Cosmic ray exposure of SNC meteorites and constraints on their derivation from Mars

There is chemical, mineralogical, and isotopic evidence that several rare meteorites originated from the planet Mars. The eight specimens (4 sphergottites, 3 nakhlites, and 1 chassignite) possess a variety of characteristics that suggest a mutual relationship. It can be predicted with reasonable confidence that these SNC meteorites were exposed to cosmic rays at relatively shallow depths for three distinct periods of time during the past approximately 10 million years. Within the context of a Martian origin, this implies that either relatively large objects were ejected from Mars at a common time and underwent three disruptive events in space or that three ejection events occurred within the past approximately 10 million years on restricted segments of Martian terrain with 1300 million year-old rocks. If mechanisms can be identified which satisfy the geochemical properties of SNC meteorites, as well as their cosmic ray exposure, and dynamical problems associated with ejection out of a large gravity field, then the case for the SNC meteorites being samples of Mars can become stronger.