Stable Orbit

[flet (Telford)]

Is it possible for a planet to have a long term stable orbit around double or even triple stars?

[hobbit]

I believe a couple of planets have been found to be orbiting binary stars. Not sure about triple.

[julianh72 (Julian)]

The short answer is "Yes".

The longer answer is "Yes, as long as ..."

Check out this link for a discussion of some of the critical issues:
http://en.wikipedia.org/wiki/Habitab...y_star_systems

"Planets that orbit just one star in a binary pair are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or "circumbinary" orbits. It is estimated that 50–60% of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges."

[Eratosthenes (Peter)]

Stable orbit?

Stability is an interesting concept - probably a philosophical problem.

I don't know of anything that is stable over all time frames.

The second law of thermodynamics is difficult to refute and has stood the test of time for several centuries.

The Hubble telescope for example is currently in a "stable" low earth orbit as we speak. But is it really? We know that the tiny frictional resistance caused by the tiny amount of particles and atoms present in that part of the thermosphere causes a tiny drag on the Hubble telescope as it orbits. It is slowing down and so it technically has a decaying orbit. If we don't anything about that decaying orbit, the Hubble will burn up in the atmosphere in 2024 and some of the debri will reach land (or water).

So without referring to a time frame or describing the entire picture, a stable orbit becomes meaningless.

[speach (Simon)]

Also do you mean an orbit that is in the 'goldilocks' zone of both or every one of the stars and doesn't stray. I suppose it's possible the stars would have to have the same mass as each other so they orbit a point between them and the plants orbit wouldn't be elliptical it would more be a figure of 8 with no joining up or a infinity sign but that would mean very complicated night day episodes. A three star system would be easier the stars would need the same mass and be very close together where the barycentre is of equal distance from each other. Then the planet could orbit in a nearly circular orbit. If you thing about it the more stars that are in the system the easier it would be to get a circular obit. Saying all that it would be most if not extremely unlikely that all this would happen. So the short answer is, if it's just a planet then yes it could happen, but if you wanted a planet in the life zone then I'd say very very very unlikely, but it can't be ruled out. Now I've got to get of this picket fence as it very uncomfortable!

Thinking further they would all have to be in the exact same plane.

[julianh72 (Julian)]

Originally Posted by speach

I suppose it's possible the stars would have to ....

I think you're over-thinking things a bit.

Consider a multiple star / planetary system which is analogous to our solar system - except instead of Jupiter, we have a second star, perhaps a few dozen times the mass of Jupiter, but significantly less than the mass of the primary star. Most of the planets orbit around the primary star, with low-eccentricity orbits both inside and outside the orbit of the Jupiter-star. Just as in our solar system, the presence of such a large secondary object has ramifications for the orbital dynamics of the other planets, but things can still stabilise with resonances between the orbits of the Jupiter-star and the nearest planets to it.

One of the smallest known stars is OGLE-TR-122b, a red dwarf star that’s part of a binary stellar system. Its radius has been measured as 0.12 solar radii, or 167,000 km, which is only 20% larger than Jupiter (but with 100 times the mass of Jupiter). The primary is a Sun-like star, but the two stars are closely separated, with an orbital period of 7.3 days. Push OGLE-TR-122b out to 5 AU, and you have the makings of the sort of system I'm thinking of.

A low luminosity star at the distance of Jupiter would certainly change our night-time sky, but it wouldn't necessarily have a great impact on our orbit or climate. (And if you struggle to imagine this system as being stable, just put the Jupiter-star somewhere out past Neptune.) There is no reason why you couldn't have an Earth-like planet at a distance of 1 AU from the primary star - smack bang in the middle of the "Goldilocks Zone".

Now imagine that some of the "moons" of the Jupiter-star are much more massive than Jupiter's actual moons, some being comparable to Earth, so they can be thought of as being "Planets" in their own right. They are much closer than 1 AU to the Jupiter-star, but because it is a red dwarf, it is far less luminous than the primary star, and indeed, some of the Earth-sized moons are in its "Goldilocks Zone".

It's not too hard to imagine a system of this type being "stable" for hundreds of millions or billions of years. It's a fascinating thought - a solar system with two stars, and two independent "Goldilocks Zones"!

[Eratosthenes (Peter)]

https://www.youtube.com/watch?t=180&v=mxpVbU5FH0s

....an interesting short video on the 5 Lagrange points for orbiting satellites. The physics professor being interviewed discusses stable and unstable Lagrange points towards the end.

[mathewb]

Hi,

If your after a planet(s) that are orbiting a binary star - try this one:

http://exoplanet.eu/catalog/ross_458%28ab%29_c/

That catalogue has a list of the majority of all the exoplanets found to date.

The one listed in the link happens to be a binary

Cheers,
Matt.

[xelasnave]

This is news to me, just when I thought I knew everything.
But clearly I now know everything.
If someone had asked me if such systems were possible I would have dismissed the idea.
Excellent thread. Thanks.

[Eratosthenes (Peter)]

Originally Posted by xelasnave

This is news to me, just when I thought I knew everything.
But clearly I now know everything.
If someone had asked me if such systems were possible I would have dismissed the idea.
Excellent thread. Thanks.

"I know that I am intelligent, because I know that I know nothing"

Socrates (died 399 BC)

[xelasnave]

Yes indeed, but I already knew that..

[Eratosthenes (Peter)]

I don't know that