Density and stress distribution in the moon.

A model is presented for the lateral variations of density within the moon. The model gives rise to a gravitational potential which is equal to the observed potential at the lunar surface; moreover, it minimizes the total shear-strain energy of the moon. The model exhibits lateral variations of about plus or minus 0.25 g/cc within 50 km depth. The variations, however, reduce to plus or minus 0.06 and plus or minus 0.008 g/cc within layers at 50 to 135 and 135 to 235 km respectively, and they become negligible below this region. The associated stress differences are found to be about 50 bar within 600 km depth, having their maximum values of about 90 bars at a depth of about 250 km. On the basis of these stress differences a strength of about 100 bar is concluded for the upper 400 km of the lunar interior for the last 3.3 b.y.