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| CATEGORIES ABOUT MASS CONCENTRATION | |
| gravimetry | |
| geophysics | |
| lunar science | |
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A mass concentration or '''mascon''' is a region of a planet or moon's crust that contains a large amount of material that is denser than average for that body. The result is a minute but measurable increase in the local Gravity . Mascons can have a variety of causes. On Earth , they frequently indicate processes occurring in the upper Mantle such as plumes of Magma . On the Moon , most mascons are thought to be remnants of Asteroid s that impacted the surface, or the effects of magmatic upwelling from the lunar interior after such impacts. The Moon's mascons alter the local gravity in certain regions sufficiently so that low, uncorrected satellite Orbit s around the Moon, are unstable on a timescale of months or years, distorting the successive orbits until the satellite impacts the surface. The lunar mascons were discovered by Paul M Muller and William Sjogren of the NASA Jet Propulsion Laboratory (JPL) in 1968 (Science, 161, 1968) from analysis of the highly precise Navigation data from the unmanned pre-Apollo Lunar Orbiter spacecraft. At that time one of NASA's highest priority "tiger team" projects was to explain why the Lunar Orbiter spacecraft being used to test the accuracy of Project Apollo navigation were experiencing errors in predicted position of ten times the mission specification (2 Km instead of 200 M ). This meant that the predicted landing areas were 100 times as large as those being carefully defined for reasons of safety. The aforementioned problem with lunar orbital effects was revealed as the cause by this discovery. William Wollenhaupt and Emil Schiesser of the NASA Manned Spacecraft Center in Houston then worked out the "fix" that was first applied to Apollo 12 and permitted its landing within 30 m of the target, the previously landed Surveyor 3 spacecraft. |
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