The Evolution of the Moon: Key Features and Interior Structure

1. Interior structure, origin and evolution of the Moon Key Features of the Moon: pages 176 - 192

2. Before and after Apollo Prior to the Apollo Missions, some scientists believed the Moon formed in the early Solar System along with the other planets and had remained a primitive body. Because of Apollo, we have learned this is not correct. In fact, the lunar samples brought back by Apollo, and subsequent remote sensing missions, have taught us a great deal about the geologic history of the Moon.

3. Implications for the origin and evolution of the Moon from Apollo missions? Oldest Moon rocks are 4.3 billion years old Depletion of volatiles (H 2 O, K, Na, Au, etc) Enrichment of high temperature elements (Mg, Al, Si, Ca, Th, U, etc). Similar oxygen isotopic ratio as the Earth. Moons orbit lies neither in the equatorial plane of Earth or in the ecliptic plane.

4. Moon quakes: Very few, and very low attenuation (i.e., they last for many tens of minutes).

5. Moon quakes: Very low attenuation (i.e., they last for many tens of minutes).

6. S-waves do not travel through liquids, hence, the Moons asthenosphere must be plastic.

7. Moon quakes originate at the boundary between the rigid lithosphere and the plastic asthenosphere, and on the side of the Moon facing Earth.

8. The Near side: Has more mare: 32% of its surface is mare covered compared with 2% of the far side (globally mare cover 17%). The Far side: Large basins filled on near side, not filled on far side. Differences: Near-side vs. Far-side

12. Magma Ocean hypothesis The Moon was molten after formation As the molten rock cooled, it crystallized Some crystals floated others sank

15. Ages of basalts in the mare of the Apollo manned and Luna unmanned landing sites

16. Impacts are the dominant surface process on the Moon Crater flux has decreased with time It would be hard to sustain life on Earth if flux was as high as during the early solar system. Impact erode the lunar surface Size range <1mm - >1,000km Age data from the Apollo landing sites allow an estimate of the number of craters formed over time. Scientist can then date surfaces by counting craters

17. Gigantic impacts during the early history of the Moon caused formation of Multi Ring Basins

18. Volcanic Features: Lava flows infill mare Impacts of comets and asteroids form huge basins 4.3-3.85 billion years ago Shock waves create fractures in the rock beneath the basin Mountain ranges form as a result of the blast Interior heat from radioactivity caused partial melting Magma rose along the fractures, filling the basin 3.9 and 3.1 billion years ago and younger

19. Lunar volcanoes Lava channels Domical hills

20. Hypotheses of the origin of the Moon giant Impact

21. Fission origin of the Moon, out of the Pacific Ocean (George Darwin)

22. Giant impact hypothesis A projectile about the size of Mars, struck the young, Earth in a catastrophic, glancing blow nearly 4.6 billion years ago. Material was jettisoned outward, and some fraction of this mass remained in Earth orbit and formed the Moon. The Moon may be mostly derived from the crust and mantle of the Earth and/or the impacting object. The giant impact and quick accumulation of material resulted in a hot, molten Moon, which accounts for the relative lack of water and other volatile elements. After the crust cooled, impacts into the Moon scarred the surface with numerous craters.

23. Artists conception of the Giant Impact Hypothesis of the Moon

24. Artists conception of the Giant Impact Hypothesis of the origin of the Moon.

25. CRAY supercomputer simulation of the origin of the Moon by a collision of Earth with a Mars-sized projectile. Note: The Moon formed mostly from the silicate portions of the projectile and Earths mantle, whereas the metal core of the impactor merged with Earths metallic core. Hence, the Moon is depleted in metal and has a lower density than earth.

27. Origin of the Moon: Which hypothesis is correct? Hypothesis Volatiles Isotopes Orbit Iron Physics Giant Impact A A B+ A B+ Fission B B F A F Capture F F A C F Co- accretion F A F F B A = v. good match; C = matches some data; F = doesnt match