はやぶさの近赤外線分光器による小惑星ィトカヮの観測について

摘要

NIRS is a near-infrared spectrometer on-board the spacecraft HAYABUSA, which rendezvoused with thenear-earth asteroid, (25143) Itokawa in September through November 2005. The spacecraft successfully arrived atthe Gate Position approximately 20 km from the asteroid on September 12, 2005. During the rendezvous phasewith the asteroid, NIRS obtained more than 80,000 spectra of Itokawa. NIRS found a variation of more than 10% inalbedo and absorption band depth in the surface reflectance of asteroid (25143) Itokawa. Spectral shape over the1-micron absorption band indicates that the surface of this body has an olivine-rich mineral assemblage, potentiallysimilar to that of LL5 or LL6 chondrites. Although diversity in the physical condition of Itokawa’s surface appears tobe larger than on other S-type asteroids, we found no mineralogical variation on the surface of Itokawa. It suggeststhat Itokawa is a primitive body.