10. Our Barren Moon

1. 10. Our Barren Moon • Lunar plains & craters • Manned lunar exploration • The lunar interior • The Moon’s geologic history • The formation of the Moon

2. Moon Data (Table 10-1)

3. Moon Data: Numbers • Diameter: 3,476.km 0.27 . Earth • Mass: 7.4 . 1022 kg 0.012 . Earth • Density: 3.3 . water 0.61 . Earth • Orbit: 3.8 . 105 km 0.0026 . Earth • Day: 27.32 days 27.32 . Earth

4. E-M Sizes & Distances to Scale

5. Earth & Moon to Scale

6. 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

7. 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

8. Orbiting a Common Center of Mass

9. 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

10. Three Basic Lunar Feature Types

11. Details of a Lunar Crater (Far Side)

12. Details of a Lunar Sea (Mare Imbrium)

13. 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

14. 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

15. Mare Orientale: Low Res. Image

16. Mare Orientale: High Res. Image http://apod.nasa.gov/apod/image/1103/orientale_lro.jpg

17. Contrasting Lunar Hemispheres

18. The Rate of Lunar Crater Formation

19. 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 of 99.5% of the 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

20. Crater Alphonsus: Up Close & Afar From Ranger 9 From Earth

21. Manned Lunar Exploration • Orbiters • Earth orbit • Lunar transfer orbit • Lunar orbit • Landers • Apollo 11Mare Tranquilitatis • Apollo 12 • Apollo 13 Barely averted disaster • Apollo 14 • Apollo 15 • Apollo 16 • Apollo 17

22. Eugene Cernan (Apollo 17)

23. 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 lunarfarside 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 commoninlarge 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

24. 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 • Basalt Rich in iron & magnesium Maria        • Anorthosite Rich 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

25. 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

26. Typical Lunar Rocks Vesicular mare basalt Highland anorthosite Impact breccia

27. Clementine Maps the Lunar Surface

28. The Lunar Interior • Chemical differentiation did occur • Lowdensity materials floated to the lunar surface • High density materialssankto the lunarcenter • The Moon does have a tiny iron-rich core • The Moon’s core is ~ 3% of thelunarmass • The Earth’s core is~33% of the Earth’s mass

29. The Moon’s Internal Structure

30. 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

31. 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 ~0.000 02 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

32. Tidal Effects on the Earth & Moon

33. 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

34. Timeline: Moon Formation by Impact

35. Hypothesis: Moon Impact Formation

36. 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 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 Important Concepts