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Formation of Giant Lunar Impact Basins Studied

hartmann lunar painting

This painting by William K. Hartmann depicts the formation of a giant impact basin on the early Moon. 


In mid-2019, PSI senior scientist emeritus William Hartmann published a lengthy open-access study in the journal Geosciences about the shift in recent years against the "terminal cataclysm" theory of lunar history (also called "Late Heavy Bombardment"). According to this theory, based on rock samples returned from the Moon, there was relatively little impact cratering on the Moon, from lunar formation about 4.5 billion years ago until a cataclysmic episode of cratering around 3.9 billion years ago. More recent evidence suggests that the impact rate  was intense at the beginning and gradually declined since then.  Recently, Italian-French dynamicist Alessandro Morbidelli published a numerical model favoring such a history. Morbidelli's work predicts very intense cratering rates around 4.4 billion years, declining since then.  Giant impact basins would have been forming frequently throughout  that period, as shown in Hartmann's painting above. Hartmann and Morbidelli have submitted a paper to the journal Meteoritics and Planetary Science, analyzing the effects of such a cratering history on lunar evolution. Their work explains  various aspects of lunar geology, such as very early formation of deep megaregolith on much of the Moon, complex history of the magma-ocean solidification, destruction of impact melts from the earliest basins, and certain observed aspects of lunar gravity from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. 


June 14, 2020
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