The conditions on Venus's surface are extremely harsh. I'm trying to conceptualize what it would be like to walk on the surface through supercritical carbon dioxide. Obviously we must neglect the high temperatures that would kill any human. Would it be like walking through water?

Typical surface conditions:

  • Supercritical carbon dioxide
  • Temperature ~ 728 $K$
  • Pressure ~ 9 $MPa$ (comparable to 900m underwater on Earth!)
  • Density ~ 65 $kg/m^3$
  • Viscosity ~ 3.55E-05 $N s / m^2$
  • Slow moving air, maximum wind speed ~ 2.5 $m/s$

A starting point: A 2.5 m/s gust of wind would have dynamic pressure equal to $$ q = {1\over2} * \rho * V^2 = {1\over2} * 65 {kg\over m^3} * (2.5 {m \over s})^2 = 203.1 Pa $$ This is roughly equivalent to an 18.2 m/s (40.7 mph) gust of wind on Earth's surface - that's an F0 on the Fujita Tornado scale! $$ V = \sqrt{2*q \over \rho} = \sqrt{2*203.1 Pa \over 1.225 {kg \over m^3}} = 18.2 {m \over s} $$

But how would the viscosity effect things? What would it feel like to wave your hand around in such a dense, viscous atmosphere?

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    $\begingroup$ There is not only the temperature to be neglected, pressure is not survival for humans too. But the density of the atmosphere is much lower than that of water. $\endgroup$ – Uwe Feb 16 '19 at 14:42
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    $\begingroup$ This question should be asked for all planets and moons with atmospheres, and collected in a dedicated Wikipedia page. That, and someone please do a youtube video about it... review style $\endgroup$ – Everyday Astronaut Feb 17 '19 at 7:42

Actually the air is not all that viscous. Compared with the viscosity of Earth's air at sea level given here, the viscosity of the Venusian atmosphere is only about twice as great. Whereas, the density of Venusian air is about 50 times as great as that of Earth's air at sea level. Density rather than viscosity thus dominates atmospheric fluid dynamics on Venus even more than it does on Earth.

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    $\begingroup$ Your comment confuses me. The viscosity of CO2 is (assumed to be) given in the question, and I have a link to the properties of air at sea level. $\endgroup$ – Oscar Lanzi Feb 17 '19 at 22:27
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    $\begingroup$ Oh sorry! I missed that completely. Looks good, thanks! $\endgroup$ – uhoh Feb 17 '19 at 22:33

What would be the real feeling:

First, you would feel extremely hot. As if you would be thrown in molten lead. It would happen some seconds. After that, your brain would become inoperational due to over-heating. These seconds were also the time until you would get mortal damage from burning. Death would happen in lesser than a minute.

The high pressure wouldn't feel, because the hot $\rm CO_2$ would quickly fill your lungs and nasal cavity. After that, your internal and external pressure will be the same. Anyways the sense would be negligible, compare to the hot.

The feeling if we ignore the temperature:

First, there is no air, which is a major problem, but we can remain relative operational for some tens of seconds. The problem of the pressure still would exist.

The density of the $\rm CO_2$ is 65 $\frac{kg}{m^3}$, which is only 6% of the density of the water. It is still a lot, in such an environment, the world-record sprinters would look probably more like the weightlifters. The main problem is not the viscosity, but the super-high drag due to the extreme density of the atmosphere (compared to the Earth).

Drag is quadratically proportional to the speed, thus the $\approx 65$ times higher density would cause the drag what we would feel on the Earth with $\approx$ 8 times higher speed. Walking with 5 km/h would have the same sense of drag like running with 40 km/h.

  • $\begingroup$ "The high pressure wouldn't feel, because the hot CO2 would quickly fill your lungs and nasal cavity." That's a weird argument. So submarine crews are just scared of pressure equilibrating in their lungs, that's why they float around in an isolated pressure environment? $\endgroup$ – AtmosphericPrisonEscape Feb 17 '19 at 0:19

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