The gamma-ray spectrometer data shows that the rocks rich in potassium, rare earth elements and phosphorus, known as KREEP, are concentrated in the Mare Imbrium rim, the nearside maria and highlands near Imbrium and the Mare Ingenii South Pole-Aitken basin and are distributed at a lower level in the highlands. KREEP is rich in uranium and thorium and is thought to represent the last remaining melt after the lunar crust formed. The distribution seen by Lunar Prospector supports the idea that the impact which formed Mare Imbrium excavated KREEP-rich rocks and ejected them over the Moon and the South Pole-Aitken basin impact also exposed KREEP-rich material.
Results from S-band tracking of Lunar Prospector and calculations based on the Doppler shift of the signal have given more detailed information on the lunar gravity field. This shows that the Moon has a moment of inertia of 0.3929 to 0.3933, implying a small dense core with a mass of 1% to 4% of the Moon's mass, in agreement with earlier estimates. This translates to a core radius of 220 km to 590 km. The smaller 220 km value holds for a core of pure iron, while the 590 km estimate applies to a core of less dense iron sulfide. This small iron core may lend support to the hypothesis that the Moon was formed by a giant impact on the Earth during its early accretion.
Seven new mascons (mass concentrations - large areas of high density material in or below the lunar crust, usually associated with impact basins) were discovered in the gravity data, three on the near-side and four on the far-side. It has been thought that the higher densities were due simply to heavy basalt filling the basins underlain by a plug of dense mantle material. However, some of the newly discovered mascons are not basalt-filled, suggesting all of the mass anomaly associated with these basins is due to the mantle plug.
Elphic, R. C., D. J. Lawrence, W. C. Feldman, B. L. Barraclough, S. Maurice, A. B. Binder, and P. G. Lucey, Lunar Fe and Ti abundances: Comparison of Lunar Prospector and Clementine data, Science, 281, 1493-1496, Sept. 1998.
Feldman, W. C., B. L. Barraclough, S. Maurice, R. C. Elphic, D. J. Lawrence, D. R. Thomsen, and A. B. Binder, Major compositional units of the Moon: Lunar Prospector thermal and fast neutrons, Science, 281, 1489-1493, Sept. 1998.
Feldman, W. C., S. Maurice, A. B. Binder, B. L. Barraclough, R. C. Elphic, and D. J. Lawrence, Fluxes of fast and epithermal neutrons from Lunar Prospector: Evidence for water ice at the lunar poles, Science, 281, 1496-1500, Sept. 1998.
Konopliv, A. S., A. B. Binder, L. L. Hood, A. B. Kucinskas, W. L. Sjogren, and J. G. Williams, Improved gravity field of the moon from Lunar Prospector, Science, 281, 1476-1480, Sept. 1998.
Lawrence, D. J., W. C. Feldman, B. L. Barraclough, A. B. Binder, R. C. Elphic, S. Maurice, and D. R. Thomsen, Global elemental maps of the moon: The Lunar Prospector gamma-ray spectrometer, Science, 281, 1484-1489, Sept. 1998.
Lawson, S.L., W.C. Feldman, D.J. Lawrence, K.R. Moore, R.D. Belian, S. Maurice, and A.B. Binder Results from the Lunar Prospector Alpha Particle Spectrometer: Detection of Radon-222 Over Craters Aristarchus and Kepler, Abstract, DPS 2001 Meeting, 4.05, Nov. 2001.
Lin, R. P., D. L. Mitchell, D. W. Curtis, K. A. Anderson, C. W. Carlson, J. McFadden, M. H. Acuna, L. L. Hood, and A. Binder, Lunar surface magnetic fields and their interaction with the solar wind: Results from Lunar Prospector, Science, 281, 1480-1484, Sept. 1998.