Two Moons

I was reading some information on a creationist website about the way that the Earth's enviorment is constructed and the number of variables that have to be tweeked to such a fine degree that if any of them were out of alignment by a small percent, life on this planet - as we know it now - would be impossible.I am curious although not instructed in this area to answer my own question, but what if the Earth had 2 moons instead of just one. I am wondering if the earth had a second moon that was 20% further away from the Earth along with the current one and it was just large enough to have the same gravitational effects that our current moon has. I don't know the math that would go into calculating the mass that this moon would need to be to achieve this, but if our planet had this arrangement of multiple moons, could the Earth still support life as it is today?For arguments sake, I'll assume that both moons are in the same rotational plane and the closer leads the farther by 120 degrees.

Well, I'm not sure but I'd be willing to bet that the arrangement wouldn't be stable for more than a few ten thousand years or maybe hundreds of thousands of years. And how it would go over long periods of time is a three-body problemn to which we've never found a general answer.The effects that our relatively large moon may have had on the development of life on Earth are far from being strongly supported. It's difficult to evaluate the evidence and the arguments without a different planet, with life, to which to compare our situation. The effects that have been proposed are not universally (or near-universally) accepted. You could probably get lots of wildly different answers to your question, each about as well supported as the next.

Evolution leads to organisms that are finely adapted for their environment. If the environment was different, then life would be different as well. You can take that as saying life as we know it would be impossible if you like. Very hard to say; but in so far as they were any differences on Earth, with different tidal cycles and so on, then it is safe to say that life would have different appropriate adaptations.As a minor aside; Earth's moon is very large in relation to the parent body. I think it would be a serious problem to have another body of comparable influence in a stable orbit. As an even more minor aside, you can't have a closer moon leading by a fixed number of degrees. The orbital periods would be different.Cheers -- Sylas

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Evolution leads to organisms that are finely adapted for their environment. If the environment was different, then life would be different as well. You can take that as saying life as we know it would be impossible if you like.

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So it is entirely possible that every other planet in every solar system in the universe does have life on it but because of the different enviorments, it is impossible for us to catalog it as life because of our exclusive familiarity of our own enviorment.

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As an even more minor aside, you can't have a closer moon leading by a fixed number of degrees. The orbital periods would be different.

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Would it be possible if the further moon had a faster orbital speed which kept it at the same distance from the inner moon?

D'oh! And I missed that! Wotta maroon!

Well, that's one possibility, but it doesn't follow from what he wrote. Another possibility is that other planets (not necessarily every other planet) have life that we have not yet detected, because we haven't detected much about planets outside our Solar system and there's lots more to look at in our Solar system. That life, if it does exist, is almost certain to be different from us but is not at all certain to be unrecognizable as life. It would not be possible for the distance between the moons to be constant unless they were at the same distance from the Earth and one were smaller than the other and the smaller one was placed at a stable Lagrange point. There are other stable relationships between three bodies but they lead to distances changing with time.

Is it more a possibility then to have a sister planet to the earth orbiting at the exact opposite point to us so as to always be hidden behind the Sun. I know we would be able to detect it's gravitational impact on the other inner planets but it sounds like that could have happened easier then for the earth to have 2 large moons orbiting around it.

Boggle. That is nothing like what I was saying.It is not remotely plausible that every other planet has life; and the question is not one of cataloging or classifying.We don't know nearly enough about life to tell how common it is in the universe, or what forms it may take. The question of whether there is life on any other planets in our solar system is an open one. If I had to put money on it, I'd suggest most likely not. Plausible candidates are Mars and Europa. Neither is particularly likely, I would guess, but it is well worth looking for it.The question is whether or not anything exists which is analogous to life on earth. Certainly, if it exists, it would be very different to life on Earth. That is not a problem; we don't have a prior classification that requires life to be exactly what we know already.The issue you raised originally was one fine tuning of life to circumstances on Earth. That is an inevitable consequence of evolution, and there is no basis for inferring that life is impossible under all other circumstances. No. Moons don't stay equidistant from each other. Does it matter? Just propose another Moon; and speculate on what differences that might make. More interesting (IMO) is speculation about no Moon at all. Were tides important in biogenesis? Does a large Moon help keep Earth geologically active, and is that important for life? I don't know.

(Added in edit: JonF has pointed out the Lagrange solution to the 3 body problem; but that does not involve an "inner" moon. I believe it is stable only if the third body is very small. This solution involves exactly the same orbital period and orbital distance for the extra tiny moon as for the existing moon; and the moons are equidistant from each other. The notion of a planet opposite the earth and behind the sun is unstable.)

Cheers -- Sylas[This message has been edited by Sylas, 02-23-2004]

If I remember it right, there are Kabbalist writings that claim we already have a second moon: Lilith, named after Adam's first wife. It's invisible, though. And I presume it must not raise tides.

Yup; I alluded to those restrictions, but it is the only known solution for constant distance. Again yup, as noted at the link I posted.

If this second moon is invisible, is it as close to the earth and is it made out of the same matter only coal black, or is it made out of Dark material like the mass of the universe?Was Eve Adam's second wife or does this other moons name mean the same thing as Eve.How did they know about a second moon. They're not refering to that tiny black moon that revolves around mars are they?

There isn't any second Moon - they were wrong. And I'd imagine that the authors were wrong about Lilith being Adam's first wife, too, as they were both mythical people.

After some googling, this is what I found:Lilith is not made up out of anything material. It is symbolic.Imagine the elipse that the orbit of the moon creates. Since it is an elipse, it has two 'focal points'. Earth occupies one of them, the other is an empty point. This point revolves around the earth roughly once every 9 years due to variations in Lunas orbit.This empty point has symbolic meaning; It counterbalances our bright Luna. It represents on one hand repressed feelings and desires, but also letting yourself go and doing things you are usually afraid to do.The name comes from a Babylonian/Syrian demon-godess who is represented by the glyph of a dark moon.I derived this mainly from the website Lilith - the dark moon - Astrodienst . It also includes a good illustration.[This message has been edited by Melchior, 02-24-2004][This message has been edited by Melchior, 02-24-2004]

I'd like to add that there's nothing in particular to rule out Venus as well as Mars and Europa. The "life" there would of necessity be hyperthermophilic and quite probably chemoautotrophic, but could still exist. After all, we have examples from our own planet (albeit only Archaea) to show that this is possible. However, I agree that we should be able to recognize it as "living" by the way whatever is found interacts with its environment if it exists.

Thread moved here from the Coffee House forum.