In chapter I a global lunar topographic map is derived from Earth based\r\nand orbital observations supplemented in areas without data by\r\na linear autocovariance predictor. Of 2592 bins, each 5\u00b0 square,\r\n1380 (64.7% by area) contain at least one measurement. A spherical\r\nharmonic analysis to degree 12 yields a mean radius of (1737.53 \u00b1 0.03)\r\nkm (formal standard error) and an offset of the center of figure of\r\n(1.98 \u00b1 0.06) km toward (19 \u00b1 2)\u00b0 S, (194 \u00b1 1)\u00b0 E. A Bouguer gravity\r\nmap is also presented. It is confirmed that the low-degree gravity\r\nharmonics are caused primarily by surface height variations and only\r\nsecondarily by lateral density variations.

\r\n\r\nIn chapter II a series of models of the lunar interior are derived\r\nfrom topographic, gravitational, librational and seismic data. The\r\nmoon departs from isostasy, even for the low-degree harmonics, with\r\na maximum superisostatic stress of 200 bars under the major mascon\r\nbasins. The mean crustal thicknesses under different physiographic\r\nregions are: mascons, 30-35 km; irregular maria, 50- 60 km; and\r\nhighlands, 90-110 km. A significant correlation between lunar surface\r\nchemistry and crustal thickness suggests that regions of thicker crust\r\nare more highly differentiated. A possible mean composition consistent\r\nwith our model is an anorthositic crust, underlain by a predominantly\r\nforsterite upper mantle which grades into a refractory rich lower\r\nmantle surrounding a pyrrhotite core.

\r\n\r\nIn chapter III a model of martian global topography is obtained\r\nby fitting a spherical harmonic series of degree 16 to occultation,\r\nradar, spectral and photogrammetric measurements. The existing\r\nobservations are supplemented in areas without data by emperical\r\nelevation estimates based on photographic data. The mean radius is\r\n(3389.92 \u00b1 0.04) km . The corresponding mean density is (3.933 \u00b1 0.002)\r\ng cm^(-3). The center of figure is displaced from the center of mass by\r\n(2.50 \u00b1 0.07) km towards (62 \u00b1 3)\u00b0 S, (272 \u00b1 3)\u00b0 W. The geometric \r\nFlattening [f_g = (6.12 \u00b1 0 .04) 10^(-3) ] is too great and the dynamic\r\nflattening [f_d (5.22 \u00b1 0 .03) 10^(-3)] is too small for Mars to be\r\nhomogeneous and hydrostatic. It is confirmed that, similar to the\r\nMoon, the martian low-degree gravity harmonics are produced primarily\r\nby surface height variations and only secondarily by lateral density\r\nvariations. Maps of the global topography and Bouguer gravity are\r\npresented. These are interpreted in terms of a crustal thickness map\r\nwhich is consistent with gravity, topography and recent preliminary\r\nViking seismic results. Using plausible density contrasts and an\r\nassumed zero crustal thickness at Hellas, the inferred minimum mean\r\ncrustal thickness is (28 \u00b1 4) km.

\r\n\r\nIn chapter IV it is shown that the topographic variance spectra\r\nof the Earth, Moon, Mars and Venus are all very similar. The variance\r\nper harmonic degree V(H;n) decreases roughly as the inverse square of\r\nthe degree, or more precisely V(H;n) \u2250 V(H;O)/(n)(n+1). On the Earth\r\nand Moon this relationship has been confirmed down to scale lengths as \r\nsmall as L \u2250 100 m. At the other end of the spectrum, the variance\r\nappears to be deficient relative to this model for scale lengths\r\ngreater than L \u2250 2000 km. The most satisfactory explanation for this\r\nphenomenon appears to be a simple equilibrium between constructional\r\nor \"tectonic\" processes which tend to roughen the surface uniformly\r\nat all scales, and destructional or erosive processes which tend to\r\nsmooth the surface preferentially at small scales. The deficiency\r\nin the low-degree variances is attributable to visco-elastic\r\ndeformation.

\r\n", "doi": "10.7907/SM57-8B66", "publication_date": "1978", "thesis_type": "phd", "thesis_year": "1978" } ]