficulties to locate presolar silicates among boundlessly abundant solar system silicates that are major constituents of meteorites. 0.001 0.01 0.1 1 10 100 1000 10000 Diamond SiC Graphite Spinel Corundum Silicate ppm
Isotope Microscope Isotope Microscope ims-1270 SIMS SIMS SCAPS SCAPS SCAPS sample Analytical methods • Isotope microscope (Yurimoto et al., 2003) Secondary Ion Mass Spectrometry: SIMS + 2-D ion detector: SCAPS
pristine altered Sample name of chondrite class C3-ungrouped Acfer 094 CO3.0 Yamato-81025 CO3.0 ALHA 77307 C3-ungrouped Adelaide Murchison CM2
17O 17O BSE BSE 18O 16O 18O 16O Adelaide (ungrouped)
28Si /16O BSE 28Si /16O BSE d17O d18O d17O d18O (‰) (‰)
Oxygen Isotopic Ratios of Presolar Silicates A total of 41 presolar silicates were found.
Olivine Pyroxene Olivine Olivine Pyroxene Olivine BSE Images of Presolar Silicates from Acfer 094 (ungrouped) 1µm from Adelaide (ungrouped) 1µm
BSE Images of Presolar Silicates from Acfer 094 (ungrouped) 1µm from Murchison (CM2) 1µm GEMS? (Glass with Embedded Metal and Sulfide)
Grain size distribution of presolar silicates number Note that unidentified silicates are not included. Nagashima et al., 2004; Nguyen and Zinner, 2004; Mostefaoui et al., 2004; Messenger et al., 2003; 2004; Floss and Stadermann, 2004; this study
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? Origins (after Nittler et al., 1997)
number of abundance presolar silicates (ppm) meteorite class 10 Acfer 094 C3-ungrouped 4 50 Yamato-81025 CO3 20 pristine 30 ALHA 77307 CO3 8 40 Adelaide C3-ungrouped 5 3 Murchison CM2 4 altered Abundances of presolar silicates in meteorites
Destruction of presolar silicates by thermal processing in the solar nebula. Destruction of presolar silicates by aqueous alterations on chondrite parent body. Abundances of presolar silicates Interplanetary Dust Particles (IDPs)450~5500 ppm (Messenger et al., 2003; Floss and Stadermann, 2004) Most pristine chondrites 10~50 ppm Aqueously altered chondrites <3 ppm
In situ isotopic survey of matrix materials in primitive chondrites are conducted. Summary A total of 41 presolar silicates are identified in 5 chondrites. 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. 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. Future work 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. Search for new types of presolar silicate grains such as grains from supernovae.