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Alpha Centauri

Based on what is known about this facinating trinary neighbor, what do you think the likleyhood of planets, what types, and the possibility of at least lower lifeforms?

How would you handle travel of the 23 AU between AC-A and AC-B and the 13K AU to Proxima?
Travel is easy: Jump! (23 AU is a LONG way sublight... several weeks with constant burn drives.)
The Alpha-Centauri AB system has a high metallicity, maybe up to twice as much as Sol, which means that the ingredients for rocky planets are within the system. Therefore I think it is likely (about 70% likely) that the AB system has some terrestial planets in close orbits to the individual stars (A & B) within about 3-4 AU's. The likelihood of a gas giant is smaller and if present would probably be a small gas giant like Neptune because the orbits of the two stars would tend to 'sweep' gas giant building material out of the binary system from 10 to 60 AU's. Outside about 80 AU's there may be gas giants but I think they would tend to be small since it's potential building components (H2) was captured into one or the other of the two stars. (1)

Both stars have HZ's within the 3 AU's (for A it is about 1.25 AU's and for B it is about 0.75 AU's). There are alot of variables connected to whether a planet actually becomes habitable (such as planet retention of an atmosphere, the composition of the atmosphere, the presence of liquid water, how much greenhouse effect there is, etc.). Therefore I think the likeihood of having a habitable planet in the AB system is about 10%. I think that if one does exist there is a high probability that life has arisen at some point (about 90%) but has to survive several potential extinction events that reduce the chances of life to developing or contuning up to the present to about 40%. Basically there is about a 30% chance of lower lifeforms. (2)

Travel from one star to the other may have to cover a distance from 11.4 AU's to 36 AU's. For a 1g starship such a trip of 11.4 AU's would take about 9.5 days and a trip of 36 AU's about 16 days. For 6g's the time is reduced to about 4 days and 7 days respectfully. (3)

(1)Based on conjecture of information from http://www.solstation.com/stars/alp-cent3.htm

(2)Based upon personal understanding of biology and the beginnings of life.

(3)Derived from MT's Referee's Companion p. 21.

I would treat Proxima Centauri as a seperate star system because we still are not positive if it is in orbit around the AB system.
No one's sure if Proxima is actually part of the system or just passing nearby.

Some interesting speculation about Alpha Centauri in 'A Planet Dweller's Dream'. by Martyn J Fogg, an essay in "Islands in the Sky", edited by Stanley Schmidt and Robert Zubrin (1996, ISBN 0-471-13561-5).

Obviously it's 10 years old so some of these speculations may already be out of date.

Fogg looks at nearby (within 25 ly) Sun-like stars and calculates the possibilty of finding both Earth-like planets and Easily-Terraformable planets (like Mars).

Alpha Centauri A: 7.8% Earthlike, habitable world, 44% Marslike, easily terraformable world.
Alpha Centauri B: 4.4% Earthlike, habitable world, 38% Marslike, easily terraformable world.

Funny that the most likely spot is also our next door neighbour.

Other nearby stars for comparison.

Beta Hydri (21.3ly): 7.5% Earthlike, habitable world, 35% Marslike, easily terraformable world.
Delta Pavonis (18.64ly): 5.1% Earthlike, habitable world, 39% Marslike, easily terraformable world.
70 Ophiuchi A (16.73ly): 4.4% Earthlike, habitable world, 38% Marslike, easily terraformable world.
82 Eridani (20.9ly): 4.4% Earthlike, habitable world, 38% Marslike, easily terraformable world.
Eta Cassiopeiae A (19.19ly): 3.9% Earthlike, habitable world, 38% Marslike, easily terraformable world.

These are the most likely within 25 ly. It might be all nonesense, but it's the only data I've found.