The Possibility of Planets in Alpha Centauri

[menellom]

I'm curious to hear the space.com community's opinion on the possibility of planets in the Alpha Centauri binary system (as well as Proxima Centauri)

A discussion with one of my friends some how led us to Alpha Centauri, my friend made the case that there would not likely be any planets (habitable or otherwise) in the system because a planet would not be able to maintain a stable orbit in a binary system.

Well, the discussion didn't sit well with me and later on I decided to crunch the numbers for myself.

Assume a hypothetical near-Earth mass planet is orbiting Alpha Centauri B at about 1 AU. At their closest, Alpha Centauri A and B are 11.2 AU apart, and while that is fairly close considering, the force of gravity between the planet and A would, at the most, only be a little less than twice the force between the Earth and Moon. Maybe I'm wrong but that doesn't sound like it'd be enough to disrupt an otherwise (mostly) stable orbit of a planet in B's habitable zone.

Just a thought but I'm hoping it can lead to a larger discussion.

 

[Solifugae]

Is the most likely gravitationally stable scenario the one where it orbits one of the stars...

Or where it orbits both?

If the second case is even at all possible, any planets would be expected to be extremely cold, and I think that the orbit/s would be elliptical.

 

[MeteorWayne]

Well, over short periods (a few billion years) it might be stable, but after that, not so much.

There was also an episode of "The Universe" on the marginally accurate History Channel discussing Centauri planets today.

 

[thnkrx]

Alpha Centauri got nixed from the primary SETI search list because while a planet or two could be in orbit about either star, the gravitational stresses were such that it would be difficult for a planet to maintain a stable orbit in either stars habitable zone. (difficult, not impossible).

Mentioned elsewhere was the possibility of frequent meteor/asteriod bombardment as asteriods in the gravitational field of the one star could be brought into the path of a planet, habitable or otherwise, orbiting the other star fairly often.

(then again, most of the nearby (8 parsecs or less) relatively sunlike stars got nixed from the SETI search list for one reason or another, including the other big favorate 'tau Ceti' - though I find their reasons for dropping that one (low metallicity) to be more disputable than the rational for dropping Alpha Centauri.

 

[menellom]

A slight correction/modification to my original statement I did some searching and the accepted 'habitable zone' of Alpha Centauri B would be around .7 AU

A planet orbiting B at 1 AU (as I had originally calculated) would experience 3.712 x 10^20 N between itself and Alpha Centauri A (a little under twice that between the Earth and Moon) At .7 AU it would actually be closer to 3.5 x 10^20 N - only a 6% difference but worth noting

As Meteor suggested the any orbit wouldn't be likely to stay stable forever, a few billion years at most. Still, the possibility of any planets existing in the system raises interesting possibilities

 

[nimbus]

There was a paper concerned by this, but I can't recall if it only covered planet formation, or planet survival.

 

[Astro_Robert]

I too thought I had recently read an article about the possibility of terrestrial planets close in to either star. I did a search on 'alpha centauri plents' and I did locate a google article, but what I read before had more information, in addition to nice pictures like these.

http://aether.lbl.gov/www/classes/p139/speed/Alpha-Centauri.html

 

[menellom]

Thanks for that Rob, interesting read. It definitely suggests the possibility that planets around either star could maintain a stable orbit for some time (if not indefinitely).

Also, the point it makes at the end is quite accurate. If an Earth-like planet were discovered around any of the stars in Alpha Centauri, demand for a plan and the technology to reach it would be immediate and passionate. Heh, NASA would get all the funding it could ever want :lol:

 

[ZenGalacticore]

I thought Alpha Centauri A and B orbited each other at about the distance Neptune is from the Sun? No? In fact, a little further than Neptune. Something like 2 billion miles. I also thought we had discovered some planets--Jovians--orbiting more distant binaries.

Seems like 2 billion miles might leave some room for at least a couple of planets. And B is a lower mass, K class star like Epsilon Eridanae, isn't it?

 

[menellom]

The closest A and B come to one another is about the same distance as Saturn from the Sun

 

[ZenGalacticore]

The closest A and B come to one another is about the same distance as Saturn from the Sun

Well, if that's the case, then I doubt that there are any planets--whether Jovian or Terrestrial-- in between the two stars. The gravitational tango would rip apart any planets. Well, wouldn't it?

 

[MeteorWayne]

It wouldn't rip them apart, but would probably eject them from the system

 

[menellom]

The closest A and B come to one another is about the same distance as Saturn from the Sun

Well, if that's the case, then I doubt that there are any planets--whether Jovian or Terrestrial-- in between the two stars. The gravitational tango would rip apart any planets. Well, wouldn't it?

Well you know there IS a planet hunting space telescope in orbit right now... there's an easy way to find out for sure.

 

[neilsox]

If a planet is at 0.8 AU from Centauri A and one at 0.5 AU from Centauri B, both tide locked to their star and close to circular orbit, with very little tilt of the axis the portion of each planet where the Sun is overhead, will be about 212 f =100 c, but the twilight zone will have comfortable temperatures for humans, most of the time. The dark side may trap most of the water in a great ice cap, unless the atmospheres are thick enough to allow some of the ice to melt at least rarely.
With a thick atmosphere, food crops can likely be genetically altered to thrive at temperatures too hot for humans, where there is enough light for photosynthesis. Neil

 

[Floridian]

Thanks for that Rob, interesting read. It definitely suggests the possibility that planets around either star could maintain a stable orbit for some time (if not indefinitely).

Also, the point it makes at the end is quite accurate. If an Earth-like planet were discovered around any of the stars in Alpha Centauri, demand for a plan and the technology to reach it would be immediate and passionate. Heh, NASA would get all the funding it could ever want :lol:

We have already found an earth like planet that might have life - Mars. But nobody gives a rats ***.

 

[amshak]

Alpha Centauri.

The posibility is there . Visite this site -
http://chview.nova.org/solcom/stars/alp-cent3.htm

 

[brellis]

Prior to the crash of the old SDC forums, I began a thread about multiple life-bearing planets orbiting a star or a binary system. Somewhere in that thread is a citation of a study showing that in the average binary system, the possibility of planet formation is likely quite common. Planets could be orbiting around both A and B or around one star.

Quick Google: http://www.space.com/scienceastronomy/0 ... stars.html

The research group also ran simulations that mimicked Alpha Centauri - the nearest binary system to Earth, where the closest the two stars come is about 11 AU. The secondary star apparently acts like Jupiter does in our solar system - limiting how far out planets can form. The results showed several terrestrial planets were possible around either of the stars.

Planets have not yet been seen in the Alpha Centauri system, but small mass planets cannot yet be ruled out.

Centauri should be examined VERY closely!