New Mars Forums

It is a bit confusing just to think about how this atmosphere would work. Earthlike temperatures and chemistries, but under a third of the gravity. On Venus we can expect pretty similar stuff to happen, but with small planets like Mars?

Maybe we're all wrong and clouds and currents would form completely differently.

The pressure would be the same as on corresponding altitudes on Earth, but the actual density of a cubic meter of air would be higher. Would this affect water chemistry? Would this affect altitude temperatures? I don't know.

Note that clouds would move around the tall volcanoes, since they're lower. I  wouldn't rule out ice on them of some sort. Water would definitely be able to perform deposition into ice at those temperatures and pressures, even if they're too high to experience liquid water.

The poles would also have a very substantial amount of ice on them.

Cold planet, Mars. Not as comfortable as Earth, but a lot of comfort can be lost before you reach inhospitable levels.

No cooling necessary for clouds. Those should form right away.

There are various ways of getting rid of the carbon that can be used in conjunction. Taking it off the planet is not a good solution. It needs to be there for organisms to utilize.

Floating photosynthetic microorganisms could fix it.

This is all wrong. If you're going to say 'twice the temperature', you should be using absolute temperature. The temperature on Earth is 287 Kelvins. If the temperature on Venus were twice that it would be 574 Kelvins with an Earthly atmosphere, over 10,000 with its runaway greenhouse effect, which adds more than 400 degrees Celsius to its temperature. On Mercury it would be over 20,000 Kelvins.

It doesn't work like that. The amount of sunlight corresponds logarithmically to the amount of heat, for planets with the same atmosphere. The main reason for this is that as something gets hotter, its specific heat decreases, causing it to absorb light as kinetic energy less efficiently. Along with that, the atmospheric distribution of heat will be much lower, since the poles will heat faster than the equator, and the equator is an extremely large area where temperature increases will spread out. Even more in-depth than that, we're talking about heating the oceans along with the atmosphere, and oceans tend to be very good at canceling out increasing heat within a certain range. Instead of having a hotter ocean surface, the extra heat would propagate deeper into the water, resulting in thermal expansion.

Notice how global warming seems to be hitting the poles a lot harder than the equator? The only reason the equator's gotten slightly hotter is that the continents limit the efficiency of transferring heat to the poles through ocean currents.

I've been over the most likely method of terraforming Venus earlier in the thread, and it involves creating a global ocean with approximately 80% coverage. This ocean would contain only a quarter of the water Earth's has, but the distribution of elevations on the surface, and the effect of thermal expansion on the upper levels of the water will cause it to have a bit more coverage than Earth's own ocean. This is essential for keeping Venus comfortable at the equator, and it's practical. You need an ocean full of photosynthesizing diatomes if you want a functioning oxygen/carbon cycle.

Those extra 10-15 C are air temperatures only. The actual ground/water temperatures are 15-25 degrees colder at least, and are certainly not going to come close to boiling.

There are many complicated things like that that enter into it. Planets with an axial tilt will be hotter on average than planets without one. Having longer days/nights will affect the temperatures too. Atmosphere thickness decreases the variability of the temperature. Venus, with a thick atmosphere, has the same temperature over the whole surface. Mercury, with no atmosphere, is hot enough to melt lead during the day, on the equator, and cold enough to freeze nitrogen on the opposite side.

The more I look at Venus, the more I think a thicker atmosphere would be good for it. It would raise the average temperatures, but it would lower the distribution of temperatures much more, so you wouldn't see the months of 50 C torture on the equator that you'd see with an Earth atmosphere. It would also lower the perceived temperatures, due to increasing the speed the air conducts heat to any organisms walking around.

(For instance, if you go outside in 15 degree weather, it's very comfortable, pleasant. If you go swimming in 15 degree water, it's incredibly freezing cold. The increasing density of the medium increases its specific heat. An atmosphere twice as thick will have a much higher specific heat, so temperature deviations from the human body's 36 C will seem correspondingly hotter/colder). Heck, it would also increase the boiling point of water and block solar radiation. Less skin cancer is a good thing.

In fact, I think I just sold myself with this post.

This is exactly what I've been saying. A thick atmosphere will not have the high escape rate that a thin one has under the same gravity, due to the real gas law. What Mars lost over billions of years could take trillions if it had the atmospheric density required to create 1 bar of pressure. An Earth-like atmosphere with a distinct ionosphere layer will be more than enough to protect from the Sun's high frequency radiation. This occurs at Earth's poles, where the magnetosphere is weak or nonexistant. It occurs when Earth's magnetosphere enters a dormant phase for hundreds of thousands of years. Not having a dynamo is not a problem.

Now, not having geological activity except for the occasional fumarole or hot spring could indeed be a problem for Mars in the long term. We'll have to see.

The atmosphere retains the planet's geological heat as well as the Sun's input. I don't know the extent to which it does this. All I know is that atmospheric physics predicts a planet with Earth's atmosphere in Venus's position as having an average surface temperature of 25-36 degrees Celsius, compared to Earth's 13-22. Not as comfortable, but good enough. Removing the atmosphere until it's comparable to Earth in its mixture and density is all that needs to be done.

It's no more geologically active than Earth. Worldwide Volcanism would actually help cool the planet down in the absence of a strong greenhouse effect. It increases the planet's reflectiveness. Nice thing to have.

3.5% of Venus's atmosphere is Nitrogen. Removing all the CO2 would result in a Nitrogen atmosphere 3.21 times as thick as Earth's.

So the question should not be 'where do we get the Nitrogen from', but 'how are we going to get rid of all this extra Nitrogen'?