Two Moons? What would happen?

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Let's think about this for a second:
Unlike earth, Mars has two moons. Let's switch the two. Instead of just one moon, what would happen if the Earth has two moons? I've been searching the Internet like crazy for answers on this, I haven't been able to find much. All I've found is stuff on moons orbiting gas giants, or what would a planet without a moon be like. Any help would be appreciated.
 

mgb_phys

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Depends on the moons.
Mars's moons are very small and so have almost no effect mars.

Two Earth moons sized moons (!) would have an effect, especially on tides.
 
Okay, let's say that Earth's second moon is slightly (about a fourth) smaller than its first moon (by first, I mean the one we already have). What would be the effect on temperature, tidal forces, etc.? We have to remember that the moon's gravity has an impact on the tides. If both moons are orbiting the Earth in the same direction, then I can assume that there will no change. However, if the smaller moon orbited in the opposite direction, it's possible that this would cause a major change in Earth's environment.
 

mgb_phys

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Temperature - not much effect, the moon doesn't block a significant amount of the sun.
Tides - tricky, tides are tricky enough as it is with two moons in different orbits it would be 'fun'.
It's not clear what the interaction of tides and weather is but odds are it's complicated but significant.
 

Nabeshin

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My gut reaction is tides would become borderline chaotic with two substantially sized moons. Also, it would be interesting to see what (if any) tidal locking and/or resonance occurs with such a configuration.
 
Okay, how could it be chaotic? If the two moons are moving in the same direction, wouldn't the tides be about the same? I can understand the tides being chaotic if the moons moved in opposite directions.
 

Nabeshin

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I'm obviously just speculating, but even if the orbital motion of the moons is fairly simple, the fact is tides do not occur exactly in synch with orbital motion. It takes a while for the tides to "catch up" to the moon's position. It is this catching up period that makes me think that with two different orbital periods, a complicated or chaotic motion could be produced.
 
Alright, we all know that a moon also affect a planet's rotation and seasonal change, so what would happen if a planet had two moons?
 

sophiecentaur

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How big and how far away? If their orbits had similar radii then they would interact a lot - 'tumbling around' each other and exchanging inner and outer positions periodically. If they each had similar mass to our present Moon then the tidal range would increase (by more than twice) and the cycles would become more complex. Would they both be in the same plane?
The scarey thing would be that you could get wild variations in their orbits. If that were to bring one very close to Earth every so often it could be a nightmare in low lying areas of coast and it could be much harder to predict, I imagine. (Hence the 'chaotic' idea, introduced earlier)
 
if we had two moons, we would more than likely lose most of the earth's tilt, greatly affecting seasons and life on earth. depending on how big the other moon is and which way it revolves, it may or may not affect tides that much.
 

Chronos

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Having two moons in stable, separate orbits would be interesting. Another lunar mass moon say at half again the distance from earth would have interesting tidal effects. Tides might occasionally resemble small tsunamis, and almost unnoticeable at other times. It is hard to say how this might affect things like ocean currents. So long as both moons were in the same general orbital plane, it would little effect on the tilt of earth's axis.
 

L2E

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imagine having the two moons orbiting each other in a binary configuration with both orbiting around the earth. I'd imagine you would probably have super long high tides at the equator with very low low tides, but seemingly normal tides as you move towards and away from the poles.
 
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Having two moons in stable, separate orbits would be interesting. Another lunar mass moon say at half again the distance from earth would have interesting tidal effects. Tides might occasionally resemble small tsunamis, and almost unnoticeable at other times. It is hard to say how this might affect things like ocean currents. So long as both moons were in the same general orbital plane, it would little effect on the tilt of earth's axis.
Wait, tides, "[resembling] small tsunamis," is "interesting"?! I'd hate to hear about what you find intriguing or terrifying. Seriously though, if it effects ocean currents that effects weather patterns... I wonder if you'd see slightly different land-masses above sea level (or below)?
 

Janus

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imagine having the two moons orbiting each other in a binary configuration with both orbiting around the earth. I'd imagine you would probably have super long high tides at the equator with very low low tides, but seemingly normal tides as you move towards and away from the poles.
Assuming that at least one of the Moon's was that mass of our own, the maximum separation between the two while maintaining a stable orbit around each other would be ~20500 km (1/3 the Hill sphere to be conservative).

If we assume that the moon's are of equal mass, Each will swing a little closer to Earth and a little further from Earth as it orbits the other, This means that when one is at its closest to the Earth, the other is at its furthest. This will tend to smooth out differences in tidal force due to the individual moons changing distance from the Earth. Any remaining difference would be very small compared to the difference due to the fact that our Moon already changes its distance by more than the separation of the two, due to the eccentricity of its orbit.

So, having two moons orbiting each other in binary fashion would not be much different than having one moon of the same combined mass.
 

L2E

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Assuming that at least one of the Moon's was that mass of our own, the maximum separation between the two while maintaining a stable orbit around each other would be ~20500 km (1/3 the Hill sphere to be conservative).

If we assume that the moon's are of equal mass, Each will swing a little closer to Earth and a little further from Earth as it orbits the other, This means that when one is at its closest to the Earth, the other is at its furthest. This will tend to smooth out differences in tidal force due to the individual moons changing distance from the Earth. Any remaining difference would be very small compared to the difference due to the fact that our Moon already changes its distance by more than the separation of the two, due to the eccentricity of its orbit.

So, having two moons orbiting each other in binary fashion would not be much different than having one moon of the same combined mass.

Sorry, I should have elaborated on what I meant rather than the two moons moving far and close to earth in their orbit, I meant that they would rotate from the north pole to east to the south to the west. so both moons would generally be the same distance from the earth at all times. though as you explained, with the maximum distance between the two moons being so small I'd imagine that moons in a binary configuration have much more effect than a single moon.
 

Chronos

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Two equally massive moons orbiting each other while orbiting earth would not have stable orbits.
 
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Two equally massive moons orbiting each other while orbiting earth would not have stable orbits.
Meaning... it would decay and they'd fall to earth? Well, that's definitely something happening! :0
 

Janus

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Sorry, I should have elaborated on what I meant rather than the two moons moving far and close to earth in their orbit, I meant that they would rotate from the north pole to east to the south to the west. so both moons would generally be the same distance from the earth at all times.
Such an arrangement is not possible. Such a polar orbit would hold its orientation to the fixed stars (minus precession) so at different points of the month it would have a different orientation as seen from Earth.
 

Janus

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Meaning... it would decay and they'd fall to earth? Well, that's definitely something happening! :0
Meaning that the moons would separate into their own independent orbits around the Earth.
 

sophiecentaur

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At certain times, the two moons would be at the same 'position' in the sky. Their total effect, however, would be greater than the effect of a single Moon at their centre of mass - the nearer moon would dominate as their separation could be comparable with the distances from the Earth. This would cause higher tides, occasionally, surely than for a single Moon.
 
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you have also got to take into account the nature of the orbit of the earth and the moon, in which that they both orbit each other especially if you look at it from a tug of war point of view of the sun, earth and the moon effectively they orbit the sun together and effectively form a binary system on their own.

the orbit of two moons around earth could easily destablise depending on their orbit for example the dark side of the moon is mountainous while the near side is fairly flat when compared to it. the far side actually looks more accreted which like numerous articles have been theorising that a smaller moon effectively accreted into the current moon. and you can't expect to have all that material and not have multiple objects form, it is just the fact that the earth is closer to the sun then planets with more moons which means that we are effectively deeper in the suns gravity well then pluto which has 4 moons.
 

sophiecentaur

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the orbit of two moons around earth could easily destablise depending on their orbit for example the dark side of the moon is mountainous while the near side is fairly flat when compared to it. the far side actually looks more accreted which like numerous articles have been theorising that a smaller moon effectively accreted into the current moon. and you can't expect to have all that material and not have multiple objects form, it is just the fact that the earth is closer to the sun then planets with more moons which means that we are effectively deeper in the suns gravity well then pluto which has 4 moons.
hi and welcome.
I think you mean the far side. During the period of the New Moon, the far side is the side that isn't dark. Pink Floyd have a lot to answer for!
 
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Interestingly some scientists believe that the earth once had two moons and that our current moon is a result of their collision. The surface differences between the far side and near side of our moon are factors that they claim support this idea. What the effects and dynamics of such a double mooned earth was they don't explain in this article however. Perhaps in a more detailed one they have. It merits a search.

Science and Technology
August 05, 2011
Scientists Think Earth Once Had 2 Moons
Jessica Berman
http://www.voanews.com/english/news/science-technology/Scientists-Think-Earth-Once-Had-Two-Moons---126841858.html


An article on the possibility of two moons in Earth’s orbit is published in the journal Nature.
 

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