INTERSTELLAR GRAINS IN METEORITES .2. SIC AND ITS NOBLE-GASES

被引:209
作者
LEWIS, RS [1 ]
AMARI, S [1 ]
ANDERS, E [1 ]
机构
[1] UNIV CHICAGO,DEPT CHEM,CHICAGO,IL 60637
关键词
D O I
10.1016/0016-7037(94)90478-2
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
We have analyzed He, Ne, Ar, Kr, and Xe in fourteen size fractions of interstellar SiC, isolated from the Murchison C2 chondrite. All are mixtures of a highly anomalous component bearing the isotopic signature of the astrophysical s-process and a more normal component, generally solar-like but with anomalies of up to 30% in the heavy isotopes. As these two components strikingly resemble predictions for the He-burning shells and envelopes of red giant carbon stars, it appears that the SiC grains are pristine circumstellar condensates from such stars. A number of elemental and isotopic ratios (such as Kr-80/Kr-82 and Kr-86/Kr-82) vary with grain size, suggesting that the SiC comes from carbon stars representing a range of masses, metallicities, temperatures, and neutron densities. The Ne-21-content of the SiC suggests a presolar cosmic-ray irradiation of up to 130 Ma, representing the interval between formation of the grains in a circumstellar shell and arrival in the solar system 4.6 Ga ago. Actually there is evidence that most of the Ne-21 (and Ne-22) is in less-than-or-equal-to 10% of the grains, suggesting that much of the SiC was degassed during or shortly before formation of the solar system. Thus the true cosmic-ray ages may be 7 to 18X longer. Apparently the gas-rich SiC grains predate the solar system by rat least 130 Ma and possibly up to 2000 Ma.
引用
收藏
页码:471 / 494
页数:24
相关论文
共 78 条
[1]   ISOTOPIC ANOMALIES OF NOBLE-GASES IN METEORITES AND THEIR ORIGINS .6. PRESOLAR COMPONENTS IN THE MURCHISON C2-CHONDRITE [J].
ALAERTS, L ;
LEWIS, RS ;
MATSUDA, J ;
ANDERS, E .
GEOCHIMICA ET COSMOCHIMICA ACTA, 1980, 44 (02) :189-209
[2]  
ALEXANDER CMO, 1993, GEOCHIM COSMOCHIM AC, V57, P2869, DOI 10.1016/0016-7037(93)90395-D
[3]   ISOTOPIC NEON CROSS-SECTIONS FOR A STUDY OF NEUTRON BALANCE AND TEMPERATURE DURING S-PROCESS NUCLEOSYNTHESIS [J].
ALMEIDA, J ;
KAPPELER, F .
ASTROPHYSICAL JOURNAL, 1983, 265 (01) :417-428
[4]  
AMARI S, 1989, METEORITICS, V24, P247
[5]   INTERSTELLAR GRAPHITE IN METEORITES [J].
AMARI, S ;
ANDERS, E ;
VIRAG, A ;
ZINNER, E .
NATURE, 1990, 345 (6272) :238-240
[6]  
AMARI S, 1991, METEORITICS, V26, P314
[7]  
AMARI S, 1990, METEORITICS, V25, P348
[8]  
AMARI S, 1991, LUNAR PLANET SCI, V22, P19
[9]  
AMARI S, 1993, GEOCHIM COSMOCHIM AC, V57
[10]   ABUNDANCES OF THE ELEMENTS - METEORITIC AND SOLAR [J].
ANDERS, E ;
GREVESSE, N .
GEOCHIMICA ET COSMOCHIMICA ACTA, 1989, 53 (01) :197-214