(Proposal ID) S12B-114

(PI) Usui, Fumihiko

(Proposal Title)
Search for Water in Outer Main Belt Based on AKARI Asteroid Catalog (II)

(Abstract)
We propose a program to search water ice and/or aqueously altered silicates on 
the surface of asteroids in outer main belt regions, which have high albedo 
measured with AKARI. The distribution of water in the main belt provides 
important information to understanding the formation and evolution of the 
solar system, because water is a good indicator of temperature in the early 
solar nebula, and it may be linked to the origin of Earth's water. The 
existence of water ice is a hot topic in the solar system studies today. Water 
ice is recently found in the outer region of the main asteroid belt and some 
of them are related with the main belt comets. Brand-new albedo data brought 
by AKARI opens the possibility of detection of water ice on asteroids like 
C-type and D-type, which contain primitive materials. Here we propose to make 
the spectroscopic observations with the Subaru telescope in the near-infrared 
wavelengths to detect water ice on these high-albedo C-type and D-type 
asteroids. Thanks to a large aperture of Subaru telescope and a high altitude 
of Mauna Kea, it can be only possible to observe a weak signal of the 
existence of water on the surface of asteroids with a certain S/N 
(typically, > 30 is required).