-2

In a hypothetical situation if we needed to move the earth slightly to avoid being hit by an asteroid

  • Could we harness Jupiter’s gravitational force to do so?
  • Is there another more efficient way to move the earth?
  • Would we need rockets?
The Square-Cube Law
  • 141,440
  • 29
  • 264
  • 586
user44559
  • 5
  • 1
  • 2
    Welcome to WorldBuilding! Please try to limit yourself to one questions per post. If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun! – Secespitus Nov 09 '17 at 11:43
  • related https://worldbuilding.stackexchange.com/questions/46508/can-humans-dislodge-earths-orbit-with-our-current-weapons – L.Dutch Nov 09 '17 at 11:58
  • 2
    So in order to avoid a small piece of rock hitting a huge piece of rock we choose to move the huge piece of rock instead of moving the small piece of rock... That's engineering in the modern age. – AlexP Nov 09 '17 at 12:00
  • Since the asteroid most likely is much lighter than earth and nobody really cares what happens to it after moving it a bit and given that we need technology that won't be available in the next 1000 years for your premise anyways, it might be easier to move the asteroid ... – Raditz_35 Nov 09 '17 at 12:00
  • See How can I move a planet – Gary Walker Nov 09 '17 at 12:14
  • You may be interested in the movie Wandering Earth – Muuski Oct 23 '19 at 22:17

3 Answers3

7

No

In short, your question reads is as if you have asked: "How can I change the flow of a river so that it fills my water-pail?". Answer: you do not. If you can could change the trajectory of a river you sure as heck can pick up the pail, carry it to the river and dunk it in. If you cannot even do that simple thing, then you cannot change the trajectory of a river.

First, if we can move(*) Earth, we can move the asteroid, since the asteroid is several magnitudes less massive than Earth. If we can already move the asteroid, we do not need to move Earth. If you cannot move the asteroid, then you cannot move Earth.

Second, in order to make Jupiter's gravity affect Earth differently than it does now, we need to move Jupiter. If we can move Jupiter, then we can move Earth, because Earth is several magnitudes less massive than Jupiter. If we can already move Earth, we do not need to move Jupiter. And conversely: if you cannot move Earth, you cannot move Jupiter.

And since we cannot move Jupiter to any meaningful extent, the answer to your question is: no, we cannot use the gravity of Jupiter to move Earth out of the way of an oncoming asteroid.

(*) In this context, "move" means "change the trajectory of".

MichaelK
  • 43,723
  • 6
  • 106
  • 189
  • To be fair (inner physicist kept coming back to this): Jupiter already moves the Earth. As does every other mass in the solar system. When talking about Earth's orbit, we normally consider it a 2-body-problem (Earth & Sun), sometimes we get creative and model 3-body-problems (Sun, Earth, & Moon) which let us establish lagrange points. But after that the math gets hard and there is little noted difference, so we stop. But in actuality, every mass everywhere is affecting Earth's orbit to the full extent possible by its distance from Earth. (hence your move Jupiter point) So it already is. – Ruscal Nov 09 '17 at 19:40
  • 1
    @Ruscal This is why I put that asterisk on the word "move"; why I wrote "make Jupiter's gravity affect Earth differently than it does now" and "we cannot move Jupiter to any meaningful extent". :-) – MichaelK Nov 10 '17 at 08:11
  • Indeed. I was tempted to write an answer that was a sub-set of my orbital dynamics lectures, but as this is WB and not Phys I had to (strongly) bite my cheek for restraint. Especially since you had already highlighted the bulk of the issue in a true and effective answer. For anyone else stumbling on this, experienced gravity is a factor of the object's mass divided by the square of the distance. Without changing the mass or distance, you can't change the existing gravitational effects. – Ruscal Nov 13 '17 at 20:16
3

We couldn't use Jupiter's gravity as it stands without moving something. If you can move Jupiter, you can move Earth, or even better still the asteroid in question, so there wouldn't be any reason for it.

Using mass to move other things via gravity is possible however. It's actually one of our plans in case we do need to move some space rocks out of our way. They call this a gravity tractor.

The gravitational force of a nearby space vehicle, though minuscule, is able to alter the trajectory of a much larger asteroid if the vehicle spends enough time close to it; all that is required is that the vehicle thrust in a consistent direction relative to the asteroid's trajectory, and that neither the vehicle nor its expelled reaction mass come in direct contact with the asteroid.

If time weren't an issue and you really need to move Earth, using the moon to move it would be the "easiest" method. Less danger this way. You don't have to worry so much about killing everyone on the surface of the moon if you fowl something up. Move the moon in a bit closer and drag Earth away with it.

This still wouldn't be easy at all. The most practical solution at the moment would be Ion Thrusters probably. You need a whole lot of them and a whole lot of power to get it all working.

Again none of this would be quick, easy or cheap. Stick to moving the dangerous space rocks instead.

oxide7
  • 749
  • 3
  • 12
1

Not really.

If you could make the distance between Jupiter and Earth shorter, then Jupiter's gravitational influence on the Earth would be closer, and stronger. I guess is that you could achieve this through creating a sizeable wormhole, and placing it on the side of the Earth corresponding to the direction you want to move it. However, if you could manufacture wormholes that size, you could just make the asteroid transverse a wormhole, clearing it of any collision. Perhaps the wormhole you're creating can only successfully travel energy or gravitational forces. In which case, you could just use Jupiter's gravity tunneled through the wormhole to alter the asteroid's course.

Actually, so long as the asteroid is less massive than the Earth, it would be easier to perturb the orbit of the asteroid than the orbit of the Earth.

There's no real scenario I can think of that justifies expending that much energy to move the Earth.