FIGURE 115 [above & below].-Messier (1) and Messier A (2) are a pair of unusual craters in northwestern Mare Fecunditatis. Messier is elliptical and has bright walls and light rays of ejecta extending at right angles to its long axis (approximately 16.5 km). Messier A is a doublet crater having two very long rays or filaments of ejecta extending westward from it. The east part of the doublet has steep, bright walls, whereas the west part is dark and appears mantled. Differences between the two parts are more clearly shown in this oblique view of Messier A composed as a stereogram. Both Messier and Messier A resemble some small experimental impact craters produced in sand by projectiles following shallow trajectories (4° or less from the horizontal) at velocities of approximately 1.7 km/s. In separate experiments using single projectiles, both elliptical craters with lateral ejecta lobes and doublet craters have been produced. Thus, it can be inferred that these lunar craters were produced by high velocity projectiles following shallow trajectories. By further analogy with the experiments, the projectiles that formed Messier and Messier A apparently traveled from east to west.-H.J.M.
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