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Atmosphere of steam

  1. Jun 12, 2009 #1
    In Hal Clement's classic tale "Close to Critical" the planet Tenebra has an atmospheric pressure of 800 bar, 3 gee surface gravity, 100 hour rotation period and about 380 C surface temperature. The atmosphere is mostly water vapour and it condenses just enough for huge rain drops to form and slowly drift down to the surface during the long night. They're still at about 370 C as they fall, so it hasn't cooled very much. Clement writes that the planet is dark, yet with so much water vapour surely there would be clouds in the upper atmosphere? Could the thermal profile of the atmosphere remain above the local boiling point all the way to the top, except at night? How would one compute that? Other volatiles present are sulfuric acid, with enough sulfur trioxide to make oleum as water evaporates during the morning. Oxygen is one of the minor gases too, enough to sustain combustion.

    Any thoughts? Is it total hogwash? We might actually find such a planet in the next few years, orbitting close to a star, but with sufficient water to avoid total hydrogen loss from EUV dissociation of the water and enough gravity to impede hydrodynamic outflow.
  2. jcsd
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