Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmdi33b..02n&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #DI33B-02
Physics
[1221] Geodesy And Gravity / Lunar And Planetary Geodesy And Gravity, [5417] Planetary Sciences: Solid Surface Planets / Gravitational Fields, [8147] Tectonophysics / Planetary Interiors
Scientific paper
A new spherical harmonic model of the lunar gravity field, complete to degree and order 100 (SGM100g), has been developed from four-way Doppler measurements of Kaguya. On nearside, a comparison of SGM100g with a previous lunar gravity models reveals a general agreement. The five principal gravity highs on Imbrium, Serenitatis, Crisium, Nectaris, and Humorum are clearly visible, as in the previous models. On farside, in contrast, the new gravity field model shows several circular signatures that correspond to topographic structures such as Moscoviense, Freundlich-Sharonov, Mendeleev, Hertzsprung, Korolev and Apollo basins that used to be identified as linear signatures in previous models. For the study of lunar basins of which diameter are comparable to lunar radius, localization by two-dimensional Fourier analysis is not appropriate. Instead, we use spectral filter of wavelet analysis. This method has an advantage to Fourier analysis that the gravity and topography models can be calculated without a loss of spectral information. This advantage is particularly important for distinguishing several compensation mechanisms of the lunar basins. New analysis reveals a difference of internal structures of basins on nearside and farside. We have classified lunar basins into Type I, Type II, and primary mascon basins. Type I basins include Korolev, Dirichlet-Jackson, and Mendeleev basins on the farside. Localized free-air gravity anomalies of Type I basins show two peaks which are representing topographic depression of the basins. Second peak has more power than expected from topography, indicating additional contribution from mass anomalies beneath basins. An agreement of second peak wavelength of topography and gravity implies genetic relationship of the central gravity high with impact process. Admittance of Type I basins show two constant plateaus. They suggests little compensation of topography. A plateau at shorter wavelength is higher than that at longer wavelength, as expected from localized topography and gravity. On the other hand,primary mascon basins on the nearside reveal the power spectrum of local gravity and topography similar to those of Type I basins. However, admittance is very different. Negative admittance and the cross sections show that the first peak of the local gravity is indeed representing broad central gravity high of primary mascon basin. Type II basins include Freundlich-Sharonov, Hertzsprung, and Orientale basins on the farside and limb. Localized free-air gravity anomalies of Type II basins show tow peaks, similar to Type I basins, while a central degree of the second peak is lower than that of the local topography, corresponding to broad central gravity high of Type II basins. In contrast to Type I basins, admittance of Type II basins show a wide variation, likely suggesting that Type II basins are transitional between farside Type I basins and primary mascon basins on the nearside. An internal structures of primary mascon basins could be inferred as an extrapolation of Type I and II basins.
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