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Lec 21: 14 November 2011 Chaps. 11 Terrestrial Planets. LAST TIME - Earth II. Our Changing Surface • Heat transfer through interior • Oceanic v. Continental Crust • Geological Activity & Plate Tectonics TODAY - Surfaces of the Terrestrial Planets • • • Earth’s Plate Tectonics Surface details & activity of Venus Surface details & activity of Mars NEXT - Water, Atmospheres, and Climate Venus Earth shows dramatic evidence of plate tectonics Venus has continents and plains, but no plate tectonics Mars has north-south asymmetry (flat northern lowlands and cratered southern highlands), but no plate tectonics Surface Features of Venus • 2 “continents” (Ishtar & Aphrodite) – e.g. Lakshmi: 11 km high; 5 km relief – cf. Himalayas 10 km high; 6 km relief – Rest of surface is low-lying & relatively flat Surface Features of Venus (continued) • Impact Craters – about 1000 of them from 2 to 280 km diameter – cf. Earth has 150; Moon has many more – very few are under 10 km (Why?) – nearly all are “pristine” – entire surface ~15% of Lunar maria density – entire surface is about 500 million years old • Catastrophic or Steady State Resurfacing? 1 Surface Features of Venus (continued) • Volcanoes – 80% of surface is basaltic lava plains – would expect more modified/filled in craters is volcanic activity was steady state than if it were catastrophic – shield volcanoes – pancake domes – lava rivers (longest 7000 km; over 40 are > Earth-based Radar Map Magellan Radar Map (Venus Orbit) 100 km; Earth has some of 10 km or so) – It takes longer to cool/solidify on Venus! Volcanic activity resurfaced Venus recently (or resurfacing Venus currently) Surface Features of Venus (continued) Lava Rivers longer than any on Earth or Moon Magellan 3-D radar images • Volcanoes – 80% of surface is basaltic lava plains – would expect more modified/filled in craters is volcanic activity was steady state than if it were catastrophic – shield volcanoes – pancake domes – lava rivers (longest 7000 km; over 40 are > 100 km; Earth has some of 10 km or so) – It takes longer to cool/solidify on Venus! Surface Features of Venus (continued) Venera 13 Color Photos From Surface of Venus • Cracks, Ridges, “Coronae”, hot spots, but No Plates 2 Best View of Mars from Earth (Hubble Space Telescope) Surface Features of Mars • Northern Hemisphere: mostly low-lying plains • Southern Hemisphere: mostly highlands (appears much darker) Surface Features of Mars (continued) • Craters and Impact Basins – Hellas (1800 km diameter; 6 km deep) – Argyre (700 km across) – crater counts indicate ages: • Southern Highlands ~ 4 billion years • volcanoes very young (<200 million years) • Northern Plains ~2 to 3 billion years Southern Highlands ~ 4 GY old Northern Plains 2-3 GY old Surface Features of Mars (continued) • Valles Marineris – rift zone 4000 km long, 500 km wide, 7 km deep • Tharsis Bulge & Giant Shield Volcanoes – Olympus Mons is 700 km wide, 27 km tall, and 2 km across the peak 3 Olympus Mons 4