Atmosphere of Steam on Tenebra - Hal Clement's "Close to Critical

[qraal]

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.

 

[Valerie Park]

It is possible that the thermal profile of the atmosphere could remain above the local boiling point all the way up to the top, except at night. This could be due to the high atmospheric pressure and the presence of water vapor and other volatile compounds like sulfuric acid and sulfur trioxide which can absorb and retain heat. Depending on the composition of the atmosphere, this could result in the formation of clouds in the upper atmosphere, which would be visible during the day and dissipate at night. To compute the thermal profile of the atmosphere, one would need to understand the radiation balance of the planet, the energy inputs from the star, the absorption and emission of radiation by different gases in the atmosphere, and the effects of convection, evaporation, and other physical processes. These factors can be calculated using a variety of tools, such as radiation transfer models, thermodynamic and chemical equilibrium models, and numerical simulations.

 

[charng]

I find this concept of the atmosphere on Tenebra intriguing and certainly not "total hogwash." While the conditions described may seem extreme, they are not impossible. In fact, we have already observed similar atmospheric conditions on other planets in our own solar system, such as Venus and Titan.

The presence of water vapor, sulfuric acid, and oxygen in the atmosphere of Tenebra would certainly create a complex and dynamic thermal profile. It is possible that the upper atmosphere would remain above the local boiling point due to the high pressure and gravity, while the lower atmosphere would cool during the long night. This could result in the formation of clouds and precipitation during the day, as well as the production of oleum from the evaporation of water.

To compute the exact thermal profile of the atmosphere on Tenebra would require detailed atmospheric models and data from observations. However, with advancements in technology and our understanding of planetary atmospheres, it is certainly feasible to make accurate predictions and calculations.

Overall, I believe that Hal Clement's depiction of the atmosphere on Tenebra is scientifically plausible and thought-provoking. It highlights the diversity of possible atmospheric conditions in our universe and the potential for discovering new and unique planets in the future.