1Our Barren MoonChapter TenGuiding Questions1. Is the Moon completely covered with craters?2. Has there been any exploration of the Moon since the Apollo program in the 1970s?3. Does the Moon’s interior have a similar structure to the interior of the Earth?4. How do Moon rocks compare to rocks found on the Earth?5. How did the Moon form?2The Moon’s Orbit• The Moon and Earth both orbit around a point between their centers called the center of mass of the Earth-Moon system • The center of mass then follows an elliptical orbit around the Sun This Picture Distorts the Earth-Moon DistanceAn Everyday Example of Center of Mass MotionMotion of the Earth-Moon Center of MassSource: Dr. James Regas Cal State Chico3Source: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State Chico4Source: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State Chico5Source: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State Chico6The Moon’s airless, dry surface is coveredwith plains and craters• 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 mariaAnother View of the Moon• Virtually all lunar craters were caused by space debris striking the surface• There is no evidence of plate tectonic activity on the MoonThe Moon’s Surface – Close up7The maria formed after the surrounding light-colored terrain, so they have not been exposed to meteoritic bombardment for as long and have fewer cratersHuman exploration of the lunar surfaceMuch of our knowledge about the Moon has come from human exploration in the 1960s and early 1970s and from more recent observations by unmanned spacecraft8The Lunar Surface Provides Clues about its Structure and Formation•Meteoroid impacts have been the only significant erosionagent on the Moon• The Moon’s regolith, or surface layer of powdered and fractured rock, was formed by meteoritic actionAll of the lunar rock samples are igneous rocks formed largely of minerals found in terrestrial rocks• The lunar rocks contain no water• They differ from terrestrial rocks in being relatively enriched in the refractory elements and depleted in the volatile elementsMare basaltHigh-lands anorth-ositeImpact breccia9Lunar rocks reveal a geologic history quite unlikethat of Earth• The anorthositic crust exposed in the highlands was formed between 4.0 and 4.3 billion years ago• The mare basalts solidified between 3.1 and 3.8 billion years ago• The Moon’s surface has undergone very little change over the past 3 billion yearsThe Moon has no global magnetic field but hasa small core beneath a thick mantleThe Formation of the Moon• The collisional-ejection theory– Successfully explains most properties of the Moon– Hypothesizes that the proto-Earth was struck by a Mars-sized protoplanet and that debris from this collision coalesced to form 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• Other alternate theories that fail in areas– Co-creation (sister), fission, capture10Source: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State Chico11Source: Dr. James Regas Cal State ChicoTidal interactions between the Earth and Moon are slowing the Earth’s rotation and causing the Moon to move away from the Earth12The Moon—Site of Future Industry? Not!Source: Dr. James Regas Cal State Chico13Source: Dr. James Regas Cal State ChicoSource: Dr. James Regas Cal State ChicoKey Words• anorthosite• capture theory• center of mass• co-creation theory• collisional ejection theory crater• far side (of the Moon)• fission theory• impact breccia• impact crater•libration• lunar highlands• mare (plural maria)• mare basalt• moonquake• refractory element• regolith• synchronous rotation• terminator• terrae• volatile
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