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Comment by Teever | Hacker News Reader

I've wondered about the feasibility of transporting the abundant CO2 in the Venus atmosphere to Mars for the purposes of terraforming both planets at the same time.

It's been a while since I've done the the envelope math but if I recall correctly there is more than sufficient CO2 on Venus to provide an atmosphere for Mars the issue is just transportation.

The last time I thought about it I considered some sort of massive floating solar powered comet builder that would cool the atmosphere into large chunks of dry ice that could then be wrapped in a metal sabot so that the comet could be accelerated to mars via a mass driver.

As with everything in space and terraforming the key is scale so the equipment used would need to built in situ out of carbon from the Venusian atmosphere.

We are of course still a ways away from mastering self replicating carbon based engineering but the idea of terraforming both planets at the same time is neat to me.

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I love this idea, but there is something missing: nitrogen. You need to extract some of that from Venus as well, and bring it with you.

But if you really want to have fun with terraforming you should make Venus earth-like. I suggest an exciting starting point: build a solar shade at the Lagrange point and block the sun. That would eliminate most of the hard problems with Venus temporarily while we did whatever work is needed to get it spruced up. CO2 freezes to dry ice below -80C or so. You could let through just enough sunlight to get the atmosphere at a pressure humans can survive- then all we need is warm clothes and an oxygen tank.

Once Venus is in that state, the problem is simpler- how to get all the carbon and oxygen separated so that the carbon stays in some kind of solid form.

Oh, and we'll want to go get a load of hydrogen, likely from Jupiter, to mix with that Oxygen to form water. Your fleet of transports moving CO2 to Mars needs to make a detour on the way back.

Edit: fixed a word and also lol, just start with building a planet-sized solar shade, says some a-hole on the internet.

You still have to spin up the planet. An earth-like atomosphere would freeze solid on the dark side, and air from the light side would be rushing into the dark side, where it would freeze, until the light side was stripped of its atmosphere too. So the atmosphere would just be a mobile ice cap on the far side, rotating around the planet once per year, with the only gaseous atmosphere being a small, constantly-moving region of sublimation at the terminator betwen the light and dark sides.

Make the atmosphere thick enough to not freeze on the far side, and it'll be absolutely boiling on the near side. The slow rotation means that there is no happy medium: either you've got an atmosphere freezing solid, or you're cooking half the planet at any given moment.

> You still have to spin up the planet.

Do we? I think what you really want is to equalize the amount of solar radiation hitting all sides. And if I can build a planet-sized solar shade, well, why not go one step further and instead make a swarm of mirrors in orbit?

When they orbit the sun-facing side, they reflect the light away from Venus. When they're opposite, they're in darkness anyway. But when they're in between, they reflect light towards the dark side of the planet!

I choose the angle of every mirror in this swarm, and thus I choose the amount of solar radiation hitting each point on the planet at all times. Thus, Venus shall have one timezone, Venus Standard Time, and I swear to you it shall not have anything like Daylight Savings Time.

Not necessary, but convenient. Venus has very little water, so maybe impacting comets at the equator in the right direction would be enough to solve both problems

That would take more than a few comets. And it might, somehow, make Venus even less livable.

I read once that to slow Earth's rotation down to a stop, you'd need to perfectly sling 6 or more moons at it.

In the short term, probably. Not all energy from those impacts will be transferred to angular momentum.

Maybe blowing up the comets before they reach the atmosphere and giving them a larger impact area could help.

If you can build a planetary solar shade, engineer blue-green algae to survive the harsh conditions, and as soon as the temp on any part of the planet drops to survivable, seed the algae. It'll explode, sucking up the carbon.

Reactionless drives would be so nice.

Not only could you transport materials around, but you could make Venus spin in 24 hours in ~10^4 years using currenr Earth electricity output and a super-conducting emDrive -- I did the math a couple years ago.

Reactionless drives are indeed nice and really really dangerous - they make Earth shattering relativistic projectiles a bit too much easy to pull off.

Pair one such drive with a nuclear reactor and have it fly away from the sun for a while and then back - it will hit ludicrous speed on the way back, likely a good fraction of C. And there is hardly anything that can be done to prevent that as it needs just energy to gain speed, not bulky inefficient reaction mass.

There's really no substitute to mind-uploading when it comes to defense against kinetic stuff.

Yep - the ultimate solution fo many dangerous sitations - make the people in danger more robust or ideally effectively immportal. Solves a lot of issues & makes otherwise very complicated safety measures into much simpler ones.

There's really plenty of reaction mass around though. Could probably get it done quicker by having a few large drone ships that harvest reaction mass from the planet or nearby asteroids.

I would love to see an economic analysis of this. How many billions for the solar shade array, for example. How many years until the planet becomes livable with an oxygen tank. How many people would pay to live on Venus, and so on.

Solar shades the expensive way (as in right now, launch from Earth): https://www.youtube.com/watch?v=6yqi0FabHHs

After kickstarting a Lunar economy so you can manufacture and launch them well outside Earth's gravity well: https://www.youtube.com/watch?v=gOr-Gd58zu8

All this effort just to get sick at the bottom of another gravity well... Surely there's a nice moon of jupiter where the slippers would be a bit cheaper?

Need some damn heavy slippers there I guess. Compared to the radiation environment there, earths van Allen belts are a walk in the park.

It’s almost as if we’ve been given a planetary system with an ideal set of building blocks to get to the next phase of life. But instead we’re going to choose to destroy the planet we currently have.

Mars is probably not geologically active and has no protective magnetic field, so my first thought was to change that by hitting it up with a larger asteroid from the belt, preferably a metal rich one with significant mass. I first thought about its moons, but they are too small. I mean to achieve a complete planetary melting.

That would be step one, step two would be waiting a few million years and see how it turns out.

Such a cataclysmic event isn't necessary. https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmo...

The bigger issue with this idea would be getting enough hydrogen to Venus to create oceans. That would require hitting Venus with comets or possibly extracting hydrogen from a gas giant which seems impractical.

If you can extract materials from a gas giant it is probably best to just live around the gas giant. Short term Venus looks more amenable to life, though.

The radiation would be a significant problem.

142 comments and this is the only one mentioning ionizing radiation. Are you and I missing something that everyone else already knows?

That depends - where does energy come from. If we never figure out fusion, then it may be we can find the energy to extract a few materials, but not enough to live there long term. Depends on the material - a large platinum (very rare, the industrial need per year is greater than the total production in a century so industry makes do with something not as good) would be worth it, while iron is everywhere on earth so not worth it.

We already produce a significant quantity of ruthenium, rhodium and palladium in spent nuclear fuel and choose not to extract them. If these metals became more widely available the market price would collapse, which now would not justify both mining or nuclear reprocessing.

Going to space to mine a nickel-iron asteroid would be out, for very much the same reason.

Going to space to mine a nickel-iron asteroid makes a lot of sense, because the material is then already in space and you can use it for orbital manufacturing without having to pay the energy cost of getting it out of Earth’s gravity well.

I specified platinum for a reason. High value, and high potential demand. I believe that if supply expanded price would go up as industrial processes switch. (diesel catalytic converters would be better with platinum, but total world supply covers less than 10% of all diesel engines so they use alternatives)

The lighter platinum group metals are widely used as catalysts to produce large-volume chemicals. Off the top of my head there's methyl acrylate, vinyl acetate, acetic acid, many more.

Rhodium is especially scarce, palladium not so much, but it's a political metal, a substantial part of world production is not in the West.

Rhodium use would go up were it more available, lots of interesting chemistry there, and political security is also worth a lot, but extraction from nuclear reprocessing isn't happening. That's the intersection of politics and the markets, where markets become political.

Could we extract hydrogen from the outer planets and just shoot it at Venus? I.e. no tanks and transport ships, just a well-aimed jet of gas.

In principle, you could ionize the hydrogen and then accelerate a proton beam in the direction of Venus. But I think Venus has an active magnetic field powerful enough that it would be deflected off into space. Plus, accelerating mass out of the gravity well of a gas giant would be extremely energy intensive. Better to go looking for sources that aren’t at the bottom of a giant gravity well.

Why not let it cool off away from a plasma phase before hitting Venus?

I suppose you could fire a proton beam and an electron beam so that they would intersect before reaching Venus.

The problem is it is too far from the local star, so it's cold there.

This is sounding a lot like the Golden Age series by John C Wright. By the time when the novel's take place, they have cleaned up the solar system of all dust and comets/meteors

I say we sacrifice Enceladus to our Mars god.

If Hollywood taught me anything, it's that drilling into the stopped core and setting off nukes are the best way to get it started again.

I'd rather do that in a different solar system. Massive planetary collision like that is bound to have some unintended side effects.

What abput a world house instead ? https://www.orionsarm.com/eg-article/460e7e5f4977b

You basically start by building a roof over part of the surface, then you pump it full of breathable atmosphere and inhabit it. Then another part and so on until you have covered the whole surface or got bored by it. A huge benefit if that you can get (localized) results almost immediately instead of pumping massive resource into regular terraformation for possibly hundreds of years to only have useful results at the very end. Also you can do this on worlds that would never hold an atmospere (Moon, asteroids) or would loose it over time (Mars).

This is a common myth based on a misunderstanding of scale in the original facts. Yes, the atmosphere will blow away, but it takes millions of years.

As humans, we only have to top it off every hundred thousand years or so.

The magnetic field isn’t really a human scale problem. My understanding is that it takes on the order of a billion years for the solar wind to blow away anything but a hydrogen atmosphere.

Uv will break water and the solar winds will blow the hydrogen away. You'll need a lens to push the protons inwards so the don't blow the atmosphere away.

What water? Atmospheric or ground,? it still seems this would be a multi million year concern.

Atmospheric. We'd need a lot of water vapor in the atmosphere to power a greenhouse effect.

No,no! If you ram a giant asteroid into Mars, you will destroy all of it's crust, there will be no geology ir way to answer the question - was there ever life?

General rule: don't lift anything out of an Earth-class gravity well that you can get from a shallower dimple in spacetime.

Carbonaceous asteroids are pretty abundant, and Mars has oxygen in great quantity. The asteroid belt is also much closer to Mars than Venus is.

Nitrogen seems to be the building block that's a bit scarce. Venus definitely has some, but it's unclear that it's the first or best source to tap.

> Carbonaceous asteroids are pretty abundant

Phobos should have plenty of carbon too, and it's not really far from it. IIRC, it's close enough that with our current tech, we could build a "space elevator" there, that drags in martian atmosphere.

I’m sure the Martian crust has plenty of carbon to form an atmosphere. It’s a very common crustal element, and extracting it in situ is going to beat out any approach that involves transporting material through space.

There was actually a recent video from PBS spacetime on YouTube that did back of the envelope math on just this subject. The result is that you would basically have to strip mine the top three meters of the entire surface to get enough carbon, and the energy required for the chemical reaction would be something like 100 years of today's global energy production.

Sounds substantially easier than any approach that involves moving a similar amount of mass up the Sun’s gravity well.

You don’t really need to move “up” necessarily, right? You can drop “down” but into a more elliptical orbit that shoots far enough out to intercept Mars.

Moving "up" or "down" still requires you to change your velocity, which costs energy.

Did you mean a skyhook?

I still feel the best bet for terraforming Mars is deorbiting ice asteroids. They are already available and already solid. Can provide co2 or water depending on asteroid type. Still need a source of N2.

I think the first step is to cool Venus down. A giant parasol in heliosynchronous orbit (a bit inwards to compensate for the push light and solar winds give) seems to be the way to go.

Mars could require less mass. I'd go for a charged ring structure diverting protons from solar winds and focusing them into a spot on the surface to replenish the planets lost hydrogen and directing electrons towards the the edges so that the atmosphere would slow them down.

Imagine the autoras. After the sun sets, you'd see all those electrons plunging through the atmosphere and screaming in blue agony as they lose speed by hitting the CO2 molecules.

If you could connect a long hose between the two planets, you could use it as a siphon :)

I have a better idea: push Venus to an orbit between Earth and Mars and wait a little until Venus cools down a bit.

Doesn't work ;)

https://what-if.xkcd.com/143/

Oh shoot. What about a long and flexible Archimedes' screw?

If anyone finds this stuff interesting I can’t recommend Issac Arthur’s channel on Youtube enough. Regular out-there content on Megastructures, terraforming and the fermi paradox always grounded in real physics.

A space elevator that lifts chunks of atmosphere up till they freeze, and whips them towards Mars from the rotational velocity at the top?

A space elevator is too hard to build on Earth. I doubt insane temperatures and sulfuric acid rain makes it easier.

A sky hook might still work for this - an aitship based launch loop or RAM ion engines.

I love the thought. I also love the line of thinking here. I feel bad for having very different, mundane thoughts around getting rich with my next side project!

Mars' atmosphere is also 95% CO2. It's the pressure that makes the temperature so high in Venus, not CO2 concentration.

> It's the pressure that makes the temperature so high in Venus, not CO2 concentration

No, it's the partial pressure of CO2.

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