"For the smaller craters, it's like if you're filling a bucket, eventually your bucket gets full, but if you keep pouring cups of water into the bucket, you can't tell how many cups of water beyond full you've gone. Looking at the larger craters at the subsurface might give us insight, because that 'bucket' isn't full yet," Dr. Soderblom added.
For those craters smaller than 30 kilometers in diameter, he discovered impacts both increased and decreased porosity in the upper layer of the lunar crust.
"Our gravity data are opening up a new chapter of lunar history, during which the Moon was a more dynamic place than suggested by the cratered landscape that is visible to the naked eye. More work is needed to understand the cause of this newfound pattern of gravity anomalies, and the implications for the history of the Moon," Dr. Andrews-Hanna explained in the October 1, 2014 NASA Press Release.