AS15-0326(P)

Figure 165

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Aristarchus is a large crater on the edge of a plateau within northern Oceanus Procellarum. In this scene the crater is viewed obliquely from the north. One of the brightest and youngest craters of its size on the near side of the Moon, Aristarchus is believed to be younger even than Copernicus. The general appearance of Aristarchus and of parts of the plateau around it led Alfred Worden, the Apollo 15 CMP, to describe this part of the Moon as .... . probably the most volcanic area that I've seen anywhere on the surface." For many years before the Apollo missions, Earth-based viewers had reported telescopic sightings of transient events centered on Aristarchus. These brief, subtle changes in color or in sharpness of appearance have been suggested as evidence for volcanic activity or the venting of gases from the lunar interior. The sightings are controversial, but Aristarchus remains a center of interest. - Michael C. McEwen

About 39 km in diameter, Aristarchus is on the borderline between medium-sized and large-sized craters. We have included it among the large craters because its well- developed concentric terraces are characteristic of most large craters that have not been too severely degraded. Its terraced walls, as well as its arcuate range of central peaks, are particularly well shown in this view. The walls and parts of the crater floor are extremely rough and cracked, a characteristic feature of other young impact craters of this size range, such as Tycho and Copernicus. The rough deposits in the floor are probably made up largely of shock melted material formed at the time of the impact. The inner, rougher portions of the rim show a series of channels, lobate flows, and smooth puddielike deposits that may represent shock-melted material deposited on the crater rim. The outer, smoother portions show the rhomboidal pattern characteristic of crater ejecta blankets. - James W. Head III