[watsisname]

At closest approach the stars are about 11 AU from each other.  Planets orbiting the B star can have stable orbits up to about 3 or 4 AU.  For comparison, the planet in question orbits at roughly 0.04 AU.

[Dragon]

Apparently stable enough not to take this planet out of its orbit. However, it's highly unlikely for there being a planet in the habitable zone of both these stars. If there's an interesting planet in alpha centauri, it's probably lurking in proxima.

Proxima Centauri is a rather pathetic red dwarf. I wouldn't count on anything habitable around it. On the other hand, both Alpha Centauri A and B are comparable to Sun and given 11AU distance between them, their habitable zones probably wouldn't really intersect (at least from what I know. Alpha Centauri is a complex system).

[watsisname]

Proxima Centauri is a rather pathetic red dwarf. I wouldn't count on anything habitable around it.

Astronomers used to think this as well, but recently we have been finding out that habitability is very complex, and a few studies have shown that we can't rule out the existence of habitable planets around M-dwarf stars afterall.

You're correct about the habitable zones of α Cen A and B (going with the original and somewhat dated definition of the term).  There would be one of these zones around each of the two stars, of about the same size as Sol's, and orbits within these zones would be stable over million+ year periods.

[redsniper]

Eh, I like io9, but they're way behind on this.  This planet was discovered last year.

Well no one told me about it!

[perihelion]

Astronomers used to think this as well, but recently we have been finding out that habitability is very complex, and a few studies have shown that we can't rule out the existence of habitable planets around M-dwarf stars afterall.

But the habitable zone around an M-class red dwarf would be so close to the star that any flare activity would utterly crispy-critter any life on the surface.  I thought that had been accepted for decades.  Has that understanding changed, or is there some other scenario that might push the "habitable zone" further out from even such a dim star?

[watsisname]

You are correct on the increased solar activity and flaring, but its implications for habitability are not that simple.   Nor is it the only factor to habitability that needs to be considered.

The biggest problem from solar activity is that it enhances atmospheric loss.  Note, atmospheric loss comes in two flavors:  thermal and non-thermal.  Thermal loss depends on the atmosphere’s composition, its temperature, and the surface gravity of the planet.  Non-thermal escape (which for most planets is less significant than many people seem to think) depends on solar wind activity / CME’s and the presence of a magnetic field.   Studies have shown that solar activity from M stars would be a problem for earth-like worlds in their habitable zones, but super-earths would be fine.   Radiation would not necessarily be a problem to surface life – much of this radiation is absorbed by the atmosphere itself.  Life on the surface may also be protected underground or water, and it has been demonstrated that life can be very radiation tolerant.  (Radiophiles)

Other important factor to consider is tidal locking.  The time it takes for a planet to become tidally locked to its star depends strongly on its orbital distance, and the habitable zone of M-stars is very close, so planets may be expected to become synchronously rotating on much shorter timescales.  This has implications for atmospheric stability, dynamics, and climate.  There can even be such bizarre outcomes as complete atmospheric collapse, where the entire atmosphere literally freezes out on the cold anti-solar side of the planet.  But studies have shown that there are a wide range of conditions for which the atmospheres of planets orbiting M-stars are stable.

Interested readers may find the following links informative:

http://online.liebertpub.com/doi/abs/10.1089/ast.2006.0125
http://online.liebertpub.com/doi/abs/10.1089/ast.2006.0128
http://online.liebertpub.com/doi/abs/10.1089/ast.2006.0124
http://online.liebertpub.com/doi/pdfplus/10.1089/ast.2006.0123
http://online.liebertpub.com/doi/abs/10.1089/153110703769016488
http://online.liebertpub.com/doi/abs/10.1089/ast.2005.5.706?journalCode=ast
http://www.sciencedirect.com/science/article/pii/S0019103597957936

[watsisname]

Eh, I like io9, but they're way behind on this.  This planet was discovered last year.

Well no one told me about it!

Actually, we did.

[perihelion]

Bugger all!  How the heck did I forget this???

[redsniper]

Eh, I like io9, but they're way behind on this.  This planet was discovered last year.

Well no one told me about it!

Actually, we did.

Well then I...

Spoiler:

forgot

... and got excited all over again.

[perihelion]

Yeah!  I mean, I am having an "oh gosh I'm such a duffus" moment, but at the same time it is still AWESOME!!!!
[insert goofy grin here]