9 replies to this topic

[Velvet D'Coolette]

I understand that the moon is very important to life on Earth. Insects, fish and other animal groups use it for navigation, timing of breeding and more, coastal-living creatures depend on its gravitational effects. Perhaps there is more, but I don't know of it.

But one thing strikes me: that if a planet supporting life were to have more than one moon, life might be difficult, or the life may have evolved very differently. What I'm looking for is suggestions for how life would be on a planet with, say, three moons?

Any ideas?

[salamander]

I'm not sure about the physics of it, but culturally it would have a big impact, calendars for instance are based on the phases of the moon.
Tides might be more extreme, say if all the moons and the sun were aligned you might get tsunamis or something. There'd be more eclipses, and different types, when two or more line up in any particular fashion.
Some stuff like people going crazy during the full moon, or menstrual cycles being effected, don't have a lot of scientific backing, but they could be a part of folk tales (people act crazy when the red moon is full, breeding is successful under the blue moon etc)
Religion and mythology would be effected big time- deities based on each moon, major events happening under a certain phase going down in history, etc.
For more major evolutionary changes, differences in seasons, climate and such, is more effected by differences in the sun(s), and the planet itself.
Like I said though I'm not an expert in science. All I know is it gets cold in my shed

[Velvet D'Coolette]

All I know is it gets cold in my shed

Your shed is on the dark side of the moon? Then it will do. Have you thought of moving it to a shadier spot?

Oh, and I learned the other week that a blue moon is one in which... I think it is, a full moon appears more than once within the same month. That doesn't sound quite right now that I repeat it, but it was something to do with the month being long enough to accommodate more of the moon's phase. So I suppose blue moons would be better for breeding on the basis of there being more time for conception to happen.

Anyway, thanks for some stunning ideas and starting points!

[Xian Shade]

The planet Remulak from the 'Coneheads' movie had 3 moons. Just see what it did to them.

[Velvet D'Coolette]

Blimey. I got Mr. Lurkey to speak!

[chief]

Tides would either be extream or they would battle against eachother. All dependong on the two moons distance between eachother. I think that would be the main affect.

It might change a bit of the Earths rotation too, as I think I heard somewhere that the moon helps keep Earth on its Axis.

[Vlad Yvhv]

We can look at the physical effects that mulitple moons have in our own solar system. But, we can only speculate as to their effects upon life-bearing planets. Just how big the moons are, how fast they orbit the planet, and all those other wonderful variables would need to be factored in, to figure out what they'd do to the planet. Likewise, life on other worlds is speculative at best. You might wind up with something like squids being the dominant intelligent life form, or even a polymorphic species like the Things. Such variations have their own impact on how societies would form. Multiple moons would probly inspire more stories and folk tails and myths and whatnot. But each moon would likely have less significance than one on a single-moon planet, because they wouldn't be as unique.

[chalcara]

The most important factor is how massive the orbiting bodies are.

Our Earth & Moon system's actually barely (not) double-planet system (depending on whom you ask: http://en.wikipedia....i/Double_planet ). The moon's massive enough that the Earth and Moon are actually rotating around each other - just that the point of rotation is still inside Earth itself.

Most moons in our solarsystem are tiny compared to the body's they're orbiting. Two, or three or twenty of those wouldn't make much impact geological, although cultures interested in the sky would most likely track them.

But if you want moons as big as ours (well, in terms of the mass ratio between moon/earth) you're ending up with tertiary or quartery body systems - and very complex orbits. And complex orbits are rarely stable. There are a few configuration that would theoretical work - like having one moon in the lagrange points or a keppler rosette - but the question is: Can/would they happen naturally? Propably. But unlikely. A hard impact on one of the bodies or just the gravitional tug of a jupiter-equivalent in the same star system could easily destroy it. Heck, the system would go boom if the star just gets a teensy bit to close to another star.

Multiple stars DO happen (http://en.wikipedia.org/wiki/Multiple_star), but multiple planets do not only have to deal with the gravity of each other, but also with the gravity of the star they're orbiting and the other big planets in the systems. The most likely result will be that one or more bodies get ejected from the planet system, till a more or less stable configuration is found.

Our own starsystem is actually pretty simple, gravity-wise. We have only one main star and the planets are far enough from each other not to disturb much. Jupiter's big enough to have prevented the formation of a planet between mars and jupiter itself (thats why we've got an asteroid belt there) and regulary chucks chunks from the Kuiper belt at us, but he also gobbles up enough fly-in comets that we can live relativly in peace, so it's all well. But still, even the orbits in our solarsystem are constantly changing. Just take our moon for example: It's slowly and constantly gaining distance from earth. One day it'll go bye bye and fly off to adventures in space and Earth will be moonless - Our only comfort is that our sun will (most likely) go boom before THAT happens.

Gravity is complicated. It's the simple systems that are stable, and even then stable usually only means "sticks around longer than just a few million years or until something big comes flying". Everything with more complex orbits is in for interesting times, which usually end either with smacking into a taller body or going to fly off into space.

But if you're setting a story into such a system, the astronomy itself would make a few fascinating story hooks.

[furrykef]

I wonder what kind of effort would have to go into computerized physics simulations to find this kinda stuff out...

[chalcara]

I wonder what kind of effort would have to go into computerized physics simulations to find this kinda stuff out...

http://en.wikipedia..../N-body_problem


Short story: 2 bodies: no problem. More than 3 bodies? It makes physics cry.

Mathematics is a harsh mistress, especially when the number of variables raises exponantially. (Note: This CANNOT fixed by throwing more powerful computers at it. The whole explenation's quite mathematical and complicated, but basically it's because things get complicated much faster than computer can become more powerful. I've read that there's hope quantum computing will fix that, but they've also been promising us a flying car for more than fifty years now. Even then, math has some inbuild limits that quantum computing won't be able to fix. http://en.wikipedia....uantum_computer )

Luckely it's not necessary to calculate orbits / collusions while considering all possible situations. Since scientists are able to pick decent approximations and limits on what they want to calculate plus the fact that you can actually model many things you want to calculate as a two-body-problem (eg, when you're interested in the effect the mass of Earth and moon has on the sun, you can treat earth/moon as one mass and the sun as the other), it's possible to make reasonable predictions and calculate the flight paths of our rockets well enough - as long you they remember to translate foot into metres...

Simulations are very much possible, useful and an important research tool (example: http://www.rdmag.com...Early-Universe/ ), but you have to pick your parameters right and even then you'll be only able to simulate certain stuff. And as always the devil's in the details. And over billions of years even the tiniest deviation can have enourmous effects.

It's one of the reason multi-body systems are so unstable: they're prone to disturb themselves and cause those tiny effects which over the time destroy the system.