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Comment by modzu | Hacker News Reader

well you said it: we know exactly how to heat up mars (greenhouse gases) but its not so clear how to cool down venus. also mars has water.

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We don't need to cool it down. We could float a platform about 49.5 km above the surface of Venus, where the temperature and pressure nearly match the earth at sea level. To launch a probe, we could simply drop it from the platform.

This article about Venus is very enlightening: https://en.wikipedia.org/wiki/Atmosphere_of_Venus

my comment was in response to parent saying venus was a better candidate for colonization than mars.

but i am totally on board with exploring venus, although im not convinced the atmospheric issues are significantly lesser than the surface, just different (hurricane winds, sulfuric acid, etc)

How would we float a platform at that height?

By attaching it to a steel balloon filled with breathing gas, which can provide lift in the Venusian atmosphere.

Inside the baloon you get a really nice habitat with the correct Temperature, pressure and gas composition for humans to live in.

Other than a basically unlimited supply of CO2 however, what would the advantage be compared to a just a space station?

With Mars, you can mine building materials from the surface.

CO2 has carbon in it. Strip off the oxygen to breathe, the rest makes very strong building material.

Attach hydrogen, you get rocket fuel. Or plastic. Bind in some nitrogen, you can have proteins. There is probably silane lower down; send down a balloon to collect it, for silicon. Or all the way to the surface, to collect rocks.

Nuke power is totally practical there; no shielding needed, or worry about leaks; you just hang it a mile below your living-space balloons.

You can live there long term since there is gravity.

Also, there is a lot of protection from radiation, from the mass of atmosphere above you and the mass of the planet below you.

Is Mars' gravity too low for long-term habitation?

I know that we know that zero-G is a negative, but do we have any idea if it's a threshold that needs to be reached, a linear response to G-force that scales from untenable to fine, etc?

I would imagine that it's going to be a gradient. Just like any other form of exercise, the more effort you put in, the more positive effect. Humans would need to put in much less effort on Mars. Once we are spread across the solar system there will probably new exercise systems for 0 and .3 G environments.

I am also unsure about how it would affect the prenatal development as the way "layering" occurs is highly dependent on gravity.

The only way to really find out is to go there and live for a while :)

We can float things in the earth atmosphere at sea level. My completely ignorant prior is that we should be able to do it there too, if the temp and pressure are the same.

Much better: the air at normal pressure is much denser, so ordinary breathing air supports a balloon.

Most methods of flying things through Earth's lower atmosphere should apply well to Venus at 50 km: balloons, planes, helicopters, etc. To gather energy for rotors, maybe we could siphon heat from below to power a generator or other type of converter.

Just playing with ideas. :-)

Send your mining robot below. It cools itself with phase change liquids, but also opens high pressure tanks to the 90 bar atmosphere. When you hoist it back, just plug those pressure tanks in to turbines connected to generators. That wouldn't be a huge amount of power, but maybe wildcat prospectors could operate like that in the early days.

Would it be enough energy to compensate for the work you'd need to do to lift the robot back up? Presumably there's some energy gained from sending it down but not enough to bring it back, especially since it is coming back heavier. I just don't know how to work the math on that.

Lisa, in this house we respect the laws of thermodynamics!

Why not use liquid oxygen as the phase change liquid? Then the gas could be caught in a bladder tethered to the ground. When it comes time to ascend, use it as a balloon?

There must be some way to exploit the temperature difference between the surface and 50km up, without mega-engineering.

Hmm, maybe some variant of a solar updraft tower where hot lower atmosphere gases are siphoned up to generate power and heat lifting balloons?

OK that's just opened my eyes a little. It sounds so obvious - if the atmospheric pressure is the same then yes we should be able to fly aircraft. Maybe not with the engines used on Earth but in principle at least. Slightly terrifying that a loss of power should result in a 50km drop to a crushing hot acid death, but probably not much worse in reality to smashing into rock like you would on earth. Very interesting comment - thanks!

> "Most methods of flying things through Earth's lower atmosphere should apply well to Venus at 50 km: balloons, planes, helicopters, etc."

The kind of flying logistics needed to operate a station like the one proposed is something that hasn't been demonstrated on Earth, so doing it on Venus seems like one hell of a stretch. The closest match is the airship aircraft carrier experiments, which did not go well. If it can't work reliably on earth, how can it work reliably above Venus?

I think it's one of those things that looks great on paper but in reality has a ton of trouble. I think airships are like that on Earth and on Venus.

Have you heard of Murphy's law?

Floating above Venus provides the benefits of a gravity well, but there's the danger of sudden buoyancy loss.

Everything about exploring space and planets is a rebut to Murphy's law.

Very cool NASA video: https://www.youtube.com/watch?v=0az7DEwG68A

We don't need to cool Venus down, but in a few hundred years we might need to cool the earth, so learning how to do that on Venus might be a good idea.

Just because you are at sea level, you can't suddenly float stuff in the air. I like your optimism though. :) I was imaging a floating city like cloud city in star wars [0].

[0] https://www.starwars.com/databank/cloud-city

This is a bit more thought out than perhaps OP applied, several theretical investigations have been done into floating cities on venus and it more or less comes down to building blimps out of gasses like nitrogen and oxygen. Because the venus atmosphere is so dense, this would actually work.

I would love to read about those investigations. Do you have any pointers?

https://m.youtube.com/watch?v=BI-old7YI4I&feature=youtu.be

What if your float thing pops? Everyone sinks and dies??

Mars' atmosphere is 95.3% carbon dioxide, which means that the problem we have to solve is not "how do we inject craptons of greenhouse gas into the atmosphere" but "how do we stop the solar wind from stripping away the atmosphere," which is not a problem we have a clear idea as to how to solve.

Contrary to popular belief, the rate that solar wind strips Mars atmosphere is so ridiculously low that we can comfortably kick the problem of stopping it down the road a few hundred thousand years. If we manage to generate a habitable climate by terraforming with additional heat and atmosphere, adding a magnetic field becomes a very low priority.

Venus has more carbon dioxide in its atmosphere and has the added bonus of the surface being pressurized like you are deep sea diving....

Sure but we got to survive till we could clear carbon dioxide

Carl Sagan once proposed an interesting concept of terraforming Venus by floating some kind of bacteria in its atmosphere. The bacteria would be constantly drifting down to the surface and dying, but with no predators and ample resources, multiplying quickly enough to replace the losses, and small enough to be kept aloft by air currents. Gradually they would transform the carbon back into solid mass, and bring the atmospheric pressures and temperatures down to earth levels.

Later on in his career he decided against that scheme, but with our progress in biotechnology, it might be the only feasible approach.

https://en.m.wikipedia.org/wiki/Terraforming_of_Venus

I wouldn't say we know exactly how to heat up Mars. Without a magnetic field, any atmosphere we conjure out of the polar regions would escape into space. We are far, far closer to completely reversing the effects of climate change on Earth than we are to teraforming Mars.

Yeah, but I believe it takes ~10 million years for a Mars atmosphere to escape.

So it could be entirely feasible to treat the Mars atmosphere as a tire, that you "inflate" every now and then to keep the pressure constant.

That would be a very wasteful use of precious volatiles though.

But we could kick up a magnetic field with superconducting rings around the poles though.

Losing 0.00001% per year is not "very wasteful" to me.

There are ideas for putting up a magnetic field based on putting a contraption in whichever L1/L2... point is between Mars and the Sun.

Convert that into tonnes, and then calculate how much biosphere could be supported with that volatile weight. And once it is gone, it is gone. It’s not a renewable resource. You’d be trading away billions of years of future Martian biosphere.

Oxygen and nitrogen are hardly rare substances in the solar system, and probably not even on Mars. There are near infinite number of "tonnes" on Mars.

Besides, if the alternative is to leave Mars dead forever, I'd rather let it live for a billion years.

But maybe I don't get what your alternative is, if any?

Nitrogen and hydrogen are basically only really available via volatiles. They aren’t components of common minerals in the rocks.

The alternative is to spin up a magnetic field with superconducting magnets to protect that atmosphere from the solar wind.

well obviously we'd need orbiters that generate an artificial magnetic field my man!

http://www.nifs.ac.jp/report/NIFS-886.pdf

We do know how to cool Venus. Build a sun shade. It’s an old idea, and a simple idea, and there’s lots of engineering literature on how it can be reasonably accomplished.

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