Implications of isotopic compositions of N and Ne in the Martian atmosphere to temporal evolution of its atmosphere and regolith

The isotopic compositions of N and Ne in the Martian atmosphere are governed by several factors, principal among which are the temporal evolution in (1) the absolute surface pressure of oxygen, (2) the physicochemical characteristics of the regolith, and finally (3) the N-15 enrichment expected due to preferential hydrodynamical escape of N-14 (due to solar wind bombardment). Each of these factors is unique to Mars. In fact, no other planet offers the uniquely favorable situations for N-15 and Ne-21 enrichments. The cosmogenic production of N-15 is, in particular, unique. It promises to provide very valuable constraints on the temporal evolution of the martian CO2 and H2O, both in the atmosphere and regolith. The rate of production of cosmogenic (spallation) N-15 is dependent on the surface pressure of oxygen, the principal target element for formation of N-15. In view of the relatively high O/N ratio in the martian atmosphere, relatively high N-15/N ratio are expected to arise from cosmogenic reactions. The added bonus comes from the fact that an appreciable production of N-15 is expected in the martian regolith because of its thin atmosphere. From model calculations it is shown that if accurate isotopic composition data become available for N and Ne, it should be possible to put robust constraints on the time averages martian oxygen surface pressure and subsurface water in the upper layers.