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Kebsis
2004-Aug-12, 09:09 PM
I read an article on alpha centuri being a good candidate for life-harboring planets, but it was published in 1997 and I was wondering if any new developments have come forth in regards to this.

Thanks

Tacitus
2004-Aug-13, 12:36 AM
I read an article on alpha centuri being a good candidate for life-harboring planets, but it was published in 1997 and I was wondering if any new developments have come forth in regards to this.


I just read a paper published in 2001 (sorry, don't have a reference - found it via Google) which confirmed earlier research that planets could form in stable orbits in the larger star's habitable zone. However one of the more common solutions to their n-planet simulations was that those orbits became unstable after 50my casing the planets to be ejected from the system.

So, given that to have life around Alpha Centauri you need planets, it appears that it's still possible - but maybe not too likely.

Mike

Normandy6644
2004-Aug-13, 03:40 AM
That would be kind of cool, especially since with some more advances in technology it is potentially reachable in terms of spacecraft.

Kebsis
2004-Aug-13, 07:41 AM
Well I dunno about actually getting their via spacecraft (manned or not) but I could certainly see being able to take more precise readings of the system with advanced telescopes and whatnot.

dvb
2004-Aug-13, 08:08 AM
Isn't Alpha Centauri a trinary system? I know I'm not well versed in this myself, but wouldn't a planet get kind of hot when its orbit is between Centauri A and B, or are they too far apart for the temperature of 1 star to effect a planet in orbit around the other? I'm also wondering if life could evolve on an imbalenced cycle where half the year most of your light comes from 1 star, and the other half receives a great deal more light from the other.

eburacum45
2004-Aug-13, 09:18 AM
No; the third member of the trinary, Proxima, is ten thousand astronomical units away, and would be a fifth magnitude star to the naked eye.

Neither of the main stars would be bright enough to warm the planets of the other appreciably; only the brighter of the two would ever appear as more than a point of light as seen from the other's planets (if any).

At its closest, Alpha Centauri A show a tiny disk, and would be 100 times as bright as the Moon as seen from a hypothetical planet around Alpha Cen B; it would turn the night sky dark blue and drown out most of the stars, but would hardly add any warmth.

dvb
2004-Aug-13, 09:30 AM
No; the third member of the trinary, Proxima, is ten thousand astronomical units away, and would be a fifth magnitude star to the naked eye.

Neither of the main stars would be bright enough to warm the planets of the other appreciably; only the brighter of the two would ever appear as more than a point of light as seen from the other's planets (if any).

At its closest, Alpha Centauri A show a tiny disk, and would be 100 times as bright as the Moon as seen from a hypothetical planet around Alpha Cen B; it would turn the night sky dark blue and drown out most of the stars, but would hardly add any warmth.

Ok, cool. Thanks for the explanation. :)

Ut
2004-Aug-13, 02:33 PM
So, given that to have life around Alpha Centauri you need planets, it appears that it's still possible - but maybe not too likely.

That's the same sort of biased thinking that says you need water, or carbon. LAWKI needs these things. We don't know a huge variety of life, univesally speaking, and have no way of knowing what kind of conditions are needed for any and all kinds of life to form. It's not like we've managed to create any ourselves...

Glom
2004-Aug-13, 04:25 PM
So could there be planets ejected from the system out there? Maybe exoarcheology might have a future.

Working on Celestia, I find that A never gets above -20 from B and B never gets above -18 from A at 1AU from either (although B is K1 so that probably isn't the best candidate anyway). Isn't the full moon -16?

Kebsis
2004-Aug-13, 07:42 PM
So, given that to have life around Alpha Centauri you need planets, it appears that it's still possible - but maybe not too likely.

That's the same sort of biased thinking that says you need water, or carbon. LAWKI needs these things. We don't know a huge variety of life, univesally speaking, and have no way of knowing what kind of conditions are needed for any and all kinds of life to form. It's not like we've managed to create any ourselves...

So you're saying you expect to find life...without a planet to live on?

Brady Yoon
2004-Aug-13, 08:15 PM
So you're saying you expect to find life...without a planet to live on?

Not expecting. He's probably trying to say that we don't know that much about life; where it can form, how it began, etc, we can't limit the formation of life to planets. Yes, planets probably are the most likely places where life can start. But we only know of one case, so it's better if we have an open mind.

Glom
2004-Aug-14, 03:55 PM
I agree with Brady. Life could easily start on a moon.

eburacum45
2004-Aug-14, 08:05 PM
But you don't get a moon without a planet; them's the rules.

Glom
2004-Aug-14, 10:11 PM
Picky, picky, picky.

Kaptain K
2004-Aug-15, 05:52 AM
Isn't the full moon -16?
Closer to -13 (-12.6 IIRC).

eburacum45
2004-Aug-15, 06:43 AM
Well, my usual source for this sort of thing let me down; Jim Kaler gives a brightness for Proxima as seen from A+B, but not A+B as seen from each other;
but I remembered a discussion of this topuic by Grant Hutchinson over at Celestia; he says that A would be a thousand times as bright as the full Moon when seen from B (at it's brightest and closest, of course)...



Since the two stars can be as close as 11AU and as far apart as 35AU, the brightness varies. At closest approach, A shines at magnitude -22.0, and B at magnitude -20.6; at farthest separation, A shines at -20.4, B at -19.0.
This is roughly 1/500th as bright as the Sun in Earth's sky

and it is bright enough to burn a hole in your retina...