Abstract
In order to examine the ``giant impact hypothesis'' for the Moon formation, we run the first grid-based, high-resolution hydrodynamic simulations for impact between proto-Earth and a proto-planet. The spatial resolution for the impact-generated disk is greatly improved from previous particle-based simulations. This allows us to explore internal fine structures of the debris disk and its long-term evolution. We find that in order to form a stable debris disk from which a lunar-sized satellite can be accumulated, the impact must result in a disk of mostly liquid debris, where pressure is not effective, well before the accumulation process starts. If the debris is dominated by vapor gas, strong spiral shocks are generated, thereby the circumterrestrial disk cannot survive more than several days.
