Local and regional lunar regolith characteristics at Reiner Gamma Formation: Optical and spectroscopic properties from Clementine and Earth-based data

A detailed remote sensing survey of the Reiner Gamma Formation (RGF) region by means of Earth-based telescopic and Clementine multispectral imaging ha s been made in the UV-visible-near-infrared domain. The spectral mixture an alysis reveals the existence of three basic end-members relevant for modeli ng the observed spectral variations in the RGF vicinity. These are MB (mare background), SWS (southwest swirl), and RGS (Reiner Gamma soil). The first two components exhibit spectral characteristics consistent with a prevaili ng contribution of mature mare soils for the surroundings (MB) and of immat ure mare crater-like soils (RGS) at RGF. The third intermediate-albedo comp onent (SWS) has general characteristics of a mature mare soil, but with a r edder continuum slope. The reported observation can be modeled by a mechani sm which would remove the finest fraction in the soil (particle diameter < 45 mu m) at RGF and redistribute it in the vicinity with a laterally variab le proportion and local accumulations such as at SWS site. According to the available set of in situ data documenting variations in the chemical compo sition, in the distribution of particle sizes, and in the degree of maturit y with depth in the mare regolith, the characteristics depicted at RGF are those of a subsurface soil layer from a depth of the order of 0.3 - 0.8 m. In our view, the simplest way to account for the whole body of information available from the present work lies in the proposition that in the area of RGF the uppermost layer of the regolith has been optically and mechanicall y modified by a process involving the fall of fragments of a low-density co metary nucleus previously disrupted by tidal interaction in the Earth-Moon system. We recognize, however, that in the present state of knowledge, one cannot rule out the hypothesized existence of a zone of seismically modifie d terrain peripheral to the Imbrium or Orientale basins just beneath the ma re surface that would be the actual source of the RGF magnetic anomaly.