On the detection of lunar volatile emissions

Abstract

ONE of the most interesting scientific results of the Apollo programme was the discovery that the Moon sporadically releases radiogenic gases^1–4. It is likely (although not yet proved) that these emissions are correlated with other detectable lunar activity such as shallow moonquakes^5,8 and the elusive visible events known as ‘lunar transient phenomena’ or LTPs^6,7. Runcorn has argued⁸ that these three types of lunar activity are linked through tidal triggering of cylindrical fault systems around the circular mare, which results in gradual settling of the mascons and venting from the cracks. Considerable evidence exists which favours such a model, including seismic⁹, pho-togeologic¹⁰ and electromagnetic induction¹¹ data. However, a search for sporadic venting using the Apollo lunar surface Suprathermal Ion Detector Experiments (SIDEs) was unsuccessful¹². This note points out that the SIDE instruments lack the sensitivity to detect even large gas emissions if the venting occurs primarily at a few well-defined LTP sites, and suggests specific flight instruments for the proposed ESA Polar Orbiting Lunar Observatory (POLO) mission^13,14 which could detect active venting, would help to determine the energy source for LTPs, and would increase our knowledge of lunar geophysics.