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Search for extinct aluminum‐26 and titanium‐44 in nanodiamonds from the Allende CV3 and Murchison CM2 meteorites
Author(s) -
BESMEHN Astrid,
HOPPE Peter,
OTT Ulrich
Publication year - 2011
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2011.01225.x
Subject(s) - murchison meteorite , allende meteorite , presolar grains , carbonaceous chondrite , meteorite , nanodiamond , chondrite , materials science , supernova , astrobiology , astrophysics , diamond , physics , metallurgy
– We report Mg‐Al and Ca‐Ti isotopic data for meteoritic nanodiamonds separated from the Allende CV3 and Murchison CM2 meteorites. The goal of this study was to search for excesses in 26 Mg and 44 Ca, which can be attributed to the in situ decay of radioactive and now extinct 26 Al and 44 Ti, respectively. Previous work on presolar SiC and graphite had shown that 26 Al/ 27 Al and 44 Ti/ 48 Ti ratios in presolar grains can be used to discriminate between different types of stellar sources. Aluminum and Ti concentrations are low in the meteoritic nanodiamonds of this study. Murchison nanodiamonds have higher Al and Ti concentrations than the Allende nanodiamonds. This can be attributed to contamination and the presence of presolar SiC in the Murchison nanodiamond samples. 26 Mg/ 24 Mg and 44 Ca/ 40 Ca ratios are close to normal in Allende nanodiamonds with upper limits on the initial 26 Al/ 27 Al and 44 Ti/ 48 Ti ratios of approximately 1 × 10 −3 . These ratios are factors of 10–1000 and, respectively, 1–1000 lower than those of presolar SiC and graphite grains from supernovae. The 26 Al/ 27 Al and 44 Ti/ 48 Ti data for nanodiamonds are compatible with an asymptotic giant branch star or solar system origin, but not with a supernova origin of a major fraction of meteoritic nanodiamonds. The latter possibility cannot be excluded, though, as the diamond separates may contain significant amounts of contaminating Al and Ti, which would lower the inferred 26 Al/ 27 Al and 44 Ti/ 48 Ti ratios considerably.