Slide 1The MoonSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35PYTS/ASTR 206 – The Moon1AnnouncementsHomework #2 due now50% credit if handed in next TuesdayMid-term #1 in 1 weekBased on the first 10 lecturesMultiple choice - bring pencils Lasts 1 hour and starts on timePYTS/ASTR 206 – The Moon2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected] MoonPYTS/ASTR 206 – The Moon3In this lecture…In this lecture…Two types of terrainHighlandsMariaGeologic features on the MoonCraters and VolcanoesFormation of the MoonGiant impacts & Magma OceansThe late heavy bombardmentFormation of the MariaThe recent yearsPYTS/ASTR 206 – The Moon4The moon is very close in comparison to other solar system objectsIt’s 30 Earth diameters awayMars (when closest) is ~6000 Earth diameters awayOther planets are even furtherPYTS/ASTR 206 – The Moon55th largest satellite in the solar systemRock-like densityNo atmosphereSo no wind action e.g. sand duneNo river channels or rainfall etc…Critical body for planetary scienceMuch of what we do in studying solid planets started with work on the MoonSimpler to understand than most planetsPYTS/ASTR 206 – The Moon6Easy to get to – heavily visited by spacecraftLate 1950s to early 1970sRobotic craft from the USA & USSRRangerLunar OrbiterSurveyorLuna Robotic Rovers (USSR)Lunokhod Manned missions (USA)Apollo1990sClementineLunar ProspectorPYTS/ASTR 206 – The Moon7More missionsChandrayaan (India)Chang’E (China)Kaguya (Japan)Smart 1 (Europe)LRO (USA) – launching soonPYTS/ASTR 206 – The Moon8MariaDark material – once thought to be seasTerraeHighlandsLight material – once thought to be the dry landTwo terrain typesTwo terrain typesPYTS/ASTR 206 – The Moon9No one knew what the far side of the Moon looked like until 1959Soviet Union launched Luna 3Far-side looks nothing like the near sideNo MariaNear sideFar sidePYTS/ASTR 206 – The Moon10Maria Highlands (Terrae)Low elevations High elevationsDarker BrighterFew craters Many craters (saturated)Smooth RoughVolcanic features Few volcanic featuresPYTS/ASTR 206 – The Moon11The Moon is a really simple planetCratersSimple craters <18km diameterComplex craters >18km diameterMulti-ring basinsPervasive ‘gardening’ from micrometeroitesUpper few km of the crust is fractured Upper few meters has been turned into regolithGeologic features on the MoonGeologic features on the MoonMoltke – 1kmEuler – 28kmOrientale – 970kmPYTS/ASTR 206 – The Moon12Volcanic features on the MareLava flow frontsSinuous rilles (Collapsed lave tubes)Vents and domesPYTS/ASTR 206 – The Moon13Mare basaltHighland AnorthositeVolcanic features on the MareApollo samplesTell us that the mare are sheets of volcanic rockPYTS/ASTR 206 – The Moon14Most of the lunar rocks look like thisBreccia Fragments of rock fused togetherPYTS/ASTR 206 – The Moon15Maria Overlapping volcanic flows and impactsSamples show a volcanic compositionBasaltHighlandsJust overlapping impactsHow did the Moon get this way?PYTS/ASTR 206 – The Moon16Facts to considerMoon depleted in iron & volatile substancesLike light elements and waterOxygen isotope ratios similar to EarthMoon doesn’t orbit in Earth’s equatorial planePossible theories (that didn’t work)Earth and Moon co-accretedExplains oxygen isotopesDoesn’t explain iron and volatile depletionEarth split into two piecesSpinning so fast that it broke apart (fission)…but the Moon doesn’t orbit in Earth’s equatorial planeCapture of passing bodyEarth captures an independently formed moon as it passes nearbyPretty much a dynamical miracleDoesn’t explain oxygen isotope similarity to EarthFormation of the MoonFormation of the MoonPYTS/ASTR 206 – The Moon17Current paradigm is Giant impactEarth close to final sizeMars-sized impactorBoth bodies already differentiatedBoth bodies formed at ~1 AUPYTS/ASTR 206 – The Moon18How does that explain the iron depletionBodies were already differentiatedAll the iron sticks around in Earth’s coreMoon rock comes from Earth’s mantle – explains Oxygen isotope similarityRed = iron Yellow = rockFrom Robin Canup, SWRI BoulderPYTS/ASTR 206 – The Moon19What does that mean for the temperature of the two bodies?Both very hot…Magma oceans 100s of kilometers deepExplains the Moon’s lack of volatile elementsFrom Robin Canup, SWRI BoulderPYTS/ASTR 206 – The Moon20Accretion of lunar material into the Moon within a few years!High-accretion rates mean surface is moltenMagma ocean probably a few hundred km thickApollo 11 returned highland fragments, first suggestion of Magma oceanIdea since extended to other terrestrial planetsCore?Light minerals floatANORTHOSITEDense minerals sinkPYTS/ASTR 206 – The Moon21When the magma ocean freezes it seals in a lot of heatWill become important later…Crustal Thickness AsymmetryAverage crust 54-62km thick (45km at Apollo sites)Far-side crust is much (about 15km) thicker Crustal asymmetry is one of the central unanswered questions in lunar sciencePYTS/ASTR 206 – The Moon22Does the Moon have a core?Remnant magnetism shows there was once a liquid coreSeismic experiments from Apollo – inconclusiveAnother major unanswered questionBetter seismic experiments would answer thisApollo seismometers were all close together Didn’t probe very deeplySwitched off in the 1970s to save $$PYTS/ASTR 206 – The Moon23Once the crust is solid – craters start to formSome of these are still very large1000s of km acrossOldest rock fragments From highlands ~4.5 Gyr agoSpike in cratering rate4.0-3.8 Gyr agoLate heavy bombardmentAll the big basins we see today date from this periodAll the inner planetssuffered this bombardmentImpact basins and the late heavy bombardmentImpact basins and the late heavy bombardmentEarliest certain evidence for life on Earth – 3.5
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