SCIENTIFIC RATIONALE FOR DEPLOYMENT OF A LONG-LIVED GEOPHYSICAL NETWORK ON THE MOON Submitted to The NRC Committee on the Scientific Context for the Exploration of the Moon

Figure 1: Location of lunar landing sites and the Apollo passive seismometer network. INTRODUCTION Geophysical observations of the Moon via a global and long-lived network of stations will yield a wealth of knowledge from regions heretofore inaccessible using the Apollo database. Data collected over a period of at least 6 years (covering one lunar tidal cycle) will yield information on the nature and evolution of the lunar interior using a combination of seismic, heat flow, and magnetic field data. These data are required in addition to the observations made by the Apollo Lunar Surface The ALSEPs contained a variety of different experiments (Table 1) that produced significant information regarding the nature of the lunar surface environment as well as the lunar interior. The impact of these data has been hamstrung by the fact that the ALSEP stations were clustered in the equatorial regions of the Moon on the near side. This is particularly significant for understanding the nature of the deep lunar interior. This white paper is written in response to the questions raised by the NRC panel on Lunar Science Priorities and Goals after the recent meeting on June 21 st , 2006. It focuses on the need for the deployment of a network of geophysical instruments to understand the nature and evolution of the Moons' interior from the crust to the core. These instruments will investigate lunar seismicity, heat flow, and magnetism. These seismometers were deployed at every Apollo site, except Apollo 17. However, the instrument at Apollo 11 failed after 21 days, presumably because it did not contain the thermal blanket that later versions did. A network of four seismometers was completed in April 1972 (Fig. 1), and operated until they were all switched off due to cost-cutting measures on 30 September 1977. During the time the network was operational, it clearly demonstrated that the Moon was seismically active, albeit on a smaller scale than Earth (e.