Recently, pairs and groups of asteroids with extremely similar orbital elements have been identified. These asteroids are thought to be young fragments from the break-up of precursor objects, and have the surface age less than one million years. From the shape and size distributions, the physics of the break-up of km-sized bodies are studied. Also, the space-weathering processes are investigated through the measurements of surface colors and conditions of different ages. A series of photometric and spectroscopic observations have been carried out for a pair of asteroids, (3200) Phaethon and (155140) 2005 UD, at Lulin observatory in Taiwan, and both C-type like unaltered surface and F-type like weathered surface are identified on the surface. This proposal aims to extend the study of asteroid break-up and surface alteration by space-weathering using PS1 sky survey data. Thanks to the wide field-of-view and cyclical imaging, PS1 survey is expected to increase the number of known asteroids by factor of 10 or more, and many pairs of asteroids with fresh surface will be detected. We focuses on the possible surface evolution from C-type like material into F-type like material by the space-weathering effect and/or thermal metamorphism. The goal of this program is to measure the colors and spectra of young surface on asteroids and understand the space-weathering processes of primitive material in solar system. 研究期間：9908 ~ 10007
