# Habitable planets in a solar system **URL:** \ **Category:** Factual Questions\ **Created:** [July 17, 2008, 8:12pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861 "2008-07-17T20:12:20Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Bricker](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@Bricker](https://boards.straightdope.com/u/Bricker)\ **Post date:** [July 17, 2008, 8:12pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/1 "2008-07-17T20:12:20Z")
If I had a handy-dandy Custom Planet Extruder™, and could pop out planets of whatever size and composition I wanted, I’d like to start over with a new solar system that has more useful real estate than we do. How should I set this new system up? (No Ringworlds, Dyson spheres, or the like need apply – I’m just talking a star of any variety that would work best, plus a bunch of habitable planets in stable orbits. How many can I have?) ---
**Author:** ![J\_Cubed](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@J\_Cubed](https://boards.straightdope.com/u/J_Cubed)\ **Post date:** [July 17, 2008, 8:21pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/2 "2008-07-17T20:21:10Z")
Just start making them and giving them a shove. Some will find a stable orbit. If two smash into each other, hey, free moon! ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [July 17, 2008, 8:23pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/3 "2008-07-17T20:23:11Z")
Stephen Dole’s **Habitable Planets for Man** used to be the standard ref of this: > **[Habitable Planets for Man: Dole, Stephen H.: 9780833042279: Amazon.com: Books](https://www.amazon.com/Habitable-Planets-Man-Stephen-Dole/dp/0833042270)** > > Buy Habitable Planets for Man on Amazon.com ✓ FREE SHIPPING on qualified orders Since then, there have been others: > **[Amazon.com: Geology and Habitability of Terrestrial Planets (Space Sciences...](https://www.amazon.com/Geology-Habitability-Terrestrial-Planets-Sciences/dp/0387742875)** > > Amazon.com: Geology and Habitability of Terrestrial Planets (Space Sciences Series of ISSI, 24): 9780387742878: Fishbaugh, Kathryn E., Lognonné, Phillipe, Raulin, François, Des Marais, David J., Korablev, Oleg, Fishbaugh, K.E., Des Marais, D.J.,... There have GOT to be internet sites and discussions on this. Like this: [http://home.comcast.net/~brons/NerdCorner/StarGen/StarGen.html](http://home.comcast.net/~brons/NerdCorner/StarGen/StarGen.html) You can download HPfM, apparently: [http://futurismic.com/2007/07/18/worldbuilders-bible-available-for-download/](http://futurismic.com/2007/07/18/worldbuilders-bible-available-for-download/) ---
**Author:** ![foolsguinea](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foolsguinea/32/14751_2.png) [@foolsguinea](https://boards.straightdope.com/u/foolsguinea)\ **Post date:** [July 17, 2008, 8:58pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/4 "2008-07-17T20:58:57Z")
Klemperer Rosettes are the way to go. Run four moderately large (about 10-20 Earth masses) planets at 12:00, 3:00, 6:00, & 9:00. These can have habitable moons & companions (maybe even Earth-type planets in their outer equilibrium points). To keep the Rosette stable, run class M planets at 1:30, 4:30, 7:30, & 10:30. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [July 17, 2008, 9:10pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/5 "2008-07-17T21:10:22Z")
There are two ways to get more real estate in a star system: use bigger planets or increase the size of the star’s [habitable zone.](http://en.wikipedia.org/wiki/Habitable_zone) The habitable zone gets wider the farther out it is — if you do the thermodynamic calculations, you find that the “width” of the habitable zone is about 10-20% of its distance from the sun. I doubt that this range will be wide enough to establish a stable [orbital resonance](http://en.wikipedia.org/wiki/Orbital_resonance), though, so you may be out of luck in shoehorning extra planets into the habitable zone. Your best bet would be to have increasing amounts of greenhouse gases in the atmosphere of the outer planets. I don’t know if there’s an upper limit on this (if nothing else, you want to keep enough oxygen in the atmosphere, and make sure it doesn’t become too thick to breathe), but in principle the more massive you make a planet, the thicker its atmosphere will be and the warmer it will be at the surface. Carbon dioxide, methane, and (to a certain extent) water vapor will give you more greenhouse-warming bang for your buck. (Ozone would too, but it’s not stable, and the further out you go from your star, the more trouble you’re going to have producing it in the upper atmosphere.) ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 17, 2008, 9:29pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/6 "2008-07-17T21:29:52Z")
[QUOTE=foolsguinea] Klemperer Rosettes are the way to go. Run four moderately large (about 10-20 Earth masses) planets at 12:00, 3:00, 6:00, & 9:00. These can have habitable moons & companions (maybe even Earth-type planets in their outer equilibrium points). To keep the Rosette stable, run class M planets at 1:30, 4:30, 7:30, & 10:30. [/QUOTE] Modify that. Six, not four, take advantage of the Lagrange points of their immediate neighbors, producing additional stability. Make it six Jovians with multiple Earthlike satellites in Earth orbit (or the equivalent for the luminosity of the relevant star), then six super-Jovians in roughly Mars orbit (same caveat), also with multiple Earthlike satellites, and at a surface temperature where their infrared radiation heats the planets to Terrestrial levels. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [July 17, 2008, 9:53pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/7 "2008-07-17T21:53:31Z")
The trouble for stars that are brighter than the sun is that they are brighter because they are more massive, which means gravity is higher which means more nuclear fusion. More nuclear fusion means faster nuclear fusion. So massive hot stars burn out very quickly and you don’t have much time for life to evolve, plus they put out a lot more higher-energy EM radiation which could be bad for children and other living things. ---
**Author:** ![Projammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/projammer/32/559_2.png) [@Projammer](https://boards.straightdope.com/u/Projammer)\ **Post date:** [July 17, 2008, 9:56pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/8 "2008-07-17T21:56:47Z")
What would be issues with running orbits out of the ecliptic? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [July 17, 2008, 10:40pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/9 "2008-07-17T22:40:41Z")
[QUOTE=Projammer] What would be issues with running orbits out of the ecliptic? [/QUOTE] Scary [conjunctions](http://en.wikipedia.org/wiki/Astronomical_conjunction). When planets pass each other in different orbital planes, the gravitational attraction between them tends to pull both planets out of their respective orbital planes. That’s not conducive to having a stable orbit. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 18, 2008, 2:53am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/10 "2008-07-18T02:53:21Z")
[QUOTE=foolsguinea] Klemperer Rosettes are the way to go. Run four moderately large (about 10-20 Earth masses) planets at 12:00, 3:00, 6:00, & 9:00. These can have habitable moons & companions (maybe even Earth-type planets in their outer equilibrium points). To keep the Rosette stable, run class M planets at 1:30, 4:30, 7:30, & 10:30. [/QUOTE] Klemperer rosettes are only marginally stable; a slight perturbation will cause them to become unstable rather quickly, and once perturbed they tend to fling off wildly in seemingly random directions; this can be demonstrated with a very simple simulation in Matlab or _Mathematica_ (or in Python or C if you don’t mind writing real code), where even tiny rounding errors in the precision of calculations will quickly cause a non-correcting orbit to spin out. Klemperer’s paper actually described a system of equal numbers of two or more different mass bodies orbiting a common barycenter; the type of rosette described by Larry Niven as the Fleet of Worlds is actually a trivial subset which is stable (although again, only marginally so) by inspection. Of course, with a central massive body such that M \>\>\> m1, m2, m3,… you could put a number of bodies in the same orbit at 60° intervals such that each fell within the other’s libration points. Such a system may be at least marginally stable, especially if M1\>\>\>M2~M3~…, although over time influences between minor bodies would affect each other’s orbits. You could also place one body in orbit of a second in orbit of a third, such that M3\<\25; this is, in fact, exactly what we have with the Sol-Earth-Luna system. Getting the density sufficient to hold onto an atmosphere might be pretty tricky, though. You could also put two worlds in a tidally-locked couplet in orbit of a much larger mass with pretty good long term stability as long as they’re reasonably close together. As for the number and arrangement of stable planar orbits, we’re not sure, although there are suspicious similarities in the spacing of orbits which have caused many to look for resonances in orbits. We don’t have anything definitive for planets, although there are some pretty clear resonances in the Jovian moons. I wouldn’t plan on spacing too many orbits close together in a habitable zone; planetary collisions are a bad day all around. [QUOTE=Projammer] What would be issues with running orbits out of the ecliptic? [/QUOTE] Very tricky; when dealing with out of plane orbits you have to account for orbital behavior in three dimensions; this is generally contrary to long term stability of the orbit, especially if you have one or more large secondary influences (a Jovian or larger planet). The real solution for maximizing habitable volume is to get away from planets completely. Spherical worlds are remarkably inefficient–remember, they give minimum surface area for volume–and have all manner of difficulty in getting things like seasons and the length of day just right. Rotating toroids or hollow spheres in massive conjunctive orbits seem like a better use of materials. The o.p. is wise to stay away from Ringworlds and Dyson shells, on the other hand; difficult to stabilize and impossible to defend. Personally, I’d hide away in the ergosphere of a massive rotating black hole with a good book. Making custom worlds seems like an appealing business until you realize that your customers are going to ask for all sorts of obscene and offensively tacky things. I mean, it’s one thing to go a nice bit of fyords, but when they want a planet that is pink and squishy and squeals every time you walk across it, I’d draw the line. Stranger ---
**Author:** ![OtakuLoki](https://avatars.discourse-cdn.com/v4/letter/o/ac8455/32.png) [@OtakuLoki](https://boards.straightdope.com/u/OtakuLoki)\ **Post date:** [July 18, 2008, 3:21am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/11 "2008-07-18T03:21:01Z")
[QUOTE=Stranger On A Train] Spherical worlds are remarkably inefficient–remember, they give minimum surface area for volume–and have all manner of difficulty in getting things like seasons and the length of day just right. Rotating toroids or hollow spheres in massive conjunctive orbits seem like a better use of materials. [/QUOTE] Would hollow spheres save enough material to be worth the ‘useless’ volume in the center, or the larger tracts of difficult to use surface at higher lattitudes? FTM, wouldn’t it be more efficient use of mass to make large, but unenclosed, toroids, and count on the spin to act to keep the atmosphere within the walls? (Sort of a mini-Ringworld, but not centered around the star, and much, much smaller.) But pink is **in** this millennium… ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [July 18, 2008, 9:01am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/12 "2008-07-18T09:01:38Z")
[QUOTE=OtakuLoki] FTM, wouldn’t it be more efficient use of mass to make large, but unenclosed, toroids, and count on the spin to act to keep the atmosphere within the walls? (Sort of a mini-Ringworld, but not centered around the star, and much, much smaller.) [/QUOTE] That would be an [Orbital](http://en.wikipedia.org/wiki/Orbital_(The_Culture)) or similar, then? Yet another reason to love Ian M Banks… ---
**Author:** ![foolsguinea](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foolsguinea/32/14751_2.png) [@foolsguinea](https://boards.straightdope.com/u/foolsguinea)\ **Post date:** [July 26, 2008, 8:21pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/13 "2008-07-26T20:21:06Z")
[QUOTE=Polycarp] Modify that. Six, not four, take advantage of the Lagrange points of their immediate neighbors, producing additional stability. Make it six Jovians with multiple Earthlike satellites in Earth orbit (or the equivalent for the luminosity of the relevant star), then six super-Jovians in roughly Mars orbit (same caveat), also with multiple Earthlike satellites, and at a surface temperature where their infrared radiation heats the planets to Terrestrial levels. [/QUOTE] Six super-Jovians at Mars-distance-equivalent orbit? OK, maybe a system the size of–I dunno–Vega’s could get the mass (ours sure doesn’t have it) but aren’t you worried about destabilizing the Jovians at Terra-distance-equivalent? ---
**Author:** ![Love\_Rhombus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/love_rhombus/32/10694_2.png) [@Love\_Rhombus](https://boards.straightdope.com/u/Love_Rhombus)\ **Post date:** [July 26, 2008, 8:57pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/14 "2008-07-26T20:57:53Z")
No spheres? Well, you could always go with a cube shape, give the cartographers fits. ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [July 26, 2008, 10:40pm UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/15 "2008-07-26T22:40:49Z")
Cubes would be _way_ easier to represent in a 2D map than a sphere. ---
**Author:** ![Satellite\_Guy](https://avatars.discourse-cdn.com/v4/letter/s/258eb7/32.png) [@Satellite\_Guy](https://boards.straightdope.com/u/Satellite_Guy)\ **Post date:** [July 27, 2008, 2:01am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/16 "2008-07-27T02:01:37Z")
I’ve noticed the posters in here talking about Jupiter-sized planets, but wouldn’t their gravity crush us? Or are you planning on populating the moons, which would be more earth-sized, with a more earth-like gravity? S^G ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [July 27, 2008, 2:06am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/17 "2008-07-27T02:06:13Z")
[QUOTE=slaphead] That would be an [Orbital](http://en.wikipedia.org/wiki/Orbital_(The_Culture)) or similar, then? Yet another reason to love Ian M Banks… [/QUOTE] Are those within the theoretical limits of carbon nanotubules, or are we talking pure Unobtanium here? If my math is correct, a 1G gravity and a rate of one revolution per 24 hours gives a diameter of approximately 3,700,000 kilometers! ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [July 27, 2008, 2:49am UTC](https://boards.straightdope.com/t/habitable-planets-in-a-solar-system/456861/18 "2008-07-27T02:49:26Z")
You want a star system like in _Firefly_, don’t you?