Towards Understanding of Lunar Polar Volatile Deposits

While there is definitive evidence from orbital neutron data that there exist anomalously high hydrogen abundances at both lunar poles, there is considerable speculation regarding the source and molecular form of the hydrogen. On one hand, it has been suggested in various studies that the observed hydrogen abundances can be explained as originating from solar wind implanted hydrogen in the lunar soil. In contrast, using knowledge of the polar cold trap temperatures, diffusion constants, and other information, it has been suggested that water is the likely form of the hydrogen. Thus, one of the most fundamental questions regarding the lunar poles is to determine the form of the hydrogen and the dominant source and/or sources for the polar deposits.

Other planetary science questions relevant to the lunar poles include: 1) What are the accumulation and loss mechanisms acting on volatiles in the polar cold traps? How do these mechanisms compare to what occurs on other planetary bodies, for example on the polar cold traps of Mercury? 2) What are the physical properties of lunar regolith when it is kept at a constant and very low (<50K) temperature? How are the properties of cold regolith modified when it may be cemented by frozen volatile elements?

Very little information is available to answer any of these questions. Thus, new data from both orbital and landed platforms will be invaluable for providing answers. In addition, since a better understanding of lunar polar resources is critically needed for the lunar exploration program, the study of lunar polar deposits is highly synergistic for both exploration and scientific applications. Specifically, this talk will review existing hydrogen abundance measurements and focus on ways our understanding of the hydrogen abundances can be improved with data from future missions.