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UA PTYS 206 - The Moon

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PYTS/ASTR 206 – The Moon1z Announcements Homework #2 due now 50% credit if handed in next TuesdayMidterm #1 in 1 weekMid-term #1 in 1 week Based on the first 10 lectures Multiple choice - bring pencils  Lasts 1 hour and starts on timePYTS/ASTR 206 – The Moon2The MoonPTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – The Moon3In this lecture…In this lecture…z Two types of terrain Highlands Mariaz Geologic features on the Moon Craters and VolcanoesFtifthMzFormation of the Moon Giant impacts & Magma Oceansz The late heavy bombardmentz Formation of the Mariaz The recent yearsPYTS/ASTR 206 – The Moon4z The moon is very close in comparison to other solar systemcomparison to other solar system objects It’s 30 Earth diameters awayMars (when closest) is ~6000 EarthMars (when closest) is ~6000 Earth diameters away Other planets are even furtherPYTS/ASTR 206 – The Moon5z 5thlargest satellite in the solar systemzRock-like densityzRock-like densityz No atmosphere So no wind action e.g. sand duneNo river channels or rainfall etcNo river channels or rainfall etc…z Critical body for planetary science Much of what we do in studying solid planets started with work on the MoonSimpler to understand than most planetsSimpler to understand than most planetsPYTS/ASTR 206 – The Moon6z Easy to get to – heavily visited by spacecraftz Late 1950s to early 1970sRobotic craft from the USA & USSRRobotic craft from the USA & USSR Ranger Lunar Orbiter SurveyorLunaLuna  Robotic Rovers (USSR) Lunokhod Manned missions (USA)() Apolloz 1990s Clementine Lunar ProspectorPYTS/ASTR 206 – The Moon7z More missionsCh d(I di )zChandrayaan(India)z Chang’E (China)z Kaguya (Japan)z Smart 1 (Europe)zLRO (USA)–launching soonzLRO (USA) launching soonPYTS/ASTR 206 – The Moon8MariaTwo terrain typesTwo terrain typeszMaria Dark material – once thought to be seasz Terrae Highlands Light material – once thought to be the dry landPYTS/ASTR 206 – The Moon9z No one knew what the far side of the Moon looked like untilof the Moon looked like until 1959 Soviet Union launched Luna 3z Far-side looks nothing like the near side No MariaNear sideFar sidePYTS/ASTR 206 – The Moon10Maria Highlands (Terrae)Low elevationsHigh elevationsLow elevationsHigh elevationsDarker BrighterFew craters Many craters (saturated)Smooth RoughVolcanic features Few volcanic featuresPYTS/ASTR 206 – The Moon11Geologic features on the MoonGeologic features on the Moonz The Moon is a really simple planetz CratersSimple craters <18km diameterSimple craters <18km diameter Complex craters >18km diameter Multi-ring basinsPer asi e ‘gardening’ frommicrometeroiteszPervasive ‘gardening’ from micrometeroites Upper few km of the crust is fractured  Upper few meters has been turned into regolithMoltke – 1kmEuler – 28kmOrientale – 970kmPYTS/ASTR 206 – The Moon12z Volcanic features on the MareLflftLava flow fronts Sinuous rilles (Collapsed lave tubes) Vents and domesPYTS/ASTR 206 – The Moon13z Volcanic features on the Marez Apollo samplesz Tell us that the mare are sheets of volcanic rockz Mare basaltz Highland AnorthositePYTS/ASTR 206 – The Moon14z Most of the lunar rocks look like thisBiBreccia  Fragments of rock fused togetherPYTS/ASTR 206 – The Moon15z Maria Overlapping volcanic flows and impactsOverlapping volcanic flows and impacts Samples show a volcanic composition BasaltHighlandszHighlands Just overlapping impactsz How did the Moon get this way?PYTS/ASTR 206 – The Moon16Ftt idFormation of the MoonFormation of the MoonzFacts to consider Moon depleted in iron & volatile substances Like light elements and waterOxygen isotope ratios similar to EarthOxygen isotope ratios similar to Earth Moon doesn’t orbit in Earth’s equatorial planez Possible theories (that didn’t work) Earth and Moon co-accreted Explains oxygen isotopes Doesn’t explain iron and volatile depletion Earth split into two piecesSf (f)Spinning so fast that it broke apart (fission) …but the Moon doesn’t orbit in Earth’s equatorial plane Capture of passing bodyppgy Earth captures an independently formed moon as it passes nearby Pretty much a dynamical miracle Doesn’t explain oxygen isotope similarity to EarthPYTS/ASTR 206 – The Moon17z Current paradigm is Giant impactEthl tfi liEarth close to final size Mars-sized impactor Both bodies already differentiatedBthbdi f d t 1AUBoth bodies formed at ~1 AUPYTS/ASTR 206 – The Moon18z How does that explain the iron depletionBdi l d diff titdBodies were already differentiated All the iron sticks around in Earth’s core Moon rock comes from Earth’s mantle – explains Oxygen isotope similarityFrom Robin Canup, SWRI Boulder Red = iron  Yellow = rockPYTS/ASTR 206 – The Moon19z What does that mean for the temperature of the two bodies?Bth htBoth very hot… Magma oceans 100s of kilometers deep Explains the Moon’s lack of volatile elementsFrom Robin Canup, SWRI BoulderPYTS/ASTR 206 – The Moon20z Accretion of lunar material into the Moon within a few years!z High-accretion rates mean surface is molten Magma ocean probably a few hundred km thick Apollo 11 returned highland fragments, first suggestion of Magma oceanId i t d d t th t t i l l tIdea since extended to other terrestrial planetsLight minerals floatANORTHOSITEDense mineralsDense minerals sinkCore?PYTS/ASTR 206 – The Moon21z When the magma ocean freezes it seals in a lot of heatfreezes it seals in a lot of heat Will become important later…z Crustal Thickness Asymmetry Average 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 sciencelunar sciencePYTS/ASTR 206 – The Moon22z Does the Moon have a core?Remnant magnetism shows there was once a liquid coreRemnant magnetism shows there was once a liquid core Seismic experiments from Apollo – inconclusive Another major unanswered questionz Better seismic experiments would answer this Apollo seismometers were all close together  Didn’t probe very deeply Switched off in the 1970s to save $$PYTS/ASTR 206 – The Moon23O th t i lidttttfImpact basins


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UA PTYS 206 - The Moon

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