zolikk t1_j8r90fu wrote on February 16, 2023 at 11:27 AM

Reply to comment by Pornelius_McSucc in Terraforming a magnetosphere possible? by Pornelius_McSucc

A funny notion concerning Venus, connected to the "necessity of a magnetosphere", is that Venus also happens to have no magnetosphere. Yet it is fully capable of maintaining a thick atmosphere over geological timescales. Despite being hotter and closer to the Sun, its gravity does the job of keeping the atmosphere on the planet. Well, other than H and He, which will be blown away by solar wind (though the Earth loses these over time as well).

Venus doesn't have water, which indeed might be related to its lack of magnetosphere. Water vapor in the upper reaches of the atmosphere can ionize, and the H can be blown off by the solar wind. This might be how Venus lost all its water in the first place, and why it has so much CO2 gas, because without water it won't become bound to rocks like it does on Earth.

So, naturally, the "simple" task of terraforming Venus is probably to "just add water". And yes, you are right, Venus might be a much better early candidate for terraforming due to this. It is closer to the Sun, it has the right gravity etc. Mars is a better candidate for early human (artificial) habitation, but if we can terraform Mars we can probably also terraform Venus and it'd produce better results. And I don't think you really need to accelerate its rotation (unless, again, you're trying to make a magnetosphere perhaps?)

kerfitten1234 t1_j8rewyz wrote on February 16, 2023 at 12:32 PM

Venus wouldn't be quite that simple. Water vapor is a greenhouse gas. Any attempt to add water to Venus would cause it's temperature to go up, not down. You'd have to cool Venus down first, then add water.

drgath t1_j8rurkx wrote on February 16, 2023 at 2:43 PM

Out of curiosity, what ways exist to cool down a planet like Venus, if you can’t just add lots of ice?

kerfitten1234 t1_j8rvx4o wrote on February 16, 2023 at 2:51 PM

Put a ring on it to shade the surface. A polar ring at about the right altitude might also give it a more earthlike day/night cycle.

danielravennest t1_j8tm679 wrote on February 16, 2023 at 9:27 PM

> the "simple" task of terraforming Venus is

To drag several cubic km of metallic asteroids to Venus orbit, heat up chunks with concentrated sunlight, and roll it into thin sheet metal. Then use it as a sunshade to block out the Sun from the whole planet.

On a time scale of 40 years the atmosphere will cool down. It takes so long because not only is the atmosphere much more massive than Earth's, but the surface rock layer just below the gas is also at the same temperature, and has to lose heat too.

The high ground on Venus will preferentially be cooler and lower pressure, so that's where you can start doing stuff.