Noble-gas-rich chondrules in an enstatite meteorite

Chondrules are silicate spherules that are found in abundance in the most p rimitive class of meteorites, the chondrites. Chondrules are believed to ha ve formed by rapid cooling of silicate melt early in the history of the Sol ar System(1), and their properties should reflect the composition of (and p hysical conditions in) the solar nebula at the time when the Sun and planet s were forming. It is usually believed that chondrules lost all their noble gases at the time of melting(2-4). Here we report the discovery of signifi cant amounts of trapped noble gases in chondrules in the enstatite chondrit e Yamato-791790, which consists of highly reduced minerals. The elemental r atios Ar-36/Xe-132 and Kr-84/Xe-132 are similar to those of 'subsolar' gas( 5,6), which has the highest Ar-36/Xe-132 ratio after that of solar-type nob le gases(7). The most plausible explanation for the high noble-gas concentr ation and the characteristic elemental ratios is that solar gases were impl anted into the chondrule precursor material, followed by incomplete loss of the implanted gases through diffusion over time.