PREVIOUS models of the lunar surface layer have necessarily been constructed on the basis of indirect evidence, such as the way in which the surface reflected sunlight and radar pulses, or the manner in which it cooled during an eclipse. The photometric properties, in particular, have been utilized in model construction, because they were considered to be very unusual1. Widespread acceptance of the Hapke “fairy castle” model2 led to general belief that the uppermost layer on the lunar surface must have a bulk density of the order of one-tenth that of solid rock.