What effects would you see on a terrestial planet in a binary system?

[jaws]

OK, this is actually for some fantasy world building but I am sure Sci-Fi buffs have a greater knowledge of the potential SFX that would be perceived by inhabitants of a planet that has 2 suns. Seasonal, day/night cycles, etc...

 

I am considering both options of an S-type orbit (around only one of the stars) and a P-type orbit (around both suns).

 

I am not really interested in making it real, just consistent enough for fantasy. Especially to consider all the cool effects that might derive from the situation.

 

Any help appreciated.

 

Sci-Fi version of the thread

[TheQuestionMan]

Re: What effects would you see on a terrestial planet in a binary system?

 

Binary Star - Memory Alpha

http://memory-alpha.org/en/wiki/Special:Search?search=Binary+Star&go=1

 

Binary Stars in Fiction

http://en.wikipedia.org/wiki/Binary_stars_in_fiction'>http://en.wikipedia.org/wiki/Binary_stars_in_fiction

 

Binary Star - Wikipedia

http://en.wikipedia.org/wiki/Binary_star

 

Binary Star - Deviant Art

http://www.deviantart.com/#order=9&q=Binary+Star'>http://www.deviantart.com/#order=9&q=Binary+Star

 

Not Binary

http://www.deviantart.com/#order=9&q=Binary

 

 

QM

[Drhoz]

Re: What effects would you see on a terrestial planet in a binary system?

 

depends - if the two stars are close binaries, they might need to be small red dwarfs. In which case the flares are going to savage. Certainly enough to make life very unpleasant on a terrestrial, nearby world - huge leaps in luminosity and UV, aurorae down to the equator, and so on.

 

Given a fantasy setting, your guess is as good as mine what that would do to magical fields.

[Hierax]

Re: What effects would you see on a terrestial planet in a binary system?

 

Search out some stuff on Alpha Centauri.

 

It's a binary star system with a decent goldilocks habitable zone and as our closest neighbor it should have the most data available to provide a model for you to use as a baseline.

[Hierax]

Re: What effects would you see on a terrestial planet in a binary system?

 

Fiction-wise maybe look at Brian Aldiss's Helliconia series apparently it's based in a binary star system and I've heard that it's a good read (haven't got around to it yet myself so I can't confirm).

 

There was a fantasy world in the late 80s that had binary star but for the life of me I can't remember what it was

[Drhoz]

Re: What effects would you see on a terrestial planet in a binary system?

 

Fiction-wise maybe look at Brian Aldiss's Helliconia series apparently it's based in a binary star system and I've heard that it's a good read (haven't got around to it yet myself so I can't confirm).

 

There was a fantasy world in the late 80s that had binary star but for the life of me I can't remember what it was

 

 

There was Medea : Harlan's World too - a shared universe on the moon of a superjovian, orbiting a pair of flare stars. Boiling dry on the Near Pole, cold enough to freeze CO2 the Far Pole, and frequent aforementioned flares.

 

Hard SF, and VERY good

[Silverhawk]

Re: What effects would you see on a terrestial planet in a binary system?

 

Fiction-wise maybe look at Brian Aldiss's Helliconia series apparently it's based in a binary star system and I've heard that it's a good read (haven't got around to it yet myself so I can't confirm).

 

I've read the first two Helliconia Spring and Helliconia Summer. They were enjoyable enough that I got the third volume Helliconia Winter. Unfortunately, its been a couple of years and I still haven't read it.

 

And I seem to recall that Aldiss had scientific consultants in developing Helliconia.

 

I guess I'm going to have to make this my next book.

[jaws]

Re: What effects would you see on a terrestial planet in a binary system?

 

Ahh sounds great I have a lot of reading to do. But I am hoping it will be worth it. Haven't built a world in a while and i feel inspired.

[Drhoz]

Re: What effects would you see on a terrestial planet in a binary system?

 

A fantasy setting would no doubt have interesting mythology about a pair of flare suns. Twin brothers, prone to fits of rage, the aurora the banners of their invisible armies?

[Kraven Kor]

Re: What effects would you see on a terrestial planet in a binary system?

 

Depends on the Binary, as stated... Alpha Centauri A and B are practically part of Trinary system, Proxima Centauri aka Alpha Centauri C being the third. A and B orbit each other, and C is essentially being pulled along by the other two.

 

A and B range from 11 to 35 or so AU apart; a planet in orbit of one would see the other as an incredibly bright star - about as bright as Mars or Venus get at their closest passes to Earth.

 

A planet in such a Binary system would be little different than one in a non-binary system, aside from a few billion years difference in life-span depending on exactly how much influence each star has on the other, etc. Basically, it is harder to attain and especially maintain a stable orbit in a binary system since you have 2 stellar masses in the equation.

 

Binary systems where the stars are closer together would, as noted, make for a very hostile environment, and one probably not conducive to worlds humans could inhabit. Flares, unstable orbits, orbits with massive elliptical variation... lots of roadblocks.

 

I got some great info with just a few Google searches that is helping me flesh out my Star Hero campaign, I can dig up my links sometime if need be but just google "habitable planets in a binary system" and enjoy.

[ajackson]

Re: What effects would you see on a terrestial planet in a binary system?

 

It depends on the details of the binary. For example, looking at the Alpha Centauri system, a planet orbiting A at 1.22 AU (roughly equivalent to 1 AU for earth) would have a distance from B ranging from about 7.25 AU to about 27.9 AU, and would have apparent magnitude ranging from around -19 to -22. From B to A is similar, but A would be somewhat brighter. This might have discernible climate effects, though the other star is still no more than few percent the brightness of the planet's primary.

[Basil]

Re: What effects would you see on a terrestial planet in a binary system?

 

I've been doing a bit of reading on this subject, and can give you a bit more info. Please note I'm no expert, and some of the following may be off. However, I believe it's correct in general.

 

The most important question is, how far apart are the stars? I classify the distances into five classes, very close, close, medium, far, and very far. If neither star is much larger (mass and diameter) than Sol, we can put numbers to those classes.

 

One important thing: stars at "far" and "very far" tend to have highly eccentric orbits (e=>.5). So when talking about distances I need to say if I mean closest, farthest, or average.

 

Stars are very far apart if the farthest distance is >5000 AU. At this point, there's a good chance passing stars will "pull apart" the pair; by 10,000 AU it's a certainty. Note, though, this may take hundreds of millions of years.

 

Stars (remember, I'm speaking of fairly Sol-like) are far apart if their closest distance is >100 AU.

 

Far and very far apart stars will act pretty much like separate stars; each can have Earth-like planets with little effect from the other star. The other star will be a bright point in the sky, moving against the background stars so slowly it can only be told by records kept for centuries or millenia. Interesting, but not much effect on the setting.

 

Stars are very close if their closest distance is <1 AU. These stars have an enormous effect on each other. In particular, they will certainly be tidally locked, so each keeps the same face toward the other. This means that each will be rotating rapidly. A magnetic field has drag when forced through a plasma, and the faster it's forced the more the drag, and the more flares, sunspots, etc. there is. When close enough, the effect is, as a book I read put it neatly, like pulling a mixer out of the batter without turning off the motor. And due to the drag, they will spiral closer and closer to each other in, astronomically/geologically speaking, a short time.

 

Mind you, it's easy to put a planet in a stable orbit around very close stars; the planet orbits the center of gravity of the pair. As a rule of thumb, if the planet/stars distance is >5x the star/star distance, it's stable---IF the star/star orbit is low eccentricity (which it would be) and the planet is orbiting in the same plane as the stars are---which means the "thrown off" stuff is going to hit the planet. In short, with stars very close, radiation becomes a life-killer.

 

Stars are close if the closest point is <10 AU (but not close enough to be "very close"). Stars that are close are a problem: although the radiation and such of very close stars isn't (as much of) a problem, there's no useful and stable orbit for the planet to be in. If it's close enough to one but not the other to be stable, it's going to bake. If it's far enough away to orbit both, it's going to freeze. Mind you, if you use a pair of O class stars at ~5 AU, you could put a planet in orbit around both and not freeze---however, O class stars put out a lot of hard radiation, so life is not likely. Also, O class stars are "very close" at that distance.

 

Stars whose closest approach is >10 AU but <100 AU are at medium distance. At this distance, a planet can orbit one but not the other at a distance conducive to life (remember, we're dealing with stars neither of which is much larger than Sol). Now, the "other" star will have gravitational effects on the planet, so the planet will not have a simple elliptical orbit, It will, however, stay within a ring or torus shaped zone around its star.

 

This is what I find the most interesting situation of a planet of a double star. The orbit will change (eccentricity, average distance, line of apsids, etc), as will the axial tilt (amount and direction) in a time frame that can be as short as a human lifetime (or as long as a few centuries). IOW, while it takes Earth tens of thousands of years for the precession of the equinoxes to make a full circle, it could take a planet in a binary system only a few centuries. Note too, that the rate of change may not be constant; indeed, it might be possible the change in the rate of change might be noticeable within a single life-time.

 

Thus, the old man of the village could, one a night in early spring, gather around the youngsters--not the children (this is not a fit matter for them)--those in early adolescence, and tell them how he remembers, when he was their age, that the tribe lived farther down the side of the valley, and that where they are right now was covered in snow half the year. The Jungle People didn't live in this valley, because it was covered with forest all the way to the bottom! And you knew spring was coming when the constellation of the Hunter, the one that's overhead right now, was just rising at sunset. For you see, oh you who look forward to the Rite of Adulthood, the sky changes, even within the memory of a single man. Indeed, I remember hearing the oldest of the tribe speak of how much the sky had changed in his life, just as you now hear me. And as some of you do, I scoffed--oh, only in my head--at such a thing. But it is true, yes,....

 

Well, you get the idea.

[Ms Superior]

Re: What effects would you see on a terrestial planet in a binary system?

 

Ms Superior arrives from the Fantasy Board, reads, and goes followed by

 

That's a magnificent idea! I don't remember ever seeing that used!

[input.jack]

Re: What effects would you see on a terrestial planet in a binary system?

 

I recently started a fantasy game with two suns and three moons.

 

Just for effect.

 

Do I have to kill all my PCs now?

[ajackson]

Re: What effects would you see on a terrestial planet in a binary system?

 

Do I have to kill all my PCs now?

Yep. As everyone knows, fantasy games are required to precisely follow the laws of physics.

[input.jack]

Re: What effects would you see on a terrestial planet in a binary system?

 

Yep. As everyone knows' date=' fantasy games are required to precisely follow the laws of physics. [/quote']

 

Dang.

 

Oh well, I guess I can go to Star Hero, where such things arent as important ;P

[jaws]

Re: What effects would you see on a terrestial planet in a binary system?

 

Stars whose closest approach is >10 AU but <100 AU are at medium distance. At this distance, a planet can orbit one but not the other at a distance conducive to life (remember, we're dealing with stars neither of which is much larger than Sol). Now, the "other" star will have gravitational effects on the planet, so the planet will not have a simple elliptical orbit, It will, however, stay within a ring or torus shaped zone around its star.

 

I am looking at 20 AU, I am hoping it will be neough for minor climate effects and for a great cycle (the period of the suns) to be 80 years so that changes can be seen in one lifetime. Especially since my years are short 256 days.

 

Suns are actually smaller than Sol so about .82 AU for my life sustaining planet on the primary witht he secondary being a red dwarf.

 

This is what I find the most interesting situation of a planet of a double star. The orbit will change (eccentricity, average distance, line of apsids, etc), as will the axial tilt (amount and direction) in a time frame that can be as short as a human lifetime (or as long as a few centuries). IOW, while it takes Earth tens of thousands of years for the precession of the equinoxes to make a full circle, it could take a planet in a binary system only a few centuries. Note too, that the rate of change may not be constant; indeed, it might be possible the change in the rate of change might be noticeable within a single life-time.

 

Thus, the old man of the village could, one a night in early spring, gather around the youngsters--not the children (this is not a fit matter for them)--those in early adolescence, and tell them how he remembers, when he was their age, that the tribe lived farther down the side of the valley, and that where they are right now was covered in snow half the year. The Jungle People didn't live in this valley, because it was covered with forest all the way to the bottom! And you knew spring was coming when the constellation of the Hunter, the one that's overhead right now, was just rising at sunset. For you see, oh you who look forward to the Rite of Adulthood, the sky changes, even within the memory of a single man. Indeed, I remember hearing the oldest of the tribe speak of how much the sky had changed in his life, just as you now hear me. And as some of you do, I scoffed--oh, only in my head--at such a thing. But it is true, yes,....

 

Well, you get the idea.

 

This is the effect I am going for but not so extreme. Keeping the second sun smaller, and a diffrent color for the lighting effects. I want to make one person on average live atleast a full cycle (80x256 days) which should be easiy with human current physiology as it is only about 58 earth years. Some of my "human" races could easily live out 2 full cycles whcih should be diffrent but never radically so.

 

Yep. As everyone knows' date=' fantasy games are required to precisely follow the laws of physics. [/quote']

 

Of course they are, especialy machitech physics. If they don't your would will be invaded by rules laweyer players that will dedicate ther gaming hours to making your DMing miserable

[Basil]

Re: What effects would you see on a terrestial planet in a binary system?

 

I recently started a fantasy game with two suns and three moons.

 

Just for effect.

 

Do I have to kill all my PCs now?

 

No, just say that gravity works a leeeetle bit differently. But don't say how it's different.

[Basil]

Re: What effects would you see on a terrestial planet in a binary system?

 

I am looking at 20 AU, I am hoping it will be neough for minor climate effects and for a great cycle (the period of the suns) to be 80 years so that changes can be seen in one lifetime. Especially since my years are short 256 days.

 

Suns are actually smaller than Sol so about .82 AU for my life sustaining planet on the primary witht he secondary being a red dwarf.

OK, a smaller "other" star will mean less disturbance of the planet's orbit. Note, though, that class M stars will have a mass of .2 to .45 that of Sol -- well, for Main Sequence stars; some of the other types (Ia, Ib, etc., etc.) are more massive. So, a red "dwarf" (which is actually a Main Sequence star) will still have a significant effect on the planet's orbit. Just not as much as my original description.

 

 

This is the effect I am going for but not so extreme. Keeping the second sun smaller' date=' and a diffrent color for the lighting effects. I want to make one person on average live atleast a full cycle (80x256 days) which should be easiy with human current physiology as it is only about 58 earth years. Some of my "human" races could easily live out 2 full cycles whcih should be diffrent but never radically so.[/quote']

 

Well, sounds to me like your results will be reasonable, given the set-up. Just remember that historical records will have the full range of climate changes, for anyone that cares to dig through the records.

[ajackson]

Re: What effects would you see on a terrestial planet in a binary system?

 

Well' date=' sounds to me like your results will be reasonable, given the set-up. Just remember that historical records will have the full range of climate changes, for anyone that cares to dig through the records. [/quote']

Assuming such historical records exist. In a sufficiently primitive society, they might not, or they might exist but not in a place the PCs have much access to.

[IndianaJoe3]

Re: What effects would you see on a terrestial planet in a binary system?

 

Assuming such historical records exist. In a sufficiently primitive society' date=' they might not, or they might exist but not in a place the PCs have much access to.[/quote']

 

"Primitive" societies on Earth have kept surprisingly sophisticated records. If it's important, it will get recorded somehow.

[Kristopher]

Re: What effects would you see on a terrestial planet in a binary system?

 

The homeworld of one the alien species in my science fiction setting orbits a star slightly smaller than the sun (K1V), which has a red dwarf (M2V) companion star distant enough to not disturb the planets in the system. IIRC, at that distance, it would be bright enough to be the brightest star in the night sky, but not obviously another sun until the civilization there is beyond the "mk 1 eyeball" as its only observational instrument.

[Basil]

Re: What effects would you see on a terrestial planet in a binary system?

 

The homeworld of one the alien species in my science fiction setting orbits a star slightly smaller than the sun (K1V)' date=' which has a red dwarf (M2V) companion star distant enough to not disturb the planets in the system. IIRC, at that distance, it would be bright enough to be the brightest star in the night sky, but not obviously another sun until the civilization there is beyond the "mk 1 eyeball" as its only observational instrument.[/quote']

 

OK, that brings up a question I've been trying to find the answer to: How small can a lighted circle be (in arcseconds, milliradians, or whatever), and still be seen as a circle and not a dot? For example, how small a star (or a moon) will be seen as an "other sun" rather than "a bright star"?

 

 

EDIT: OK, thanks to this post by Cancer, I can say it's about 1 to 2 minutes of arc. An M5V star would have a radius about .358 that of Sol: call it 249,000 km. So, it would be seen as a point (i.e., have a visual diameter of 1 minute of arc) at 11.44 AU; and perhaps at as little as 5.72 AU (visual diameter of 2 minutes of arc).

 

Interpolating the data I have, indicates an M2V would have a radius ~.473 that of Sol, giving distances of 30.26 AU and 15.13 AU. Still fairly close.

 

Oh, and the distances for Sol are 31.99 AU and 15.99 AU. Which means that from Uranus and Neptune, Sol may be seen as only a dot, and that from Pluto, for most of its orbit, it will be.

[jaws]

Re: What effects would you see on a terrestial planet in a binary system?

 

OK, that brings up a question I've been trying to find the answer to: How small can a lighted circle be (in arcseconds, milliradians, or whatever), and still be seen as a circle and not a dot? For example, how small a star (or a moon) will be seen as an "other sun" rather than "a bright star"?

 

 

EDIT: OK, thanks to this post by Cancer, I can say it's about 1 to 2 minutes of arc. An M5V star would have a radius about .358 that of Sol: call it 249,000 km. So, it would be seen as a point (i.e., have a visual diameter of 1 minute of arc) at 11.44 AU; and perhaps at as little as 5.72 AU (visual diameter of 2 minutes of arc).

 

Interpolating the data I have, indicates an M2V would have a radius ~.473 that of Sol, giving distances of 30.26 AU and 15.13 AU. Still fairly close.

 

Oh, and the distances for Sol are 31.99 AU and 15.99 AU. Which means that from Uranus and Neptune, Sol may be seen as only a dot, and that from Pluto, for most of its orbit, it will be.

 

Yes, i fuggured I may have to exagerate the visual size of the dwarf which is about .6 Sol.

 

Class Temperature in degrees Kelvin Mass (Mass of our sun = 1) Radius

(Radius of Sun=1)

Terrestrial Equivalent Orbit

in AUs (life)

Lifetime in billions of years K5 4350 .670 .684 .39 long

Considering the distance I may have to exagerate the visuals of its size to vary between 2'' at its most distant point to 4'' at its nearest. I can balme it on the atmosphere or magic or something.

 

Using this for help at world builders

[Ryjrunr]

Re: What effects would you see on a terrestial planet in a binary system?

 

Yes, i fuggured I may have to exagerate the visual size of the dwarf which is about .6 Sol.

 

Class Temperature in degrees Kelvin Mass (Mass of our sun = 1) Radius

(Radius of Sun=1)

Terrestrial Equivalent Orbit

in AUs (life)

Lifetime in billions of years K5 4350 .670 .684 .39 long

Considering the distance I may have to exagerate the visuals of its size to vary between 2'' at its most distant point to 4'' at its nearest. I can balme it on the atmosphere or magic or something.

 

Using this for help at world builders

 

cool site!