Physical Sciences: Cracking of Lunar Mare Soil

THE tendency of lunar soil to break into clods when disturbed was recognized from Surveyor 1 photographs 1,2 . Pictures of disturbances produced in bearing tests with the Surveyor 3 soil mechanics surface sampler 3 suggested to some observers that the soil layer in Oceanus Procellarum tends to crack into thin flat “tiles” (Figs, 1 a and 2 a ) and, therefore, that it consists of a thin, rather rigid crust over a softer substrate. Pictures of areas disturbed by the Apollo 11 closeup camera in Mare Tranquillitatis (Fig. 3 a ) and by the Apollo 12 lunar module descent engine in Oceanus Procellarum conveyed a similar impression 4,5 . None of the authors of these works were misled, and, indeed, they warned against this interpretation 3–5 . Nevertheless, photographs made by the Apollo 12 astronauts of the areas disturbed by Surveyor 3 help to clarify the matter.