Detection of an excessively strong 3-µm absorption near the lunar highland crater Dufay

Using the near-infrared spectral reflectance data of the Chandrayaan-1 Moon Mineralogy Mapper (M 3 ) instrument, we report an unusually bright structure of 30 × 60 km2 on the lunar equatorial farside near crater Dufay. At this location, the 3-μ m absorption band feature, which is commonly ascribed to hydroxyl (OH) and/or water (H2 O), at local midday is significantly (∼30%) stronger than on the surrounding surface and, surprisingly, stronger than in the illuminated polar highlands. We did not find a similar area of excessively strong 3-μ m absorption anywhere else on the Moon. A possible explanation for this structure is the recent infall of meteoritic or cometary material of high OH/H2 O content forming a thin layer detectable by its pronounced 3-μ m band, where a small amount of the OH/H2 O is adsorbed by the surface material into binding states of relatively high activation energy. Detailed analysis of this structure with next-generation spacecraft instrumentation will provide further insight into the processes that lead to the accumulation of OH/H2 O in the lunar regolith surface.