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Here are a few speculations I have made based off of my limited knowledge of those systems. They are based off of current finds etc., etc.


To really predict what worlds are around what star, we need to have a better understanding of the planet formation process, then with what we can detect, say a gas giant with an elongated orbit, we can perdict if there are other, smaller worlds within.

Alpha Centuari System

What we know,

Double star system, perhaps a triple. The stars are heavier in metals than the sun. No gas giants detected. The system is a little older than our own.

Speculations

Since it's a double star system, any jupiter size planet could not form and if it did, it would have been ejected.

There's probably an asteroid very close to Alpha Centauri A, due to the pull Alpha Centauri B exerts.

Any planets around either star, which are possible though they cannot have a distance of more than a few AUs from their parent star, would be slightly heavier than the Earth system, due to the high metals content of the nebula that they formed out of. There's most likely a heavy venus-type world there, given the amount of light in the system and the fact Alpha Centauri A is slightly brighter than our own Sun.

They Alpha Centauri system would be a dry system, in that Alpha Centauri B, which orbits about where Saturn is, would eat all the water baring comets that bombarded earth and Alpha Centauri B's heat would have evaporated more water into space during formation.

If there is life on any of the Centauri worlds, it would have more than enough time to go from single cell to advanced. However, the lack of water would restrict it and slow down evolution. The light from Alpha Centauri B is not effective enough to help any world's plant life on a world orbiting Alpha Centauri A. However, a world orbiting Alpha Centauri B, would be in a position to receive the light from two stars, which would speed up plant growth.

Tau Ceti

What we know,

Tau Ceti is dimmer than our own sun. It has no gas giants and a large oort cloud. It is also about 8 billion years old, making it an ancient system.

Speculations; Since there's a large oort cloud, there's a good chance comet bombardment to any terrestrial planet, if there is one. Since it has a low metals count, the protodisk that formed around Tau Ceti probably didn't have any massive planets. Any worlds around Tau Ceti would be "Wet" worlds, rich in water, however, it will most likely be in the form of ice. The low metals means low gravity worlds. Probably Mars-like.

If a world in the habitablity zone around Tau Ceti was lucky enough to have a moon form, there's a good chance of life. However, a large moon like ours is rare. So, most likely, any world that developed life would have suffered a "Snow Ball" effect and would most likely be frozen, awaiting stellar evolution to warm it up. With no liquid water and not moon to create plate technonics, a world such as this would be a sterile, frozen solid world.

E. Eridandi

What we know; This is a young star with a dust disk and a jupiter-sized planet in a jupiter-like orbit.

Speculations; There's a good chance of a future earth-like world in that system. It probably won't be as massive as the Earth, and might have to be closer to the star, given the sub-stellar world's eccentricity.


Procyon

What we know; a large type F star with lost of mass and metals.

Speculations; Since the star has a large habitability zone, there's a good chance of multiple worlds that can have liquid water. Since the system is young, there's probably primordal worlds there. However, Procyon B, now a white dwarf, was a red giant about 100 million years ago. This would have super heated any worlds in the Procyon system. They will most likely be dry if not Venus-like. They will have more mass than the earth.

Procyon is a good system for humans to colonize. Given the possibility of worlds, the solar energy and the proximity of Lutyen's star, 1 light year away.

Red Stars

They are the most numerous, longest lasting and dimmist stars in the galaxy. If there's extrasolar life, it will probably be on a world that orbits a type M star. However, it would have to be so close it would be tidally locked. I mean, real close. Closer than Mercury is to our sun. So, the chances of an extra solar world orbiting a red star with liquid water is about the odds of planet orbit AUs. So maybe one out of every ten?

Excellent observations.

I believe that we're probably better at determining where to look for systems we might inhabit, than we are at determining when or how? I remember growing up in the 1960's, where we all heard predictions of how we'd be living on the moon or Mars by the turn of the century. Oops!

Perhaps if life exists around one of the possible systems you mentioned, they may have a better chance of finding us, etc.

My opinion is that mankind on earth will never actually branch out and live on other planets in our solar system, much less other star systems. Not in our lifetime, or the lifetimes of our great, great grandchildren. But you know what? That shouldn't stop dedicated people like you and me, and many others out here from trying! It would be great if a self supporting spacecraft could someday head out towards our nearby star systems, and at least be able to eventually transmit direct data from that system back to earth, whether they are able to survive there or not.

Remember the old TV show, "Lost In Space"? They headed toward Alpha Centauri on a 4 year voyage (near the speed of light) in suspended animation, etc.,etc.. They did not know for sure if they would be able to survive when they got there, or just have to live in the spacecraft the rest of their lives (hoping to find raw supplies on systems). Well, if you think about it, man's first voyage to another system won't have any guarantee of finding a system that will support us! I think it's worth it.

Until then, it's great to explore which stars out there might support planets like ours, or ones we might be able to live on. Sorry to get a bit off topic, but thanks for the great info!

I think that by the time we have the ability to get to Alpha Centauri in a reasonable amount of time, we will already have the technology to determine if there is an Earth-like planet there or not.

It has recently been proposed that Alpha Centauri B would be more than adequate to fill in the role of a missing gas giant, as far as sending inward volatile-rich bodies. Likewise, Alpha Centauri A would probably perform the same role for B's planets.

As far as large moons being rare (per the Tau Ceti speculations), there is no evidence yet to say either way. Venus may well have had a large moon, albeit one which was later destroyed (Here's an article on the theory), while it is also speculated that moon-forming objects existed by the hundreds in the very early solar system.

Pretty good speculations.

...John...

As for Procyon, it's going subgiant, which means any worlds that were habitable during the system's relatively brief time on the main sequence would have got roasted by the increasing luminosity of Procyon A, let alone Procyon B going red giant.

Not sure you can really extrapolate that the mass of the planets will be greater in the Procyon system. If anything, the protoplanetary disc would have been truncated by Procyon B, which was once the more massive star (and hence more luminous, so it would evaporate materials out of the disc?), which would hinder planet formation.