# An odd question on orbital dynamics

1. Dec 16, 2012

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Is there any kind of celestial event that could occur that could completely lock the earth's rotation such that it is constantly facing the sun, in the same way the moon is tidally locked to the earth?

What would it take? Could it be caused by the passage or entrance of a new gravitational body into the solar system?

2. Dec 16, 2012

Staff Emeritus
Yes. It's called time. Give it a few tens or hundreds of billion years, and it will happen on its own.

3. Dec 16, 2012

### Staff: Mentor

The earth will fall into the (expanding) sun long before that would happen.
Impacts of asteroids, fly-bys of very massive objects or stuff launched into space can modify the rotation of earth. You need a lot of mass for any significant change, however.

4. Dec 16, 2012

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Okay, let me rephrase.

Is there any mass, position, linear and rotational velocity configuration of a foreign planet or body entering the solar system that could reduce that timescale for the earth's tidal locking to something in the order of days, weeks or months?

5. Dec 16, 2012

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Is it possible without impact?

6. Dec 16, 2012

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Ah yes, this sort of thing. I wouldn't know where to begin calculating what kind of regime is plausible, but I'm guessing the nearby passage of a planet with mass greater than the earth could cause such a dramatic perturbation of the earth's rotation?

Would the more distant passage of a star be equally plausible?

7. Dec 16, 2012

### Staff: Mentor

No. Not without ripping earth apart. You would need many fly-bys or a very close orbit (which is tricky to achieve with a massive object) - in any case, I think the timescale would be at least millenia or more, but I did not check the numbers. It would produce serious, probably periodic floods everywhere apart from some mountains and increase volcano activity a lot.

More distance and more mass can increase the timescale of the influence a bit, but if the numbers get too large you ruin the orbit of earth as well (long before you see a slowed rotation).

8. Dec 16, 2012

Staff Emeritus
It can't be done with a flyby. You need a net torque with no net force.

9. Dec 16, 2012

### Staff: Mentor

A flyby would induce tides, which give a torque (similar to the earth/moon system). You get a net force and change the orbit, too, of course. As you need multiple flybys, those could cancel in the long run. Not very realistic, but it might be possible to do that in a planned way.

10. Dec 16, 2012