Cosmogenic nuclides: Observable effects of Martian volatiles

Cosmic-ray-produced (cosmogenic) nuclides in returned martian samples could be used to study the amounts and distributions of volatiles in the recent past on Mars. In planning for the Gamma-Riay Spectrometer experiment that is scheduled to fly on the Mars Observer, we have done many calculations on the nuclear reactions that should occur in the martian surface, studying especially the production and transport of neutrons. We have found that three aspects of Mars can very significantly affect the production of cosmogenic products in Mars: the martian atmosphere and the presence of H 2 0 in or C02 on the surface of Mars. These volatile components can greatly affect the energy and spatial distributions of neutrons, especially those with thermal or near thermal energies, in the surface of Mars (1). In turn, these neutrons produce many cosmogenic nuclides that can be observed in samples returned from Mars.