Sachio Kobayashi

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.

Localization of Minodronate in Mouse Femora Through Isotope Microscopy

Minodronate is highlighted for its marked and sustained effects on osteoporotic bones. To determine the duration of minodronate’s effects, we have assessed the localization of the drug in mouse bones through isotope microscopy, after labeling it with a stable nitrogen isotope ([15N]-minodronate). In addition, minodronate-treated bones were assessed by histochemistry and transmission electron microscopy (TEM). Eight-week-old male ICR mice received [15N]-minodronate (1 mg/kg) intravenously and were sacrificed after 3 hr, 24 hr, 1 week, and 1 month. Isotope microscopy showed that [15N]-minodronate was present mainly beneath osteoblasts rather than nearby osteoclasts. At 3 hr after minodronate administration, histochemistry and TEM showed osteoclasts with well-developed ruffled borders. However, osteoclasts were roughly attached to the bone surfaces and did not feature ruffled borders at 24 hr after minodronate administration. The numbers of tartrate-resistant acid phosphatase–positive osteoclasts and alkaline phosphatase–reactive osteoblastic area were not reduced suddenly, and apoptotic osteoclasts appeared in 1 week and 1 month after the injections. Von Kossa staining demonstrated that osteoclasts treated with minodronate did not incorporate mineralized bone matrix. Taken together, minodronate accumulates in bone underneath osteoblasts rather than under bone-resorbing osteoclasts; therefore, it is likely that the minodronate-coated bone matrix is resistant to osteoclastic resorption, which results in a long-lasting and bone-preserving effect.

Redistribution of Sr and rare earth elements in the matrices of CV3 carbonaceous chondrites during aqueous alteration in their parent body

We measured the abundances of Sr and rare earth elements (REEs) in the matrices of five CV3 carbonaceous chondrites: Meteorite Hills (MET) 00430, MET 01070, La Paz ice field (LAP) 02206, Asuka (A) 881317 and Roberts Massif (RBT) 04143. In the MET 00430 and MET 01074 matrices, the Sr/CI and light REE (LREE, La–Nd)/CI ratios positively correlate with the amounts of Ca-rich secondary minerals, which formed during aqueous alteration in the CV3 chondrite parent body. In contrast, in the LAP 02206 and RBT 04143 matrices, although the Sr/CI ratios correlate with the amounts of Ca-rich secondary minerals, the LREE/CI ratios vary independently from the amounts of any secondary minerals. This suggests that the LREE/CI ratios in these matrices were produced prior to the parent body alteration, probably in the solar nebula. The LREE/CI ratios of the LAP 02206 and RBT 04143 matrices reveal the mixing process of matrix minerals prior to the accretion of the CV3 chondrite parent body. The mixing degrees of matrix minerals might be different between these two matrices. Because solid materials would be mixed over time according to the radial diffusion model of a turbulent disk, the matrix minerals consisting of LAP 02206 and RBT 04143 matrices might be incorporated into their parent body with different timing.