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Author Topic: Hi all, looking for expert help :)  (Read 7122 times)

Offline mjtobias

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Hi all, looking for expert help :)
« on: 06/01/2015 18:12:03 »
Greetings,

I'm currently working on a fantasy series that takes place on a planet far, far away (yeah, I know), and I'm looking for some expert advice. I'd like for the planet to exist in a binary star system and have multiple moons (one of the plot points involves highly unpredictable and unstable seas and tides). I fully admit I'm not much of a scientist, though I do have an amateur's interest in quantum mechanics and basic physics and math.

In any event, my primary goal is to get the science right. Sure, I could make up an alternate universe where our rules of physics don't apply, but that seems like it would be even more complicated.

Anyway, I look forward to interacting with many of you and hope that some of you can help me make my world credible.


 

Offline PmbPhy

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Re: Hi all, looking for expert help :)
« Reply #1 on: 07/01/2015 07:17:05 »
Greetings,

I'm currently working on a fantasy series that takes place on a planet far, far away (yeah, I know), and I'm looking for some expert advice. I'd like for the planet to exist in a binary star system and have multiple moons (one of the plot points involves highly unpredictable and unstable seas and tides). I fully admit I'm not much of a scientist, though I do have an amateur's interest in quantum mechanics and basic physics and math.

In any event, my primary goal is to get the science right. Sure, I could make up an alternate universe where our rules of physics don't apply, but that seems like it would be even more complicated.

Anyway, I look forward to interacting with many of you and hope that some of you can help me make my world credible.
I'm a physicist myself so I could try to help. What you're looking for is someone who knows celestial mechanics. While I know some of it I don't know all of it. That doesn't mean that I can't learn it. Let me look into it. However if I can help you it will come at a cost.
 

Offline CliffordK

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Re: Hi all, looking for expert help :)
« Reply #2 on: 07/01/2015 09:12:44 »
Feel free to post any questions and comments you have here. 

The tides should be predictable with several moons (or large nearby planets), but they may seem a bit erratic. 

A highly elliptical orbit around the central star (sun) would also create variable tides.
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #3 on: 07/01/2015 14:15:33 »
Well, thanks for the responses :)

One idea I've been kicking around is having long periods (say, 7 year intervals) of relatively mild weather, mostly warm and rather tropical followed by the same length interval of relatively harsh weather, cold with a good deal of precipitation. What type of conditions regarding orbit, planet-tilt, et. al. would this require? Or is it even feasible? How would a binary star system affect this?

Thanks for the help!
 

Offline CliffordK

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Re: Hi all, looking for expert help :)
« Reply #4 on: 07/01/2015 17:10:06 »
Keep in mind that we define days and years based on the spin and orbital period of Earth. 

If another planet had a slower spin or longer orbital period, then they would probably define time differently from us.

In our solar system, Jupiter has an orbital period of just under 12 years.  So, depending on the planetary tilt and eccentricity of the orbit, a planet (or moon) in Jupiter's orbit might have a 6 year summer, and a 6 year winter.

It would be mighty cold that far from the sun, unless one had a sun that was much hotter than our own.

Keep in mind that we also have multi-year weather patterns on Earth including El Niņo, La Niņa, NAO, PDO, AMO, etc without necessarily all the fancy orbital characteristics.
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #5 on: 07/01/2015 17:52:10 »
Keep in mind that we define days and years based on the spin and orbital period of Earth. 

If another planet had a slower spin or longer orbital period, then they would probably define time differently from us.

In our solar system, Jupiter has an orbital period of just under 12 years.  So, depending on the planetary tilt and eccentricity of the orbit, a planet (or moon) in Jupiter's orbit might have a 6 year summer, and a 6 year winter.

It would be mighty cold that far from the sun, unless one had a sun that was much hotter than our own.

Keep in mind that we also have multi-year weather patterns on Earth including El Niņo, La Niņa, NAO, PDO, AMO, etc without necessarily all the fancy orbital characteristics.
Thanks for the response.

What I envision is a planet that is basically like our own, with roughly the same orbital period and rotation speed and tilt. I will likely incorporate some small variance, perhaps make the years 350 days rather than 365 and each day 28 hours instead of 24 (these are just possibilities. I've yet to drill down quite this far into the details.) The primary differences are the extra star and moons. Of course, depending on what's required, I could place the planet further away from or closer to one or both stars and adjust the parabola of it's orbit.

I'm also aware of the variety of weather phenomena that affect our weather patterns and will likely include some similar, though distinct, phenomena into my world.
 

Online chiralSPO

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Re: Hi all, looking for expert help :)
« Reply #6 on: 07/01/2015 19:13:37 »
Sounds like a nifty idea! I am an amateur astronomy enthusiast, but by no means an expert, so perhaps I can be of limited help.

There are many types of binary star systems. To get a planet in a stable orbit you probably want to have the stars fairly close together compared to how far the planet is from each of them (case A in attachment--NOTE: these are not drawn to scale!). It may also work if one star is very massive and the other star is significantly less massive (least massive stars are red dwarfs http://en.wikipedia.org/wiki/Red_dwarf, which are still about 7.5% as massive as our sun), with an orbit much farther out than the plant's orbit (case B). You may even be able to work out a solution for a planet orbiting a small star, which itself orbits the larger star (case C; imagine if Jupiter were large enough to be a red dwarf, then one of its outer moons could be said planet)--I don't know how likely it would be to have a moon orbiting a planet orbiting a star orbiting a star though...

If you opt for the planet orbiting both stars (case A; circumbinary orbit) note that the habitable zone around the stars may be much further out than ours is: it might not be unreasonable to have an orbit that takes 7 of our years... The closer the stars are to each other the faster they will appear to move around each other in the sky of said planet. This will probably have the least variation in the amount of light reaching the planet. Case C would probably have the greatest variation. My guess is the least variation would still be enough to make things interesting without making the planet inhospitable...

These three cases are extremes for which the calculations are easiest, and stable solutions are more likely to be found--of course there are many different ways that the three bodies could orbit one another...

Just for kicks: there is also known system that has four suns and a planet with a (somewhat) stable orbit! (http://www.bbc.com/news/science-environment-19950923 and http://arxiv.org/abs/1210.3612)

« Last Edit: 08/01/2015 01:06:40 by chiralSPO »
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #7 on: 08/01/2015 01:10:41 »
Sounds like a nifty idea! I am an amateur astronomy enthusiast, but by no means an expert, so perhaps I can be of limited help.

There are many types of binary star systems. To get a planet in a stable orbit you probably want to have the stars fairly close together compared to how far the planet is from each of them (case A in attachment--NOTE: these are not drawn to scale!). It may also work if one star is very massive and the other star is significantly less massive (least massive stars are red dwarfs newbielink:http://en.wikipedia.org/wiki/Red_dwarf [nonactive], which are still about 7.5% as massive as our sun), with an orbit much farther out than the plant's orbit (case B). You may even be able to work out a solution for a planet orbiting a small star, which itself orbits the larger star (case C; imagine if Jupiter were large enough to be a red dwarf, then one of its outer moons could be said planet)--I don't know how likely it would be to have a moon orbiting a planet orbiting a star orbiting a star though...

If you opt for the planet orbiting both stars (case A; circumbinary orbit) note that the habitable zone around the stars may be much further out than our is: it might not be unreasonable to have an orbit that take 7 of our years... The closer the stars are to each other the faster they will appear to move around each other in the sky of said planet. This will probably have the least variation in the amount of light reaching the planet. Case C would probably have the greatest variation. My guess is the least variation would still be enough to make things interesting without making the planet inhospitable...

These three cases are extremes for which the calculations are easiest, and stable solutions are more likely to be found--of course there are many different ways that the three bodies could orbit one another...

Just for kicks: there is also known system that has four suns and a planet with a (somewhat) stable orbit! ( newbielink:http://www.bbc.com/news/science-environment-19950923 [nonactive] and newbielink:http://arxiv.org/abs/1210.3612 [nonactive])

I've actually considered all three of these and I agree (with the little I know) that A would likely be the most realistic option, though I prefer C, I'm just not sure if I could make such a scenario work.

Regarding A, what do you suppose that would look like to the citizens of my world? Two relatively small suns rotating around one another...would they be able to see them moving in the sky? Would they see two small suns and just be able to see their different positions throughout the day? These are the kinds of things I need to know for descriptive purposes. I imagine a long, oblate orbit around these stars would account for a very long year, with pretty cold winters twice, though the orbit would have to be extremely oblate to account for any harsh dry and hot periods, and I'm afraid that such an orbit would be highly unstable.

Then again, that's what I'm here for :)

As I wrote, I'd prefer scenario C if it's possible, but I imagine that would result in half a year with no darkness. Am I wrong about that?

Thanks for the response...I'm enjoying reading and learning :)
 

Online chiralSPO

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Re: Hi all, looking for expert help :)
« Reply #8 on: 08/01/2015 04:31:21 »
I doubt that there could be many habitable solutions of type C systems, but I might not have an open enough mind...

As far as how citzens of your world might perceive a type A system:

The two stars could probably orbit each other with a period of hours to weeks. The stars could be very different from each other in terms of size, mass, color (temperature) and brightness (http://en.wikipedia.org/wiki/Stellar_classification) It probably makes the most sense for the two stars and planet all to move in roughly the same plane, in which case the stars would always appear close to each another in the daytime sky and would eclipse/transit one another (could look interesting if they are very different sizes or temperatures). Maybe the two stars could orbit each other in a plane that is quite different from the plane in which the planet orbits, in which case they might never eclipse/transit...

If the stars were very close together and very far from the planet, it may not even be obvious that there are two bodies--it may just look like a single sun that changes brightness (and possibly color).
 

Offline CliffordK

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Re: Hi all, looking for expert help :)
« Reply #9 on: 08/01/2015 05:46:04 »
I'm trying to imagine what it would be like to replace Jupiter with a Red Dwarf sun.  It may actually be relatively stable.  Perhaps push it a little further out?

Once a year, it would be lined up behind the sun, and would be about 43+8 = 52 light minutes away.
Once a year it would be on opposite sides of the earth from the sun, and 43-8 = 35 light minutes away. 
Other times of the year, it would be at other angles. 

I'm seeing notes that the minimum brightness would be about 0.00125% that of the sun (and 4 to 6 times the distance). 

It might toss the tides around a bit, especially during those times when the Sun, Earth, Moon, and Jupiter (red dwarf) were aligned.

No doubt the extra star would throw the seasons out of kilter on a 12 year (6+6) orbit, especially during those times when it was opposite Earth (closest pass) during either the summer or winter which might lead to a warmer than normal summer/winter (even just a degree or two might make a difference) which would be followed by the opposite season 6 months later (when it was at the furthest part of the orbit) and a cooler than normal winter/summer.

When hitting in the spring, it might be a warm spring, and hitting in the fall, a lengthened growing season.
 

Offline JohnDuffield

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Re: Hi all, looking for expert help :)
« Reply #10 on: 08/01/2015 13:10:50 »
One idea I've been kicking around is having long periods (say, 7 year intervals) of relatively mild weather, mostly warm and rather tropical followed by the same length interval of relatively harsh weather, cold with a good deal of precipitation...
Check out the Helliconia trilogy by Brian Aldiss. Here's a couple of bits from the reviews:

"The planet Helliconia orbits the sun-like star Batalix every 480 days (a "small year"). Batalix in turn orbits a white supergiant star, Freyr, once every 2498 Earth years (1825 Helliconian small years). During this time, Helliconia undergoes climate changes ranging from Arctic to Saharan..."

"This is world building at its very best. There is nothing 'unnecessary' about its rich, original and a diverse detail, that is at once 'alien' and disturbingly familiar. Helliconia is a world where biology, ecology and society is turned upside down and inside out the better to present a theme no less than the birth and death of civilization. What if winter lasted one thousand years? Would we come out on the other side with our technology intact? Or would we be doomed, like the Helliconians to a recurring and deadly cultural amnesia? This is a huge book, with a huge theme that is masterfully handled. The writing is beautiful and evocative and very thought provoking..."

 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #11 on: 08/01/2015 16:02:29 »
I'm trying to imagine what it would be like to replace Jupiter with a Red Dwarf sun.  It may actually be relatively stable.  Perhaps push it a little further out?

Once a year, it would be lined up behind the sun, and would be about 43+8 = 52 light minutes away.
Once a year it would be on opposite sides of the earth from the sun, and 43-8 = 35 light minutes away. 
Other times of the year, it would be at other angles. 

I'm seeing notes that the minimum brightness would be about 0.00125% that of the sun (and 4 to 6 times the distance). 

It might toss the tides around a bit, especially during those times when the Sun, Earth, Moon, and Jupiter (red dwarf) were aligned.

No doubt the extra star would throw the seasons out of kilter on a 12 year (6+6) orbit, especially during those times when it was opposite Earth (closest pass) during either the summer or winter which might lead to a warmer than normal summer/winter (even just a degree or two might make a difference) which would be followed by the opposite season 6 months later (when it was at the furthest part of the orbit) and a cooler than normal winter/summer.

When hitting in the spring, it might be a warm spring, and hitting in the fall, a lengthened growing season.

If I were to create my world with this scenario, where Jupiter is the red dwarf and once a year it is on the opposite side of the earth away from the sun, would that result in 24 hours of sunlight for the citizens of earth? Or would it be more like day and dusk rather than day and night?
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #12 on: 08/01/2015 16:03:24 »
One idea I've been kicking around is having long periods (say, 7 year intervals) of relatively mild weather, mostly warm and rather tropical followed by the same length interval of relatively harsh weather, cold with a good deal of precipitation...
Check out the newbielink:http://www.amazon.co.uk/Helliconia-Trilogy-Brian-Aldiss/dp/0006482236 [nonactive] by Brian Aldiss. Here's a couple of bits from the reviews:

"The planet Helliconia orbits the sun-like star Batalix every 480 days (a "small year"). Batalix in turn orbits a white supergiant star, Freyr, once every 2498 Earth years (1825 Helliconian small years). During this time, Helliconia undergoes climate changes ranging from Arctic to Saharan..."


Thanks, I'll check it out.
 

Online chiralSPO

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Re: Hi all, looking for expert help :)
« Reply #13 on: 17/01/2015 14:35:34 »
I just came across a simple toy solar system builder you might be interested in playing with:http://apod.nasa.gov/apod/ap150112.html

there are probably better ones out there, but this one entertained me for a good 20 minutes...
 

Offline RD

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Re: Hi all, looking for expert help :)
« Reply #14 on: 17/01/2015 15:14:17 »
... I'd like for the planet to exist in a binary star system ...

http://en.wikipedia.org/wiki/Three-body_problem

The results of the three-body-problem can be chaotic ... 
t=25s
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #15 on: 17/01/2015 15:48:10 »
... I'd like for the planet to exist in a binary star system ...

newbielink:http://en.wikipedia.org/wiki/Three-body_problem [nonactive]

The results of the three-body-problem can be newbielink:http://en.wikipedia.org/wiki/Chaos_theory [nonactive] ... 
t=25s
Thanks, I'll check it out :)
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #16 on: 17/01/2015 15:51:42 »
I just came across a simple toy solar system builder you might be interested in playing with:http://apod.nasa.gov/apod/ap150112.html

there are probably better ones out there, but this one entertained me for a good 20 minutes...
Looks interesting, thanks :)
 

Offline CliffordK

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Re: Hi all, looking for expert help :)
« Reply #17 on: 17/01/2015 22:27:35 »
If I were to create my world with this scenario, where Jupiter is the red dwarf and once a year it is on the opposite side of the earth away from the sun, would that result in 24 hours of sunlight for the citizens of earth? Or would it be more like day and dusk rather than day and night?
I'm not quite sure.  One could do the calculations.  It may be like a bright full moon (but a smaller point source), or somewhat brighter than the moon.

One would have to do light intensity/distance calculations, and compare it to that of the moon.

With the moon, of course, it is more visible on cloudless nights, which would then depend on where one is located.  Here in Oregon, we get a lot of cloudy days in the winter, and sunny days during the summer.  But there are still a few clear nights.

The trick in your fictional system would be to get the size of the dwarf star just right so that the luminous effects would be significant, but the gravitational effects would be bearable. 
 

Offline mjtobias

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Re: Hi all, looking for expert help :)
« Reply #18 on: 17/01/2015 22:34:37 »
The trick in your fictional system would be to get the size of the dwarf star just right so that the luminous effects would be significant, but the gravitational effects would be bearable.

I've had a couple of posters in other forums suggest that such a scenario would be almost impossible, since even the smallest red dwarf's gravitational pull would make the system so unstable as to make habitability virtually unthinkable.
 

Offline CliffordK

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Re: Hi all, looking for expert help :)
« Reply #19 on: 18/01/2015 12:39:11 »
Maybe... 
You are writing FICTION, so you can include anything that seems believable.   ;)

I was looking up Alpha Centauri A & B, as well as Proxima Centauri that make up either a binary, or a trinary system. 

A & B orbit each other about every 80 years with an eccentric orbit between 11.2 AU and 35.6 AU  (somewhere between the distance from Saturn to the Sun, and Pluto to the Sun).

There is speculation that there may be an Earth-sized planet orbiting very close to Alpha Centauri B (the dimmer star), along with computer programs supporting the possibility (but no observations) of a planet on the inner edge of the habitable zone around α-Centauri B.

I don't have the calculations, but it seems that it should be possible to tinker with the orbits just a bit to get something stable.  A star a bit bigger than Jupiter (and somewhat further out), and a planet like Earth, but perhaps slightly closer to the host star.  But, I don't have anything to accurate track orbits.
 

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Re: Hi all, looking for expert help :)
« Reply #19 on: 18/01/2015 12:39:11 »

 

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