PTYS_411_511_5_venus_history - History of Venus PTYS...

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PTYS 411/511 Geology and Geophysics of the Solar System Shane Byrne – shane@lpl.arizona.edu Background is from Pioneer Venus History of Venus
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PYTS 411/511 – History of Venus 2 Venus today Comparison to Earth Venusian atmosphere Water and magnetic fields Geologic record Volcanic resurfacing Tectonic features The lack of craters Putting events in order Resurfacing models In this lecture Surface activity on the Moon and Mercury mostly died off about 3 Ga Surface history of Venus is only available from ~1.0 Ga onward (not dissimilar to Earth) Surface activity and history of Mars spans its entire existence …as opposed to…
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PYTS 411/511 – History of Venus 3 81.5% of the mass of the Earth Slightly higher mean density (5230 kg m -3 ) Formed in a similar location – 0.72 AU Implies a similar bulk composition Comparisons to Earth
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PYTS 411/511 – History of Venus 4 Earth has obvious topography dichotomy High continents Low ocean floors Venus has a unimodal hypsogram No spreading centers No Subduction zones No plate tectonics Topography
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PYTS 411/511 – History of Venus 5 Massive CO 2 atmosphere with intense greenhouse effect 93 bars,740 K at mean surface elevation Altitude variations 45-110 bars, 650-755 K No day/night or equator/pole temperature variations 3 distinct cloud-decks Composed of sulfuric acid droplets Produced by photo-oxidation of SO 2 Effective scavenger of water vapor Layers differ in particle size Very reflective (albedo 70%) keeps surface much cooler than it would otherwise be 100 ms -1 east-west at altitude of 65 km Drives cloud layer around planet in ~4 days Reasons for super-rotating atmosphere are unknown True surface (243 day - retrograde) rotation period found with terrestrial radar. Atmosphere of Venus
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PYTS 411/511 – History of Venus 6 Earth and Venus should be the same… Venus absorbs roughly the same amount of sunlight as the Earth. Venus has roughly the same amount of carbon as the Earth …but… Venus has no plate tectonics Earth’s carbon get recycled through the crust Venusian carbon accumulates in atmosphere – regulated by ‘Urey reaction’? CaCO 3 + SiO 2 = CaSiO 3 + CO 2 (calcite) + (silica) = (wollastonite) log 10 P CO2 = 7.797 – 4456/T Equilibrium gives 92 bars at 742 K What went wrong? All these differences can be traced back to the lack of water on Venus
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PYTS 411/511 – History of Venus 7 Why didn’t this happen on the Earth ? Earth has water that rains Rain dissolves CO 2 from the atmosphere Forms carbonic acid This acidified rainwater weathers away rocks Washes into the ocean and forms carbonate rocks Carbonate rocks eventually recycled by plate tectonics The rock-cycle keeps all this in balance Sometimes this gets out of sync e.g. snowball Earth – stops weathering
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This note was uploaded on 01/01/2011 for the course PTYS/ASTR 411/511 taught by Professor Shanebyrne during the Spring '08 term at University of Arizona- Tucson.

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PTYS_411_511_5_venus_history - History of Venus PTYS...

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