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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
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
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
deck, and is re-radiated downwards.
Temperature builds up until an equilibrium
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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- Spring '11