Oxygen Isotopic Compositions of Asteroidal Materials Returned from Itokawa by the Hayabusa Mission

Laboratory analysis of samples returned from an asteroid establishes a direct link between asteroids and meteorites and provides clues to the complex history of the asteroid and its surface. Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in 16O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.

对从小行星返回的样本进行的实验室分析确立了小行星和陨石之间的直接联系，并为小行星及其表面的复杂历史提供了线索。陨石研究表明，每个太阳系天体都有独特的氧同位素组成。球粒陨石是最原始的陨石，一直被认为来自小行星，但小行星自身的氧同位素组成尚未确定。我们使用二次离子质谱仪测量了由“隼鸟号”航天器从小行星25143系川带回的岩石颗粒的氧同位素组成。这些颗粒的组成相对于地球物质贫16O，这表明S型小行星系川是平衡普通球粒陨石LL群或L群的来源之一。这是球粒陨石与其母体小行星之间的直接氧同位素联系。