Characterization of Presolar Material in the Cr Chondrite Northwest Africa 852

Leitner, J.; Vollmer, C.; Hoppe, P.; Zipfel, J.

doi:10.1088/0004-637x/745/1/38

Cited by 63 publications

(111 citation statements)

References 70 publications

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“…Enrichments in 15 N are also observed in bulk CH (up to 1,100‰), CB (up to 1,500‰), and CR (120−190‰) chondrites (23). Moreover, CR chondrites are characterized by the highest abundance of presolar grains among carbonaceous chondrites (24). Absolute ages of CH and CB chondrules constrain the accretion of their parent bodies to ∼5 My after CAIs (25), that is, later than other carbonaceous chondrite parent bodies [i.e., ∼2.5-3.5 My (26)].…”

Section: Isotopic Evidence For Primordial Molecular Cloud Mattermentioning

confidence: 91%

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

Kooten

Wielandt

Schiller

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

173

124

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The short-lived 26 Al radionuclide is thought to have been admixed into the initially 26 Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54 Cr and 26 Mg*, the decay product of 26 Al. This correlation is interpreted as reflecting progressive thermal processing of infalling 26 Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26 Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26 Mg*-depleted and 54 Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26 Al. The 26 Mg* and 54 Cr compositions of bulk metal-rich chondrites require significant amounts (25-50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants. molecular cloud | outer Solar System | metal-rich chondrites | isotopes | chondrite accretion regions L ow-mass stars like our Sun form by the gravitational collapse of the densest parts of molecular clouds comprising stellarderived dust and gas. Collapsing clouds swiftly evolve into deeply embedded protostars that rapidly accrete material from their surrounding envelopes via a protoplanetary disk (1), in which planetesimals and planetary embryos form over timescales of several million years (2). Chondritic meteorites (chondrites) are fragments of early-formed planetesimals that avoided melting and differentiation and, therefore, provide a record of the earliest evolutionary stages of the Sun and its protoplanetary disk. Most chondrites contain calcium−aluminum-rich inclusions (CAIs) and chondrules, which formed by high-temperature processes that included evaporation, condensation, and melting during short-lived heating events (3). CAIs represent the oldest dated solids and, thus, define the age of the Solar System at 4,567.3 ± 0.16 Ma (4). It is inferred that CAIs formed near the proto-Sun during a brief time interval (<0

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Section: Isotopic Evidence For Primordial Molecular Cloud Mattermentioning

confidence: 91%

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

Kooten

Wielandt

Schiller

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

173

124

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“…For two data points on grain sizes, the vertical error bars cover the maximum and the minimum sizes, and the horizontal ones are the suggested ranges of peak metamorphic temperatures. The sizes of presolar silicate grains are 0.1-1.7 µm and 0.07-0.6 µm in petrologic types 1-2 and 3 chondrites, respectively (Zinner 2003;Hynes & Gyngard 2009;Nguyen et al 2010;Leitner et al 2012;Hoppe et al 2015). The metamorphic temperature of type 3 chondrites is likely to be between 500…”

Section: Isotopic Diffusion In Thermally Evolving Planetesimalsmentioning

confidence: 97%

“…Since the diffusion coefficient is obtained for a temperature range of 1100 Dohmen et al 2002), we extrapolate the results down to lower temperatures. Measurements with the transmission electron microscope show that the chemical compositions of presolar silicate grains vary on the scale of a few tens nanometer (Nguyen et al 2007;Busemann et al 2009;Leitner et al 2012). While it would be interesting to see how the diffusion coefficients depend on stoichiometry of elements in silicate, there is no data for silicate compositions with a variety of Mg/O, Fe/O and Si/O ratios.…”

Section: Isotopic Diffusion In Thermally Evolving Planetesimalsmentioning

confidence: 99%

“…On the other hand, while they were traveling to the presolar nebula, many of them might be fragmented into grains smaller than 0.1µm due to shattering in the interstellar turbulences (Hirashita & Yan 2009). It is nonetheless important to point out that such small (< 0.1µm) presolar grains have been rarely detected in the currently available samples; the typical size distribution of presolar silicate grains spans the range from ∼ 0.1 to ∼ 1 µm (e.g., Zinner 2003;Hynes & Gyngard 2009;Nguyen et al 2010;Leitner et al 2012;Hoppe et al 2015).…”

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confidence: 99%

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Diffusion of Oxygen Isotopes in Thermally Evolving Planetesimals and Size Ranges of Presolar Silicate Grains

Wakita

Nozawa

Hasegawa

2017

ApJ

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Presolar grains are small particles found in meteorites through their isotopic compositions which are considerably different from those of materials in the Solar System. If some isotopes in presolar grains diffused out beyond their grain sizes when they were embedded in parent bodies of meteorites, their isotopic compositions could be washed out, and hence the grains cannot be identified as presolar grains any more. We explore this possibility for the first time by self-consistently simulating the thermal evolution of planetesimals and the diffusion length of 18 O in presolar silicate grains. Our results show that presolar silicate grains smaller than ∼ 0.03µm cannot keep their original isotopic compositions even if the host planetesimals experienced maximum temperature as low as 600• C. Since this temperature corresponds to the one experienced by petrologic type 3 chondrites, the isotopic diffusion can constrain the size of presolar silicate grains discovered in such chondrites to be larger than ∼ 0.03µm. We also find that the diffusion lengths of 18 O reach ∼ 0.3 − 2µm in planetesimals that were heated up to 700-800• C. This indicates that, if the original size of presolar grains spans a range from ∼ 0.001µm to ∼ 0.3µm like that in the interstellar medium, the isotopic records of the presolar grains may be almost completely lost in such highly thermalized parent bodies. We propose that isotopic diffusion could be a key process to control the size distribution and abundance of presolar grains in some types of chondrites.

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“…Leitner et al (2012) (Weisberg et al, 1993) and oxygen isotopic composition (Schrader et al, 2011). Therefore, lower range of dD value in NWA 801 might be resulted from heterogeneous nature of CR chondrites or unique nature of NWA 801.…”

Section: Characteristics Of D-rich and 15 N-rich Carbonaceous Matter mentioning

confidence: 99%

Deuterium- and <sup>15</sup>N-signatures of organic globules in Murchison and Northwest Africa 801 meteorites

2015

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Characterization of Presolar Material in the Cr Chondrite Northwest Africa 852

Cited by 63 publications

References 70 publications

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

Diffusion of Oxygen Isotopes in Thermally Evolving Planetesimals and Size Ranges of Presolar Silicate Grains

Deuterium- and <sup>15</sup>N-signatures of organic globules in Murchison and Northwest Africa 801 meteorites

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