If the Earth became a rogue planet would there be any way to push it into orbit again?

Question

I've recently begun writing a sci-fi story about what would happen if an asteroid or another larger object would fly close enough to the earth to knock it out of its orbit and send it flying away from the sun making it a rogue planet.

I began wondering if you could do anything if you had time in preparation. How can you send it back into its original orbit after it has been pushed out and would there be any consequences to doing so?

And if the earth reached one of the other planets and we managed to push it into the same orbit as it what would be different if it is even possible?

If any of the questions make no sense scientifically or are just badly worded please do tell me. I also know that I ask a lot of very wide questions but any help is greatly appreciated.

Answer 1

For any body moving in space, changing its orbit requires being able to exert a force on it. In the same way as a space rocket executes well calculated maneuvers to change its orbit, the same would need to happen in this case.

The problem is that, at the moment, we have no technology to exert any appreciable force on a body the mass of Earth. We "struggle" already to push something as light as a manned space probe aiming for the Moon, and as any engineer working with space programs can tell you, the load is the most critical parameter when sending something out there.

Moreover, if Earth was bumped out of its orbit, it would probably affect at least the closest neighbors, Mars and Venus. Even assuming there was the technology to move Earth back in its orbit, I would not exclude that the perturbations to Mars and Venus happened while we were busy fixing the mess would not backfire in a distant future.

Answer 2

With our current level of technology, it seems unlikely. That's because the energy to change Earth's orbit in any significant way is much greater than the combined energy output of all countries.

According to Inside Energy, the world used 575 quadrillion Btu in 2015. That's roughly 5.75 $\times$ 10¹⁸ joules. The Earth has a mass of 6 $\times$ 10²⁴ kg, so if all the energy we produced in 2015 was used to push the Earth in any direction, we would give it a ∆v of less than 0.000001 m/s. In laysman terms, we wouldn't see any difference in the shape of Earth's orbit. We would notice it burning hot around the equator for the effort, though.

---

As an alternative, we might try and capture another body to reverse the effects of whatever made the Earth go rogue again. But energy is really the currency of the universe, and this endeavor would cost even more energy than just pushing the Earth. We might extract some energy from extraterrestrial sources by making a small rocket go back and forth among gas giants - take some of their own kinetic energy. But that would take too long, and would be unfeasible once the Earth is already out of the solar system.

---

If you wish to prevent a body from making the Earth going rogue, consider that it would take at least a considerable planetary mass to cause the Earth to reach escape velocity regarding the Sun. You would have to deflect a planet coming at a speed greater than our own escape velocity (since it would be coming from outside the solar system), which would take even more energy. We just can't do it.

---

Of course, everything I said above is considering our current level of technology. In the far future, we might be able to avoid the inconvenience of being pushed out of the solar system by dodging incoming stars. We might do so with the aid of a stellar engine - check this awesome Kurzgesagt video.