AS15-0293(M)

Figure 97

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Craters, craters, craters! The far side, even more than the near, presents a tortured record of the bombardment suffered by the Moon throughout its history. This scene exemplifies the relentless attack of impacting objects from space and from the lunar surface that has characterized most of lunar history.

The craters in this far-side area come in various shapes, sizes, and degrees of degradation attesting to a variety of formative processes, energies of formation, and ages. Each individual circular crater was probably produced by the impact of a body from interplanetary space- the larger the crater, the higher the energy; that is, the larger the body, or the greater its velocity upon impact. The first and largest such impact erased all earlier features and produced the crater that fills most of the scene, Gagarin, 265 km in diameter (rim crest outlined). A series of smaller craters followed, starting with crater A (46 km), itself heavily cratered, and ending with the sharp funnel-shaped craters and crater C(14 km). The young age of crater C is demonstrated by the sharpness of its rim crest and its halo of extremely fine, fresh ejecta and secondary craters. During the rain of objects from space, clots of lunar material ejected from impact craters outside this area landed here to form irregular secondary craters. Examples (D) are the elongate partly filled crater near the upper right corner and the elongate but deeper craters in the upper left. Conceivably, however, some irregular craters were formed by volcanism, a process that at one time was widely believed to be the cause of most irregular craters on the Moon. At some time late in the history of the region, an even more distant impact hurled a loose cluster of debris to form the group of sharp, circular (high-energy) craters in the left center of the picture.

In this section of SP-362 other primary and secondary craters will be illustrated as will some possible volcanic craters and some craters whose properties are too obscured to reveal their origin-like crater B and its twin Iying inside the older crater A in this picture.   -D.E.W.