First evidence for silica condensation within the solar protoplanetary disk

Mutsumi Komatsu*, Timothy J. Fagan, Alexander N. Krot, Kazuhide Nagashima, Michail I. Petaev, Makoto Kimura, Akira Yamaguchi

*この研究の対応する著者

研究成果査読

23 被引用数 (Scopus)

抄録

Calcium-aluminum–rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (Δ17O ∼ −24) compositions, most likely near the protosun. Here we describe a16O-rich (Δ17O ∼ −22 ± 2) AOA from the carbonaceous Renazzo-type (CR) chondrite Yamato-793261 containing both (i) an ultrarefractory CAI and (II) forsterite, low-Ca pyroxene, and silica, indicating formation by gas–solid reactions over a wide temperature range from -1,800 to -1,150 K. This AOA provides direct evidence for gas–solid condensation of silica in a CAI/AOA-forming region. In a gas of solar composition, the Mg/Si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the AOA formed in a parcel of gas with fractionated Mg/Si ratio, most likely due to condensation of forsterite grains. Thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by -10× in H and He that cooled at 50 K/hour at total pressure of 10−4 bar. Condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks.

本文言語English
ページ(範囲)7497-7502
ページ数6
ジャーナルProceedings of the National Academy of Sciences of the United States of America
115
29
DOI
出版ステータスPublished - 2018 7 17

ASJC Scopus subject areas

  • 一般

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