Question on Red Dwarf Binary Tidal Locking

[Althistorybuff]

Question from an amateur writer:

 

Most planets around Red Dwarf Stars, at least close in, are tidally locked due to proximity.

Would this change for planets orbiting a pair of very Close Binary Red Dwarf stars (probably a two or three day mutual orbit)?

 

Since the planet is being dragged by two different suns, often from two different locations when the planet is orbiting from the "side" and can see the suns from two different angles, would the planet be tidally locked is some way?

 

Maybe locked to the common barycenter between the stars?

Or would this dual source of gravity allow for the planet to retain its rotation, perhaps even encouraging it?

 

Also, related, do tidally locked planets retain their magnetic fields, at least strong ones, if they don't rotate/spin?

 

Are tidally locked planets potentially difficult to retain life without a strong magnetic field?

 

Thanks.

[imatfaal]

Would a planet closely orbiting a binary not be a three body problem? At a great distance you can reduced the binary to a single mass and get a great approximation - but close orbit would mean that you would need to take each star separately. If it is a three body problem then there is no analytical solution and also more often than not no common outcome. Iff the planet is small enough in comparison to the star then I guess you could model the two stars as a two body problem and obtain a complex solution and then map a route for the planet - but I could not begin to tell you the mass ratios that would allow that simplification

 

On an extraneous side note - have a read of the Three Body Problem by Liu Cixin. Chinese Sci-Fi which is very different and terrifying in its backstory. Edit - it also directly relates to your OP question

[Althistorybuff]

I would assume that the star would outweigh any planet by hundreds of thousands (each star) so I'm not sure if the three body problem would apply.

[imatfaal]

From what I can gather the following scenarios will NOT be stable

1. Orbiting just one star of binary with the distance to the star not being orbited around at greater than 1/6 of the distance to star being orbited

2. Orbiting both stars if the distance to stars is not significantly greater than distance between stars - at least 2 and a half times the distance

 

That does not mean outside that space the orbits will be stable.

[Althistorybuff]

Thanks, I think that those were the general ratios I've been hearing.

I'm leaning towards the planet orbiting both closely-locked suns.

I can't seem to get much response on whether this orbit around two gravitational masses would halt tidal-locking. I've tried a few forums.

Edited March 22, 2017 by Althistorybuff

[imatfaal]

Thanks, I think that those were the general ratios I've been hearing.

 

I'm leaning towards the planet orbiting both closely-locked suns.

 

I can't seem to get much response on whether this orbit around two gravitational masses would halt tidal-locking. I've tried a few forums.

 

The answer is kinda moot - if the planet is close enough to be so influenced by the central mass of two very close stars and thus become tidally locked then it will not be in a stable orbit. If it is stably orbiting a close binary at a decent distance then it will probably not be tidally locked.

 

However there maybe be stable orbits which are also close - it is just that we can neither predict nor analyse them; so it may be tidally locked or it may not.