FRACTIONATION OF NITROGEN ISOTOPES ON MARS - THE ROLE OF THE REGOLITHAS A BUFFER

We have measured the adsorption of molecular nitrogen (N-2) on palagon ite, and molded the adsorbed nitrogen inventory on the martian regolit h. We were motivated by the fact that models of isotopic evolution pre dict stronger N-2 fractionation than reported by Viking. Possible scen arios for reconciling models with the observation include a heavy CO2 atmosphere early in the planet's history, continued outgassing of N-2 throughout the history of Mars, or a substantial adsorbed inventory. I n this paper we investigate the plausibility of the last explanation. We find that the regolith reservoir of adsorbed N-2 is inadequate by i tself to buffer the atmospheric isotopic composition, but may play a r ole depending on the total regolith surface area available. (C) 1994 A cademic Press, Inc.