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The Moon
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What We See
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Where We’ve Been
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The Big Features Oceanus (ocean) Maria (Mare) (sea) Craters
Highlands – bright, cratered regions Lowlands/Maria – dark, flat regions
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Other Features Mountains Valleys
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Librations The result of
wobbling of the Moon’s axis toward/away from earth Relative motion of the observer as Earth rotates Non-circularity of moon’s orbit (change in size)
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What’s it made of? I…am…IRON MOON Ti abundance
(blue = lots, orange/purple = less) But…no dipolar magnetic field. The moon’s weak B field comes from magnetic minerals.
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The Real Dark Side of the Moon
Note which side the maria are on. Why only that side? Anorthosite: igneous rock rich in Ti, Fe Basalt: fine-grained igneous rock caused by cooling magma
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Mascons
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Lunar Prospector measures neutrons from H
Water? Lunar Prospector measures neutrons from H 1996: Clementine indicates ice in deep craters 1998: Lunar Prospector indicates ice 1998: LP crashed into surface; no water seen 2009: Moon Mineral Mapper aboard Chandrayaan-1 detects water Chandrayaan-1 (water in blue)
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LCROSS Launched with LRO in 2008
Atlas-Centaur rocket impactor targeted Cabeus crater Impactor (2305 kg/10,000mph) produced ejecta plume LCROSS probe flew through the plume and crashed, relaying data Data indicate 5% of plume mass was water
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Where did the moon come from?
4 theories Fission (moon broke off from earth) Sisterhood/Co-accretion (formed at the same time) Capture (moon formed somewhere else but drifted by and ended up in the Earth’s gravitational field) Giant Impactor (something hit the earth and the resulting material formed the moon)
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Which one is right? Fission 2. Sisterhood/Co-accretion
Composition of E and M are similar, but not that similar. Not enough mass in the Pacific Basin to account for the moon. 2. Sisterhood/Co-accretion See #1 about composition. E and M should be the same age; M is younger.
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Which one is right? 3. Capture
E and M are too similar for the moon to have formed elsewhere Angular momentum of the E/M system isn’t right for the moon having flown in and stopped 4. Giant Impactor Given a Mars-sized impactor, mass is right Volatile metals and lack of water on the moon indicate high temperatures in the past. Simulations show it’s viable (angular momentum OK) Lower density of moon, lack of iron are consistent with violent impact
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Whack-a-Moon t=0 Eventually, the cloud becomes a disk and then a moon.
The impactor core becomes the moon’s core Intense heat is consistent with lack of volatiles and lack of similarity to the earth. t=24h
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