Lunar color boundaries and their relationship to topographic features: A preliminary survey

By combining UV negatives with IR positives of the full Moon, it is possible to suppress albedo differences and to enhance color differences between various lunar regions. Areas within the lunar maria exhibit the greatest color variations, and many have sharp boundaries. In contrast, the terrae in general show only feeble color variations, although small terra regions situated near or surrounded by maria sometimes display enhanced redness. The mare color boundaries in some cases coincide with the edges of clear-cut lava flows, the bluer material overlying the redder. One wedge-shaped area of bluer material corresponds with a prominent sinuous rille, the rille source being situated precisely in the point of the wedge. This area has obliterated portions of two ray systems, showing that the bluer material was deposited later than both the surrounding redder material and the ray material. On the other hand, rays from the crater Olbers A cross both colored areas impartially. Other examples of ray obliteration by bluer deposits are found elsewhere. From Apollo and Surveyor analyses, it is found that there is an apparent correlation between degree of blueness and titanium content of the surface materials. The following conclusions may be drawn:

1. The various maria were deposited over considerable lengths of time; this does not support the fusion-through-impact hypothesis.
2. The bluer materials, which appear to be those of high Ti content, are the more recent.
3. The hypothesis that sinuous rilles are lava drainage channels is supported.
4. The terrae covered by this study are mostly monotonous, suggesting constant composition, but a few anomalously red isolated regions may be of substantially different composition.