Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material

摘要

The Apollo 11 and 12 core-sample tubes were 2 cm in diameter; therefore, particles of larger diameter were excluded from the samples. The percentage of 2-cm and larger particles from the Surveyor I particle-count data was combined with the Apollo 11 data, then the data were normalized and plotted as a logarithmic normal distribution. The Surveyor I curve smoothly joins the Apollo 11 averaged core 1 and core 2 curves. The percentage of 8 mm and greater particles from Surveyor I data was combined with the Apollo 12 size-distribution data and the data were normalized. A sharp break in both curves occurs at approximately the 30-percentile point, a fact that can be explained by the theory that the material actually is composed of two populations: one population caused by comminution from the impact of the larger-sized meteorites and the other population caused by the melting of fine material by the impact of smaller-sized meteorites. The Martian atmosphere would vaporize the smaller incoming meteorites and would retard incoming meteorites of intermediate and large size, causing comminution and stirring of the particulate layer. The combination of comminution and stirring of material would result in fine material being sorted out by the prevailing circulationof the Martian atmosphere and the material being transported to regions where it would be deposited. As a result, the Martian surface in the regions of prevailing upward circulation probably is covered either by a rubble layer or by desert pavement; regions of prevailing downward circulation probably are covered by sand dunes.