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Saint Fool
10-08-2008, 06:44 AM
This is just an earworm of an idea so I'll be happy with links or books that I can read, but this is the set up:

A binary star system with two stars similar to our own. Only one of the stars has planets, one that is habitable. My earworm is that every few years, the orbit of my habitable planets falls between the two stars at their closest approach to each other, creating a period of time where the surface of the planet is uninhabitable and the population must go underground in order to survive.

I'm fairly certain that this set-up has been used before (nothing new under two suns) but I want to know that it is possible.

Sarpedon
10-08-2008, 05:09 PM
I see no reason it couldn't work, so long as the other star is bright enough and close enough to have an effect on your planet.

Suppose your Secondary star (s2) is half as bright as your primary star (s1), and s1 is the same brightness as our sun. So your planet orbits at 1 AU, receiving the same amount of solar energy from S1 as Earth does. If S2 orbited S1 at the same range as Jupiter orbits our sun (around 5 AU), then at its closest it would get to the planet is 4 AU. If it is half as bright as S1, then the amount of energy the planet would get from it is 1/32 the amount of energy it would get from S1, because of the inverse square law (the amount of energy received is divided by the square of the distance).

This should inform you of how bright the stars need to be. Perhaps S1 is the dimmer star, and S2, farther away is several times brighter.

Julie Worth
10-08-2008, 05:21 PM
Some readers might wonder how complex life could have evolved on such a world. But that's not a problem if they're immigrants.

TychoBrahe
10-08-2008, 05:27 PM
I'd be worried about the gravity situation. I'm not sure if planets in such a system could have orbits similar to those in our own; they'd probably end up being highly elliptical, and the planets might eventually become ejected from the solar system entirely. If your habitable planet's orbit brings it directly between the two suns at their closest approach, for instance, it'll be pulled in two directions by the two individual suns. Likewise, at the other end of the orbit, the planet will feel the effect of the two suns pulling in the *same* direction (although the pull of the further sun will be geometrically less at this point).

It's been ages since my college physics classes, but I do remember one of my professors saying that the "three body problem" had never been solved. Not saying a stable solution doesn't exist, but your planet would probably have a bizarre oddball orbit that may have a variety of extremes that would make habitation difficult at various times (not only the heat extreme).

MelancholyMan
10-08-2008, 07:45 PM
My background: B.S. Physics, M.S. Aerspace Engineering, (specialty orbital dynamics.) I do orbital dynamics in my job every day when I'd rather be writing. Alas. But maybe I can help you here and the day won't be a total waste.

First let me see if I understand your solar system: A binary system. Each star has its own planetary system. When the two stars are at perigee conditions on the habitable planets become too warm for life to survive on the surface. This happens every few years. We'll call the star with your habitable planet S1, and the other star S2.

What you describe has certain difficulties. If S1 and S2 are of comparable mass, and their period is on the order of 2-3 years, then they are closer to each other than the sun and Mars. I haven't coded up this scenario but my gut feeling says that in this configuration there aren't going to be any stable orbits around either S1 or S2 unless those orbits are very close - which is bad for life.

If S1 has a mass much greater than S2 it might be possible if the orbit of S2 is highly elliptical. But there are still problems. Jupiter is 10% large enough to be a star. I.e., it needs about 90% more mass. So at a minimum S2 is 90% larger than Jupiter. That would make it big. So for S1 to be large enough to be much more massive than S2, S1 is going to have to be really big. Significantly more massive than the sun. Based on solar type alone, there are going to be problems. A much more massive red star may not be hot enough. A much more massive blue star is going to be too hot and put off way to much hard radiation. And then a massive body swinging through the inner solar system every few years is going to play hell with the planetary dynamics. Again, I haven't run a simulation for this particular scenario (though have played around with qualitatively similar simulations in the past) but I'm thinking it would not be very stable.

Now what might work is a binary system with a period of the few years; perhaps a fairly large G-class star similar to our sun but more massive and hotter. Orbiting it is a much smaller, hot star, with a period of a few years. The habitable planets orbit both stars with a much longer period. Perhaps on the order of ten years. Perhaps at times, when the two stars are right next to each other in the sky, conditions become unbearable, though how life would evolve on such a system escapes me. And if it gets that hot, I'm having trouble imagining a stable atmosphere or long term retention of surface water.

Your scenario implied the surface becomes too hot, but it makes more sense to think that at certain points in the orbit the surface becomes too cold. In this scenario the water can freeze and everything can become dormant. Sort of like an ultra-winter. Millions of cycles of too-hot lead to no water.

To clarify the three body problem, it has no closed form solution of the form (position = a function of position and time.) All this means is that you can't just plug in a future time and calculate the future state. However, it can be solved numerically and is all the time. Space missions are all multi-body problems and are solved all the time to incredible accuracy. Good enough to guide a spacecraft to Titan and drop a probe onto the surface. That's pretty darn good.

Deb Kinnard
10-09-2008, 02:07 AM
I don't remember exactly, but don't double stars orbit a common center of gravity?

ManyAk
10-09-2008, 02:11 AM
All I'll add is make sure that when the planet is between your 2 suns, that it doesn't burn and explode.

Saint Fool
10-09-2008, 04:07 AM
Wow, y'all smushed that earworm flatter than flat, LOL. Thanks for sharing your knowledge and helping me not commit a scientific boo-boo. Of course, I could always throw in a powerful magician or gods who make it all work, but that would be cheating.

Now back to the smaller, but possibly more perilous orbits of my Victorians.

Thanks again.

MelancholyMan
10-09-2008, 06:18 AM
I would go with your idea anyway. It's a cool idea. Seriously, no one is going to care if your world doesn't obey the laws of physics, least of all me. You asked so I answered. But please don't let the fact that it is not physically possible kill your idea. 99% of everything on StarTrek, and 100% of StarWars is completely unworkable within the physical framework that we understand. Just imagine where George Lucas would be today if someone told him we can't travel faster than light so he shelved StarWars. Remember, you are writing fiction. As long as your universe is internally consistent it will work just fine. And that doesn't mean it has to satisfy Newton's Three Laws!

Smiling Ted
10-09-2008, 08:11 AM
Wow, y'all smushed that earworm flatter than flat, LOL. Thanks for sharing your knowledge and helping me not commit a scientific boo-boo. Of course, I could always throw in a powerful magician or gods who make it all work, but that would be cheating.

Now back to the smaller, but possibly more perilous orbits of my Victorians.

Thanks again.

How important is the binary system, as opposed to its effects - that is, a planet whose surface is uninhabitable every few years?

If it's the uninhabitable part you're interested in, you don't need a binary star to achieve it. There are lots of things that might make things nasty on a planetary scale:

1. A primary star that has a regular period of solar flare activity...a variable star, for instance.

2. An asteroid swarm that intersects your planet's orbit on a regular basis.

3. A nearby (in stellar terms) pulsar that regularly irradiates your planet.

and the list goes on...

Julie Worth
10-09-2008, 03:33 PM
I would go with your idea anyway. It's a cool idea. Seriously, no one is going to care if your world doesn't obey the laws of physics, least of all me.

Exactly, this is SF, not a theory to be published in a journal. The second sun is much lighter, of course, and it doesn't take much of an increase in radiation to push the planet into an overheated state--a few percent will do it. As for stability of the orbit, that's where some character waves his arms and talks about planetary resonances. Look at the real solar systems that have been discovered. Many of them are monsters that no one would have dreamed were possible.

The second, much smaller, sun could also orbit inside the orbit of the planet, and every great while its orbit would line up just so. It would normally appear as a very bright star, but at those bad times it would balloon up to where it was no longer a point.

MelancholyMan
10-09-2008, 05:32 PM
Exactly, this is SF, not a theory to be published in a journal. The second sun is much lighter, of course, and it...

No. Avoid technical descriptions. This is all you need:

... and when the two stars were closest to our planet, the surface became too warm for life to survive so we had to move underground...

You never have to mention it again. Believe me, no one is going to question this if your plot is interesting and your characters are compelling.

Chase
10-09-2008, 06:24 PM
S'fool,

I think you've got some good advice to go for it. A similar idea is the 1941 classic short story by Isaac Asimov, "Nightfall." It's won countless awards, is in dozens of anthologies, and has been made into a movie.

The planet in question is within a complicated six-star system where its inhabitants never know darkness -- except every two thousand years when the planet ends up on the outtermost limits of the system and experiences . . . you got it . . . nightfall. Not to be a total spoiler, the resulting darkness is catastrophic.

My point is that even Asimov left the physics involved somewhat vague.

Mike Martyn
10-09-2008, 09:13 PM
If you want the inhabitants to have evolved there, perhaps let them do so in a single star environment. Your second much smaller star comes zinging in at 90 degrees to the plane of the eclptic and goes into tight orbit around the main star.

OK MeloncholyMan, I know the odds are long and I know even a modest star is going to mess up planatary orbits but good. Ah but think of the planatary collisions! Oh the humanity!

Sarpedon
10-09-2008, 09:54 PM
You could always say that any planets prone to colliding with one another have already done so, billions of years back, pulverizing themselves, and the few remaining planets are relatively close to their parent star.

This might give this particular system a rather active comet/meteor schedule, but thats not a bad thing, is it?

benbradley
10-09-2008, 10:34 PM
S'fool,

I think you've got some good advice to go for it. A similar idea is the 1941 classic short story by Isaac Asimov, "Nightfall." It's won countless awards, is in dozens of anthologies, and has been made into a movie.

The planet in question is within a complicated six-star system where its inhabitants never know darkness -- except every two thousand years when the planet ends up on the outtermost limits of the system and experiences . . . you got it . . . nightfall. Not to be a total spoiler, the resulting darkness is catastrophic.

My point is that even Asimov left the physics involved somewhat vague.
I was thinking of that story too, but that was a long time ago (and early in Asimov's writing carreer) and I wonder if a story like that would be published thesedays. Certainly hard SF fans would question the plausibility of all but the simplest planetary systems.

You could always say that any planets prone to colliding with one another have already done so, billions of years back, pulverizing themselves, and the few remaining planets are relatively close to their parent star.

This might give this particular system a rather active comet/meteor schedule, but thats not a bad thing, is it?
That would certainly make life on the planet more "interesting," with history filld with events like this (http://en.wikipedia.org/wiki/Tunguska_event), some them having hit populated areas.

I could see that resulting in a culture that would discourage lerge, densely popuated cities, from the fear of losing too many people from one strike.

Saint Fool
10-11-2008, 08:42 AM
An odd sucking sound is heard .... could it be? YES! The earworm has regenerated itself. Thanks for the encouragement and good suggestions. Printed out. In the idea folder.

PS - Nightfall was the story that actually got me interested in science fiction.

HeronW
10-11-2008, 08:14 PM
I've a binary in a sf tale, where the sapian development happened before the suns had hissy fits, everyone moved below the surface. One can still go out in the 'day' if suited up, otherwise the radiation and heat will do nasty things.

Think Edgar Rice Burroughs 'Warlords of Mars' etc, the sf is pure fantasy but it's a good story!