Science concept 2: The structure and composition of the lunar interior provide fundamental information on the evolution of a differentiated planetary body

Barnes, Jessica; French, Renee; Garber, Joshua; Poole, Wil; Smith, Phillipa and Tian, Yunsheng (2012). Science concept 2: The structure and composition of the lunar interior provide fundamental information on the evolution of a differentiated planetary body. In: Kring, David and Durda, Daniel eds. A Global Lunar Landing Site Study to Provide the Scientific Context for Exploration of the Moon. LPI Contribution No. 1694. Houston, TX: Lunar and Planetary Institute, pp. 47–131.



Each of the Science Goals addressed by Science Concept 2 is linked: data regarding the crust, mantle, and core must be obtained in order to understand the thermal state of the interior and the planetary heat engine. Much about these Science Goals is currently unknown: crustal thickness and lateral variability are constrained by gravity and seismic models which suffer from non-uniqueness and a lack of control points; mantle composition is ambiguously estimated from seismic velocity profiles and assumed lunar bulk compositions; mantle structure is obtained through seismic velocity profiles, but fine-scale structure is not resolved and any structure outside the Apollo network and below 1000 kilometers depth is unknown; the size, composition and state of the core are obtained through models with few constraints, where the size and state are dependent on an unknown composition, making any core characteristic estimates highly variable; and the thermal state of the interior is constrained by heat flow measurements and characteristics of the core, but current heat flow data are not representative of the global heat flux and core models are non-unique. Besides elucidating the principle objectives of each Science Goal, addressing this Science Concept will also provide data regarding formation and evolution models of the Moon (i.e., the Giant Impact (e.g., Canup, 2004a, 2004b) and Lunar Magma Ocean (LMO; e.g., Wood et al., 1970) hypotheses, the details of which are debated or unknown.

Understanding the formation and evolution of the Moon provides important information on planetary and solar system evolution as a whole. The relative lack of geologic activity on the lunar surface provides a window into processes active during early Solar System formation that have since been removed from the Earth‘s surface. Likewise, the small size of the Moon implies a faster cooling history, preserving records of initial composition and interior structure (NRC, 2007).

The most comprehensive hypothesis for the formation of the Moon is the collision of an object twice the size of the Moon with the proto-Earth. Thus, the composition and thermal evolution of the Moon and Earth were intimately linked at the beginning of the solar system (NRC, 2007). While these two bodies have evolved independently of each other, a more complete understanding of the composition and structure of the lunar interior will shed light on the early history of Earth.

Other studies of Science Concepts in this volume suggest landing sites and data collection that will help address Science Concept 2. In particular, the knowledge gained by addressing Science Concept 1 will help elucidate the early thermal history of the Moon (assisting Science Goal 2d). Proposed sample return for Science Concepts 3, 5 and 6 will contribute to current knowledge of crust and mantle lithologies (assisting Science Goals 2a, 2b). However, it should be noted that no other Science Concepts overlap with understanding the lunar core (Science Goal 2c). The contributions of other Science Concepts to the one considered here are outlined in more detail in each Science Goal section.

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