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This question already has an answer here:

The sun is going out, so we decide to use the earth as a generation ship. We plant bombs in various locations of earth's crust and core, which uses a portion of the earth as propellant to send the larger portion towards our destination.

This appears to have several advantages:

  • We can save nearly the entire human race.
  • We don't need to build a massive structure capable of artificial gravity.

However, there also appear to be other disadvantages:

  • Weather. This is going wreak havoc on our ecosystem.
  • Mass relocation. Let's not kill everybody that was on the propulsion portion of the earth, yeah?

Some other details:

  • The explosions aren't simultaneous. We'll ensure that the acceleration towards our target is a gradual one.
  • We'll also assume that the governments are on board. This is a radical move, but we'll assume the conditions were extreme enough.
  • We've got enough energy stored to last us the journey. We do need to leave because eventually our supplies will run out.

Would a futuristic civilization capable of building a traditional generation ship be able to send the earth as a generation ship instead? If not, what additional hurdles would they need to solve?

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marked as duplicate by L.Dutch, Josh King, dot_Sp0T, Frostfyre, Bellerophon Jun 17 '17 at 18:43

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ You need to consider that your scenario takes place 5 billion years from now and pretty much anything you want might work because someone invented a way of doing it. That far into the future all is left to the imagination. Our current understanding was obtained in about 300 years, we cannot even begin to make suggestions what might be possible in 5 billion. $\endgroup$ – Raditz_35 Jun 16 '17 at 16:11
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    $\begingroup$ Very related. $\endgroup$ – MozerShmozer Jun 16 '17 at 17:53
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    $\begingroup$ @Raditz_35: The only thing that's even close to certain is that the human race will be extinct long before 5 billion years from now. $\endgroup$ – jamesqf Jun 17 '17 at 4:33
  • $\begingroup$ better and not totally theoretically impossible methods of moving Earth: 1) Build super giant gravity generators to generate gravity ahead of the planet Earth to pull it along. 2) build super giant warp drive generators to move Earth through space faster than light. 3) create the mouth of an artificial wormhole ahead of Earth as it orbits the Sun. Earth will enter the wormhole and emerge from the other mouth in a distant solar system where it will have the right velocity to go into orbit around another star. $\endgroup$ – M. A. Golding Jun 17 '17 at 23:26
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Planting bombs to leave orbit is utterly infeasible and is a scale error. There are many questions here already about moving planets and you can read the extensive discussions that have already taken place.

We'll ensure that the acceleration towards our target is a gradual one.

Graph

You need to understand about orbits. Try playing Kerbal Space Program.


If the sun goes out, what is the benifit of leaving a dark sun for a dark interstellar wandering? You have the same issues of dealing without sunlight, already! Breaking orbit does not buy you anything.


Would a futuristic civilization capable of building a traditional generation ship be able to send the earth as a generation ship instead? If not, what additional hurdles would they need to solve?

No. It is much harder to move a planet than it is to make a space ship. So a civilization capble of launching a generation ship will be nowhere near capable of sending their world on a similar voyage!

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    $\begingroup$ When the sun dies it will not just go out, it will eat the Earth. When the sun runs out of hydrogen, it will turn into a red giant and expand to the radius of Earth's orbit. space.com/22471-red-giant-stars.html $\endgroup$ – BobTheAverage Jun 16 '17 at 16:05
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    $\begingroup$ @BobTheAverage It really depends "go out", because red giant is billions of years away, it may not be what the OP is talking about. The OP might be talking about someone flipping the light switch on neptune. $\endgroup$ – Yakk Jun 16 '17 at 17:34
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    $\begingroup$ Admittedly, KSP cheats in some places, so its orbital mechanics aren't 100% (it uses a nearest-cone approximation and bypasses the Three Body Problem) but it's certainly better than pencil and paper. $\endgroup$ – Draco18s Jun 16 '17 at 18:58
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    $\begingroup$ @BobTheAverage Good point; it isn't realistic that anyone could survive the pressure to reach the surface of Neptune where the switch is. $\endgroup$ – Yakk Jun 16 '17 at 19:44
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    $\begingroup$ @Yakk I think you misunderstand Bob's point. It's not the pressure to hit the switch, it's the fact that the switch is clearly going to be heavily guarded by the neptunian guards. $\endgroup$ – k_g Jun 17 '17 at 0:54
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As JDlugosz's answer pointed out, the kind of acceleration to change a planet's orbit is huge. The change in velocity to escape the sun's gravity is even larger than that. However the sun will not simply go out, it will turn into a red giant and then a white dwarf. White dwarves are almost eternal.

However the question makes a fundamental error about the death of the sun. When the sun fuses all of its hydrogen, it will not merely go out, it will swell into a red giant that will engulf the Earth. Fortunately this is a gradual process, and Earthlings have a billion years to prepare. You can move the Earth out to mars's orbit, and find ways to deal with all of the other problems that come with the sun being huge and red. Presumably red giants still have a habitable zone. From the previously linked source:

Stars spend approximately a few thousand to 1 billion years as a red giant. Eventually, the helium in the core runs out and fusion stops. The star shrinks again until a new helium shell reaches the core. When the helium ignites, the outer layers of the star are blown off in huge clouds of gas and dust known as planetary nebulae.

After you got comfortable around Mars, huge clouds of gas and dust appear and threaten the Earth again. Somehow you survive this using your several billion years in the future technology. Once the red giant sheds most of its mass, it turns into a white dwarf. Now you have to move your planet back in a close orbit around this tiny stellar remnant. If the Earth has survived all of this, you are set for a very long time, white dwarves are close to eternal.

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  • $\begingroup$ The eternal lifetime of a white dwarf; do you include a black dwarf? If not, we are only talking trillions of years. Eternal pfah. If so, a black dwarf really isn't useful for making a planet habitable, but they should last much longer than mere trillions of years. $\endgroup$ – Yakk Jun 16 '17 at 17:38
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    $\begingroup$ @Yakk When something's lifetime is on the same order of magnitude as the lifetime of the universe, I start throwing the word eternal around. Protons are not strictly speaking eternal. Nothing is. But no I don't include black dwarfs. $\endgroup$ – BobTheAverage Jun 16 '17 at 17:43
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In addition to what JDługosz has said, you are talking about blowing up a perfectly functional generation ship and expecting it to still work.

Earth has been supporting human life for about a million years. By breaking Earth into chunks you will disrupt just about every system on the planet such as:

  • The atmosphere
  • Gravity
  • The hydrologic cycle
  • The magnetosphere
  • The oceans

This will make things much worse for all life on the planet.

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What JDługosz and others have said plus:

Even if you could get the Earth out of the Sun's gravity well (reach escape velocity) without destroying it in the process, the plants will die and then everything will freeze.

If you don't make it out before the expanding red giant phase engulfs the Earth, everything on the surface will be crisped and the atmosphere and water will be burned off.

Of course, you could drill down into the crust until you reach an area that is kept warm by the core of the planet to build living space. That should stay warm for quite a while. The drilling (getting enough material up to the surface to make enough livable space) and reinforcing it (the deeper you go the more rock is pushing down on your cavern) will take a lot of resources. You have now turned the deep caves into a generation ship that will take at least as much effort to make as actual ships. Then you have to lug 5.972 × 10^24 kg of unusable rock just to deliver a dead planet with people living in it to another star.

And, if you have the tech and energy to safely move the planet and provide a source of light and heat for the surface, why not just fix the Sun? That problem should be at least in the same level on the Kardashev Scale.

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You are making the mistake of consider the Earth "stiff", when you should be treating it as about as fragile as foam. Any explosion strong enough to move the Earth from its orbit is likely to crack up the Earth into pieces; even the collision that we believe created the moon probably did not alter the orbit of Earth by much at all; while making the entire surface molten for many miles deep.

On the other hand, I have seen mathematically correct plans for altering Earth's orbit; the idea is to take an asteroid about 1/2 of 1% of the Earth's mass (around half the mass of the Moon) and put it into a steered elliptical orbit around the Sun and Earth. There are points in this orbit furthest from the sun that, with very tiny course corrections (executable by rocket) can gradually pull Earth into a more distant orbit (or, if the orbit closes inside the orbit of the Earth, a tighter orbit). Over the course of few million years this could move the Earth into the orbit of Mars (although, simultaneously, we should probably move Mars too, to avoid a collision).

The move would be so gradual that Earth would experience nothing but a high tide every few years (say what we'd currently consider a combined sun+moon high tide). So no damage to Earth, no relocation, no nuclear bombs (on the Earth), etc. And clearly technology, since we know it already, executable in any technological future (not a Mad Max future, but any scientific, space worthy future).

In my opinion, however, using the asteroid belt (and whatever we need from Earth) to construct enough life ships to sustain the entire human population would be smarter and more efficient plan than trying to move the fragile Earth. There are only about 16 billion acres of habitable land on Earth, so perhaps 2 acres per person. Less than half of that is arable (farm worthy).

Moving the entire earth means moving a cone, that ends in a two acre spread and is 4000 miles long (to the core of the planet) for every person on Earth!

Surely a ship with an easily obtainable steel shell would be better: iron is plentiful in asteroids, heat is plentiful even from a dying sun, and carbon is plentiful, hence steel is plentiful.

If this steel shell were even a mile thick, it would be 1 mile vs 4000 miles; but now you have something stiff, so many forms of propulsion can move it relatively fast without the acceleration damaging it or breaking it. A mile thick is undoubtedly overkill, but I am making the point the ship would undoubtedly be safer, faster, and more maneuverable than the planet.

Moving the planet would be pure sentimentality, which would go out the window when survival is on the line. All we really care about is the outer shell of the planet, a few miles deep at most. Ships could contain all the necessary habitats; including a reproduction of the entire Serengeti, the Amazon and other rain forests, every habitable acre on the planet: And more than that if we so choose. Of course we don't have to build just one ship; we can build an Armada of hundred-million-acre ships (California is 101 million acres) (roughly a square, 400 miles per side), each with a nice blend of landscaping features.

If we had the technology to actually move the planet, why be lazy? Chances are intelligent machines are doing 100% of the labor and we are just waiting for them to finish, so use that technological know-how to ditch Earth and build Paradise.

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I'm afraid the idea isn't feasible (although it is pretty cool!).

Firstly, the power needed to move the earth out of its orbit would be astronomical (a lot more than an explosive blast not capable of destroying the earth). If anything, such an explosion would alter the earths tilt in its orbit rather than change the orbit.

As an example, to move the Earth from its present orbit out to Mars' orbit, it would take about 1.4 × 1033 joules.

Consider that a one megaton nuclear blast generates 4.18 × 1015 joules, and assuming that we had a billion years in which to move the Earth, this is the equivalent of detonating one 100 megaton bomb every 10 secs over that Billion years

References : https://www.physicsforums.com/threads/what-would-it-take-to-move-earth.63459/ http://www.thespacereview.com/article/2547/1

Secondly, the power of such explosions (even if they are ineffective would alter the environment of the earth beyond being able to sustain life (Unless of course humans now have some other form of habitats etc.).

The thread referenced above also has a very interesting way of moving the earth, which basically involves using the gravitational pull of an asteroid to 'nudge' the earth into a different orbit. This would depend however on fine control of the asteroid.

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  • $\begingroup$ The threads here on WB have the same suggestion. $\endgroup$ – JDługosz Jun 16 '17 at 17:31
  • $\begingroup$ +1 for: "the power needed to move the earth out of its orbit would be astronomical" ba dum tss! $\endgroup$ – Theraot Jun 17 '17 at 1:14
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Your only hope is to open a worm hole directly in front of earth orbit, and direct the wormhole to your destination.

Since your billions of years into the future hopefully the technology will exist. If it doesn't then human kind is truly a failure.

Suck the last bits of energy from the sun to create said wormhole. This presumes wormhole create will be hard, but in 1-3 billion years it will probably be easy.

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    $\begingroup$ Yes! The ability to teleport a planet directly from our system's habitable zone to the habitable zone of another star without having to spend centuries in the atmosphere-freezingly cold void is the technology you'd need to make interstellar planet relocation worthwhile. Anything less, and it's easier to just take ships and build a new home on/in/from whatever you find when you get to the new system. $\endgroup$ – Robyn Jun 17 '17 at 12:53
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This is not a new idea. using planet Earth as a spaceship was first proposed by the Canadian-born nuclear physicist Darol Froman who had worked on the development of the hydrogen bomb.

Froman proposed using the deuterium in Earth's oceans as the source of fusionable fuel to propel Earth through space. In fact, by his estimates the Earth could be kept functioning for about eight billion years. This would be sufficient time to travel to a system 1300 light years away.

“To some of us, the most comfortable and unimaginable spaceship would be the very planet Earth. Therefore, if its present position does not satisfy us, whether for this or that motive, then, let us transport ourselves to another place with the whole of the Earth. In this way, we would not worry ourselves with the usual problems of space voyages. For instance: the problem of radiation would disappear thanks to the atmosphere and also because we would travel at a slow speed."

Rocket propulsion systems or a version of the nuclear pulse propulsion system suggested by the OP seem recklessly dangerous to the safety of the planet let alone provide an adequate form of technology to make planet Earth into a viable spaceship. Froman didn't detail what means would propel his spaceship Earth, but he suggested what could be used to make the concept energetically feasible.

For a science-fictional version of making Earth into a spaceship your attention is directed to the Kyyra sequence of novels written by Stanley Schmidt The Sins of the Fathers (1974) and Lifeboat Earth (1978). Just the thing for escaping from an explosion at the centre of the galaxy.

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  • $\begingroup$ Is the physcis better in those novels than in Space: 1999? $\endgroup$ – JDługosz Jun 17 '17 at 17:07
  • $\begingroup$ @JDługosz. Stanley Schmidt was a physicist before becoming editor of Analog. The physics is far better than Space 1999, but that is setting a very low bar. Schmidt published an article in Analog explaining the science background including its speculative physics, to the novels. This was prior to his assuming its editorship. Super-science balanced with a sensibility and an awareness of real physics. Kind of like John Cramer's science-fiction. $\endgroup$ – a4android Jun 18 '17 at 2:45
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Earth's biggest hassles are getting up to speed and holding onto thermal energy that would radiate away.

There are, obviously, ways to solve both problems. But under what condition would this be faster, safer, or cheaper? The obvious motive seems to be to preserve Earth's history, in which case it might be launched while a fair amount of the population disembarks on spread out spacecraft.

If you want the earth to drift, maybe have a sudden disappearance of the star send earth flying out into space with a little lifesaving help from tech or have it be sucked along by a rogue object. It could temporarily get trapped and disrupts our orbit.

Another alternative is long term orbit adjustment, expending huge amounts of energy over a very long period of time to disrupt the orbit. Don't forget the world spins though. Keep in mind that stars actually convert matter into energy, becoming less massive as they age.

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    $\begingroup$ Good idea on why you might indeed want to save the whole planet. But note that suction does not work in space! $\endgroup$ – JDługosz Jun 16 '17 at 21:35
  • $\begingroup$ @JDługosz Sucked by gravity XD thought the impossibility would prevent ambiguity but I guess that was the wrong approach to take here. $\endgroup$ – user39453 Jun 16 '17 at 23:33
  • $\begingroup$ Do you have any estimation on how much the mass of the sun will shrink due to mass-energy conversion (without the "blow everything away during the red giant" phase)? $\endgroup$ – Paŭlo Ebermann Jun 17 '17 at 17:44

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