Can Earth "Keep" Another Moon?

[Motokid600]

If Pluto-Charon are orbiting a barycenter along with four other moons... My god that's gotta be a gravitational nightmare. I simply ..cannot wait for New Horizons to get out there and confirm all this. That will be a day of days.

As for another moon around Earth...I don't believe orbital resonance would ever be achieved. We'd never be able to hang onto it. There was a few instances of temporary satellites. One asteroid was constantly dipping in and out of the Earth's SoI ( as vague as that term is ) for a good while. And another actually orbited Earth. Turns out it was one of the Saturn V's S-IVB stages.

[Moon Goddess]

While I'm sure it's not possible I wish we did have a Minimus. Would have given us another target after the moon for the space race. Might have made the history of the space program better.

[Motokid600]

While I'm sure it's not possible I wish we did have a Minimus. Would have given us another target after the moon for the space race. Might have made the history of the space program better.

If we had another moon our entire species would've evolved differently. Not so much physically, but fundamentally.

[Camacha]

Another problem is that the moon moves outward

I have been wondering why this is, as we all know a higher orbit costs more energy. It turns out the tidal interaction with the earth - the actual deformation of the earth - is causing a bulge that is pulling the moon ahead. This causes the lunar orbit to lengthen, but the earth rotation to slow down.

Tl;dr: the moon moves outward by taking energy from earth's rotation.

If we had another moon our entire species would've evolved differently. Not so much physically, but fundamentally.

We also might have physically; the moon is a major stabilizing factor for earth. This stability has enabled life to develop as it did. With a much more unstable earth, which might have been tumbling or changing its poles often, life would not have been able to exist or would look probably much different.

Edited September 17, 2013 by Camacha

[Temstar]

Can anyone explain why this is? We all know that a higher orbit costs more energy, so where is the moon getting this? It should be losing energy with all the tidal interactions, not gaining it.

I have been wondering for a while now.

It gains energy from the fact that rotation of Earth is slowing down due to dissipation of Earth's angular momentum from tides. The tidal bulge on Earth caused by the moon is not exactly inline with the moon since Earth is rotating once every 24 hours and so is trying to drag that tidal bulge forward, while the moon rotates around the Earth once every 28 days or so and so lags behind the bulge. The extra gravity from the material of the bulge pulls the moon forwards and gives it a small prograde acceleration while at the same time drags against the surface of the Earth slowing the rotation down:

http://en.wikipedia.org/wiki/Tidal_acceleration

If giant impact hypothesis is correct and the moon is indeed formed from impact of a Mars sized proto-planet against the proto-Earth then immediately after the impact Earth would've had a day only 5 hours long and the newly forming Moon would be in a much lower orbit than now. The tidal effect has already slowed Earth's day by 19 hours and moved Moon out to its current orbit and that trend will continue, unless:

http://what-if.xkcd.com/26/

[Camacha]

You were quick to hit reply, but slow to reply, hah

and that trend will continue

I believe other mechanisms will stop that trend after a while, one of which is of course the moon getting further and further away with less and less tidal interactions taking place. That should not be the only thing going on though.

[victory143]

Wow, theres a alot of science here.

[Camacha]

Wow, theres a alot of science here.

Can you smell it?

[Pds314]

As far as I can tell, Earth should be able to have multiple moons, provided of course that their orbits aren't close together.

Certainly another moon can exist in Orbital resonance, even several could. The thing is that they currently don't exist like that, and that unless we make it happen, Earth is unlikely to be taking in any large asteroids any time soon.