My world, Anyare, has too many people on it. Instead of having a disaster, I want them to colonize another planet. Like Jupiter. By using Jupiter’s gases, and by attaching a giant propeller, is it possible to relocate Jupiter? All of Jupiter’s gases would be used up in the process of relocation, so it would leave a hot, significantly smaller planet. This would be solved by using the heat and hydrogen to create water. Look that up! There is a new jet engine that’s only byproduct is water! This sounds possible, doesn’t it?😂
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2$\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$– Community BotCommented May 21 at 12:27
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3$\begingroup$ You need to consider Jupiter's gravity. The gas would need to be accelerated above the escape velocity of Jupiter. It would take a heck of a lot of energy just to do that. $\endgroup$– David RCommented May 21 at 13:53
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1$\begingroup$ An SF novel worth seeking out: The Jupiter Theft by Donald Moffitt. The method employed to steal Jupiter is imaginative, to say the least, and somewhat persuasive. $\endgroup$– John DallmanCommented May 21 at 18:30
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6$\begingroup$ Not sure how a propeller would have any hope to move a planet. there isn't much atmosphere in space. There are no solid attachment points on a gas giant that be used with known materials. Unless your world/universe respects cartoon physics? $\endgroup$– Gault DrakkorCommented May 21 at 19:57
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1$\begingroup$ "heat and hydrogen to create water" in Earth's atmosphere using its oxygen. $\endgroup$– philipxyCommented May 22 at 1:15
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6 Answers
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The closest thing I could find is Isaac Arthur's youtube video on what is called a "fusion candle". The idea may work when we invent a truly stable and long-lived fusion reactor which can fuse hydrogen into helium without turning into a hydrogen bomb. The reactor has two jets running in opposite directions: One downward (towards the surface of the gas giant) in order to counteract the downforce from the other jet which jettisons gas into space. The principle is using jet to change speed and direction of the gas giant. Unfortunately, this is not feasible even in the far future. The reason being the negligible effect of the jet on the planet's orbit. It would require millions of such candles to yield a tangible result within the lifetime of the project designers.
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$\begingroup$ Isaac Arthur usually assumes a few future developments that put these projects in a different context. Namely extended life-time, so projects of a few hundred or a thousand years are not of the table. And an highly industrialized space economy, so making a million of something isn't a big deal. $\endgroup$ Commented May 21 at 13:25
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4$\begingroup$ @MennovanLavieren a great many sci fi projects start with "first, disassemble and disperse the entirety of planet Mercury" $\endgroup$– g sCommented May 21 at 18:35
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$\begingroup$ Plus Jupiter is a gas giant. There might be a "surface" or "core" of metallic hydrogen, but of course if you get rid of the gas, the pressure will abate and the core will expand. Note: This gas jettisoning will need to be at the escape velocity of Jupiter, and mass still is conserved, so I think instead of moving Jupiter via rocket, this method will end up pouring Jupiter a short distance away, or perhaps Saturn will claim the excess mass. $\endgroup$– chiggsyCommented May 22 at 15:03
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$\begingroup$ @chiggsy you can accelerate gas way faster than Jup's escape velocity, up to a thousand times faster if need be, it's just the portions accelerated will be smaller for the same energy expense. So not even Saturn or Sun would pretend to grab that gas, might be not even the galaxy would possess enough pull to counter that velocity. $\endgroup$– VesperCommented May 23 at 8:06
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$\begingroup$ @Vesper Ok, that's fair enough, but did you not want to do something with Jupiter? If you blow all the gas into intergalactic space then Jupiter will be gone, there's nothing down there but gas. Still same problem as before: When you blow enough of that gas away,Jupiter's core, of metallic hydrogen, which is the only soild thing about it, will experience phase change and rapid expansion. It's not like a neutron star, held together by gravity. Just pressure. $\endgroup$– chiggsyCommented May 25 at 0:29
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It is no plausible for humanity to relocate a planet or even our Moon (let alone Jupiter), to any significant extent at anytime in the foreseeable future and in all likelihood it will never be possible. Jupiter is simply too massive by too many orders of magnitude compared to the feeble efforts of mankind.
Jupiter has a huge gravitational well and any conceivable propellor would not be big enough, would not be strong enough, would not be able to rotate fast enough and would very rapidly be swallowed by Jupiter itself as the propellors orbit decayed.
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At a high enough civilization energy manipulation level, sure.
The problem is that the level required is probably not what you imagine your planet to be at. A K-2 civilization has already harnessed the entire output of a star; they have a dyson sphere or swarm that produces useful energy, and a civilization that exists almost entirely in space.
Planets aren't big enough to support the industry of such a civilization. They don't have a large enough surface to radiate the heat!
Moving Jupiter or disassembling it is a K2 civilization level problem. Jupiter is really big, and its gravitational binding energy is huge.
A chemical rocket both (a) doesn't work, because H2 only burns when you combine it with an oxidizer, and if Jupiter had oxidizers it would already be converted to water, and (b) is the wrong energy scale.
You will want things like planet-mass fusion rockets or self replicating robots powered by solar mirrors and microwave power transmission or other relatively exotic technologies.
In addition, such a civilization would find it easier to disassemble Mercury, Mars and Venus and build a new planet to spec than they would find to strip Jupiter of its atmosphere and/or move it a substantial distance.
In fact, on the way to K2 civilization, they probably already disassembled Mercury and converted it to solar power collectors.
The problem of getting a civilization's worth of people off a planet is still an annoying one, because the easy ways of doing so require so much power that the waste heat ends up boiling the planet. For the disassembly of Mercury that wasn't a huge problem, as the planet was being disassembled anyhow, but it gets in the way of having a biosphere on the planet you are leaving.
Anyhow, two semi-practical ways of moving Jupiter is to put a planet-scale ship in its atmosphere that runs a fusion rocket in two directions (down to support it, and up and out of the atmosphere to thrust). The gasses thrust out of the atmosphere act like a rocket this way. This isn't very practical, because you end up dumping so much heat into Jupiter itself that it will overheat.
Removing the gasses of Jupiter won't give you a rocky planet, not for a long long time. The surface of Jupiter is going to be exotic fluid/gas/solid substances due to huge pressure. By the time you strip the atmosphere above it, you'll have created a new Jupiter's worth of gas in the exhaust plume, which will over time gather under the force of gravity to... produce a new Jupiter with a different trajectory.
So what you are really doing is tearing Jupiter apart.
To that end, you can build some kind of floating system to shoot gasses from Jupiter up into orbit. Then capture it in orbit and do what you want with it. That will still take an insane amount of time for even a K2 civilization, but it doesn't waste as much effort on giving the planet a kick.
All of this ends up being much harder than just grabbing some rocky planets and smashing them "gently" together, waiting a few thousand or million years (with some speed up via active cooling), then using that resulting planet.
Even using "smash" to make a core, then carefully placing cooler material on top with insane numbers of beanstalks, is going to be faster and more practical than dismantling Jupiter sized planets.
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$\begingroup$ Consolidating a plume of exhaust into a new Jupiter won't be possible because of the plume's initial length. Let's say you blew off 1% of Jup over a year to slow the rest of it by several dozen m/s, this translates into escape velocity at infinity of several km/s, making the plume's length be 3.15e7 times larger, and its density would be comparable to a nebula, as the accelerator is not precise and the exhaust has a certain angle of divergence. The resultant cloud would also have a internal speed difference of the same value as Jup's over the year, and Jup is moving in an orbit... $\endgroup$– VesperCommented May 23 at 8:14
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$\begingroup$ This all means that the plume is not directed to the same sky point all the time, and is spread wider than straight; so the resultant gas cloud would not be gravitationally bound to itself and could only be absorbed by other planets, Jup included (but not in this year, the orbits of Jup and that gas should intersect before Jup would be able to capture it back). Otherwise, a very good answer. $\endgroup$– VesperCommented May 23 at 8:18
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Possible: Yes
It is possible to relocate planets. Check out the Grand Track Hypothesis, which describes the early history of our solar system in terms of the movements of the Big Planets into and back out of near solar orbits. The migration takes a while, so you're people will have to be patient! Propellers won't do it, but messing about with gravity might!
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I used to think that Jupiter's atmosphere would be very flammable because it had so much hydrogen, but it takes oxygen to make that happen. Almost all the oxygen in the solar system (outside the sun itself) is already either combined with hydrogen to make water, or with carbon to make CO2 (not methane, as I originally said!), or with something else to make rock or some other material. The free oxygen in earth's atmosphere is an anomaly caused by life.
And burning hydrogen with oxygen is never going to make enough thrust to move Jupiter, even if the oxygen were available. Chemical rockets simply are not energetic enough. In fact, according to this article, the effective exhaust velocity of a hydrogen-oxygen rocket is only about 4.4 km/s, much less than the escape velocity Jupiter (even less than that of the earth). So the rocket propellant would just fall back down to Jupiter, with exactly zero net acceleration of the planet.
So fusion is really the only way to go, and even that is truly not realistic. Then again, depending on the kind of story you want to write, maybe that's OK. You could imagine a bunch of space-based lasers, thousands of miles across, focusing on a point in Jupiter's atmosphere, setting it off like a million hydrogen bombs exploding per second. Again, completely unrealistic, but maybe kinda cool.
Larry Niven's novel A World out of Time actually imagines doing something like this with Uranus and using it as a gravitational tug to drag the earth to a safer orbit when the sun starts to expand in a few billion years.
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$\begingroup$ You just need a hotter candle to ignite hydrogen alone! Just turn to fusion! $\endgroup$– vidarloCommented May 22 at 6:18
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Plausible: yes. Possible: not in any acceptable time frame
After all, an ion engine powered by fusion and floating in Jup's atmosphere could accelerate gas particles fast enough for them to leave Jup's gravity well, thus accelerating Jup as a whole. Accumulating mass in L4/L5 of Sun/Jup would also alter Jup's orbit, the easiest thing energy wise would be moving trojans/greeks into one camp instead of bringing in mass from other places, yet Jup is BIG, not as big as SPAAACE tho, but it's big enough to require a significant percentage of Jup's mass to be affected by any kind of movement (blowing off with fusion candles/ion thrusters, or relocating as asteroids), thus this would require a lot of time to perform while using energies available to a civilization with only a single rocky planet at its disposal (aka Kardashev type 1 or below). So, the idea of colonizing Jup is off.
If there are other rocky planets in their system, they might decide to go colonize them instead, after all, blowing off the entirety of Jup's atmosphere (which is about 99% of Jup's mass BTW) is very energy consuming, and at that scale you're more like destroying a gas giant, instead of moving; while if there is a rocky planet somewhere nearby (Jup is also pretty far, Venus/Mars are way closer space wise and energy wise), with fusion candle tech it might be possible to move them instead to some orbit that would allow easier colonization and/or ambient temperature and solar flux. However, even this movement should be too slow to not resolve local problems on Anyare before attempting this. Only the option of colonizing a world as is is possible.
