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Phil Macias Reminders AY6 Section 9 Phil Macias Reminders • I have HW1-4, and the midterms if you haven’t picked them up. • Office hours: M 4-5 and W 1:30-2:30 • HW 5 will be returned tomorrow in class where HW6 is due • There will be an official final review on Monday, June 17th (details being ironed out) Overview • Mercury • Bulk properties, surface features, interior • Venus • Atmosphere, surface regions and landmarks Mercury: The Moon’s Twin? • 1.4 times the size of the moon • 4.5 times the mass (denser!) • No atmosphere • Shows history of many impact events Surface Features • Mercury’s surface features are very similar to the moons • The types of terrain are broken down into: • Heavily Cratered Terrain • Intercrater Plains • Smooth Plains • Hilly and Lineated Terrain Heavily Cratered Terrain • Analogous to lunar highlands • High crater density • Formed during the heavy bombardment period • Crater ejecta blankets are smaller, secondary craters closer Heavily cratered terrain at Mercury’s south pole Smooth Plains • Analogous to lunar maria • Low crater density (younger) • Contain wrinkle ridges • Lighter than lunar maria • Association with impact basins implies volcanic origin Intercrater Plains • Heavily cratered plains found between large craters • Volcanic origin implies global expansion • Could also possibly be formed by widespread impact ejecta blankets (Cayley Plains) Hilly and Lineated Terrain • Network of hills and troughs superimposed on previous structure • Diametrically opposed to Caloris Basin • Probably the result of seismic activity during impact event that formed Caloris Movie! Astronomy 6: Graeme Smith. Chapter 6. 11 Formation of a thrust fault & lobate scarp Figure 1: Formation of lobate scarps on Mercury by thrust faulting. Compression forces cause the crust to fracture (break) in the region shown by the dashed line. Continued compression causes crust on one side of the fracture zone to be forced up over crustontheotherside,producinga thrust fault, and an escarpment that collapses under gravity. Lobate Scarps • Found amongst intercrater plains and uplands terrain • Produced by thrust faults • Could be formed during the global contraction of mercury Mercury’s Interior Mercury Moon Venus: Earth’s Evil Twin • 0.95 times the size of Earth • 0.82 times the mass of Earth • Orbits at 0.72 AU • Surface obscured by clouds (has an atmosphere) • Retrograde rotation Venus’ Atmosphere • 96% Carbon Dioxide 3.5% Nitrogen 0.5% Other stuff • Much more massive than Earth’s atmosphere • Pressure at surface is 90 times that on earth • Why are the temperatures so high? The Greenhouse Effect put earth at 0.72 AU?? The Venusian Surface The Venusian Highlands • Cover about 10% of the surface • Ishtar Terra: About the size of Australia, contains Maxwell Montes, Lakshmi Planum, Fortuna Tessera • Aphrodite Terra: About the size of Africa, contains many chasms and some volcanoes Venusian Uplands • Comprise most of the surface of Venus • Landers have found most to be covered in low iron granite, also some basaltic rock • Appear to be regions of solidified lava fields subjected to erosion Smooth Lowland Plains • Called “planitia”, these are covered by lava flows, where flood basalts have erupted from the crust • Covered in ridges and fractures (crust has been pulled apart) Water Loss on Venus • Scientists estimate an original water layer on Venus 3m thick. • The process by which Venus lost its water is known as photodissociation • Sunlight breaks down a water molecule, hydrogen escapes and oxygen oxidizes surface Landforms on Venus • Highest point: Maxwell Montes (11km) • Lowest point: Diana Chasm (-3km) • Venus has much less cratering than Mercury or the moon, and no small craters are found. Why? Venusian Volcanism • Volcanism has played an extremely important role in shaping Venus’ surface • Magellan has seen thousands of tiny volcanoes, shield volcanoes, pancake domes Astronomy 6: Graeme Smith. Chapter 7. 19 upwelling mantle plume converging convection flows Figure 1: Hot plumes of material in the mantle of Venus can exert forces on the surface crust. In the upper panel the crust is stretched and fractured, in thebottompanelitiscompressedand uplifted. Venusian Volcanism • Arachnoids are the result of magma that accumulates but does not reach the surface. Less than 200 km in size • Coronae are also seen on the surface, and are even larger Venus Exobiology • Possibly, 4 billion years ago Venus could have been more hospitable • Over time, Venus heated up by runaway greenhouse and Earth remained within the habitable zone • Movie!.
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