Presentation #305.03 in the session “Moon and Mercury 2”.
A transient lunar atmosphere formed during a peak period of mare basalt volcanic outgassing and lasting up to about ~70 Ma was recently proposed. In a separate approach, we utilize forward-modeling of individual lunar basaltic eruptions and the observed geologic record to predict eruption frequency, magma volumes, and rates of volcanic volatile release. Typical lunar mare basalt eruptions are predicted to have volumes of ~102–103 km3, last less than a year, and have a rapidly decreasing volatile release rate. The total volume of lunar mare basalts erupted is small and the repose period between individual eruptions is predicted to range from 20,000-60,000 years. On the basis of this approach, we find that only under very exceptional circumstances could sufficient volatiles be released in a single eruption to create even a tenuous atmosphere. The frequency of eruptions was likely too low to sustain an atmosphere for more than a few thousand years. Transient, volcanically-induced atmospheres appear to be inefficient sources for volatile delivery to permanently shadowed lunar polar regions and appear incapable of creating temporary environments that might favor astrobiological activity. We attribute the differences between our estimates and previous estimates to earlier use of maximum impact basin depths as average depths, and assignment of all excess volumes below datable units to one age (e.g., 5.9 x 106 km3 assigned to 3.5 Ga in the case of Imbrium). Our results suggest that the vast majority of volatiles in lunar polar cold traps were more likely to have originated from volatile-rich impacts, rather than volatile release from volcanic eruptions, similar to findings about polar cold-trap volatile deposits on Mercury. In order to refine these lunar estimates, future lunar exploration goals should include further analysis of detailed lava flow thicknesses, ages, volumes, volatile contents and repose periods, as well as better determination of the interior structure of mare deposits in large impact basins.