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Lunar Geology John Young from Apollo 16, April 1972 Harrison Schmidt 12/1972 Apollo 17 Relative Size and Distance Object Size Moon 1.0 units Earth 3.7 units Separation 110.6 units Sun 400.5 units Relative Size of Earth and Moon From which side is the sun light coming? Moon Data Note the Picture Difference Naked eye view of the Moon ? Can You Spot the ”Face of the Man in the Moon”? Tycho Crater Young crater Circular Ray crater 85 kilometers across Clearly visible from Earth Close to the southern polar Surrounded by a bright ejecta blanket. Clavius 232 km = 144 miles 4.9 km deep South of Tycho Palomar 200 inch Mare Imbrium Largest of the 14 dark plains of the near side of the Moon London to Rome Rilles Apollo 11 site near the center of the top edge Apollo 11 Landing Site Clementine Images at Different Wavelengths Moments before impact with Alphonsus 3/24/65 Alphonsus is about 129 km wide Low Lands and High Lands Surveyor 3 Lands on the Moon Landed in 4/67 Visited in 11/69 Apollo 12 Astronauts Allen Bean Pictured Pete Conrad Photographer Apollo 15 Lunar Rover Buzz Aldrin, Seismometer Detected Moonquakes Regolith Billions of years of pounding by space debris have pulverized the Moon’s surface which is now bone dry yet sticks together like wet sand. Tides Mare Basalt – Gas dissolved under pressure forming bubbles Anorthosite – Highlands, perhaps part of the original lunar crust. Breccias – formed by compression after heating due to impacts Orbits of Jupiter and Saturn may have shifted about 4 billion years ago causing gravitational perturbations on the asteroid belt. Where Did the Moon Come From? Lunar Colonization Key Ideas • Appearance of the Moon: The Earth-facing side of the Moon displays light-colored, heavily cratered highlands and dark-colored, smooth-surfaced maria. The Moon’s far side has almost no maria. • Virtually all lunar craters were caused by space debris striking the surface. There is no evidence of plate tectonic activity on the Moon. Key Ideas • Internal Structure of the Moon: Much of our knowledge about the Moon has come from human exploration in the 1960s and early 1970s and from more recent observations by unmanned spacecraft. • Analysis of seismic waves and other data indicates that the Moon has a crust thicker than that of the Earth (and thickest on the far side of the Moon), a mantle with a thickness equal to about 80% of the Moon’s radius, and a small iron core. Key Ideas • The Moon’s lithosphere is far thicker than that of the Earth. • The lunar asthenosphere probably extends from the base of the lithosphere to the core. • The Moon has no global magnetic field today, although it had a weak magnetic field billions of years ago. Key Ideas • Geologic History of the Moon: The anorthositic crust exposed in the highlands was formed between 4.3 and 4.0 billion years ago. • An era of heavy bombardment formed the maria basins between 4.0 and 3.8 billion years ago, and the mare basalts solidified between 3.8 and 3.1 billion years ago. • The Moon’s surface has undergone very little change over the past 3 billion years. Key Ideas Key Ideas • Meteoroid impacts have been the only significant “weathering” agent on the Moon. • The Moon’s regolith, or surface layer of powdered and fractured rock, was formed by meteoritic action. • All of the lunar rock samples are igneous rocks formed largely of minerals found in terrestrial rocks. • The lunar rocks contain no water and also differ from terrestrial rocks in being relatively enriched in the refractory elements and depleted in the volatile elements. Key Ideas • Origin of the Moon: The collisional ejection theory of the Moon’s origin holds that the proto-Earth was struck by a Mars-sized protoplanet and that debris from this collision coalesced to form the Moon. This theory successfully explains most properties of the Moon. • The Moon was molten in its early stages, and the anorthositic crust solidified from low-density magma that floated to the lunar surface. The mare basins were created later by the impact of planetesimals and filled with lava from the lunar interior. • Tidal interactions between the Earth and Moon are slowing the Earth’s rotation and pushing the Moon away from the Earth.