Porosities of lunar meteorites: Strength, porosity, and petrologic screening during the meteorite delivery process

Porosity has been directly measured for eight lunar meteorite breccias and calculated for two more on the basis of literature density measurements. Lu nar meteorite regolith breccias display systematically low porosity in comp arison to otherwise analogous Apollo regolith breccias. Among seven meteori tic regolith breccias, porosity ranges from 1 to 11% and averages 7.5 +/- ( 1-sigma) 3.2%, whereas for 44 analogous Apollo samples (porosities mostly c alculated from literature density data) the average is 25 +/- (1-sigma) 7%. The origin of this disparity is enigmatic, but the trend probably reflects mainly a bias in favor of strong, compact breccias among fragments that ma nage to survive the violent process of launch to lunar escape velocity (2.3 8 km/s). In addition, compaction during launch may play an important role. The population of lunar meteorites is clearly not a random, unmodified samp le of lithic materials near the surface of the parent body.