Double stars and exoplanets

[chiltonstar]

May be a daft question, and certainly shows my ignorance, but as 50% of stars are said to be doubles and many have exoplanets, have we found a situation yet where an exoplanet is "shared" by two stars, moving in a figure-of-eight orbit, either in a plane or a 3-D shape?

Chris

[ronin]

I suspect not.

A planet would be closely bound to a star and a double star system would orbit around a centre of gravity that is defined by the stars masses. These would most likely be a greater distance apart.

I would not expect a planet to be far enough away from one planet to fall under and change to the second star.

They are close orbiting stars but I would say any planet would be ejected from such a system.

It may well be that unless a binary is well seperated that no planet would/could stay in such a system. They tend to be unstable and something gets ejected.

[Planetesimal]

The planet Kepler-16 orbits a binary star system:

http://scienceblogs.com/SETI/2011/09/15/kepler-16-exoplanets-around-bi/

[Tiki]

No 'fancy' orbits found so far. (And very far from being a daft question.) I strongly suspect that it is not known whether such orbits are theoretically permissable.

Newton pretty much solved the problem of two orbiting bodies on not much more than the back of an envelope (he did discover calculus to help in this task so i am in no way trivializing the work of The Great Man). Three (or more) orbiting bodies have not yet been succesfully described mathematically, despite being systematically tackled by scientific heavyweights. Most work has been done using computerized number crunching techniques. It is generally believed that in star-star-planet systems that planetary orbits are very sensitive and are thus likely to be relatively unstable unless the stars themselves are close together. The implication of this is that any possible 'fancy' orbits are likely to be relatively short-lived thus making it less likely that we would be able to obseve them.

There are plenty of fancy orbits possible in the vincinity of rotating black-holes though.

[chiltonstar]

No 'fancy' orbits found so far. (And very far from being a daft question.) I strongly suspect that it is not known whether such orbits are theoretically permissable.

Newton pretty much solved the problem of two orbiting bodies on not much more than the back of an envelope (he did discover calculus to help in this task so i am in no way trivializing the work of The Great Man). Three (or more) orbiting bodies have not yet been succesfully described mathematically, despite being systematically tackled by scientific heavyweights. Most work has been done using computerized number crunching techniques. It is generally believed that in star-star-planet systems that planetary orbits are very sensitive and are thus likely to be relatively unstable unless the stars themselves are close together. The implication of this is that any possible 'fancy' orbits are likely to be relatively short-lived thus making it less likely that we would be able to obseve them.

There are plenty of fancy orbits possible in the vincinity of rotating black-holes though.

I had in mind a situation with two stars orbiting each other (fairly closely), with the planet switching orbit as it approached the equal-gravity point when peturbed by a slight gravity change caused by another large planet orbiting one of the stars, or another associated star nearby??

Chris

[Ptarmigan]

he did discover calculus

Umm, well, err, at the risk of going a bit off topic :-) the Great Man developed a method of "fluxions" to help him.

However the calculus that we use today is based on a method of "infinitesimals" developed by Leibniz.

This "who invented what" question led to yet another war betwixt Newton and many others.

Ok, back to orbits :

[Ptarmigan]

where an exoplanet is "shared" by two stars, moving in a figure-of-eight orbit,

My first thought was "No", that a planet could be in a stable orbit _close_ to one of the stars if the stars were far apart, or, if the stars were close then the planet would have to be far distant from both.

But not a fig8 type senario.

Interesting question tho' so I went googling and found this

"Figure-eight orbits are unstable, and can eject the planet from the system."

from a NASA/Goddard site

http://imagine.gsfc....rs/980122c.html

Which I suppose begs the question how could a planet form in that situation to be then ejected some time later ?

Exit left scratching head >>

[stem1989]

I was in a lecture about exoplanets recently and they touched on this, they have found exoplanets orbiting in dual star systems BUT very close to the star, no figure of 8 is possible as it would be quickly ejected out as it would be too unstable an orbit.