期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 117, 期 4, 页码 1884-1889出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1904573117
关键词
interstellar dust; presolar grains; exposure age dating; cosmochemistry; meteorites
资金
- NASA [NNX11AG77G, NNX15AC53G, 80NSSC19K0504, NNX15AF78G, 80NSSC17K0251]
- Tawani Foundation
- NSF Graduate Research Fellowships [DGE-1144082, DGE-1746045]
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) [200081/2005-5]
- US Department of Energy by Lawrence Livermore National Laboratory (LLNL) [DE-AC52-07NA27344]
- LLNL Laboratory Directed Research and Development (LDRD) Program [19-FS-028]
- Swiss National Science Foundation
- NASA [NNX11AG77G, 145931, 808247, NNX15AC53G] Funding Source: Federal RePORTER
We determined interstellar cosmic ray exposure ages of 40 large presolar silicon carbide grains extracted from the Murchison CM2 meteorite. Our ages, based on cosmogenic Ne-21, range from 3.9 +/- 1.6 Ma to similar to 3 +/- 2 Ga before the start of the Solar System similar to 4.6 Ga ago. A majority of the grains have interstellar lifetimes of <300 Ma, which is shorter than theoretical estimates for large grains. These grains condensed in outflows of asymptotic giant branch stars <4.9 Ga ago that possibly formed during an episode of enhanced star formation similar to 7 Ga ago. A minority of the grains have ages >1 Ga. Longer lifetimes are expected for large grains. We determined that at least 12 of the analyzed grains were parts of aggregates in the interstellar medium: The large difference in nuclear recoil loss of cosmic ray spallation products He-3 and Ne-21 enabled us to estimate that the irradiated objects in the interstellar medium were up to 30 times larger than the analyzed grains. Furthermore, we estimate that the majority of the grains acquired the bulk of their cosmogenic nuclides in the interstellar medium and not by exposure to an enhanced particle flux of the early active sun.
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