Letter to the Editor

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

¹ Image Analysis Group, TU Dortmund University, Otto-Hahn-Str. 4, 44227 Dortmund, Germany
e-mail: christian.woehler@tu-dortmund.de
² Physical Research Laboratory, Ahmedabad 380009, India
e-mail: megha@prl.res.in
³ Sternberg Astronomical Institute, Moscow State University, Universitetskij Pr., 13, 119234 Moscow, Russia
e-mail: a_tolok@mail.ru

Received: 20 May 2019
Accepted: 6 September 2019

Abstract

Using the near-infrared spectral reflectance data of the Chandrayaan-1 Moon Mineralogy Mapper (M³) instrument, we report an unusually bright structure of 30 × 60 km² on the lunar equatorial farside near crater Dufay. At this location, the 3-μm absorption band feature, which is commonly ascribed to hydroxyl (OH) and/or water (H₂O), 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-μm absorption anywhere else on the Moon. A possible explanation for this structure is the recent infall of meteoritic or cometary material of high OH/H₂O content forming a thin layer detectable by its pronounced 3-μm band, where a small amount of the OH/H₂O 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/H₂O in the lunar regolith surface.