10. Our Barren Moon. Moon Data (Table 10-1) Moon Data: Numbers. Moon Data: Special Features 1. The Moon As Seen From Earth

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1 10. Our Barren Moon Lunar plains & craters Manned lunar exploration The lunar interior The Moon s geologic history The formation of the Moon Moon Data (Table 10-1) Moon Data: Numbers Diameter: 3,476.km Earth Mass: kg Earth Density: 3.3. water Earth Orbit: km Earth Day: days Earth Moon Data: Special Features 1 The Moon is the Earth s only natural satellite The Moon is 1 of 7 large Solar System satellites The Moon has essentially no atmosphere The Moon s near side has 2 different surfaces The lunar highlands are very heavily cratered The lunar lowlands have 14 maria (i.e., seas ) The Moon s far side has only 1 mare Moon Data: Special Features 2 The Moon s interior has a very small iron core The Moon s differential gravity causes tides Gravity differences on opposite sides of the Earth The Moon is intimately involved with eclipses Solar eclipses: the Moon is in the middle Lunar eclipses: the Earth is in the middle The Moon As Seen From Earth Synchronous axial rotation 1-to-1 spin-orbit coupling 1 spin on its axis for every 1 orbit around its parent object The Moon points only one face toward Earth The Moon seems to wobble left & right Caused by changing orbital speed along an elliptical orbit The Moon seems to nod up & down Caused by the 5.15 tilt of the Moon s rotational axis Surface visibility Bright & dark areas Cratered bright lunar highlands Smooth dark lunar maria

2 Three Basic Lunar Feature Types Details of a Lunar Crater (Far Side) Details of a Lunar Sea (Mare Imbrium) The Moon s Two Hemispheres The near side Very diverse Lunar maria 14 seas Lunar terrae (highlands) lands Extensively cratered The far side Very homogeneous Lunar maria 1 sea Lunar terrae (highlands) lands Extensively cratered Mare Orientale Most prominent feature on the Moon s far side Is not a mare in the traditional sense It is not flooded with dark basalt lava Lunar far side crust was too thick to be penetrated It is a multi-ringed basin Is a mare in one sense It is a very large impact basin Probable cause Impact by a large asteroid or comet Mare Orientale: Low Res. Image

3 Mare Orientale: High Res. Image Contrasting Lunar Hemispheres The Rate of Lunar Crater Formation Old Unmanned Lunar Missions Impacters Ranger program 3 of 9 spacecraft Precursors to unmanned lunar landings Transmitted TV pictures until impact Orbiters Lunar Orbiter program 5 of 5 spacecraft Precursors to manned lunar landings Returned 1950 images covering 99.5% of lunar surface Clementine mission Mapped lunar surface in UV, visible & IR wavelengths Lunar Prospector mission Evidence of up to 6 billion tons of lunar ice Landers Surveyor program 5 of 7 spacecraft Soft-landed at various locations on the lunar surface Crater Alphonsus: Up Close & Afar Manned Lunar Exploration Orbiters Earth orbit Lunar transfer Lunar orbit orbit Landers From Ranger 9 From Earth Apollo 11 Apollo 12 Apollo 13 Apollo 14 Apollo 15 Apollo 16 Apollo 17 Mare Tranquilitatis Barely averted disaster

4 Eugene Cernan (Apollo 17) The Lunar Surface Many craters visible from Earth telescopes ~30,000 craters > 1.0 km in diameter ~ 85% of the lunar near side is covered with craters ~ 98% of the lunar far side is covered with craters Millions of craters actually exist on the lunar surface Craters are typically circular Angle of impact has very little significance Central peaks are common in large craters Upthrown crater rims are common on large craters Maria are larger than craters Tension fissures & pressure ridges are common Rest ~2.0 to 3.0 km below the average lunar surface Comparable to Earth s ocean crust Flood basalts similar to Columbia River basalt flows Moon Rocks Lunar rock formation All lunar rocks result from heating & cooling Heat is derived from impact processes Strong evidence of chemical differentiation Lunar rock types Igneous rocks Cooled from magma BasaltRich in iron & magnesium Maria AnorthositeRich in quartz & feldspar Highlands Impact breccia Cemented by magma Only appreciable lunar mechanical weathering process Lunar regolith Blanket of stone Fragments of existing lunar rock ~2 to 20 m thick Fragments of incoming meteorites Moon Rock Ages Basic physical processes Radiometric age dating Radioactive starting isotope Parent isotope Stable ending isotope Daughter isotope Measure the decay rate of the parent isotope Measure the parent to daughter isotope ratio Basic results Mare basalts ~3.1 to 3.8 billion years old Highland anorthosites ~4.0 to 4.3 billion years old Period of intense bombardment ~3.8 to 4.6 billion years ago Typical Lunar Rocks Clementine Maps the Lunar Surface Vesicular mare basalt Highland anorthosite Impact breccia

5 The Lunar Interior Chemical differentiation did occur Low density materials floated to the lunar surface High density materials sank to the lunar center The Moon does have a tiny iron-rich core The Moon s core is ~ 3% of the lunar mass The Earth s core is ~33% of the Earth s mass The Moon s Internal Structure Lunar Magnetism The past Ancient igneous rocks retain a weak magnetic field Implies a partially molten core when surface solidified The present No appreciable magnetic field Implies an almost completely solidified core Moonquakes Only ~ 3,000 per year Earth has ~ 1.5 million earthquakes per year Magnitude from ~ 0.5 to 1.5 Far weaker than on Earth Originate ~ 600 to 800 km beneath the surface Far deeper than on Earth Triggered by tides produced by Earth s differential gravity Vary by a factor of 2 due to the highly elliptical lunar orbit Earth Moon Dynamics Some evidence Reflectors put on lunar surface by Apollo astronauts Extremely precise distance measurements Moon is moving away from Earth ~3.8 cm. yr 1 Basic physical processes Differential lunar gravity raises ocean tides Earth s axial rotation drags tidal bulge ahead ~10 This is caused by friction along ocean bottoms This in turn causes two things Earth s tidal bulge pulls the Moon into a higher orbit Earth s tidal friction slows Earth s rotation ~ sec. yr 1 Some implications The month will become progressively longer The dream of really long days will at last be realized One face of Earth will always face the Moon Tidal Effects on the Earth & Moon The Formation of Earth s Moon Fission hypothesis Doubtful Earth s axial rotation was extremely fast Capture hypothesis Doubtful Earth s gravity captured a planetesimal Co-creation hypothesis Doubtful Particles in Earth orbit accreted into the Moon Collisional ejection hypothesis Probable Earth was obliquely impacted by a planetesimal Only 1.23% of the combined masses became the Moon Absence of lunar volatiles supports this hypothesis Intense heating was an inevitable part of the impact Low average lunar density supports this hypothesis Very little of Earth s iron core was ejected

6 Hypothesis: Moon Impact Formation Timeline: Moon Formation by Impact Moon data ~27 % Earth s diameter ~0.23% Earth s mass ~60 % Earth s density The Moon as seen from Earth Radically different near & far sides Synchronous rotation (1-to-1 S.O.C.) Cratered highlands & craterless maria Lunar exploration Unmanned Impacters, orbiters & landers Manned Orbiters & landers The lunar surface Crater & maria visibility Lunar rocks Basalt & anorthosite Impact breccia Important Concepts The lunar interior Chemical differentiation Asymmetrical lunar crust Mantle-dominated Minimal iron core Lunar magnetism Weak ancient magnetic field No appreciable present mag. Field Earth-long-term Moon tidal dynamics Lengthening days & months Increasing Earth Moon distance Formation of Earth s Moon Fission hypothesis Capture hypothesis Co-creation hypothesis Collisional ejection hypothesis