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Thread: Advice on science fiction idea

  1. #1
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    Question Advice on science fiction idea

    Hey all, Torg here. I think it may have been over a year since I have posted here, but I have certainly lurked. Always an interesting place!

    Anyway, for the past six months I have had the idea for a science fiction scenario or story in my head and I have been elaborating it more and more. I don't know if anything will ever come of it, but I would love to get a reality check on certain elements before I put more thought into things. I am also not sure if this should be here or in the "small media at large" section, so feel free to move it if appropriate. So, to all of you out there knowledgeable about astrophysics, I'd like to see if anyone has any opinions on my idea for the layout of the Centauri system, which is heavily involved in my scenario.

    It is my understanding that orbits would only be stable within about 2 AU of either element of the Centauri system, discounting the possibility of gas giants ever forming. I have read several articles recently about the plausibility of terrestrial planet formation, however. One paper examined computer simulations of planet accretion from lunar-mass planetisemals and found it was robust within about 1.5 to 2 AU away from either star in the Centauri system. Another looked at the plausibility of planetisemal formation from dust and found that perturbations from the other star would prevent THAT accretion outside of about 0.75 AU from either star. There are those that argue that without gas giants water would not be directed to the inner planets and those that argue that the instability caused by the second star would do the job - I am siding with the latter for now. It is also my understanding that the Centauri system has a higher metallicity than our system, and hence there would have been more heavy elements to form planets.

    My system design relies on planetary migration. I have read theories about how Uranus and Neptune formed in closer than they are now and proceeded to migrate outwards by flinging icy debris from the outer system inwards. I am going to assume that the planets formed in the inner system of either star woud do the same thing and accrete slightly more from the dust and rubble entering the inner system.

    I am less interested in the system about Alpha Centauri B. I am picturing a rockball close in to the star because there is less material in that smaller volume, followed by a large (1-2 earth mass) venus-type world and some cold (since for earth-intensity sunlight you would need to be about 0.75 AU out) rockballs further out, unsure if they should be big enough to keep an atmosphere like Mars.

    Centauri A, the brighter of the pair, I am more interested in. Here I am again picturing a rockball close in, followed by a very large venus-type world (3-ish earth masses), with a moon similar to the Earth's, at around 1 AU. Further out, around 1.2 to 1.3 AU out (somewhere around where you get earth-intensity sunlight) is a planet within 15% of Earth's mass with an asteroidal moon slightly beyond geosynch, on which life has arisen.

    Since Centauri A is 1.5 times as bright as the sun and 5 billion years old or so, and stars brighten significantly over the course of the main sequence, it has brightened significantly since it formed. As such, this third planet was once much much colder than now, and it has sustained many more impacts than the Earth has due to there being more rubble immediately outside its orbit. Either as a result of these factors, or possibly just because it is very hard to do, life has never gone through most of the complex transitions that occurred here. You have all kinds of algae in the oceans and rudimentary plants growing in wet areas on land, and oxygen-producing photosynthesis has evolved producing an atmosphere with less oxygen than here.

    Nothing appreciable orbits the star system's center of mass at great distance.


    Any advice on if this is realistic at all, or other ideas, would be appreciated! Thanks!

  2. #2
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    Quote Originally Posted by Torg View Post
    Hey all, Torg here. I think it may have been over a year since I have posted here, but I have certainly lurked. Always an interesting place!

    Anyway, for the past six months I have had the idea for a science fiction scenario or story in my head and I have been elaborating it more and more. I don't know if anything will ever come of it, but I would love to get a reality check on certain elements before I put more thought into things. I am also not sure if this should be here or in the "small media at large" section, so feel free to move it if appropriate. So, to all of you out there knowledgeable about astrophysics, I'd like to see if anyone has any opinions on my idea for the layout of the Centauri system, which is heavily involved in my scenario.

    It is my understanding that orbits would only be stable within about 2 AU of either element of the Centauri system, discounting the possibility of gas giants ever forming. I have read several articles recently about the plausibility of terrestrial planet formation, however. One paper examined computer simulations of planet accretion from lunar-mass planetisemals and found it was robust within about 1.5 to 2 AU away from either star in the Centauri system. Another looked at the plausibility of planetisemal formation from dust and found that perturbations from the other star would prevent THAT accretion outside of about 0.75 AU from either star. There are those that argue that without gas giants water would not be directed to the inner planets and those that argue that the instability caused by the second star would do the job - I am siding with the latter for now. It is also my understanding that the Centauri system has a higher metallicity than our system, and hence there would have been more heavy elements to form planets.

    My system design relies on planetary migration. I have read theories about how Uranus and Neptune formed in closer than they are now and proceeded to migrate outwards by flinging icy debris from the outer system inwards. I am going to assume that the planets formed in the inner system of either star woud do the same thing and accrete slightly more from the dust and rubble entering the inner system.

    I am less interested in the system about Alpha Centauri B. I am picturing a rockball close in to the star because there is less material in that smaller volume, followed by a large (1-2 earth mass) venus-type world and some cold (since for earth-intensity sunlight you would need to be about 0.75 AU out) rockballs further out, unsure if they should be big enough to keep an atmosphere like Mars.

    Centauri A, the brighter of the pair, I am more interested in. Here I am again picturing a rockball close in, followed by a very large venus-type world (3-ish earth masses), with a moon similar to the Earth's, at around 1 AU. Further out, around 1.2 to 1.3 AU out (somewhere around where you get earth-intensity sunlight) is a planet within 15% of Earth's mass with an asteroidal moon slightly beyond geosynch, on which life has arisen.

    Since Centauri A is 1.5 times as bright as the sun and 5 billion years old or so, and stars brighten significantly over the course of the main sequence, it has brightened significantly since it formed. As such, this third planet was once much much colder than now, almost frozen over, and it has sustained many more impacts than the Earth has due to there being more rubble immediately outside its orbit. Either as a result of these factors, or possibly just because it is very hard to do, life has never gone through most of the complex transitions that occurred here around 600 million years ago. You have all kinds of algae in the oceans and rudimentary plants growing in wet areas on land, and oxygen-producing photosynthesis has evolved producing an atmosphere that is something like 13% oxygen. The most complex animal-like life is tunneling worm-like things.

    Nothing appreciable orbits the pair's center of mass at great distance.


    Any advice on if this is realistic at all, or other ideas, would be appreciated! Thanks!
    I think the idea of terrestrial planets forming in the alpha Centauri system then migrating outwards is unlikely. The migrations of the solar system's outer planets are attributed to interactions with the residual planetesimal disk (and each other). Much closer in to the star things are far different.

    I think you should choose a different stellar system. aCen is hackneyed anyway. Remember Lost In Space?

  3. #3
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    think the idea of terrestrial planets forming in the alpha Centauri system then migrating outwards is unlikely. The migrations of the solar system's outer planets are attributed to interactions with the residual planetesimal disk (and each other). Much closer in to the star things are far different.
    Thanks for that, I've taken some astrophysics in college but it is not my major, its things like this that are the reason I decided to ask. Was trying to apply a mechanism I'd seen invoked to explain something here somewhere else, looks like I did not look into it enough.

    As for Centauri being cliche... There is a REASON it is cliche. I don't know, it seems to me that simply what is nearby dictates things. At Centauri you have two relatively sunlike stars only 4.3 light years away. The next closest at all sunlike place is what, Epsilon Eridani 10 lightyears away and with a crazy-eccentric Jovian planet? Tau Ceti (11.9 LY) and 40 Eridani (16.5 LY) are also interesting... but again, they are further and Tau Ceti seems to have a low metallicity...

  4. #4
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    Quote Originally Posted by Torg View Post
    Thanks for that, I've taken some astrophysics in college but it is not my major, its things like this that are the reason I decided to ask. Was trying to apply a mechanism I'd seen invoked to explain something here somewhere else, looks like I did not look into it enough.

    As for Centauri being cliche... There is a REASON it is cliche. I don't know, it seems to me that simply what is nearby dictates things. At Centauri you have two relatively sunlike stars only 4.3 light years away. The next closest at all sunlike place is what, Epsilon Eridani 10 lightyears away and with a crazy-eccentric Jovian planet? Tau Ceti (11.9 LY) and 40 Eridani (16.5 LY) are also interesting... but again, they are further and Tau Ceti seems to have a low metallicity...
    Nearby is a problem. I like HD 108874 -- nice Jovian right in the habitable zone, could have some interesting satellites -- but it's 223 ly away.

    Noone really understands stellar system formation, so I don't think taking some liberties matters, especially in science fiction.

  5. #5
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    That sounds like an AWESOME system. Boy, if that were at all close I might drop Centauri in a heartbeat...

    Oh, another point to raise regarding Centauri - what is anyone's take on debris in the system, asteroids and the like? I know there arent appreciable dust discs. Does it seem likely to anyone else that anything that wasn't pretty close to one of the two stars has been ejected by now? That would leave just the stars and any terrestrials that managed to form.

  6. #6
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    For the purpose of a work of fiction you can have whatever you like. One or three planets inside the 2 AU distance sounds fine... and we do not yet know that is not what we might find orbiting the Cent., pair. As for the actual composition of the group. We will not need to wait for too long. Giant strides in our ability to see a Earth like planet so near must soon be within our grasp.

  7. #7
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    Quote Originally Posted by astromark View Post
    As for the actual composition of the group. We will not need to wait for too long. Giant strides in our ability to see a Earth like planet so near must soon be within our grasp.
    It might be wiser to choose a more distant star then, lest the author's speculations be refuted before the book is published.

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