Geological Sciences 287: Planetary Evolution: The Moon

Academic Year 2002-2003, Semester II
M Hour (3:00-5:20 PM Mondays, and other arranged times)
Lincoln Field 105

Professor James W. Head
Lincoln Field 104

Dr. Harald Hiesinger
Lincoln Field 110

A. Background: In the Planetary Evolution sequence of courses, characteristics of planetary bodies are examined to illustrate critical geological problems related to planetary formation and evolution. The Moon offers a basic cornerstone in this sequence. Second only to the Earth, the Moon is the most well-known planetary body. Dozens of spacecraft have been sent to the Moon, humans have landed on and explored its surface six times, automated vehicles have traversed many kilometers across the surface and returned samples from three different sites. The returned Apollo and Luna samples were collected in situ and in context and provide a detailed chronological, petrogenetic, and geochemical picture of the Moon. Seismometers and other instruments deployed on the surface and flown in orbit provide important constraints on the internal structure of the Moon and its relation to its thermal evolution. Detailed images, together with analysis of returned samples and geophysical observations, provide fundamental information about the nature of key planetary processes such as impact cratering, volcanism, and tectonism. On the Moon humans have explored impact crater interiors, sampled impact basin ejecta, walked on lava flows, obtained cores of pyroclastics, driven across wrinkle ridges, and extensively probed the regolith. Although additional key information is required, our present knowledge of the Moon is unparallelled elsewhere in the Solar System in terms of breadth and depth.

Furthermore, the Earth's Moon provides a fundamental framework of understanding of the processes and evolutionary history of planetary bodies other than the Earth. For example, our understanding of the structure of planetary interiors and their thermal evolution is largely based on the lunar example. Processes of planetary crustal formation are linked to key observations and conclusions from the Moon (e.g., impact generated magma oceans and crustal formation). Models of the flux of impacting projectiles are largely linked to the lunar baseline (e.g., terminal cataclysm, shape of flux curve in the inner Solar System). The lunar megaregolith structure model underpins models of the hydrosphere and cryosphere for Mars. Lunar impact basin evolution models influence loading and flexure models on the planets. Lunar regolith models strongly influence how we view soil layers on Mercury, Mars and the asteroids. Lunar samples, crustal structure and thermal evolution form the basis of our thinking about the ascent and eruption of magma on other planetary bodies. The Moon is the 'type locality' for globally continuous lithospheres (one-plate planets) and the interpretation of the interplay of global tectonic features and thermal evolution on the other one-plate planets.

Finally, the record on the Earth's Moon provides insight into the early history of the Earth itself. For example, there is extensive evidence that the Moon originated following the impact of a Mars-sized projectile into the Earth in its earliest history, and that the very forces that formed the Moon changed the Earth inexorably. The first one-third of Earth history, largely missing from the Earth's geological record, may find parallels in events in early lunar history.

For these reasons, the development of an understanding of what we know and what we don't know about the Earth's Moon is one of the most important aspects of the study of Planetary Evolution. Acquisition of a detailed understanding of the Moon will be critical in your recognition and assessement of problems on other planetary bodies, and this fact will remain so throughout the next few decades and likely forever. The recent NAS/NRC "Decadal Study" made the strong case that the Moon, because of the depth of our knowledge and its close proximity for future exploration, will always remain a cornerstone and keystone in the understanding of the Solar System. Indeed, missions to the Moon will be launched in the near future by the European Space Agency and Japan, and the US NAS/NRC "Decadal Study" placed a lunar farside sample return mission as a very high priority for NASA.

B. Course Goals: Thus, the focus of this course will be to provide a basic understanding of the nature and evolution of the surface and interior of the Moon, primarily through an analysis and assessment of the geological processes operating there, and their relation to lunar geological, petrogenetic, and thermal evolution. The course organization reflects these goals.

In a broader Planetary Evolution context, this course is designed to address the following themes, questions and objectives: