Asteroidal surface studies by laboratory light scattering and LIDAR on HAYABUSA

Our laboratory measurements of bidirectional reflectance by a layer of olivine particles with radii in 45–212 μm suggest that the intensity of backscattering light from the rough surface is significantly enhanced, compared with that from the smooth surface. Furthermore, it is found that the backscattering light by rough surface decreases more gradually than that expected by smooth surface with incident angle. This result implies that the light detection and ranging instrument (LIDAR) on HAYABUSA (Japanese asteroid sample return mission, MUSES-C) has a potential ability to reveal the existence of a regolith layer on a very small (<600 m) asteroid 25143 Itokawa (1998SF36) due to enhancement of reflected light of LIDAR in the limb region of the target asteroid, compared with that expected for the smooth bulk surface at the same incident angle. The current status of LIDAR before the in situ measurements scheduled in September–November 2005 is briefly summarized.