Noble-gas-rich chondrules in an enstatite meteorite.
Chondrules are silicate spherules that are found in abundance in the most primitive class of meteorites, the chondrites. Chondrules are believed to have formed by rapid cooling of silicate melt early in the history of the Solar System, and their properties should reflect the composition of (and physical conditions in) the solar nebula at the time when the Sun and planets were forming. It is usually believed that chondrules lost all their noble gases at the time of melting. Here we report the discovery of significant amounts of trapped noble gases in chondrules in the enstatite chondrite Yamato-791790, which consists of highly reduced minerals. The elemental ratios 36Ar/132Xe and 84Kr/132Xe are similar to those of 'subsolar' gas, which has the highest 36Ar/132Xe ratio after that of solar-type noble gases. The most plausible explanation for the high noble-gas concentration and the characteristic elemental ratios is that solar gases were implanted into the chondrule precursor material, followed by incomplete loss of the implanted gases through diffusion over time.
Okazaki
R
R
Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University 33, Hakozaki, Fukuoka 812-8581, Japan. okazaki@eqchem.s.u-tokyo.ac.jp
Takaoka
N
N
Nagao
K
K
Sekiya
M
M
Nakamura
T
T