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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

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

Venus

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?

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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 >

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)

Earth-based Radar Map Magellan Radar Map (Venus Orbit)

Lava Rivers longer than any on Earth or Moon

Magellan 3-D radar images

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 >

100 km; Earth has some of 10 km or so) – It takes longer to cool/solidify on Venus!

Surface Features of Venus (continued)

•  Cracks, Ridges, “Coronae”, hot spots, but No Plates

Venera 13 Color Photos From Surface of Venus

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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

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Olympus Mons