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Lunar Prospector: Against All Odds

[ Part 1 | Part 2 | Part 3 | Part 4 | Epilogue | Appendices ]

Images are all approximately 100kb in size so please be patient.

+ Figures E-1 through E-6

Figure E-1: Lunar Prospector’s low-resolution gravity map of the Moon. In order to gain gravity-mapping data, a spacecraft’s velocity must be determined to an accuracy of at least 1 mm/sec. The Lunar Prospector tracking data are accurate to 0.2 mm/sec! This accuracy, coupled with the facts that undisturbed data were repeatedly obtained for periods of up to 56 days and at altitudes as low as a few km, allowed Lunar Prospector scientists to produce the first, highly accurate global maps of the Moon’s gravity field. The large red areas are those where the gravity is up to 0.25% higher than in the surrounding areas (see the panel to the right), i.e., the so-called Mascons of the circular maria. View image

Figure E-2: Lunar Prospector’s high-resolution gravity map of Mare Humboldtianum (this mascon mare is located at 60° N latitude and on the eastern, front side limb of the Moon in Figure E-1). This map, which shows the gravity field and topography of the Mare Humboldtianum area, clearly demonstrates the extremely high quality of the Lunar Prospector gravity data. The gravity high in the middle of the mare is up to +180 mgal (a mgal is an acceleration of 0.001 cm/sec2, the Moon’s gravity is 162,250 mgal or 1/6 of that of the Earth) or 0.1% higher than that of the average Moon. A trough of low gravity, as low as –220 mgal, surrounds the gravity high. Positive gravity anomalies, like this one, are caused by the density contrast between the dense mare basalts and mantle plugs (both 3.4 g/cm3) in the maria and below them, respectively, and the less dense crustal rocks (2.8 g/cm3) surrounding the maria. The gravity low troughs surrounding the gravity highs are caused by the downward warping of the lunar crust under the heavy load of the dense mare basalts. View image

Figure E-3: Lunar Prospector’s low-resolution magnetic map of the moon. This map shows that the weak lunar magnetic fields are concentrated and strongest (yellow and orange areas) in the areas 180° from the major maria basins, e.g., the basins of Mare Imbrium, Mare Serenitatis, Mare Crisium, Mare Orientale, and that magnetic field are absent or very weak (light and dark purple) in the mare basin areas themselves. These results are interpreted by Lunar Prospector scientists to mean 1) that the giant basin forming impacts demagnetized the rocks in the impact areas, 2) as the impact ejecta swept around the Moon in all directions, moving toward the opposite side of the Moon, plasma in the ejecta (formed from vaporized rock) swept up the preexisting magnetic fields and concentrated them at the point where the eject met itself 180° from the impact point and 3) in the presence of this concentrated magnetic field, the hot, shocked rock landing in that area became thermally and shock magnetized. View image

Figure E-4: Lunar Prospector’s high-resolution map of the magnetic fields in the area surrounding the bright lunar feature called Reiner Gamma in the western part of Oceanus Procellarum. View image

Figure E-5: Lunar Prospector’s Gamma-Ray Spectrometer (GRS) high-resolution (2° or 60 km), global map of the distribution of the trace element thorium over the Moon. This first global map of thorium proved the much earlier developed concept that KREEP (potassium [K], Rare Earth Elements and Phosphorus, a trace element-rich material containing thorium) was excavated from the crust-mantel boundary (where it was deposited during the initial differentiation of the Moon) by the Mare Imbrium Basin Forming Impact and distributed over the Moon’s surface. As can be seen from this global thorium map, the 1000 km wide Mare Imbrium (centered on the left map) is surrounded by high concentrations (red and yellow) of thorium that were deposited in the rim areas of this gigantic crater or, as lunar scientists call it, impact basin. The secondary concentration of thorium (shown in the right map) on the lunar far-side is partially due to the concentration of impact eject 180° from the Imbrium impact site. View image

Figure E-6: This detailed, high-resolution thorium map of the Mare Imbrium region in Figure E-5 provides more information about the petrological evolution of the Moon. After thorium-rich KREEP was excavated by the Mare Imbrium Basin Forming Impact and deposited around the basin, these KREEP-rich ejecta deposits were partially buried by later mare basalt lava flows and the ejects from other large impact events. As this high resolution Lunar Prospector map shows, later impacts, that formed 30 to 50 km sized craters, re-excavated the buried KREEP-rich materials and re-deposited them on the lunar surface immediately around such craters, i.e., Kepler, Aristarchus, Mairan, Aristillus and Arago. View image

+ Figures E-7 through E-10

Figure E-7: Lunar Prospector’s Gamma-Ray Spectrometer (GRS) low-resolution (5° or 150 km) maps of the distributions of the trace elements thorium, potassium and uranium, all components of KREEP (see Figure E-5 caption). The distribution of the three important trace elements are essentially identical and are the result of KREEP being excavated by the Imbrium Basin Forming Impact and being distributed around the Moon in its ejecta (see Figure E-5 caption). In addition to these GRS maps, the Neutron Spectrometer (NS) data yielded information on the distribution of two additional KREEP trace elements, samarium plus gadolinium, whose distribution is also essentially identical to that of thorium. View image

Figure E-8: Like terrestrial igneous rocks, lunar materials are composed mainly (98% to 99% in the case of lunar materials) of just 7 element: Iron (Fe), magnesium (Mg), titanium (Ti), aluminum (Al), calcium (Ca), silicon (Si) and oxygen (O). Lunar Prospector’s low-resolution (5° or 150 km) Gamma-Ray Spectrometer (GRS) maps of the global distributions of the 7 major elements clearly show that the lunar crust consists of two major petrological units – the Fe-, Mg- and sometimes Ti-rich mare basalts and the Al-, Ca-, Si- and O-richer highland rocks. View image

Figure E-9: Lunar Prospector’s maps of the lunar Polar Regions showing their distributions of hydrogen (H) as mapped by the Neutron Spectrometer (NS). The H is thought to be concentrated in the permanently shadowed craters of the Polar Regions in the form of water ice (H20). View image

Figure E-10: Lunar Prospector’s Alpha Particle Spectrometer (APS) map shows that radon gas is being released (count rater higher than 0.07/sec) at higher rates than the very low average crustal rate at the young craters Aristarchus (resolution element centered on -45° East Longitude and 22.5° North Latitude) and Kepler (resolution element centered on –35 ° East Longitude and 7.5° North Latitude). View image

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