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So, a fairly high-tech civilisation is looking to terraform Venus. This will first involve accelerating its rotation from 243 days to 24 hours, in order to cool it down and strengthen the magnetosphere. Having explored the idea of crashing an asteroid/moon into the planet in this question: amount of mass needed to speed up Venus rotation, I have deemed this an unpalatable idea; steering the missile might not take long, but the time taken for the surface to cool down, quite simply, will.

So, what are some other methods to speed up venus’ rotation without a massive collision, which a civilisation below the first kardashev level could use?

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  • $\begingroup$ Without knowing what tech your civ has, it's tough. $\endgroup$
    – Boba Fit
    Feb 3, 2023 at 16:18
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    $\begingroup$ Btw, you don't need to reheat a planet's core to provide a magnetosphere. There are better alternatives. $\endgroup$
    – BMF
    Feb 3, 2023 at 21:16
  • $\begingroup$ Oops. I saw "first kardashev" but missed the "below". So I deleted my answer. AKA not possible. $\endgroup$
    – DKNguyen
    Feb 4, 2023 at 7:23
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    $\begingroup$ VTC:Duplicate of your own previously asked questions. (List). I'm even going to down vote because, frankly, asking the same question over and over and over is the echt definition of "this question does not show any research effort." $\endgroup$
    – JBH
    Feb 5, 2023 at 5:52

6 Answers 6

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Probably not possible

XKCD author Randal Munroe already did some math on how much energy we would need to spend to get rid of leap seconds on Earth. We would need to hit the Earth with a Chicxulub-sized rock every other day for a decade.

For another question I mathed out the energy involved in such an impact. Just one impact like that releases about as much energy as what will ever be available in fissile materials in the crust of the Earth.

A K1 civilization can use two orders of magnitude more power than that. A civilization that is just transitioning to K1 might be able to do it using their whole energy budget and would still take millennia, but really below K1 they would be limited to energy sources in the planet + some solar so they wouldn't be able to change the angular speed of a planet much.

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    $\begingroup$ This. I wanted to come up with something clever, but the sheer energy needed to affect a change in rotation is out of the question for a sub-K1 civilization. $\endgroup$
    – BMF
    Feb 3, 2023 at 17:38
  • $\begingroup$ @BMF I could have sworn I saw a mention of a K1 civilization in the OP's post. Maybe it was one of his comments that was removed? $\endgroup$
    – DKNguyen
    Feb 4, 2023 at 7:22
  • $\begingroup$ @DKNguyen from the OP post: "which a civilisation below the first kardashev level could use?" $\endgroup$ Feb 4, 2023 at 17:10
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    $\begingroup$ @TheSquare-CubeLaw Yeah, I just noticed that. I missed the "below". $\endgroup$
    – DKNguyen
    Feb 4, 2023 at 18:53
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No Hard Science

If we aren’t using the hard science tag, then we can start to have some fun.

  • Add moons: If your civilization can move large bodies out of orbits, then drop a moon or two spinning around the planet. Yes, you’re talking a fairly slow process, but if the goal is to speed up the planet without messing up the surface, it might work.

  • giant jets: Another pretty wild idea would be to build huge jets to vent excess atmosphere. Like an Ancient Greek steam engine, blast jets of high- energy particles off the planet. Again, extremely slow, and likely only part of the solution, but it’s an idea.

  • Sun spinner: Do you remember the little solar-powered spinners in a vacuum, where one side is dark and the other light? I don’t know how the details would work, but if you blocked PART of the surface with orbital shields to help cool the planet anyway, leave one side unshielded. The pressure of photons should push on one side, but not the other. It would (surprise!) really slow, but (again) carrying out two tasks at once. Possibly reflectors pushing on the other side but in the opposite direction? Such mirrors may also allow an interim artificial day/night cycle. Or maybe excess atmosphere can be selectively ablated somehow.

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Use blimps, make the Sun do the work

Let's start by looking at why the planet is rotating the way it is. It's close enough to the sun that it should be tide locked, but instead we find a planet that's actually counter-rotating.

Here's an explanation of why. The short version is that its thick atmosphere is blowing at 900mph due to convection and the solar wind pushing on its leading edge. The atmosphere is thick enough, and the pressure at ground level is so high, that it counters the tidal force enough to give it 18 days of counter-rotation per year.

Let's reverse this. Float an ocean of blimps in the upper atmosphere, with a reflector that kicks light back out of the atmosphere on the leading side of the planet, and one that directs it to the ground on the other side. This should reverse the direction of the wind in a relatively short time span.

When the wind is fully reversed, you tether the the blimps to the ground, increasing the atmospheric drag, producing rotation. Let the sun do your work for you!

While that's going on, you can grow moss on the blimps and start converting CO2 to oxygen. This can also be tuned to allow Venus's surface to cool. The sulfuric acid would precipitate out.

I don't know where you'd get the water to grow the moss. With all of the oxygen you're generating, you'd want to move hydrogen in from Jupiter, but I'm sure a K1 can figure that out.

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  • $\begingroup$ Fascinating article! This seems to me similar to how raw eggs rotate differently than boiled ones :) $\endgroup$
    – ntg
    Feb 5, 2023 at 7:52
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Use Mirrors Creatively

Let's say, for the sake of argument, you have a mirror in place to keep the sun off Venus so that it cools down. Why do you need to make the planet spin? If you want a day-night cycle, just put a mirror in orbit that acts as an artificial sun. It will catch some of the sunlight and focus it back on the planet, but instead of being at the mercy of the sun, you can change the speed, size and angle of your sun-mirror to control how the sun works on your planet.

Give the mirror a little bit of an inclination relative to the sun and planet to give it seasons like on earth, although you might make them less extreme, cooler summers and warmer winters.

According to that gruff engineer guy: "But if your determined to spin up this [female doggo], theres always plan B"

Use a Space Elevator

If you have the technology and material science expertise to build one, just build one and use a rocket at the end to spin it up.

If you don't however have that kind of engineering prowess, or don't like space elevators, then just building cables from the surface to high above the exosphere (outermost layer of the atmosphere) maybe halfway between low and medium orbit (about 1/6 the way to geosync) and use rockets to keep the space station(s) aloft, and secondary engines to make them spin.

The rotation of the stations would drag the planet with it, albeit rather slowly (lest the cables be ripped out of the ground), and transfer the new angular momentum into planetary rotation.

If you want to be cheap about it, put solar collectors on the stations and beam power from the giant mirror-shield you'd need to cool the planet off, and use it to power the engines.

Not only will you shade and cool off the planet, you could use this energy to syphon off the Venusian atmosphere and power CO2 and N2 hall-effect engines, or just superheating the gas into a plasma with directed sunlight and run the station like a thermal rocket.

You Have Bigger Fish to Fry

Personally, I would be more concerned with how the hell you plan on moving that much frozen CO2 off the planet, as you'd need something reminiscent of a dyson swarm (it isn't even that big, just a thin belt of mirrors lower to the sun than mercury) collecting a few exawatts (maybe just two or three) to power your operations. (For reference, the sun puts off a few hundred thousand exawatts, each being one thousand petawatts, each of those being the combined energy consumption of earth.)

I recommend watching Kurzgesagt's videos on the topic of terraforming Venus and Mars, as they both have helpful information. Especially if you want to do it on the fast and on the cheap.

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    $\begingroup$ There's no stable synchronous orbit around Venus; Its rotation is so slow that any potential synchronous orbit would have a semimajor axis more than 50% larger than Venus' Hill sphere's radius. As a result, traditional space elevators are out. $\endgroup$
    – notovny
    Feb 4, 2023 at 23:47
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    $\begingroup$ @notovny ah, crud. I forgot that it needs to be rotating in the first place to work. $\endgroup$ Feb 5, 2023 at 0:04
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This is a quasi-hard sci idea. I don't think a civ < 1 Kardashev could even begin this. But an equal and opposite reaction.

Construct a tube around the planet, near ground level or maybe underground, containing an almost ideal vacuum, lined with superconducting magnets. Circular rail-gun. Produce and beam in who-knows-how-much power across the solar system. Absorb and beam out the waste heat, somehow. And then just accelerate a really big ball of iron around in the opposite direction for a really long time.

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Black holes obviously

Make miniature black holes in the lab. They will drift down to the centre of the planet. The overall mass of the planet will not change but the black holes will concentrate the mass at the centre. The planet will gradually collapse into the void at its core and its overall radius will shrink. The ice-skater effect (Law of Conservation of Angular Momentum) will cause the planet to spin faster.

The terraformers are confident that, once the correct radius has been achieved, they will somehow be able to stop the shrinkage. This information is currently top-secret.

Edit I thought I had invented the term "ice-skater-effect" when it comes to planetary rotation but, lo and behold, I looked it up and someone got there before me! https://mirror.uncyc.org/wiki/The_Ice_Skater_Effect

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    $\begingroup$ "Make miniature black holes in the lab." No. People really underestimate how much energy that takes. Think about it, a Star 100s of times more massiv than the sun imploding SOMETIMES makes a black hole. There is absolutly no way anything under K3 can even realistically consider making a black hole. $\endgroup$
    – ErikHall
    Feb 4, 2023 at 19:22
  • $\begingroup$ Unfortunately, black holes don't "drift" downwards, they fall at maximum local acceleration, completely unhindered by any material constraints, unless they're charged so strongly that the charged container made for them is already tearing itself apart. Also, black hole dropped into the planet slowly eats it, causing earthquakes at least. Also, black holes radiate Hawking radiation more strongly the smaller they are, so a "miniature" black hole blazes like a star and loses mass quickly. $\endgroup$ Feb 5, 2023 at 1:32
  • $\begingroup$ to add to @ChristopherHostage , any, literally any, black hole you could even attempt to make when you are K3 has a mass of a few ton´s at most. Meaning it would disappate duo to Hawking radiation, for all intend, instantly. Releasing all of that energy. Furthermore, such a black hole would be so small that it would be physically impossible to "feed" it with mass. As the Event Horizon would be to small. $\endgroup$
    – ErikHall
    Feb 5, 2023 at 4:33

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