Summary Slides Geo 50 – October 10, 2012 All Summaries Prior to the Midterm

The Moon: History of Exploration  Telescopic Phase: Galileo  Photography: Mid-1800’s  Sputnik  Gagarin  Kennedy’s National Goal  Space Missions: The US-USSR Space Race 1959Luna 3 (Farside) 1964Ranger 7, 8, Luna 9 (Soft Lander) 1966Surveyor I, III, V, VI, VII Lunar Orbiter I-V Apollo Luna 16, 20, Lunakhod I, II, Zond spacecraft 1990’sGalileo, Clementine, Lunar Prospector 2000’sJapanese, US, Indian, Chinese missions  Future Plans A lunar base? 1969

The Moon - Characteristics and Surface Provinces CharacteristicsMariaTerrae a. AlbedoLowHigh b. ElevationsLowHigh c. TopographySmoothRough d. Global distributionNearside (17%)Farside (83%) e. Surface features Craters Mountains Faults Trenches Lava Flows Volcanoes Ridges Sinuous Channels f. Composition

The Interior of the Moon  Results Less Natural Activity than Earth - ~10-20 quakes per year; <2 on Richter Scale - Energy expended ~ lbs TNT; ( of Earth) - Quakes occur at great depth - ~ km depth on the Moon - ~25 km depth on Earth - No correlation with surface features! - Occur coincident with lunar orbit cycles - Moonquakes are due to tides raised in the Moon by Earth and Sun - Seismic structure: - Revealed three major layers - Crust: 0-60 km;V p < 6.5 km/sec - Mantle: kmV p ~8 km/sec - Small core? km S-waves attenuated P-waves slower

The Interior of the Moon  Implications Layering Broadly Similar Between Earth and Moon - Layered interior: Chemical and mechanical Important Differences: - Core:Small on the Moon 0.2 lunar radius versus 0.5 Earth radius - Lithosphere:Thick on the Moon 1000 km on the Moon versus 100 km on Earth What are implications for: Subsidence? Plate Tectonics? - Relationship of surface provinces.

The Interior of the Moon  Results Less Natural Activity than Earth - Mechanical layering - Present: Partially molten at ~ km Thick lithosphere!! - Past: What is the thermal evolution?? Area: 4π r 2 Volume: 4/3π r 3 - Positive gravity anomalies in mare - Mascons - Upper low velocity zone: Origin? - Role of impact cratering? - Megaregolith

The Lithosphere of the Moon  Impact Cratering Mechanics Energy Partitioning and the Geological Effects E h + E c + E pv + E e + E s KE Reservoir of Kinetic Energy of Projectile (Velocity, Density, Size) Impact HeatingComminution Plastic/Visco us Deformation Ejection of Material from Crater Seismic Waves Energy DistributionAssociated Processes E h ≈ 25%Impact Melt, Welding, Metamorphism E c ≈ 8%Fragmentation E pv ≈ 20%Internal Deformation E e ≈ 50%Lateral Transport, Mixing, Secondary Cratering E s << 1%Massive Moonwide Moonquakes, Landslides, Degradation

The Lithosphere of the Moon  Lunar Craters and the Cratering Process Sources of Information - Natural Earth craters - Explosion craters - Experimental impacts Impact Cratering Mechanics - Stages in cratering events - Energy partitioning and the geological effects The Lunar Cratering Record - Morphology of fresh craters - Multi-ringed impact basins Summary - Impact Cratering as a Planetary Process

The Lithosphere of the Moon  Summary - Impact Cratering as a Process Major Source of Energy Forms and Modifies Rock Material Sculptures Planetary Surfaces Major Degradational Process Large-Scale Tectonic Process Significant Process for Vertical and Lateral Mixing of Materials Operates Over Very Short Time Periods, but Influence is Long- Lasting Produces Thermal Anomalies Significant in Planetary History (Density, Degradation, Flux) Role on Planets with Atmospheres and impact on life (?)

The Lithosphere of the Moon  Summary - Volcanism as a Process 17% of Lunar Surface Covered With Mare Basalt Mostly on the Nearside Major Depositional Process Large Number of Flow Units Composition Volcanism Active for Long Time Thermal Evolution of the Interior Ascent and Eruption Style Eruption Rates

Lunar Tectonics Summary Moon is a one-plate planet. Very quiet seismically. Early period of heating and mild expansion. Mare volcanism in basins, loading, flexure. Later period of cooling and mild contraction. Heat loss mechanism is conduction. Tectonics: Vertical, loading and flexure, not lateral like Earth.

Moon: Insights into the formative years of planetary history. Ancient age of lunar crust. Magma Ocean: Concept of wholesale melting. Linkage of geological observations and accretionary theory. Moon formed from impact of Mars-sized object into early Earth. Lunar Interior: Crust, lithosphere and thermal evolution. Differentiation, segregation instability and overturn. The Moon as a “one-plate” planet in contrast to Earth. Impact cratering is a fundamental geological process. Cometary volatiles may accumulate near poles. The Moon is a record of the first half of solar system history.

The Lithosphere of Mercury  Impact Craters and Basins: What is the influence of increased gravity? Morphology: Looks like lunar farside - See craters from 100 m to 1000 km - Similar to the Moon but also different Changes in crater morphology with increasing diameter - Interior of craters - Bowl-shaped <10 km - Transitional - Central peaks, flat floors, terraced walls - Interior terracing common: related to gravity? - Depth-diameter relationship - Exterior of craters - Secondary craters closer to the rim - Density of secondaries higher - Gravity keeps ejecta from travelling far Basins - Peak rings at greater than 100 km - Earlier transition than on the Moon Role of gravity and impact velocity Conclusions

The Lithosphere of Mercury  Volcanic Activity and Igneous Processes: Conclusions - Significant volcanic plains like lunar maria, but flood basalt mode and no albedo differences. - Different mineralogy? - Volcanism is very likely to have occurred in intercrater plains. Evidence is somewhat equivocal. - Could be basin ejecta - Could be flood lavas with no vents - Explosive volcanic activity: Evidence is seen (pits, pyroclastic deposits): relation to plains? - Crustal formation processes likely to be different: No anorthositic crust, higher crustal density. - Primary crust may blend with secondary crust!

The Lithosphere of Mercury  Tectonism and Mountain Building: No plate boundaries No strike-slip and lateral offset No major extension, graben - Some small graben in Caloris Basin Some wrinkle ridges in plains Major global scarps - Large scale, long - 100’s of km long, 1-2 km high - Globally distributed - Timing - After cratered terrain - Synchronous with smooth plains - Cause - Global compression - Cooling of lithosphere? - Solidification of core? Summary - One-plate planet - A shrinking planet and global scale changes - Is this how plate tectonics starts?

Mercury: Summary  Planetary formational process led to the high metal/silica ratio in Mercury.  Geological history of Mercury: Moon-like but materials and processes differ:  Impact cratering  Volcanism: Very extensive, flood basalt style; intercrater plains likely volcanic.  Tectonism: Global and long-wavelength folding. Origin of plate tectonics?  Polar Processes: Ice in polar craters. Sources and preserved record.  What are the radar reflective materials at the poles?  Volatile species and their sources and sinks?: New discoveries on Hollows.  Is Mercury still geologically active? Still an open question!