1. Bulk density 3.3 gm/cm3
2. Moment of inertia (close to homogeneous sphere), 0.39 MR2
B. Mineralogy and crustal ages
1. Highlands (rough topography scatters visible wavelengths and looks white) -- greater than 4 b.y. old
2. Mare (smooth topography scatters less light than highlands and looks darker) -- 3-4 b.y. old
3. Crustal rocks are earthlike silicates, including basalts (pyroxene and olivine), anorthosite-norite-trolcolite, plagioclase (anorthite and albite)
4. 50 km crust with Al2O3 enrichment overlying a depleted mantle. Crust was formed in early history by gravitative differenentiation of the lunar mantle.
5. Lunar chemistry is more refractory than earth but depleted in iron compared to earth, consistent with a high temperature origin and favoring the hypothesis of origin as a collision splashing out a portion of the earth's mantle.
C. Lunar seismology.
1. The upper 1-2 km of the lunar crust is highly scattering to elastic waves, consistent with a heavily fractured and recemented (brecciated) crust .
2. A low velocity zone for P waves is detected at 400 km depth near the point where the melting temperature of the dry silicate mantle is reached at 1700o C.
3. S waves are not detected below 1600 km, perhaps signifying another partial melt zone in the lunar core.
4. Seismic activity is mostly impact events, with some moonquakes in the deep interior, which seem to be correlated with peaks in the solid lunar tide.
D. Temperature structure and heat flow
1. Determined primarily from electrical conductivity measurements.
2. Steep temperature gradient to 400 km depth (conduction zone) followed by gentler gradient close to the adiabatic gradient (convection zone).
3. Heat flow is 17 ergs/cm2/sec (earth is 62 ergs/cm2/sec) -- consistent with a smaller body that has been able to cooled much more than the earth since its time of formation.
4. Specific luminosity is higher than the Earth's , suggesting greater radiogenic heat production.
E. Gravity and density
1. Geopotential surface (lunoid) is cigar-shaped, with long axis faciing earth.
2. Mascons (mass-concentrations) correlate with the mare (Mare Ibrahim, Mare Serentatis) -- origin due to impact melting and filling of craters by denser basalts.
3. Far side density is slighly lower, reflecting possibly thicker crust.
4. Topography variations expected to be about a factor of 5 greater than Earth computed from estimated yield stress, gravitational acceleration , mass, and radius (dr = s a3/gM).
5. Decorrelation of gravity potential and topography occurs at 400-600 km, suggesting a "plate" thickness 4 to 6 times larger than earth.
For images and more information see the Nine
Planets moon page.