[thijson]

The issue with Venus and Mars is that there is no magnetosphere. Over geological time periods the hydrogen is slowly lost into space. All that CO2 in the atmosphere could become H20 given enough introduced hydrogen, and photosynthesis.

[Robotbeat]

Yes, geologic times, so like 100 million years or more, not relevant to human life timescales. But even Venus has substantial atmosphere still, including substantial amounts of hydrogen still (with enhanced deuterium concentration due to the atmospheric loss… which could actually be worth mining for nuclear power export).

Making a magnetic field on those timescales is easy, tho, compared to the other challenges. If you cool Venus down, you can place superconducting wires around the equator to generate a magnetic field. This is much easier than the terraforming you had to do.

[pavel_lishin]

Would it be possible to have the wires floating in space, instead of placed down on the surface?

[21asdffdsa12]

So parallel inward orbiting solar sails?

[PaulHoule]

Venus has a lot of atmosphere but very little water, maybe 1/1,000,000 as much in the atmosphere as we have in the atmosphere + ocean.

If you are interested in hyperlarge structures you could maybe spread out a really big foil to catch hydrogen from the solar wind and react it with oxygen in one form or another to make a large ocean.

[userulluipeste]

That induced hydrogen, which you're looking for, can very well be the material particles in the solar wind. They don't reach much the Earth because are mostly charged protons and thus collide with Earth's magnetosphere. However, the lack of a strong magnetosphere on Venus means that, once that carbon dioxide layer gets reduced to lower levels and the reactive (free) oxygen can stay below a certain altitude, that shower of hydrogen should naturally become water. Therefore, the key to water on Venus is the reduction of carbon dioxide levels and production of free oxygen.

I've touched this idea before: https://news.ycombinator.com/item?id=26575155

[glenstein]

My understanding is, insofar as we're talking about protection from radiation, Venus compensates for its lack of a magnetosphere with incredibly thick atmospheric cover that does the same work, in fact does it better than here on Earth. That's not to say we would say no to a magnetosphere if such a thing could ever be achievable.

[vidarh]

There's a degree of induced magnetosphere on Venus. Coupled with the atmosphere, you're far more shielded from radiation even floating high up in the Venusian atmosphere than on Mars.