Masumi Shimojo, National Astronomical Observatory of Japan, Tokyo, Japan, Tomoko Kawate, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan, Takenori J. Okamoto, National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan and Takaaki Yokoyama, University of Tokyo, Department of Earth and Planetary Science, Bunkyo-ku, Japan