It's been 20 years since planetary scientists first realized that chunks of the Moon and Mars were practically falling into their laps as meteorites. And, while thankful for the free samples, they've always puzzled over why these two worlds are represented roughly equally on Earth. To date collectors have snatched up 24 distinct meteorites from the Moon (some of which were found in multiple pieces or paired with other finds) and 28 from Mars.
The puzzle arises because the lunar specimens should outnumber their Martian counterparts by more than 100 to 1....
Trevor Gould