Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)
Ibaraki University
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University
Waseda Research Institute for Science and Engineering, Waseda University
Research Center for Advanced Information Science and Technology, University of Aizu
The new era of lunar explorations aiming future settlement of humans in the space have been starting. In this era, one of the most important topics is ''water ice'' on the lunar polar regions that has been suggested since 1960s. In 1990s, two lunar orbiters, Clementine and Lunar Prospector provided some important results interrelated with the existence of polar water ices on the Moon, particularly in the permanent shadowed area of Shackleton crater. However, the water ice existence in the Shackleton still has not been confirmed by later various observations. On the other hand, the concentration of hydrogen on the lunar polar regions originated from solar wind proton implantation is likely true. LEND neutron spectrometer onboard LRO showed the highest hydrogen concentration at some regions of extremely low temperatures (less than or equal to 40K) should reach 470 ppm, that is corresponding to 0.42wt% of water ice if an appropriate amount of usable oxygen is given. We note that the amount of the highest hydrogen concentration detected at the lunar polar regions is the same order as that have been reported for the element found in minerals of some of lunar samples.