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Man, science is the best.

I've always wondered about binary systems. How close (or far) do the stars orbit from each other?

Also, how long before scientists start giving planets crazy sci-fi names instead of...well..."b"?

I'd've thought they'd put a number on it rather than a letter - ie, if our sun is Sol, Mercury is Sol 1 or Sol I, Venus Sol 2 or Sol II, Terra Sol 3/Sol III, Mars Sol 4/Sol IV, etc. - so this would be Alpha Centauri B.I/Alpha Centauri B.1, with the letter indicating subsystem/star for multi-star systems.

hi hi

According to my sources at solstation.com:

Alpha Centauri A and B orbit with an average distance of about 23.7 AUs, swinging from 11.4 and 36 AUs distant in a highly elliptical orbit that lasts 79.9 years.

In a binary system, a planet must not be located too far away from its parent star, or its orbit will be unstable. If that distance exceeds about one fifth the closest approach of the other star, then the gravitational pull from the second star can disrupt the orbit of the planet.

Weigert and Holman in 1997 stated that recent (for the time) numerical integrations suggest that stable planetary orbits exist: within three AUs (four AUs for retrograde orbits) of either Alpha Centauri A or B in the plane of the binary's orbit; only as far as 0.23 AU for 90-degree inclined orbits; and beyond 70 AUs for planets circling both stars.

The presence of one close-orbiting planet usually indicates the presence of others, and many astronomers are now expected to devote more resources to detecting such potential planets around star B.

All in all, very exciting.

The AB periapsis of 11 AU is about Saturn distance, and the apoapsis of 36 AU is about Neptune/Pluto distance.



It will be really interesting to see what kinds of planetary orbits such a system will have as more data shakes out over the coming years. In particular, I wonder whether the planets of A and B will be in the same plane (indicating that the two stars formed from the same disc), or whether they will be different indicating that the two stars formed from separate discs and subsequently captured each other. Though continuing discovery may be problematic for existing science fiction canon.

Regarding nomenclature: I believe planets are designated in the order in which they're found (rather than in the order from the primary), so it seems to me these designations are unlikely to stick in the long term if a complete planetary system is eventually identified. And of course, if we ever actually went there, they would be given more conventinal names. Though I suspect "Alpha Centauri" will always stick... it just sounds so nice.

Count Casimir wrote:Man, science is the best.

I've always wondered about binary systems. How close (or far) do the stars orbit from each other?

Also, how long before scientists start giving planets crazy sci-fi names instead of...well..."b"?

Woud you prefer P3X595?

hi hi

I dunno, who can forget P3X-595? Its probably even more famous than P3W-451.

Alpha Centauri already has something of a legend surrounding it. Its present in science fiction literature and I think its mystique will carry on, at least until people start colonizing the place, at which point they'll probably pick something with fewer syllables.

Too bad we won't be alive when this happens, but it would be interesting to see what kind of life evolved on that planet. Do the two suns generate more radiation? Does this effect the the planet in some way if they do?

Is going to be a world like what was in Pitch Black, or Tatooine, or is it something else.


OOOh, the geek in me is coming out full blast with this.

Given how close it is to the star Mercury is more like it.

For a planet around either star, the secondary star would provide significant illumination, so there would be two "day" periods that would overlap to varying degrees during the year. "Night" would only occur during the parts of the year when the planet was on the opposite side of both stars. Then there's also the third star, Proxima Centauri, to consider, but I expect that wouldn't be any brighter than our moon.

But the biozone is going to be somewhat flexible for either star, because the secondary illumination is going to be very signficant, and the farther away from the primary you get, the closer you get to the secondary star (at least in certain parts of the year). Though the seasons may be widely variable because of this.

Well, I guess we now have a candidate for a light-sail probe. How many decades before we actually try ?

Arioch wrote:For a planet around either star, the secondary star would provide significant illumination, so there would be two "day" periods that would overlap to varying degrees during the year. "Night" would only occur during the parts of the year when the planet was on the opposite side of both stars. Then there's also the third star, Proxima Centauri, to consider, but I expect that wouldn't be any brighter than our moon.

But the biozone is going to be somewhat flexible for either star, because the secondary illumination is going to be very signficant, and the farther away from the primary you get, the closer you get to the secondary star (at least in certain parts of the year). Though the seasons may be widely variable because of this.

That's a really cool idea for a fantasy setting. Lots of fantasy settings with multiple moons, not enough with twin suns. Hmm....

asimov's nightfall.
nice little story.

Absalom wrote:Well, I guess we now have a candidate for a light-sail probe. How many decades before we actually try ?

Less than one, if ESPRESSO finds a second earth there.

Count Casimir wrote:

Arioch wrote:For a planet around either star, the secondary star would provide significant illumination, so there would be two "day" periods that would overlap to varying degrees during the year. "Night" would only occur during the parts of the year when the planet was on the opposite side of both stars. Then there's also the third star, Proxima Centauri, to consider, but I expect that wouldn't be any brighter than our moon.

But the biozone is going to be somewhat flexible for either star, because the secondary illumination is going to be very signficant, and the farther away from the primary you get, the closer you get to the secondary star (at least in certain parts of the year). Though the seasons may be widely variable because of this.

That's a really cool idea for a fantasy setting. Lots of fantasy settings with multiple moons, not enough with twin suns. Hmm....

It's not really fantasy, but twin suns do form part of the backstory of Arthur C. Clarke's 2001 series of books. Unfortunately, he never goes into much detail, other than to mention the sheer confusion Earth's biosphere undergoes while adjusting to a near 24/7 daylight cycle that lasts for the better part of the year.

Mr Bojangles wrote:

Count Casimir wrote:

Arioch wrote:For a planet around either star, the secondary star would provide significant illumination, so there would be two "day" periods that would overlap to varying degrees during the year. "Night" would only occur during the parts of the year when the planet was on the opposite side of both stars. Then there's also the third star, Proxima Centauri, to consider, but I expect that wouldn't be any brighter than our moon.

But the biozone is going to be somewhat flexible for either star, because the secondary illumination is going to be very signficant, and the farther away from the primary you get, the closer you get to the secondary star (at least in certain parts of the year). Though the seasons may be widely variable because of this.

That's a really cool idea for a fantasy setting. Lots of fantasy settings with multiple moons, not enough with twin suns. Hmm....

It's not really fantasy, but twin suns do form part of the backstory of Arthur C. Clarke's 2001 series of books. Unfortunately, he never goes into much detail, other than to mention the sheer confusion Earth's biosphere undergoes while adjusting to a near 24/7 daylight cycle that lasts for the better part of the year.

Part of the (relative) rarity of twin suns in comparison to multiple moons is probably because it's a lot easier to figure out or guesstimate (for the author) what multiple moons would do (funky tides, etc) than it is to figure out what multiple suns would do ... unless you're orbiting both stars, not passing between them (for whatever reason, probably some funky out-of-plane orbit), or the secondary component is far enough away that the light is sufficiently diffused to not be much brighter than bright moonlight.

You're probably right, javcs, but it'd still be a fun idea. The Times of Light and Darkness, underground cities, all that cheesy stuff. Mmm...

Count Casimir wrote:You're probably right, javcs, but it'd still be a fun idea. The Times of Light and Darkness, underground cities, all that cheesy stuff. Mmm...

Oh, most definitely. It'd certainly be fun ... the problem would be making the indigenous life fit in with the multiple sun-aspect, and not doing something to mess things up for the audience.


As an aside, one other place where multiple suns were involved, and mattered, was in the movie Pitch Black.

javcs wrote:Part of the (relative) rarity of twin suns in comparison to multiple moons is probably because it's a lot easier to figure out or guesstimate (for the author) what multiple moons would do (funky tides, etc) than it is to figure out what multiple suns would do ... unless you're orbiting both stars, not passing between them (for whatever reason, probably some funky out-of-plane orbit), or the secondary component is far enough away that the light is sufficiently diffused to not be much brighter than bright moonlight.

There is definitely complexity there (3-body problem, anyone?) And that's likely why we never get the nitty-gritty details. But, such scenes do look pretty sweet as Casimir points out. In the case of the 2001 series, the second sun is actually what used to be Jupiter. Monoliths were used to collapse it until fusion started. So, no orbits were changed, everything is where is should be, and Clarke definitely made heavy use of his own saying "any sufficiently advanced technology is indistinguishable from magic."

Still, a very enjoyable series of novels. I'd recommend them.

Mr Bojangles wrote:

javcs wrote:Part of the (relative) rarity of twin suns in comparison to multiple moons is probably because it's a lot easier to figure out or guesstimate (for the author) what multiple moons would do (funky tides, etc) than it is to figure out what multiple suns would do ... unless you're orbiting both stars, not passing between them (for whatever reason, probably some funky out-of-plane orbit), or the secondary component is far enough away that the light is sufficiently diffused to not be much brighter than bright moonlight.

There is definitely complexity there (3-body problem, anyone?) And that's likely why we never get the nitty-gritty details. But, such scenes do look pretty sweet as Casimir points out. In the case of the 2001 series, the second sun is actually what used to be Jupiter. Monoliths were used to collapse it until fusion started. So, no orbits were changed, everything is where is should be, and Clarke definitely made heavy use of his own saying "any sufficiently advanced technology is indistinguishable from magic."

Still, a very enjoyable series of novels. I'd recommend them.

Oh, it was definitely a good one. 2010, wasn't it?
Still, we never really got that much detail on the effects of Jupiter being ignited on Earth - we got details on the effects on Jupiter's moons, but on Earth, all we got (IIRC) was that there were 'changes' and 'upheaval' and nocturnal species got messed up (when Earth was in the part of its orbit where it was between Sol and Jupiter).
Even in 3001, there wasn't much detail ... and there'd been a lot longer to figure things like that out, but on the flip side, those details didn't matter for the story.

Yep, multiple moon/sun scenes generally look pretty cool - and details on what effects they have get left out because, really, most of the time, that's not going to be an issue in the story, and the vast majority of people won't even think about it, much less care - they're just going to care that it looks awesome and whatever plot/story-related points they get informed of.

javcs wrote:

Mr Bojangles wrote:Oh, it was definitely a good one. 2010, wasn't it?
Still, we never really got that much detail on the effects of Jupiter being ignited on Earth - we got details on the effects on Jupiter's moons, but on Earth, all we got (IIRC) was that there were 'changes' and 'upheaval' and nocturnal species got messed up (when Earth was in the part of its orbit where it was between Sol and Jupiter).
Even in 3001, there wasn't much detail ... and there'd been a lot longer to figure things like that out, but on the flip side, those details didn't matter for the story.

Yep, multiple moon/sun scenes generally look pretty cool - and details on what effects they have get left out because, really, most of the time, that's not going to be an issue in the story, and the vast majority of people won't even think about it, much less care - they're just going to care that it looks awesome and whatever plot/story-related points they get informed of.

It was indeed 2010 when Jupiter was lit off. And, those are pretty much the same details I remember regarding the second sun and how it affected Earth. It really just boils down to "hey, that makes for a pretty shot!" Personally, my favorite detail in 3001 was the ring around the world.