8 replies to this topic

[MeridianStarGazer]

I think they range from Saturn's distance to Pluto's distance every 79 years.

The 11 year solar cycle here only varies by 0.1%. over there, the variance is 1%. Maybe this is what Game of Thrones meant by long summer and long winter, short summer and short winter.

[photoracer18]

Its the 3-body problem in all its hierarchal-form glory. In this case the main AB pair never get closer than about 4300 AU to Proxima Centauri.

[louisr65]

I think they range from Saturn's distance to Pluto's distance every 79 years.

The 11 year solar cycle here only varies by 0.1%. over there, the variance is 1%. Maybe this is what Game of Thrones meant by long summer and long winter, short summer and short winter.

Depends on your definition of liability, I guess.

 

At periapsis, the A & B components are separated by 8.4AU, so significantly inside Saturn's orbit. If I remember the orbital models correctly, the widest stable orbit around one of the individual stars would be 1.2 AU. Since the A component is ~1.5Lsol, anything in a stable orbit would be decidedly toasty - Venus-like, in fact, if not worse, which I, personally, would indeed regard as a liability.

 

You should be able to find stable orbits in the habitable zone for B but since it would be inside .5AU I think there's a non-negligible possibility of a spin-orbit resonance developing - which would also be rather awkward. Don't quote me on that, though - astrodynamics isn't my specialty. I can say that a major climate influence will be the variable insolation from A, which a back-of-the envelope calculation suggests will range from an extra .6% to 4.5% over the orbital cycle. Throw in the 1% cyclic variation you mention and you're looking at up to 5% variation in insolation. All else being equal, on Earth that would translate to somewhere between 15 & 20 degrees of variation in mean surface temperature. Not necessarily a liability, but it would be very interesting indeed from an ecological viewpoint.

[MeridianStarGazer]

Still interesting to point a big telescope at, and send a probe to. On Earth, animals hybernate and have mating seasons, and desert plants look dead in the summer and bloom and grow when it rains. So it sounds possible. But it also makes it less tempting to send a generation ship there.

[louisr65]

I think they range from Saturn's distance to Pluto's distance every 79 years.

 

PS: Apoapsis is only ~27AU, so about 2/3 Pluto's distance.

[MeridianStarGazer]

The elliptical binary system likely means the stars gobbled up any kuiper belt or asteroid belt. Just my guess. That means the planets in the habitable zone better be habitable or we can't terraform them so easily. Also less freely floating matter for us to build more ships from.

[MeridianStarGazer]

Several stars passing near earth in the next 20,000 years are red drawfs. By near, I mean 10 light years. Sirius is a bright A0 star, not even F, and it is a binary with a white drawf that orbits every 50 years. I wonder how elliptical the distances are.

[MeridianStarGazer]

I looked through the list on wikipedia. Most stars passing near are red dwarfs, and many are in binary or trinary systems. There might be more that are too tight to split.

Many are halo stars that are passing fast. The closest K and G stars are over 10 light years. One looks like a binary. Another, a G, is 8-10 billion years old and has 28% as much metal as our sun. I wonder if that means fewer rocky planets, or that the metal is there but outside the star somehow.

I now know why Ceti listens to them and not alpha Centari. The Centari system has younger stars. Probably younger planets.

4.3 light years was maybe possible for a voyage. But pushing 15 light years, good luck getting a generation ship to last that long. If we find bacteria on Mars underground, the depth of dirt is how thick the ship walls need to be.

[MeridianStarGazer]

The faster a star spins, the stronger its magnetic field. Too slow, and I wonder if you are safe from cosmic rays. Too fast, and I wonder if you can safely pass through the belts when you leave, or if that is how it works.

Many nearby k and g stars rotate slower than the sun does.

Stars with less metalicity tend to have fewer planets.

Most nearby g and k stars are in binary systems that pass close to each other.

It is looking to me like all with 17 light years are not worth visiting, and listening to them or sending a message is pure desperation. Many are too young. Where we live is very nice and not like other star systems.