The atmospheric pressure and temperature at about 50 to 60 km above the surface of Venus is nearly the same as that of the Earth, making its upper atmosphere the most Earth-like area in the Solar System. But it has thick sulfuric acid clouds and there's almost no water and no oxygen.

This Wikipedia article about the sulfur-iodine cycle gives this chemical equation:

2H$_2$SO$_4$ --> 2SO$_2$ + 2H$_2$O + O$_2$ (830$^0$ C)

Could concentrated sunlight be strong enough in the atmosphere of Venus to heat the sulfuric acid above 830$^0$ C ?

Or could a MMRTG deliver sufficient heat to create water and oxygen this way ?

  • $\begingroup$ Earth-like conditions imply that the equilibrium of that reaction lies heavily to the left. As you introduce heat, it shifts towards the right. The source of the heat doesn't matter, e.g. focussed sunlight or any kind of reactor would do. $\endgroup$ Commented Aug 17, 2019 at 18:32
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    $\begingroup$ Even if this worked, the SO2 would just recombine with the water and the oxygen to reform the acid. $\endgroup$
    – Mike H
    Commented Aug 17, 2019 at 21:41
  • $\begingroup$ @MikeH It's just logic that in a chemical process you separate the formed products to prevent them from recombining. $\endgroup$
    – Cornelis
    Commented Aug 18, 2019 at 8:36
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    $\begingroup$ @Conelisinspace Logic yes, however the practicalities of separating gases might be challenging while floating on top of the atmosphere. And where would you put a few billion tons of SO2? $\endgroup$
    – Mike H
    Commented Aug 18, 2019 at 21:02
  • $\begingroup$ @MikeH Yes it would be very challenging to separate superheated steam from the SO$_2$, i only can think of cooling down to water and then let the gases escape into the clouds again. $\endgroup$
    – Cornelis
    Commented Aug 18, 2019 at 21:34

1 Answer 1


Optically focusing sunlight does not work when you are deep inside the clouds, collecting your raw material. Inside the cloud, the light will be diffuse and seemingly coming from all directions, even reflecting up from below your ship.

If you are able to alternate flying altitude, you could use the lower altitude for cloud mining, then rise higher to get direct sunlight above the clouds that you could optically focus for refining. The ambient temperature will also be lower at high altitudes, making the excess heat from the chemical refining processes easier to handle. (There are also other considerations and trade-offs to different flying altitudes, and local weather needs to be understood better as well.)

From the chemistry point of view it makes no difference if the heat is from focused sunlight or something else, so you can use any kind of power available to generate the heat. Even if you can't focus the diffuse light inside the clouds, the diffuse light can still power photovoltaic cells, for example.

  • $\begingroup$ A well composed answer, but i would like to have evidence that with focused sunlight the temperature will become higher than 830$^0$ C. $\endgroup$
    – Cornelis
    Commented Aug 18, 2019 at 8:30
  • $\begingroup$ Not any kind of power can generate the necessary temperature of at least 830$^0$ C. Can you demonstrate for instance that a MMRTG can deliver such high temperature ? $\endgroup$
    – Cornelis
    Commented Aug 18, 2019 at 13:31
  • $\begingroup$ I think the required power would depend on the mass being heated. A good answer might be the ratio of mirror diameter to reactant mass, for example. Not sure if there is a good precedent for calculating this kind of rating. $\endgroup$ Commented Aug 18, 2019 at 14:15
  • $\begingroup$ I looked up the specific entropy of H2SO4, which is 1.601 J/gK for liquid form. Purely on paper, heating 1 kg of the stuff by 800 degrees kelvin then takes 0.355 kWh of energy. If you get about 1 kW per square meter from sunlight (based on Earth, could be low for Venus), you can heat 1 kg in about 20 minutes with 1 m2 of parabolic mirror surface. $\endgroup$ Commented Aug 18, 2019 at 18:00
  • $\begingroup$ Isn't there something wrong with your calculation ? Would after 40 min, the stuff be 1600$^0$ C , and so on ? $\endgroup$
    – Cornelis
    Commented Aug 18, 2019 at 21:19

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