High mobility of landslides on the lunar crater rims

The Kaguya (Selene) lunar orbiter which was launched by JAXA in 2007 brought about a lot of topographical data using laser altimeter (LALT), terrain (wide-view) camera, and HD TV camera. This mission revised the lunar atlas with highest resolution of 10 m. The number of LALT surveyed points is about 6.7 million. Their evaluated precision is about 4 m, and the positioning precision is about 80 m (1 STD, respectively). Most of the obtained topographic data are implemented in Google Moon, which are available in the public for free of charge. JAXA revealed that there are numerous landslide topography especially along the lunar crater rims. In order to compare the mobility of those in Mars, we have examined the apparent friction (H/T) in major craters. Apparently, those landslides are distributed on rather older and dissected crater rims. It means their occurrence must be much later than the crater formation. In most cases, the H/T values of those landslides are around 0.1, like long-runout landslides on the Mars and Earth. Past studies proved that ground water might have taken most important role in the presence of such low H/L landslide events on the earth and Mars. However, there have been no evidence nor implication reported, of past water existence on the moon. Possible mechanisms of these low H/T on the crater are (1) moon quake due to nearby meteor impact; (2) shear resistance reduction due to long-term physical/chemical weathering and existence of little ground water; (3) exotic mechanism including tectonic function.