THE AGE AND FREQUENCY OF COMETARY IMPACTS ON THE MOON FROM AN ANALYSIS OF DIFFUSE STRUCTURES

Five concentration centers were found on the total area of 145978 km2 of diffuse formations on the lunar surface. These concentrations are l ocated mainly on the back side of the Moon and may be considered to be imprints of recent impacts of two and more comets. Preliminary albedo estimates for the diffuse structure of the Gerasimovich crater, which is on the back side of the Moon, performed using images delivered to the Earth by Zond-8 spacecraft, confirmed that various formations of t his type have identical properties. Compaction of the reflecting surfa ce of lunar regolith in the process of its contact with the comet resu lts in a formation of a surface layer of immature soil. We chose spect ropolarimetric ratio 0.42/0.64 mum as a remote index of soil maturity and found it correlating with morphological maturity index. From 15 sa mples taken from different locations on the lunar surface a dependence of maturity index upon exposure age was derived. This dependence yiel ds an age of 8 x 10(6) years for diffuse structures. Diffuse structure s on the Moon are likely to be a record of cometary shower in the inne r part of the Solar system dating back to 10(7) years ago.