[bh42]

Mars has a lot less sun and atmosphere then the Earth, so terraforming it would involve a large investment in greenhouses and nuclear energy.

But Venus has an excess of sun and heat, and parts of its super dense atmosphere could potentially host floating algae, which absorb CO2 and rain down to the surface when they die. (Where they could burn and release all the CO2 again, but maybe a tiny bit stays out of the atmosphere.)

I guess what I'm saying is, we might be able to "seed" Venus and then sit by and watch as a carbon sink is created. And with less CO2 the atmosphere would start to cool off.

Now my very amateur understanding of Venus is that because the greenhouse effect creates super hot temperatures the magma underneath the crust of Venus does not form hot and hold spots like it does on Earth, it does not flow or erupt. There are no volcanoes, the crust is too "baked", too hard and thick.

But over long periods of time the crust still tends to break up: At a massive scale, planet wide, the whole planet surface is then covered with lava, the lava eventually cools and the cycle starts again.

This is why the surface of Venus looks suspiciously smooth except for a very few, very recent craters.

Now imagine we are able to "infect" Venus with life and it does manage to suck CO2 of the atmosphere and cool down Venus to the point where the surface of Venus can support liquid water.

It seems that could either trigger another planet wide cracking of the crust or maybe just huge volcanic eruptions. But I think once life is widely distributed even that could not expunge it. And with a much cooler atmosphere softer elements would not be baked out of the crust and the Venus crust would start to resemble Earth's crust, complete with softer and harder and lighter and heavier components and volcanoes.

And one day we could move in.

[hugh3]

If you want to wait long enough for Venus to start having plate tectonics, you're going to be waiting a long time.

By this point it's probably easier to tow Mars to a better orbit. Or just blow Venus up and make a (partial) Dyson sphere.

[dennisgorelik]

I have a better idea:

1) Populate Australia and Siberia first.

2) Convert some oceans into land (or cover oceans with land).

3) Colonize Antarctica.

If you still have not enough land to play with -- consider spending money on playing with Moon, Mars, and Venus.

[charlief]

If you want to populate somewhere, how about Canada and the unpopulated, beautiful plains out there to the north. It is already colonized but has virtually zero population density. The fact is people don't live there for socioeconomic, environmental, and political reasons. I don't think populating Antarctica and Siberia holds much value except as an experiment. There are plenty of places for people to live in.

If you refer to turning Siberia, Northern Canada, Antarctica into a useful piece of agricultural land, yes that theoretically has value, but I doubt is practical given the risks to our climate. Plus I hope advances in agriculture and mining will not require terraforming those regions.

I think the main value of going to the Moon, Mars, or Venus is to have people be on multiple terrestrial bodies to hedge some extinction risk, to begin some sort of space exploration infrastructure in the future, and maybe find significant economic value in mining. We need those benefits even if we haven't colonized or terraformed all of Earth.

[Vivtek]

The main value of going to the Moon and Mars is shallower gravity wells. The Earth is the largest terrestrial body in the Solar System - the most expensive place to live in terms of getting somewhere else, except for the gas giants where we can't live anyway.

Of course, in terms of life support it's by far the cheapest place around.

[InclinedPlane]

You are laboring under the notion that people want to travel to and live on other planets because there is not enough habitable land on Earth.

That's not the case. People want to go, that's all that matters. Eventually technologically and economically it'll be feasible for that want to be met, and it will be.

[cookiecaper]

This is kind of "putting all your eggs in one basket", though. If we're going to be terraforming and altering global or continental environs, we might as well do so on the Moon or Mars so that we have some insurance in case of nuclear war/meteor/other apocalyptic death scenarios.

[bld]

If you go through all the trouble to adapt to living in space for travel between the planets, why bother landing? Colonize the asteroids and short period comets, which are full of resources and much easier to access. No landing vehicles and ascent rockets are required. The gravity is so low that a spacecraft optimized for interplanetary travel can dock with them, or loiter nearby and transfer people & goods with space tugs.

Of course, it's a matter of preference. Many would still prefer to live on a planet. A dispersed civilization that includes the small bodies would be even more resilient to any one collision. More eyes out among the asteroids would also increase the chances of spotting potential collisions.

[dennisgorelik]

1) It's much cheaper protect yourself from nuclear war and meteors while staying on the Earth (e.g. digging down) than move to the Moon. Moving to Mars/Venus is even worse than Moon.

2) If you want to "insure" our civilization from disappearance -- focus on developing smart machines that can travel anywhere and carry our civilization accomplishments to other places. Sending people to other planets/asteroids is extremely inefficient in comparison with other options.

[jessriedel]

As charlief said, it's all about existential risk.

[jules]

Not cool enough to get the public to agree to put lots of funds into.

[Retric]

Seems like building a solar shield to reduce incoming light would be the simplest approach.

[hugh3]

On Venus? Still won't get you close to habitability. I'm not sure how long it'd take it to radiate its excess heat away, but it'd be a long time. And then you've still got an atmosphere which is horrendously poisonous and corrosive.

Besides, once you've got the technology and materials to build a solar shield which is an appreciable fraction of planet-sized, you might be questioning whether a planet is really the best place to live. Why not just live in your giant space stations?

[Retric]

Venus is 0.722 AU from the sun so it revives about twice the energy per m^2 than the earth does. Even if you where to remove the greenhouse gas problem it would be nowhere close to habitable.

If you look at the Day/Night cycle on earth 1 week without sunlight would probably drop Venus into sub zero temperatures. Depending on how much over kill you provided a few months would be plenty of time to cool down to reasonable levels.

[hugh3]

Even if you where to remove the greenhouse gas problem it would be nowhere close to habitable.

Per unit surface area, how much less sunlight do you get at Earth's poles than at Earth's equator? That's too hard for me to figure out off the top of my head (taking the seasons into account), but I'm pretty sure it's at least a factor of two. So I think a planet with an Earthlike atmosphere in a Venusian orbit would be habitable in the polar regions.

[Retric]

The summer temperature at earth's north pole is for June, July and August is 0°C or 273K. Assuming pure radiative cooling, twice the incoming sunlight (2 * 273K^4)^1/4 = 50.85 degrees Celsius or 123.53 degrees Fahrenheit for three months at a time. Which is at the outer edge of habitable.

However, the atmospheric pressure at the planet's surface is 92 times that of the Earth. So the difference in temperature in the summer is far less than the earth because a lot more energy is transferred to the poles. If you where to somehow remove that atmosphere not just change it's composition the poles may just barely become habitable.

Also wind speed is temperature dependent (Wind being a heat engine) so even with earths atmosphere a lot more energy would make it to the poles in summer.

[vlisivka]

Why you need to build planet-sized shield? Why not pollute top layers of atmosphere with something bright? SO2 will be good choice. One satellite with few tons of SO2 can pollute Venus atmosphere in few weeks, and it will stay polluted for thousands of years.

[InclinedPlane]

I don't get it, is this a joke?

There is already a crap-ton of SO2 in Venus's atmosphere (about 40 teratonnes, to be precise), that's where the sulfuric acid clouds come from. If we sent a supertanker full of SO2 to Venus every single day for a thousand years we wouldn't affect the amount of SO2 in the atmosphere by even 1%.