Ranger Moon Pictures

Press, Volume CIV, Issue 30739, 1 May 1965, Page 7

Ranger Moon Pictures

The successful flight of Ranger IX brought to a close the 263 m dollar Ranger programme. Has it proved worth while, and, from the American taxpayer’s point of view, worth the expenditure? The answer to the first is that the Ranger programme, after six initial failures, finally exceeded expectations. Nearly 20,000 high-quality pictures of the moon’s surface were obtained, and almost half of them show details invisible through earthly telescopes. They are providing a wealth of new data on the moon's surface texture and topography and on the mysterious craters. But, at 15,000 dollars a picture, was it profitable? This cannot be gauged until the first moon expedition lands safely—or otherwise—on the surface of the moon. The Ranger photo-evaluation team has found that the moon is smooth enough for manned landings, and some of the team members feel sure that it is firm enough to support the landing vehicle. This is reassuring to the planners of the 20,000 m dollar lunar expendition, and they are pressing on with the vehicle construction. And if no further changes prove necessary, and if the landing is a success, then we may judge that the Rangers were indeed profitable. The three successful Ranger flights have shown that craters are the dominant features on the moon, right down to objects of the smallest size. Craters only one foot in diameter were revealed. However, the most exciting find is that there are at least two markedly different types of crater. Some are definitely impact craters, as has been thought all along. But a great many crates, particularly those which look like dimples rather than impact marks, are a result of some kind of subsidence or slumping action. Many of these occur in long chains—suggesting the opening of a sub-surface crack and the subsidence of fairly finely broken surface material at 'points along the crack. Others

suggest the collapse or sagging of material overlying a cavity underneath the moon’s surface. The existence of such cavities would throw new light on the birth of the moon, suggesting that the moon was formed cold and never became very hot, and it points to a possible hazard to the moon expedition. Another interesting finding is that the density of small craters, a few hundred yards or less in diameter, is constant in different areas on the moon, even though the density of larger craters may vary widely. For example, the floor of the big crater Alphonsus contains about three times the number of craters above 500 yards in diameter than does the surface of Mare Cognitum. This suggests that the floor of Alphonsus is older than the Mare and therefore bears the record of more cratering events. The density of craters smaller than about 300 yards in diameter is the same in both places because little craters are eroded at the same rate as they are continually being formed.