2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 2
Presentation Time: 8:35 AM


NEAL, Clive R., Univ Notre Dame, 156 Fitzpatrick Hl Engrng, Notre Dame, IN 46556-0767, neal.1@nd.edu

With the end of missions to the lunar surface in the 1970s, the general public adopted the impression that exploration of the Earth's Moon was complete, even though only 5% (max.) of the lunar surface had been explored and our understanding of the lunar interior is still subject to much speculation. The Apollo Passive Seismic Experiment placed 5 highly sensitive seismometers on the lunar nearside, 4 of which operated until Sept. 1977. The seismometers did not allow the deep interior of the Moon to be studied in detail because they were located in a small area; the data from this network only provided clues about the lunar interior (Apollo seismic data provide little constraint on lunar structure and composition below 700-800 km). This small seismic array aperture limited both the spatial sampling of seismic events (the magnitude of most moonquakes are extremely small and cannot be detected at a great distance) and the depth of the sampling of the interior by long-distance ray paths. Interpretations based on these data are ambiguous. For example, the higher velocities at > 500 km have been interpreted to represent the presence of garnet [Hood & Jones, 1987, PLPSC 17/JGR 92], but also an increased proportion of Mg-rich olivine [Nakamura, 1983, JGR 88]. While innovative modeling approaches have refined the original data [Khan & Mosegaard, 2002, JGR 107; Lognonné et al., 2003, EPSL 211], comprehensive and definitive interpretations of the lunar mantle remain elusive and fundamental questions remain unanswered. Such questions include: What is the nature, structure, & thickness of the crust on the lunar near and far sides? Is garnet present in the lunar mantle? Are “nests” producing periodic Moonquakes present on the far side? Is there a Moon-wide ~500 km discontinuity (magmasphere vs. magma ocean)? Is there a definitive lunar core? If so, what is its size & composition? Are the core & mantle completely solid or do plastic zones still persist? The questions posed here also apply to other terrestrial planets. Therefore, establishing a global Lunar Seismic Network (LuSeN) serves two purposes: 1) to better understand the nature of the lunar interior; 2) act as a technology testbed for exploring the interiors of other planets. Data from such networks will be key to establishing fundamental knowledge of planetary differentiation processes.