No. 11: Summer 1980
In at least three lunar locations, enigmatic bright-and-dark swirl patterns drape craters and mare terrains. Ranging from 10 kilometers across to less than 50 meters, they may be ribbon-like, open-looped, or closed-looped. The swirls are sharply defined but do not appear to scour or otherwise disturb the terrains where they occur. Similar swirl patterns have been recognized on Mercury. Two intriguing characteristics of the lunar swirl patterns are:
(1) They coincide with strong magnetic anomalies; and (2) They appear to be very young, being superimposed on top of essentially all lunar features of all ages. Schultz and Srnka suggest that recent cometary impacts created the patterns.
(Schultz, Peter H., and Srnka, Leonard J.; "Cometary Collisions on the Moon and Mercury," Nature, 284:22, 1980.)
Comment. The terrestrial implications are obvious: our earth must have been hit, too. Perhaps at the Tunguska site there are similar swirl patterns -- now obliterated by vegetation.
Reference. Lunar swirl patterns are cataloged in Section ALE5 in The Moon and the Planets. To order, visit: here.