To Moon, Or Not To Moon?

[BolianAuthor]

Okay... I had an idea for my "Shades of Gray" story, that I thought would be cool, and also amusing, but I'd like to know if it's scientifically possible, before I go ahead and use it.

In the story, a human asks one of the Grays if their world (Orvan) has a moon. The Gray responds, by saying "Sometimes", to a puzzled human.

My thought was this...

That since the Gray's homeworld is in the Zeta Reticuli system, which is a binary, and orbits the second star, that perhaps orbiting the FIRST star, is a small planetoid, maybe like Phobos or Charon, that has such an elliptical orbit, that once every one hundred thousand years or so, that small planetoid gets close enough to Orvan, to be temporarily captured by its gravity, and orbits it as a moon, until the next interval, when Orvan's gravity again flings it back into its old orbit, around the FIRST star.

I was wondering if this concept is at all doable?

[All Seeing Eye]

Once this moon is caught by the planets gravity why would this Moon then be released? once caught I can't see any reason why it would escape the planets orbit.

[Silvercrest]

I agree. The only way it would happen is if another body passed close enough to tear the moon out of its orbit around the planet, and somehow cast it back to its original orbit. But if that occurred, the effects on Orban would be horrific. (The Grays wouldn't be saying "sometimes we have a moon", they'd be saying "sometimes we have a cataclysmic event that effectively ends our civilization.")

[backstept]

and if it was pulled back out of orbit by one of the suns you'd think that would also have a great affect on the planet as well . . . [edit: Silvercrest said it better ]

maybe the moon has a highly elliptical orbit around just one of the stars while the planet orbits both stars? the moon would periodically be outside of the planet's orbit as well as visible at night
it wouldn't technically be a moon, but another planetoid that occasionally become close enough to appear to be a moon

[Kaziarl]

Depending on where the orbit goes, if it's eliptical it could move far enough away from the planet to get caught by something else.

[Neopeius]

BolianAdmiral wrote:

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Okay... I had an idea for my "Shades of Gray" story, that I thought would be cool, and also amusing, but I'd like to know if it's scientifically possible, before I go ahead and use it.

In the story, a human asks one of the Grays if their world (Orvan) has a moon. The Gray responds, by saying "Sometimes", to a puzzled human.

My thought was this...

That since the Gray's homeworld is in the Zeta Reticuli system, which is a binary, and orbits the second star, that perhaps orbiting the FIRST star, is a small planetoid, maybe like Phobos or Charon, that has such an elliptical orbit, that once every one hundred thousand years or so, that small planetoid gets close enough to Orvan, to be temporarily captured by its gravity, and orbits it as a moon, until the next interval, when Orvan's gravity again flings it back into its old orbit, around the FIRST star.

I was wondering if this concept is at all doable?

No.

ZR2 and ZR1 have 9000 AU between them. By comparison, Pluto is about 40 AU from the Sun.

[Kaziarl]

Neopeius wrote:

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No.

ZR2 and ZR1 have 9000 AU between them. By comparison, Pluto is about 40 AU from the Sun.

I don't know alot about this, but can two stars be a binary system that far apart? I would think that would be far outside each others gravity well for it to work.

[Neopeius]

Jolly old saint Q wrote:

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I don't know alot about this, but can two stars be a binary system that far apart? I would think that would be far outside each others gravity well for it to work.

That's only one seventh of a light year. Proxima Centauri is bound to the Alpha Centauri system at a distance of some 15,000 A.U. Our Oort Cloud is bound to our sun out to 1.5 light years.

[BolianAuthor]

Thanks for the insight, guys... I guess Orvan has no moon, then. I was originally going to say it had no moon anyway, but if I DID give it one, I was gonna use something like that idea. Thanks again, for the answers!

[Neopeius]

BolianAdmiral wrote:

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Thanks for the insight, guys... I guess Orvan has no moon, then. I was originally going to say it had no moon anyway, but if I DID give it one, I was gonna use something like that idea. Thanks again, for the answers!

If the Gray's are starfarers, they probably have some incredible engineering capability. What if they harvest asteroids and park them in orbit for exploitation? So sometimes, the planet has moons.

[Kaziarl]

Ok, I stand corrected. Thanks. Now what about the elliptical orbit for the moon? Would it be possible for a moon to be caught, orbit it a couple times, then get pulled back out by the gravity of one of the suns? I know that doesn't happen to our moon, because it doesn't get that far away from our planet, but if it's an elliptical orbit, it might.

[Neopeius]

Jolly old saint Q wrote:

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Ok, I stand corrected. Thanks. Now what about the elliptical orbit for the moon? Would it be possible for a moon to be caught, orbit it a couple times, then get pulled back out by the gravity of one of the suns? I know that doesn't happen to our moon, because it doesn't get that far away from our planet, but if it's an elliptical orbit, it might.

Are you asking if it can happen in other binaries with less separation than ZR? Such a situation isn't going to be stable. I can see an elliptically orbiting moon getting captured by a larger body but not really the other way around.

In any event, if this moon's orbit is so elliptical that it *can* be caught up, then it won't really be a moon from the standpoint of the planetary inhabitants. It'll be a planetoid that occasionally comes close to the planet.

[Silvercrest]

Silvercrest wrote:

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I agree. The only way it would happen is if another body passed close enough to tear the moon out of its orbit around the planet, and somehow cast it back to its original orbit. But if that occurred, the effects on Orban would be horrific. (The Grays wouldn't be saying "sometimes we have a moon", they'd be saying "sometimes we have a cataclysmic event that effectively ends our civilization.")

Oops, I wrote "Orban" instead of "Orvan". Sorry about that!

[smithaa02]

BolianAdmiral wrote:

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Okay... I had an idea for my "Shades of Gray" story, that I thought would be cool, and also amusing, but I'd like to know if it's scientifically possible, before I go ahead and use it.

In the story, a human asks one of the Grays if their world (Orvan) has a moon. The Gray responds, by saying "Sometimes", to a puzzled human.

My thought was this...

That since the Gray's homeworld is in the Zeta Reticuli system, which is a binary, and orbits the second star, that perhaps orbiting the FIRST star, is a small planetoid, maybe like Phobos or Charon, that has such an elliptical orbit, that once every one hundred thousand years or so, that small planetoid gets close enough to Orvan, to be temporarily captured by its gravity, and orbits it as a moon, until the next interval, when Orvan's gravity again flings it back into its old orbit, around the FIRST star.

I was wondering if this concept is at all doable?

What is interesting is what you describe is somewhat similar to the concept of 'Planet X' (aka Nibiru) in UFO mythology (something you already seem familiar with based on your Zeta references). Basically the premise is that a large object has an elliptical orbit with our own sun (much like many comets like Haley's do) and this object comes around every 11,000 years and which due to a close pass to earth makes a mess of things. The poles shift, massive earthquakes and meteorological phenomena result. The present state of human civilization and technological advancement collapses (like Mu and Atlantis). An interesting book on the subject that I just happen to be reading at the moment is called 'Worlds in Collision' by Immanuel Velikovsky. He makes the case for sudden earth changes using a plethora of examples. Such as the ice sheets from the last ice age not lining up with our present poles (they seemed to skip Siberia and were present in Africa). Mammoths frozen to death with food in their mouths. Numerous native and religious references to the sun stopping and even rising in the wrong direction. The great flood from the bible matching other floods from other cultures. Pole shift evidence from the mid-Atlantic ridge. Tibetan references to the Himalayas being underwater and much more... Incidentally we are about due for another pole shift (aka Armageddon) which if the Mayan calendars are correct should happen around 2012 and send human civilization back into another stone age. Lot's of story ideas available from the planet X mythology...

[Shaw]

BolianAdmiral wrote:

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In the story, a human asks one of the Grays if their world (Orvan) has a moon. The Gray responds, by saying "Sometimes", to a puzzled human.

If this "sometimes" is an integral part of your story, then maybe we should look at it from a different perspective.

What if this planet has a sub-planetary body trapped in it's L2 Lagrangian point? This body could be in permanent eclipse and only noticeable as a spot in the night sky where you can't see any stars. Every so often, when the companion star is close enough in orbit, the body is illuminated in phases that look like our lunar phases. But for the majority of the time you just wouldn't see it unless you were really hunting for it in the sky.

Would something like that work?


Alternately, imagine a world where a sub-planetary body is trapped in the L1 Lagrangian point. If it were large enough it would provide a partial solar eclipse all the time. and in some places a near full eclipse (or at least make the Sun look like a big bright ring at high noon).

There are lots of interesting possibilities if you spend a little time studying orbital mechanics. The key thing is to try to imagine how such different dynamics might look when looking up at them in the sky.