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RE: Quintuple Star System - TSSL - 07-10-2015

Looks to me like the contact binary may be the likeliest to have a conducive habitable system. The other three stars are far enough that there's room even for planets beyond the snow line. The detached binary stars are still quite close to each other, so plenty of planets could form around them; however, it's not clear where the fifth star is, and whether that would interfere with their planets. Maybe they haven't placed its orbit yet? In any case, the article doesn't give its parameters.

Granted, if the binaries used to be farther apart, and have spiraled in, there might have been less room for planets when they formed.

The source article also notes that the system may have formed about 9 to 10 billion years ago, which would make them pretty old. They might not have had enough material for really big planets. Those they did have, at least, would be less likely to have substantial metals and overall likely to be less dense. Combined with their age, that'd mean they might be likelier to have tectonically dead worlds.

Edit: Fantastic picture! Very evocative.

RE: Quintuple Star System - Bear - 07-10-2015

I don't think I get this neighborhood being a stable situation for a planetary orbit - at least not on a long enough scale for a full ecosystem to evolve.

The thing about contact binaries and multi-star systems is you get massive stellar tidal forces. Wouldn't a contact binary be transferring its own angular momentum to the orbital radii of (more distant) orbiting bodies, including the other stars, at a fairly rapid clip?

As best I can figure it, by the time you're located far enough away from the star for your orbit to be stable for ~3M years, you're located outside the habitable zone.

RE: Quintuple Star System - TSSL - 07-10-2015

Well, a quick gander at Wikipedia suggests that for circumbinary planets "theoretical calculations indicate the minimum stable separation is roughly two to three times the size of the stars' separation" with a citation from Scientific American in 2013. I've seen three times the orbital radius as a rule of thumb for circumbinary planets a couple places elsewhere, as well. The book What if the Earth Had Two Moons includes a scenario with an alternate Earth around a contact binary; the author is a professor of physics and astronomy. He did not think that tidal forces would render this impossible.

I'm not necessarily advocating for a garden world, since those are rare, but a planet that can support life and be a terraforming candidate, that seems plausible.

On a more whimsical note, I'd like to suggest "Horus" as a possible name for the contact binary. If it's in the Solar Dominion, that'd fit their preferences, a contact binary has a vaguely "eye of Horus" look (at least to my mind), and a quick look at the EG shows that it appears not to have been used yet. Conveniently, Egypt has at least three other sun gods I can think of: Ra (or Re), Amun (or Amon) and Aten. Since Amun and Ra are sometimes joined, maybe the separate binary stars could be Amun and Ra, and the fifth star could be Aten.

RE: Quintuple Star System - stevebowers - 07-10-2015

The rule we use in OA is 'three times the separation'; this applies to circumbinary planets and to distant binaries, where the planets orbit one star of a pair.
This came originally from an essay by Isaac Asimov, I understand, although some observed planets in real binary systems orbit more closely than this limit.

Both rules apply in this system. Both pairs of stars are two or three million km apart, so the smallest orbit around each pair is about nine million km. Similarly the stars orbit about 21 billion km apart, so a planet could be 7 billion km from either pair without being disrupted. Even with a 50% margin of error that allows planets in the habitable zone around both pairs.

The names TSSL has suggested have already been used in another quintuple star system in the Solar Dominion - Fons Luminis
based on Alula Australis, which is another (mildly contentious) quintuple star.

RE: Quintuple Star System - TSSL - 07-15-2015

Oh Blush , serves me right for just checking article titles instead of looking inside. At least I can console myself that I had such a good idea that it's been already used... Rolleyes

The big question still seems to be the position of the fifth star, which is associated with the detached binary. This site says it was found about 1.2 billion miles away, which is about 13 AU, while this site says up to 2 billion miles away. So even if we assume the closer separation, that leaves room for terrestrial planets... except that it doesn't take eccentricity into account. Considering that the articles don't mention significant eccentricity for the other orbits, maybe it's less likely that it is particularly eccentric. It is, apparently, an old system, so maybe they've had time to even out a bit. (Though a little eccentricity could have fun results on climate.)

RE: Quintuple Star System - Drashner1 - 07-15-2015

Why assume, or require, any planets at all? We've said in various places that most people live in space habs in the setting. But we have almost no examples of this. Why not use this system to start changing that?

Have all the stars orbited by orbital band of smaller habs (below Mcendree cylinder or space ring size) and emphasize the vast and diverse population who live in them. To me that seems much more interesting than yet another planetary system.



RE: Quintuple Star System - stevebowers - 07-15-2015

In a quintuple system there is room for both planets and habitats.

Three out of the five stars could be dominated by habitat-based cultures, but I'm quite keen to put a terrestrial planet around the contact binary - note that this is not a configuration that we have anywhere else in the scenario yet...

RE: Quintuple Star System - radtech497 - 07-15-2015

A habitable planet (assuming an albedo of 0.306 and an Earth-like atmosphere) is possible in a 0.607 AU orbit around J093010B (the contact binary); the varying luminosity should not be too worrisome as long as the planet is rotating and the atmosphere can distribute the warming evenly. The mean surface temperature for such a planet is 278.302 K (about ten degrees cooler than Earth), still high enough to maintain water as a liquid.

This orbit is also well away from the orbits of the three other stars in the system, so there should not be a problem in that respect.

The relatively low metallicity (56.23% of Sol) favors the formation of a few lower-mass planets in the system, though there will probably be no more than one SubJovian as the most massive world.


RE: Quintuple Star System - TSSL - 07-15-2015

Okay, some thoughts on the contents of the system, which I'll admit are largely, though not entirely, inspired by browsing Wikipedia. This got really long, so I've summarized my suggestions at the end.

Let's assume that is correct in stating that the system formed 9-10 billion years ago by fragmentation from a single protostellar disk. That means it's quite old, so there's a decent chance it's poorer in metals than the sun. In particular, likely to have fewer of the products of Type Ia supernovae (notably iron) but not quite as depleted an amount of Type II supernova products (the alpha elements), which information I'm getting from Wikipedia, so it's not entirely clear how reliable this is. Now, I've found elsewhere that we have found some really old planetary systems, including one with five planets very close to the star. An article I found somewhere online, but neglected to save the link, suggests that metal poor stars are likely to form planets closer to the star, but not as many farther away, because planet formation takes longer, so the far away ones lose the protoplanetary disk before they can form. Wikipedia's article on planet formation suggests, furthermore, that metallicity has a higher effect on whether or not large planets get to form, and less so on smaller planets. So we may be looking at a system that consists largely of smaller bodies. This article also suggests that gas giants influence inner planets by encouraging fewer, larger bodies.

Now, if we look at the detached binary, which has the additional star associated with it, this additional star is perturbing away much of the outer system past the frost line, though there's still some room. Taking all these factors together, I would suggest that this inhibited the formation of large bodies in the detached binary's outer system. Instead, this outer system formed an icy asteroid belt, one which extends farther than ours, with a higher total mass, but fewer dense elements. Maybe a couple of dwarf planets there. Nowhere near the extend of, say, the Kuiper Belt, however. Closer in, rocky bodies managed to reach more substantial size and clear some orbits; with density likely to be higher closer to the star, a couple of decent planets intermediate between Mercury and Mars that are in close orbits, followed by a few barely-planets in intermediate orbits. Those may be quite eccentric due to all the perturbations from having three stars in close proximity, with the farthest approaching the frost line. Maybe the barely-planets could be dwarf planets instead. If the detached binary used to have a somewhat wider orbit, at least around when it formed, potentially that could contribute to the system's scarcity, and also encourage eccentricity when it evolved. So this could be a good system for lots of habits. Volatiles might be a bit scarcer, too, what with the comparative lack of material beyond the frost line, but maybe all the eccentricity would've spread them around more.

The extra star associated with them would be a bit less chaotic, and have had more room beyond the frost line, though still not a lot. Small terrestrial planets and an icy nebulous panthalassic, maybe? With small tide-differentiated moons?

The contact binary has a lot more room, so it could have the potential to be somewhat more conventional. Orbits closer to circular and all that. More volatiles. Potential for planets that aren't so tiny. On the model of the known very old system, maybe there'll be a planet that orbits particularly close to the contact, which may even be one of the more massive terrestrial bodies of the system. No natural garden worlds, and considering the scarcity of iron and the age of the system, probably nothing with much plate tectonics, but there could be something like a somewhat more habitable Mars, which may harbor microbes. And then trailing off a bit, maybe a gas dwarf or two, then some ice balls, then just a scattering like the Kuiper Belt. Though I don't think planets would extend as far, really. Not as much material, nor as much incentive for migrating outwards.

However, one monkey wrench which would affect this proposal, and might be quite exciting to boot! Apparently fragmentation is one theory of a possible trigger for the formation of brown dwarfs and gas giants, which is probably rarer than accretion, but this system already probably went through fragmentation to form all these separate stars! Adding in a brown dwarf might be excessive, but a fragmented gas giant, maybe even a superjovian, could be exciting. Without as dense a protoplanetary disk, it might not be inclined to spiral inwards, so it might just stay orbiting around either in the distant reaches around the contact binary, or possibly around the other three, or even one at both places. If both, I'd suggest the former be superjovian, being as there's less disruption in that environment, and it could be closer to a star, and the latter be more like a Neptune. They could be good places for bubblehabs, which I hear are underrepresented, especially the smaller one, which would have a more agreeable gravity. They'd have potential for moons, especially the big one, which could have captured some of the planetesimals/dwarf planets, and maybe have room for something Mars like in size from its own accretion disk, though totally frigid.

Summary of my suggestions:

Contact binary: Epistellar superhot Earth-sized planet, almost certainly tide-locked, no atmosphere, probably molten on the day side, good view but not good real estate. A few smaller Terrestrial planets, including one in the habitable zone which is a good candidate for terraforming, with native microbial life, sort of intermediate between Earth and Mars, with very small core, barely any iron, and largely tectonically dead. A gas dwarf, an ice ball or two, and then a bunch of smaller bodies, like the Kuiper Belt... until, fairly far out, there's a superjovian with its own frigid moons, including one close to Mars in size.

Detached binary: Nothing bigger than Mars. A couple of planets close to the star; farther out, the planets get increasingly smaller and more eccentric in their orbits. Eventually it becomes an asteroid belt, with some dwarf planets, generally very eccentric. Poor in volatiles and iron. Plenty of carbon, I guess? Anyway, settlement would be likelier to involve habs than just settling the planets, meeting that design goal. (Maybe this could go to someone other than the Solar Dominion, like the Deeper Covenant or something, even though they're not red dwarfs. Or even an unaligned polity!)

Fifth star: Small terrestrial planets, with one icy nebulous panthalassic world. Could be a good place for living in habs as well.

And also a Neptune-like small gas giant that manages to orbit the detached binary and the extra star... maybe. That'd be cutting the "three times" rather closely. But it'd be a fun place for bubblehabs. (Alternatively we could attach it to the detached binary or the fifth star.)


RE: Quintuple Star System - TSSL - 07-15-2015

(07-15-2015, 02:24 PM)radtech497 Wrote: A habitable planet (assuming an albedo of 0.306 and an Earth-like atmosphere) is possible in a 0.607 AU orbit around J093010B (the contact binary); the varying luminosity should not be too worrisome as long as the planet is rotating and the atmosphere can distribute the warming evenly. The mean surface temperature for such a planet is 278.302 K (about ten degrees cooler than Earth), still high enough to maintain water as a liquid.

This orbit is also well away from the orbits of the three other stars in the system, so there should not be a problem in that respect.

The relatively low metallicity (56.23% of Sol) favors the formation of a few lower-mass planets in the system, though there will probably be no more than one SubJovian as the most massive world.


This popped up while I was constructing my mammoth reply...

What figure are you using for luminosities? gives temperatures, masses, and radii, which should allow calculating that, but I don't know how to derive them for the contact binary, since it only gives a common temperature for the two.

Do you have any additional information on orbit parameters or the like?