Answers to such questions call for the recovery and analysis of samples of lunar materials from a variety of regions on the moon. Most of the analysis will have to be done on the earth. Determining the age of a sample of lunar material or making a chemical and mineralogical analysis of it requires instruments that cannot be deployed on the lunar surface within the next few years, particularly with little or no prior knowledge of the character of the materials to be analyzed.
The study of returned lunar materials will in fact provide one of the most intriguing challenges ever faced by natural scientists. How much of the moon's history and how many of the lunar surface processes can be understood from a few isolated samples of lunar material, aided by the fairly detailed knowledge of the surface morphology obtained from photographs? The possibilities are considerable, because the lunar surface is not subject to many of the chemical processes that occur on the earth's surface, such as the changes accompanying erosion and sedimentation. Furthermore, the distribution of material over the surface of the moon by the impact of meteorites suggests that a substantial amount of material in any given place may have come from great distances without significant changes in chemical composition.
Efforts to trace the evolution of the moon, to understand its gross internal structure and to explain the characteristics of its major morphological features will require knowledge of the kind and amount of internal energy released by moonquakes, heat flow at the surface and volcanism. The occurrence of moonquakes would reveal something of the distribution of stress with depth. The seismic waves arising from moon quakes would provide a powerful tool for deducing the distribution of basic physical properties with depth. Measurement of heat flow at the surface, combined with estimates of the distribution of radioactive elements in the lunar rocks, would make possible a determination of whether or not internal energy is in fact the cause of volcanism on the moon. Data for attacking these problems will be needed from a number of widely distributed points on the moon.
The Problem of the Mascons
The space vehicles employed in the Lunar Orbiter missions not only made excellent photographs of the lunar surface but also yielded a startling discovery having to do with the gravitational field of the moon. If the moon were a symmetrical spheroid, internally as well as externally, a satellite would move around it in a well-defined elliptical orbit at a smoothly varying speed. In actuality the moon, like the earth, is not quite a symmetrical spheroid, which introduces perturbations in satellite orbits. Over and above these perturbations, however, there are others introduced by lateral variations in the moon's density. As the Lunar Orbiter vehicles were tracked in their orbits it was noted that they gained speed whenever they passed over one of the moon's ringed maria, or dark circular "seas". Analysis of these motions by Paul M. Muller and William L. Sjogren of the Jet Propulsion Laboratory led to the finding that over the major circular maria (Imbrium, Serenitatis, Crisium, Humorum and Nectaris) there is a substantial excess of gravity.
What is the cause of these gravitational variations? The large positive anomalies associated with the maria imply concentrations of mass, now abbreviated as "mascons". An example of the concentration involved is provided by the estimate that the gravitational anomaly over Mare Imbrium is equivalent to one produced by a sphere of nickel–iron 70 kilometers in diameter centered at a depth of 50 kilometers.
The discovery of lunar mascons has given rise to much speculation and debate about their origin. It has also revived interest in exploring the lunar maria, which many investigators had dismissed as unlikely to be as rewarding scientifically as other areas of the moon. Do the mascons represent remnants of giant iron asteroids that struck the moon and subsequently were buried and fragmented, or were they formed by some other mechanism?
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Add CommentThe Apollo missions were truly 50 years ahead of their time. 50 years societally & technologically. We ought still to look back at what our ancestors achieved, with the resources at hand, and the will in mind, in awe.
Reply | Report Abuse | Link to thisI disagree hotblack, the Apollo missions were 7-10 behind the times. If Wernher von Braun was given the opportunity earlier, we would have gotten to the moon by 1959-62. The German scientist was way beyond his time. In one word "Brilliant". Why doesn't Nasa have any of these guys around?
Reply | Report Abuse | Link to thisPerhaps technology. But Werner Von Braun as a Nazi was societally 1000s of years behind. Better to not have achieved the moon landing and other technological goals than be a Nazi
Reply | Report Abuse | Link to thisdoron, surely you must be aware that Von Braun was a reluctant Nazi. He earned the enmity of his superiors on several occasions because of his outspoken vision of rocket-enabled space travel and exploration, rather than rocket-enabled world domination. Von Braun was not enthusiastic about the Nazis or the war. This characteristic almost cost him his life. Viewing the past through the lense of the present affords many opportunities to wax morally superior to one's ancestors. The moon landings were a culmination of Von Braun's inspired vision of human progress, and had nothing to do with the Nazi Party. Perhaps you had better get your own house in order, doron - before you ask the entire human race to discard any dreams of reaching beyond, for fear of disturbing a tree or a slumbering faun.
Reply | Report Abuse | Link to thishotblack - Do you know how much I despise those who state that "so-and-so was ahead of their time" simply because the ball got dropped later on? Apollo was firmly of its time. The moon mission could have been completed earlier than 1969 had it not been for delays. Saying that Apollo was 50 years ahead of its time is the same as saying its OK that we're currently doing nothing of consequence in space. I vehemently disagree with this state of affairs. I will add, hotblack, that using your logic, Apollo wasn't just 50 years ahead of its time. If the Chinese make it to the moon by 2020, Apollo will be officially 61 years ahead of its time. If you ignore the Chinese and just count NASA, well... you might have to wait a pretty long time to find out. They'll probably not go their again. We entered our long decline a while back.
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