The Nature of the Lunar Maria.

Abstract

It is shown that the surface temperature of the moon determined as a function of time by Pettit and Nicholson from infrared measurements in the lunar eclipse of June 14, 1927, is consistent only with a lunar surface composed of dust, in agreement with Wesselink's conclusion from data of Pettit for the later eclipse of October 27, 1939. The location of the observed area in the first eclipse permits direct inference of a dust cover for the lunar highlands. For the second eclipse, it is pointed out that a significant fraction (approximately one-quarter) of the projected receiver area covered virtually the whole extent of Mare Vaporum. From solutions of the equation of heat conduction obtained by others, the theoretical fall of temperature with time in the latter eclipse is calculated on the assumption that the surface of Mare Vaporum consists of bare rock but the surrounding highlands are covered with dust. The predicted march of the temperature differs so greatly from Pettit's determination that the presence of exposed lava on the surface is precluded, specifically for Mare Vaporum and by implication for any mare. The logical difficulties are discussed which this result poses for theories identifying the surfaces of the maria with lava flows. It is shown that the best over-all fit to Pettit's data for temperature versus time is obtained among suggested models of the lunar surface by one corresponding to Gold's theory that the maria are craters filled with dust. For this theory, no inconsistencies are found with respect to lunar temperatures inferred by infrared or microwave methods.