Submitted by Pornelius_McSucc t3_113l5ul in space
zolikk t1_j8r77xq wrote
Reply to comment by Pornelius_McSucc in Terraforming a magnetosphere possible? by Pornelius_McSucc
I don't think it's in any way critical to that. Those kinds of harmful waves, from UV to gamma, are mainly helped by having a thick enough atmosphere - its exact composition can matter too though (mainly for UV absorption). But initially all this requires is just dumping a lot of gas of your desired makeup onto Mars. The medium term stability of that atmosphere depends mainly on chemical (and eventually biologically driven) reactions near the surface...
Mars has weaker gravity so it won't be able to help hold onto the thick atmosphere long term. This is where a magnetosphere helps, because it can protect molecules in the upper atmosphere from being ejected by solar rays when in normal conditions they wouldn't reach escape velocity. But Mars' gravity is too low anyway, even with a magnetosphere it wouldn't be able to hold an Earthlike atmosphere forever.
The "easy" solution is to just keep adding required gases into the atmosphere. Which, if you were able to do it the first time, you can probably keep doing. This would still be a matter of millions of years, it's not like your Martian biosphere suddenly runs out of oxygen just because you forgot to add this year's oxygen supply.
Pornelius_McSucc OP t1_j8r86h2 wrote
I honestly think the better move for a permanent terraform would be Venus, and Mars would work well with a "temporary" terraform like you describe. Venus is the only planet with real potential to be a sister Earth. There are multiple processes theoretically possible that would convert its atmosphere to the right composition and lower the temperature, at an exponential rate. These methods in conjunction could completely change Venus in a matter of a few centuries. The biggest thing it seems would be to accelerate its rotation. Which is a lot more difficult for a type 1 civ than all the other tasks such as adding water and converting the atmosphere. The energy and technology required to exert a meaningful positive rotational force on the planet is well, astronomical. And you also have to consider that to turn on the geological magnetism you may need to divert a moon to Venus. But I think Mars could be great practice for these things on a planetary scale.
zolikk t1_j8r90fu wrote
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
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
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
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
> 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.
3d_blunder t1_j8vhssr wrote
Getting Venus to spin at a comfortable rate is IMO the big sticking point: doing so would probably involve so much energy the planet would be pure lava and take millennia to cool down.
northaviator t1_j9782ch wrote
Venus turns to lava regularly, on a geologic time scale. It's why there aren't many craters on Venus.
3d_blunder t1_j97s6ki wrote
TIL! Still, what mechanism could we use to increase its spin? If it happened to blow a big chunk of the atmosphere away I think that's a plus, no?
I'm still surprised that "total sun-shading" seems to have a consensus cooldown period of less than a decade.
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