2_Grand Tour pt

03 n2 35 781 ar 0006 093 o2 0003 210 ne 0001 0002

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Unformatted text preview: phere is composed mainly of CO2. Atmospheric composition determined by spectroscopy from ground based telescopes and direct sampling and analysis from robotic balloons and landers. Gas CO2 Venus 96% Earth 0.03% N2 3.5% 78.1% Ar 0.006% 0.93% O2 0.003% 21.0% Ne 0.001% 0.002% Venus: Why All That CO2? Venus: Why All That CO Earth: CO2 cycling “sources” Venus: No cycling No oceans or plate tectonics (?) on Venus, so no "sinks" for CO2. CO2 stays accumulated in a thick atmosphere. “sinks” Venus: Greenhouse Heating Venus: Greenhouse Heating Greenhouse Effect on Venus: The top clouds of Venus’s atmosphere The reflect about 75% of the incident sunlight; 25% filters through and heats the surface. The heat radiated by the surface (IR radiation) then tries to escape, but it is absorbed by CO2 and by the lower cloud absorbed deck, and is re-radiated downwards. Trapped! Trapped! Temperature builds up until an equilibrium Temperature is reached at T ~ 480oC! 480 Venus: Runaway Greenhouse Venus: Runaway Greenhouse Early Venus… Venus’s surface (not to mention interior) was probably too hot from the beginning to ever have had large bodies of liquid H 2O. Most of Venus’s original endowment in H2O likely turned to vapor and was progressively photodissociated and lost by exospheric escape. With no significant bodies of liquid H2O to absorb and dissolve atmospheric CO2 and lock it up as carbonate rocks, CO2 was allowed to build up massively in Venus’s atmosphere. Because CO2 is an effective greenhouse gas, temperatures on Venus rose progressively higher until liquid H 2O was no longer even possible on Venus. Venus experienced a Runwaway Greenhouse Effect from which it never recovered. Venus: Topography Two "continents": Aphrodite (Africa-sized) & Ishtar (Australia-sized) w/ highest peak at 11 km: Maxwell Montes. Venus...
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