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So, in the early years of interstellar colonisation, a planet called Uwa Ohuru starts to be terraformed. Uwa Ohuru is a Venus-like planet with a thick co2 atmosphere, (though not so thick that this co2 is at supercritical pressures) and scalding surface temperatures of up to 100 C or more.

Terraforming this planet will involve transporting 4 x10^19 kg (40 quintillion) of hydrogen from the local sun, 0.2 AU away, and dumping it into the atmosphere. This will react to form water vapour by the Bosch reaction, which will rain down to form lakes, seas and oceans. After this, it will be elementary to introduce plants, animals etc.

What I am asking about is the first part. These terraformers have the goal of completing this first step by the turn of the century or thereabouts; a timespan of 30-40 years. How can this much hydrogen be transported to this planet in such a short timespan?

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    $\begingroup$ There's a problem you have to solve first: how are you extracting the hydrogen from the star and cooling it? $\endgroup$ Commented Jan 8, 2023 at 20:01
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    $\begingroup$ Well, quite obviously, they need to transport 1.3E18 kg (1,300 billion tonnes) of hydrogen per year at a distance of 30,000,000 km. FedEx will be happy to quote a price. (Full disclosure: I have no affiliation whatsoever with FedEx.) $\endgroup$
    – AlexP
    Commented Jan 8, 2023 at 20:16
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    $\begingroup$ Do you have a gas giant planet handy? Or an ice giant planet? Or at least an icy moon? Any of these is a much more available source of hydrogen. $\endgroup$
    – fraxinus
    Commented Jan 9, 2023 at 13:52
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    $\begingroup$ There's a lot of hydrogen in the sun... perhaps you could deliver the planet into the sun. Technically fulfilling the contract. $\endgroup$
    – kaya3
    Commented Jan 9, 2023 at 14:16
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    $\begingroup$ Not even counting the temperature of the hydrogen at its source, how are you preventing or removing the heat generated just by dropping so much mass on the planet? $\endgroup$ Commented Jan 9, 2023 at 14:57

7 Answers 7

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They can't, just use some asteroids or moons.

Stars have massive gravity wells, and extracting resources from them is a huge pursuit that you wouldn't expect to finish within centuries. You'd need a dyson sphere style arrangement to do it, and probably would need to do something like ram a planet into the sun to knock loose the hydrogen.

As such, a much more realistic pursuit is to just ram a large asteroid into your planet. Ceres or whatever the local version is large enough, or a few moons from gas giants. This requires vastly less power, is much less hot, and could be done easily in a few decades with enough spaceships to move them.

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    $\begingroup$ Asteroids and moons have much more than just hydrogen in them. It would be much easier to find an ice belt or comets and redirect them into the atmosphere. You still get "contaminants" other than hydrogen, but at a much lower rate. As the story "The Martian Way" by Isaac Asimov shows, a cubic mile of water would be about what's needed (IIRC), and that might be easy enough to find in a single chunk. $\endgroup$ Commented Jan 9, 2023 at 17:59
  • $\begingroup$ They want a lot of hydrogen, more than comets or such would typically contain. They want a lot more than a cubic mile. See the opening post. $\endgroup$
    – Nepene Nep
    Commented Jan 10, 2023 at 1:26
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You're raising 4e+19kg of mass from the well of a star... well, that's going to take a lot of energy. At the 'surface' (for some definition of surface that applies to suns) our star Sol has a gravity around 28 times Earth, if I didn't drop some decimals somewhere in the calculation.

Best case scenario you're trying to lift free orbital hydrogen rather than mining the sun itself (quite a difference in transverse velocity), which according to Hohmann means you're going to have to add something like 20 km/sec to the orbital velocity of your hydrogen.

In total (again, assuming I'm not a complete dunce with the numbers) that's something on the order of 8e+27 joules - that's 8 octillion joules, or the energy of complete conversion of ~89 billion kg of matter. That's a not insigificant fraction of our sun's total energy output per second... but I guess you've got 30 years so you can amortize that to only around 8.5 quintillion (~8.45e+18) watts.

I'm already swimming in decimals here, so I won't even try to figure out the numbers for lifting from the sun itself, but I'm going to have to assume that it's going to be another order of magnitude. At least.

So... if those numbers are even close (and I'm honestly begging anyone to correct them), I think you're going to be extremely pushed to get this done in a few decades.

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    $\begingroup$ Just drop a big rock into the sun and catch the part that splashes. $\endgroup$
    – fectin
    Commented Jan 9, 2023 at 13:25
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    $\begingroup$ @fectin That would raise some mass, but not give it the tangential velocity required for an orbit. That's where I focused most of my calculations. $\endgroup$
    – Corey
    Commented Jan 10, 2023 at 1:40
  • $\begingroup$ That's the "catch" part - zoom a planet right through the splashing blob. (This will have no repercussions or unwanted effects whatsoever...) $\endgroup$
    – fectin
    Commented Jan 10, 2023 at 11:55
  • $\begingroup$ @fectin So... move a moon-sized mass of rock into a collision course with the sun, with enough energy to produce the largest CME of all time, timed to impact at the right moment so that the planet you're trying to terraform gets bathed in stellar plasma, which it will smash through in a matter of hours at best... I'm feeling like that might be tiny bit counter-productive. Just saying. $\endgroup$
    – Corey
    Commented Jan 10, 2023 at 22:51
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Blower.

Your blower orbits the star well down in the photosphere. Like the star the blower is powered by fusion, its fuel gathered from the star. In the star the fusion is happening down in the core. The blower gets hotter than the photosphere around it.

The blower uses fusion out in the photosphere to gather starstuff, heat it very hot and eject it from the star in a plume. This might be constant or it might be a sputtering series of explosions. The blower is trained on the world which needs hydrogen (and it will necessarily also get a fair bit of helium too) and this hydrogen will be coming in hot - some as hydrogen gas molecules but a lot as hydrogen and helium plasma and a lot of bare electrons. These reactive species will be ready to get busy with the CO2 of your world.

If you determine that your blower is not sending out hydrogen quickly enough to meet your needs, add more blowers. This might be a good idea anyway as from any particular position in this very low orbit any given blower will not always have a straight shot at the planet.

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    $\begingroup$ How would any mechanism work if there is no material which could survive that temperature? $\endgroup$
    – vsz
    Commented Jan 9, 2023 at 5:16
  • $\begingroup$ @vsz active cooling mechanisms. Push the heat out nearly as fast as it arrives. Most of the machine would probably be heat rejection by mass. $\endgroup$
    – BMF
    Commented Jan 9, 2023 at 7:40
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    $\begingroup$ @vsz Numerous ideas have been floated over the years by various sources on how to deal with this (for example, the cooling lasers used in Brin’s Sundiver), but the general consensus is that you have to use active systems to dump the energy back into the photosphere at a controlled rate faster than you’re absorbing the energy in the first place, ideally in a way that uses some of that heat to power the cooling mechanism itself. $\endgroup$ Commented Jan 9, 2023 at 20:46
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    $\begingroup$ @BMF The surface of the sun is the boiling point of tungsten. Far hotter than lava or molten iron. There is no material that can withstand this. An active cooling mechanism would somehow have to keep every part of the machine much cooler than the environment (a feat HVAC systems do not achieve). While staying buoyant in hydrogen gas. And dealing with extra heat from the fusion reactors. $\endgroup$ Commented Jan 10, 2023 at 23:00
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    $\begingroup$ @BMF: For any heat pump, no matter the mechanism, the hot end has to be hotter than the environment. What is this hot end going to be made out of? Also, "orbits the star well down in the photosphere". If is not floating but instead in orbit it must move about 400km/s. In the relatively dense photosphere (not the corona). That is not going to happen, so I assume that it would be either orbiting in the corona or floating in the photosphere. $\endgroup$ Commented Jan 11, 2023 at 7:09
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Magnets

Bear with me.

All the material that's swirling around the upper layers of a star has a strong electric charge. That's why these cool solar flares are visible:

Solar flare

Lifting material from the "surface" of the star is hard because of the deep gravity well and because anything you place there to do the lifting is going to get obliterated. So, use a magnetic field to "flare" material away from the star. Ideally, create a path that leads the material all the way to the planet, but failing that you could collect it at a safe distance and then haul it yourself.

You will need magnets a bit stronger than you can buy on geek web stores. Even forgetting the distance, you'll be competing with the star's magnetic field (which is obscene). This will require very careful and deliberate planning about how to slip your magnetic field into the mix. Solar cycles will probably impact your project, too, meaning that your progress could be limited by factors outside your control.

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  • $\begingroup$ Use a real image instead of an artists impression? $\endgroup$ Commented Jan 10, 2023 at 23:07
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Make the Sun hotter

Your terraformers can raise a set of reflecting mirrors to a low solar orbit, aiming them all to a certain point of its photosphere. If they would be large enough and able to maintain orbit while reflecting incoming light (and whatever mass they encounter, they had to be somewhat close to the sun and have to also be large enough, in the scale of thousands of kilometers across), they could be focused to a single point on the star's photosphere, effectively creating a local overheating. This, combined with chaotic nature of the star's magnetic field, will eventually provoke it to unleash a coronal mass ejection from there. Given that your sentient beings are deemed powerful enough to set deadlines to terraforming, they should be also able to calculate the influence so that the mass ejection would be aimed at the planet. Then, collect the ejected mass on the orbit and beam it down.

Yet, it's not guaranteed by Earth's science that this effect would actually provide enough matter to cover the terraforming needs of your heroes, so they should better stick to a back-up plan, and throw a large comet down the planet. Anyway there's no one yet on the surface to care about.

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    $\begingroup$ This is a nice idea, but it's not possible to focus light from the sun onto a spot on the sun, it would violate conservation of étendue. (Basically, the problem is that the mirrors have to be close to the sun to be able to focus onto it, but that means the sun is big from their POV, therefore its image will also be big and not a small spot.) ...What you could do instead is to use solar cells to power lasers, though that is obviously a lot more complex and lossy. $\endgroup$ Commented Jan 10, 2023 at 9:44
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    $\begingroup$ Well, it might be enough to redirect small portion of incoming solar light to the focusing spot, thus even flat mirrors could do, if there would be enough of them. "Etendue" is a nice issue, yet I don't need perfect focus, I need about 16x the energy flux at the spot so its temperature would raise 2x, and create enough disturbance to make the star unleash a CME. Anyway normal lenses can't make perfect focusing, as the Sun is not a dot light source, yet they are used to ignite stuff here. $\endgroup$
    – Vesper
    Commented Jan 10, 2023 at 10:53
  • $\begingroup$ Powering lasers with solar energy IMHO involves more losses than reflecting with a mirror, even if there won't be a small area of focusing, and even if 99% of energy reflected won't help the process. $\endgroup$
    – Vesper
    Commented Jan 10, 2023 at 10:55
  • $\begingroup$ Etendue means you can't do better than a flat mirror just above the surface which reflects light back down. But lasers powered by harvested hydrogen fusion would work, since the energy released by fusion vastly exceeds the gravity well, as long as the efficiency of the whole process was somewhat reasonable. $\endgroup$ Commented Jan 11, 2023 at 7:43
  • $\begingroup$ @KevinKostlan you're expecting those lasers to run on fusion energy of scattered hydrogen, no? Otherwise good old solar power elements would do better. I say there's not enough hydrogen reaching the orbit where lasers would have to be in order to not get burned up to provide enough matter to effectively ignite in fusion. $\endgroup$
    – Vesper
    Commented Jan 11, 2023 at 7:46
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Wormhole(s)

A slight frame challenge, but you don't fly a ship into the star, scoop out a bunch of Hydrogen, and then fly it back to the planet. Too much gravity and heat for anything short of Star Trek level tech, and even then the quantities of Hydrogen are to much.

Instead you drop a wormhole generator into the star. Its matching pair is in the path of the planet's orbit. The generator triggers, the wormhole opens, and the sun's pressure shoots the Hydrogen into the planet's path. Your scientists calculate the drop so that the generator portals just enough of the gas before it is destroyed by the star and the wormhole collapses.

Of course, depending on how long the generators can survive and the size of the wormhole, it may actually take multiple generators. And you may also need some other ships at the far side of the wormhole to keep the gas from dissipating too much before the planet gets there to pull it in. But in the end, far simpler, safer(?), and faster than flying out of a star and dragging all the gas back to the planet.

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My first thought is that since this is in space, giant Bubbles - essentially a thin membrane type material to enclose the gas and transport it.

In the context of Earth, currently - we are producing around 4 Billion tonnes of oil a year - so with a little future magic, moving 1,300 Billion tonnes of Gas isn't unfeasible.

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    $\begingroup$ Assuming you got the 1.3 billion tonnes per annum from Alex's comment - that estimate is three orders of magnitude too low. It might take quite a lot of future magic to move 1,300,000 billion tonnes of gas per year. $\endgroup$
    – Penguino
    Commented Jan 8, 2023 at 22:08
  • $\begingroup$ If Alex's comment is wrong - then yeah, the latter half of my answer would be likewise wrong :D $\endgroup$ Commented Jan 8, 2023 at 22:52

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