Inspired by this question, suppose that the Earth decided to move its orbit much further out to reduce the effects of, say, global warming or the effects of a dying sun (or far enough to make this question interesting).

Say that the world, united, built a great rail system that circumnavigated the globe along Earth's orbital plane. On this rail was a device that could be directed and positioned precisely. It was also able to move along its length such that it could be positioned relative to Earth or its orbit, or anything else along Earth's orbital plane. This device was also capable of producing a thrust. It could be nuclear explosions, water ejected at great velocity, rocket plumes, etc.

My assumption is that the Earth would have to take a long-term approach to moving the planet, so the solution would be something that could be sustained over a long period of time

The question is what would be an appropriate ejection mass and over what time period would it take to move the Earth to a reasonable new orbit that would significantly change our climate? The concerns would be the ejection mass itself having a negative effect on Earth's climate or quality of life in general, i.e. nothing that would create a toxic atmosphere.

Interested in the kind of device, where it's ejecta exits (in the troposphere or past the exosphere), its frequency of use (ongoing, every hour, every month, once a year...) and its practicality.

  • $\begingroup$ Your idea would affect the rotational period (the length of the day) more than it would the orbit. To create an orbital change without messing with the rotational period, you need two side-by-side equatorial railgun thingies, firing opposite to each other. $\endgroup$
    – John Feltz
    Commented Dec 30, 2016 at 3:39
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    $\begingroup$ @JohnFeltz both pointed towards where you want to go, right? $\endgroup$ Commented Dec 30, 2016 at 5:35
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    $\begingroup$ Changing planetary orbits is best done by exchanging momentum with another object, as explained here: worldbuilding.stackexchange.com/questions/47410/… $\endgroup$
    – Thucydides
    Commented Dec 30, 2016 at 6:06
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    $\begingroup$ The question you reference showed how ridiculous the energy requirements are for moving the earth. If you wish to change earth's climate, why not just orbit some large mirrors to add or remove sunlight to affect total heat? This would require much less effort for our level of technology. Unless you postulate a type II or III civilization with appropriate magic, moving the earth into a different orbit without killing everything on it is rather improbable. $\endgroup$ Commented Dec 30, 2016 at 9:32
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    $\begingroup$ @MarkRipley I get that the requirements are insane, such that I'm keen to understand what slow, but steady, method might work. Time scales could be on the order of 1,000 years or more in need be. I guess another way to look at it – is it possible to put an engine on a planet and putter around to some other location in space, assuming time and cost weren't the issue? My constraint was that the engine itself shouldn't kill off the planet whilst it's doing its thing. $\endgroup$
    – quip
    Commented Dec 30, 2016 at 14:19

1 Answer 1


Any form of reaction (IE Rocket power) is just going to require WAY too much energy to move the mass of the Earth in any realistic fashion - see your original linked question for the actual calculations! There just is not enough reaction mass to achieve moving a the mass of the planet.

In terms of effective reaction mass - The ONLY way I could see doing that would be to tap the molten core - and cause it to fire out past the gravity well of Earth - but how to do that and apply the thrust in only one direction? can't see it. AND even if you could get the thrust going in one direction - say through one of the poles - We'd lose the Molten Core! This would forever change the entire geological system of the Earth! I think this would cause the Earth to crumble - and create massive destruction - Pretty much an Extinction Level Event...

There is an approach I would expect to be far more survivable than any form of thruster - Massive rocket engines on rails, Nuclear explosions etc. They would ALL just pump so much excess heat into the ecosystem that it would likely be an Extinction Level event. And if you tried to use water - you'd just spray all our water out into space - and I can't see it having enough mass to move the planet any appreciable distance.

I think the only way to achieve orbital shift is with tech we do not currently have - we would need to control gravity and cause there to be a sufficiently large gravity well dragging the earth into a new orbit.

This avoids the excess heat - BUT it's going to have pretty significant tidal effects (read regular tsunamis) AND Earthquake activity will jump massively. This will probably fire up (pun intended) volcanic activity as well. Having said that - if it is done carefully - and over a long period of time - it could probably be achieved without an Extinction Level of side Effects...


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