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One of my more brilliant characters is taking a terraforming class and at one point, early in the story, she has to leave the action to take an exam. The question presented in that scene is listed below, and by authorial coincidence, she wil encounter such a solar system during a deep space survey. So I want her answer to make sense for my smarter readers.

Please describe a solar system where the goldilocks zone planet(s) do not orbit a gas giant or sun. For purposes of this question, said solar system can be of manufactured origin as long as the resulting system is stable across astronomical time.

Could an arrangement of three or more proximal stars produce one or more points of balanced gravitation pull, each of which could hold a planet such that it would rest in a stationary position relative to all stars in the system?

If so, what would it be like?

  • Would these stationary planets spin on their own axis or must they be tidally locked?
  • Could these stationary planets have moons?
  • Could their host suns have additional non-stationary, close-orbiting planets?
  • Aside from occasionally blocking some sunlight, could the motions of those planets have any geological effects on the stationary planet?

What should she write?

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    $\begingroup$ Locked planets do spin. $\endgroup$ – JDługosz Aug 14 '16 at 17:20
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    $\begingroup$ I added science-based instead. That matches your intent as clarified in the comment. $\endgroup$ – JDługosz Aug 14 '16 at 18:44
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    $\begingroup$ @Henry Taylor: no, that won't tear a planet apart. Its own gravity will hold it together: if it wouldn't, the planet could not have formed in the first place. $\endgroup$ – John Dallman Aug 14 '16 at 19:13
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    $\begingroup$ What about a rogue planet flying through a nebula? It's not part of a "solar-system" but ambient temperature can get up there I think. $\endgroup$ – Marky Aug 14 '16 at 19:26
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    $\begingroup$ I think you need to take your final ideas to Physics to check them over. I think many of the ideas presented in the Answers here are not accurate or proper interpretations of the system or whatnot. That it, it won’t really work. $\endgroup$ – JDługosz Aug 15 '16 at 1:58

15 Answers 15

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Could an arrangement of three or more proximal stars produce one or more points of balanced gravitation pull, each of which could hold a planet such that it would rest in a stationary position relative to all stars in the system?

Not exactly

It would be similar to Lagrangian points. L1, L2, L3 are totally unstable. But L4 and L5, unstable on their own, can be "orbited". You can have a natural astronomical body orbiting totally empty point in space, created by gravity and rotation of two stars.

For three stars, analysis gets funnier. Something remotely like L4 and L5 might be possible, but I can't imagine it being more stable.

For all your bullet points, answer is "yes, it is possible". Except it's not really plausible to have both geological effects and not knock such planet out of its weak stability.

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    $\begingroup$ +1 : Orbiting an empty spot in space is very cool! I will use that someday. Maybe in this project if the plot evolves a little. I love the idea of the ship running across such a planet and the seasoned officers thinking that it must be proof of solar system engineering, until my POV character, a fresh cadet explains it, referencing back to an exam question from a scene the beginning of the book. Yes. This might work! Thanks $\endgroup$ – Henry Taylor Aug 14 '16 at 17:54
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    $\begingroup$ -1 Lagrangian points ARE orbits. They are merely orbits that have a fixed point in relationship with the relative positions of two other objects. They are STILL ORBITS. $\endgroup$ – Aron Aug 15 '16 at 7:58
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    $\begingroup$ @Aron if you want to argue about what word "orbit" means, English Language & Usage is your site. It has nothing to do with worldbuilding, or with this question, really. $\endgroup$ – Mołot Aug 15 '16 at 9:43
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    $\begingroup$ @Henry: "Orbiting an empty spot in space is very cool!" It may interest you to know that Jupiter does this. It's large enough that the centre of its orbit falls outside of the radius of the Sun. Nothing with any non-trivial mass actually orbits some other body, technically; it orbits the centre of mass of the two-body system. Oftentimes, though, as with Earth, that centre of mass falls inside the radius one of the bodies (the Sun) so we sort of forget about it and just say we're orbitting the Sun. Obviously this gets more complex in models with more than two relevant bodies :) $\endgroup$ – Lightness Races in Orbit Aug 15 '16 at 11:51
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    $\begingroup$ @LightnessRacesinOrbit Don't forget the Pluto/Charon/Sol system. Pluto and Charon orbit their common center of mass, which is outside either body, and the pair in turn orbits the Sun. $\endgroup$ – a CVn Aug 15 '16 at 14:01
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You won’t find an arrangement of 3 or more stars in a stable configuration to begin with, other than those having vastly different sizes so the little ones orbit the big one like planets, or a hierarchical binary configuration.

A Klemperer rosette could be engineered, though. These are still not stable and perturbations will eventually destroy it if not actively maintained.

But the rosette is probably the closest you’ll find: you get multiple small bodies (planets) alternating with stars!

rosette

As for your secondary questions, any additional bodies will destabilize it immediately.

If you want more than one sun that stays put in the sky (or relative positions anyway) you could have a very massive star in the center, a tiny star orbiting it like a planet, and the plat at the L3 or L4 point. But I don’t think you could get the mass ratios of two stars high enough, and such giant stars are very short lived!

See my earlier question and references therein for more ideas.

If artificial, anything goes: a black hole or neutron star in the center that is engineered to produce light as a necro-star; tiny artificial suns orbiting the planet, etc. I’m looking at some combination of that in my cubeworld design.


See also Sean Carroll’s blog post on N Bodies:

I can’t help but show these lovely exact solutions to the gravitational N-body problem. …

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  • $\begingroup$ Thanks! +1, not only for the answer which does give me hope for salvaging my plot, but also for all the help with the tags. This gets me thinking about the ramifications of finding something like the rosette during a deep space survey. Given the obviously non-natural origin of such a configuration and its' need for continuing maintenance as proof that the god-like race that built it is still around, a prudent captain would turn around and run away. Let a diplomatic envoy handle first contact with the gods. Thanks! $\endgroup$ – Henry Taylor Aug 14 '16 at 19:08
  • $\begingroup$ Btw, “its” is the posessive pronoun. Not it's nor its' but you get points for creativity! $\endgroup$ – JDługosz Aug 14 '16 at 19:10
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    $\begingroup$ I expanded my answer. For engineered systems you can come up with any number of un-natural solutions. $\endgroup$ – JDługosz Aug 14 '16 at 19:11
  • $\begingroup$ To your first part. NASA recently discovered not only a stable configuration of three stars but also containing the exoplanet HD 131399Ab. Two small stars spinning quickly around each other, this group is spinning in combination with a third large star. The planet spins around the large star. See here (artist's impression in the video shows the combination quite clearly): nasa.gov/feature/goddard/2016/… $\endgroup$ – Otto Abnormalverbraucher Aug 17 '16 at 12:20
  • $\begingroup$ @OttoAbnormalverbraucher what you described is an example of hierarchical. A binary system, one member which is also a binary. 3 and 4 stars are arranged this way. $\endgroup$ – JDługosz Aug 17 '16 at 14:22
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Actually, I think this is a non-sustainable situation. Given the law of gravity, the planet will be pulled in one direction or another by other orbiting bodies, if not the host star itself. Essentially, anything with a gravitational pull will affect it, and therefore will force it to move in one direction or another.

Should you find/create a situation in which there is a host star with no other celestial bodies orbiting it, you are still faced with the gravitational pull of the star itself.

In other words: it needs centrifugal force (from orbiting the host star) to counteract the gravitational pull of the star trying to swallow it.

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  • $\begingroup$ @Fayth85, Even with two or more host stars? $\endgroup$ – Henry Taylor Aug 14 '16 at 17:38
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    $\begingroup$ @HenryTaylor it might be possible for you to find a stable region between two host stars, where the two gravitational pulls cancel each other out, yes. But then you create a new problem. How do you make sure the stars don't pull each other in? The more you try to make the situation make sense, the less sense it will make. Start with the laws of nature, then figure out where that can lead you -- not the other way around. $\endgroup$ – Fayth85 Aug 14 '16 at 18:13
  • $\begingroup$ So two stars, each close enough to influence the orbit of my planet would probably be too close to avoid drawing each other into a collision. Okay, scratch one interstellar spectacle. $\endgroup$ – Henry Taylor Aug 14 '16 at 18:53
  • $\begingroup$ @HenryTaylor It might be possible to have the two stars just outside of each other's gravity well (so to speak), and have the planet between them. But actual numbers for such a system are beyond my ken. $\endgroup$ – Fayth85 Aug 14 '16 at 19:09
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    $\begingroup$ +1 Unstable orbits. There are locations between two stars where the gravity cancels, but the stars are moving so the points are also moving. It is like balancing an egg on its end. It can't be done (and your eggs weigh an octillion kg) $\endgroup$ – James K Aug 14 '16 at 21:44
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(Warning: I am not a physicist, nor do I play one on TV). There could be mistakes here.

If the stars around the planet have to be fixed as well (in some inertial frame), then the answer is no. There are no stable equilibrium points in any stationary gravitational field. The first paragraph of the Wikipedia page on the Earnshaw's theorem contains a proof:

Informally, the case of a point charge in an arbitrary static electric field is a simple consequence of Gauss's law. For a particle to be in a stable equilibrium, small perturbations ("pushes") on the particle in any direction should not break the equilibrium; the particle should "fall back" to its previous position. This means that the force field lines around the particle's equilibrium position should all point inwards, towards that position. If all of the surrounding field lines point towards the equilibrium point, then the divergence of the field at that point must be negative (i.e. that point acts as a sink). However, Gauss's Law says that the divergence of any possible electric force field is zero in free space. In mathematical notation, an electrical force F(r) deriving from a potential U(r) will always be divergenceless (satisfy Laplace's equation):

${\displaystyle \nabla \cdot \mathbf {F} =\nabla \cdot (-\nabla U)=-\nabla ^{2}U=0.} \nabla \cdot > \mathbf{F} = \nabla \cdot (-\nabla U) = -\nabla^2 U = 0.$

Therefore, there are no local minima or maxima of the field potential in free space, only saddle points. A stable equilibrium of the particle cannot exist and there must be an instability in at least one direction.

The proof is stated for the electric field, but the same argument holds for the gravitational field (for which Gauss's law holds).

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    $\begingroup$ Ah, that proof applies to the electric or magnetic field. Indeed you can’t have an orbit based on electric charge, because the force will see off-center due to speed of light delay. Gravity is different. See here. This answer is incorrect for gravity, as you can see that it claims that orbits can’t exist! $\endgroup$ – JDługosz Aug 15 '16 at 1:39
  • $\begingroup$ I think this theorm does not consider the use of additional forces present in the system. In particular, the centrifugal force will ballance the center attaction and make a circular orbit possible. Likewise, a rosette will stay in formation because the whole thing is spinning. $\endgroup$ – JDługosz Aug 15 '16 at 1:46
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    $\begingroup$ @JDługosz The theorem holds for gravity too, as stated at the top of its Wikipedia page. The theorem does not prohibit orbits: it applies to stationary fields in an inertial frame. If the objects (and hence the fields) are orbiting, then they are not stationary and it doesn't apply. If there is centrifugal force, then the frame isn't inertial and it doesn't apply. In a non-stationary setting, there are counterexamples such as the Lagrange points. And no, a rosette is not stable. $\endgroup$ – Federico Poloni Aug 15 '16 at 7:11
  • $\begingroup$ In his formation, I'm assuming that the bodies will keep station relative to each other but the whole thing can be rotating. Since gravity doesn’t have negative charges, it’s trivial that a static collection of objects will simply fall together. $\endgroup$ – JDługosz Aug 15 '16 at 14:13
  • $\begingroup$ @JDługosz I agree with you. It is less trivial that there are no stable equilibrium points in a static gravity field, though, if you assume that the stars which generate the field are fixed in their position. $\endgroup$ – Federico Poloni Aug 15 '16 at 14:28
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Disclaimer: So this is a bit more about answering what I think the intent of the question is rather than the actual question itself, because it violates some of the assumed facts of the scenario. (Specifically the assumption of a ‘solar system’ existing in the first place)

A rogue planet flying through a nebula could have the necessary ingredients to maintain a ‘goldilocks zone’ for quite a while. I’m not an astrophysicist so the probability of this situation is more than likely exceedingly low and might not actually be possible. According to http://abyss.uoregon.edu/~js/ast122/lectures/lec22.html (which has alot of info about nebulas) the temperature of nebulas range from 10k to millions of K, among several different ‘types’ of nebula; a happy area where the ambient temperature is correct could make a goldi-locks zone; enough but not too much energy comming in.

A strong magnetic field from the planet will be a necessity to keep the planetary gases from being too flooded by the possibly harmful nebular gases … or maybe it’s flying through a nebula of loose oxygen and nitrogen?

Nebulas can also be tens of parsecs in any given dimension, so if your rogue is going pretty slow it should have plenty of time in the area to develop life. Going as fast as we are will be a problem because (I believe) the SOL solar system will cross a parsec in about 50,000 years, (parsec 3.08*10^16 meters vs 72,000 kph travel speed). Even with a hundred parsec nebula, at that speed you only have around 5 million years. Not enough for anything terribly complex to come about so it will have to travel slower then we’re used to.

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These conditions would not be present in our modern-day universe, but there was a time in the early universe when the entire universe was a goldilocks zone.

This short paper from Dr. Loeb of Harvard University talks about how 10-17 million years after the Big Bang the leftover background radiation from the early, very hot universe would be at a temperature such that liquid water could exist anywhere that was not being heated by another source. Keep in mind that the universe is now 13.7 billion years old, so this period of a universal goldilocks zone occurred a long time ago in the (relatively) very early universe and for a relatively short period of time.

As the universe expands, the leftover background radiation from the early, very hot universe cools with time. This background radiation fills the whole universe and sets sort of a baseline temperature for the universe. Before 10 million years after the Big Bang, the background radiation would have heated things too much for liquid water to stay liquid, it would boil instead. After 17 million years after the Big Bang, the radiation had cooled to the point that it wouldn't keep things warmer than the freezing point of water any more.

Since then, the radiation has continued to cool and is what we now see as the cosmic microwave background.

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Well, massive bodies that are foundation of your system, are attraction centers of the system, and the equilibrium point in the middle will be unstable. See this plot for example (it is the sum of three inversed square functions with different central positions, this is representative of gravity forces in system), the resulting shape might seem like almost a flat bowl in the middle, but it is actually curved. Once the body leaves the point (0,0) the gravitational pull will only be increasing in the direction of one of the attraction centers.

If additional planets are added in, they should be placed symmetrically as well, to balance each other's pull on the central planet. And then still, a neighboring solar system flying by at the edge of observable universe could bring doom on the system.


But here goes the interesting part: the unstable equilibrium can become stable, when oscillations are considered.

In relation to a rotating system, we can explain the dynamic equilibrium as follows: the force applied to body doesn't have to be exactly zero, it should average to zero over the time too small for the body to move significantly. I've been performing the calculations here to describe, at which speed the massive body should move around its orbit in order for smaller one to stay in place in the center of such orbit, with massive body being the Sun equivalent moving in a circle of 1 a.u. and the smaller one being the Earth. I'd be ashamed to tell how much exactly time has passed before I've realized, that it's the same speed as the speed of the Earth orbiting the Sun in natural way, which is quite a feasible value which means dynamics doesn't prohibit that.

Indeed another massive partner (or several) will be needed to condition the circular movement of the star, a single one will suffice, placing the planet in the center of binary system. The presence of another light source will definitely require increasing the distance to allow the existence of goldilocks zone and not burning inferno in the center, but that'd be well in the range of feasibility. (Considering intensity being ~(1/r)^2 it will need sqrt(2)-times greater radius. Additional considerations will need to be made to account for a planet not having dark side which effectively doubles the heated surface, but I guess it's all within reasonable, we're just talking about Saturn-Sun distance and speed now (planet's mass irrelevant here).

In comparison with a single star, the presence of second star will actually increase the stability of central region since, its gravitational pull will be subtracted from the first one (while still not making it stable without the rotation as noted earlier).


Thus, if you actually make a pair of stars go round each other on a safe distance, the region in the middle of them will be quite calm. Maybe for more than a single planet.

Analogy here could be stirring a tea, which has leaves in it. As you move spoon, you'll see that leaves fragments, while attracted by spoon movement, are accumulated in the middle of the cup. Get a bigger vessel, and you can see, what happens when there are two spoons, or if a spoon is in the middle.

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    $\begingroup$ Thank you for what looks like an extraordinary amount of work. I appreciate it and will use parts of it as my character's answer. The idea of multiple, slightly mobile planets sharing the same gravitic quiet zone is a little troubling to me, as I think they would attract each other then roll around on each other's surface which would not be good for any occupants. But a single planet in that situation, very cool. Thanks +1 $\endgroup$ – Henry Taylor Aug 14 '16 at 23:52
  • $\begingroup$ I think you’re trying to invent Klemperer rosettes? $\endgroup$ – JDługosz Aug 15 '16 at 1:50
  • $\begingroup$ Right, the point in the center is unstable. Without active correction it will come crashing down. Multiple bodies hqving a barycenter at this center will be far worse and destablize the ring of stars as well, almost instantly. For example look at the nature of the chaotic orbits of (Pluto/Charon)’s 3 moons. $\endgroup$ – JDługosz Aug 15 '16 at 1:54
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No. While you can create multi-star systems with stationary points in them where an object will not fall these are never stable.

Look at a planet sitting there. There will be tiny nudges over time (say, an impact by a dinosaur killer) and those will impart a velocity to the planet. For the planetary position to be stable that motion must somehow be stopped--and that needs someplace for the energy to go.

That energy goes into moving the planet vertically (I'm talking about the reduced-dimension drawings used to illustrate the warping of spacetime, I'm not talking about the north-south direction!) within the gravity well of its parent. For vertical movement to be possible the planet must be on a non-flat bit of spacetime—but if the spacetime is not flat then a stationary object will react by falling into the center of the nearest gravity well.

If you could somehow make a planet with negative gravity it would be happy to sit still in many multi-stellar configurations (as to such a planet the spacetime would curve in the opposite direction, turning any local peaks into valleys) but such a planet would throw off its atmosphere and inhabitants.

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    $\begingroup$ So the statistical likelihood of at least one dinasaur killer must be subtracted from the already unlikely probability of the planet being captured by the multi-star sweet spot, making the entire thing practically impossible, unless the planet pushed against the gravity of the surrounding stars which is also probably impossible. Thanks for saving me from the ridicule of future readers! +1 $\endgroup$ – Henry Taylor Aug 14 '16 at 19:00
  • $\begingroup$ You don't even need a dinosaur-killer. Assuming that there are other stars in your universe, even light-years away, their gravity will upset it. Gravity has indefinite range. The gravity of a single star is very weak at interstellar distances but your situation has no intrinsic stability at all. $\endgroup$ – John Dallman Aug 14 '16 at 19:11
  • $\begingroup$ @JohnDallman Yeah, my original version added the flap of the wings of a space butterfly as doing the same thing, just slower. I redesigned the post and apparently omitted that. $\endgroup$ – Loren Pechtel Aug 14 '16 at 21:13
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If you have several stars, you can have lots of wacky trajectories - including orbits around empty spaces (where some interesting gravitational point is located).

Now, there's a problem with designing stable many-stars system, but there's a way to "solve" it:

Controlled singularities (not black holes)

If civilisation you have at hand vastly exceeds ours at math, they could've solved something useful for n-body problem.

Usually our mathematical objects behave nicely - you ask them what would happen at time T and they answer. However, there are some problematic points where math is stretched too much or simply broken so you can not really predict what would happen after that point. Those problematic points are called singularities.

For example, if you had ideal rigid needle and ideal rigid billiard ball launched straight at it tip, little deviation in ball's position or direction may result in huge change of its trajectory after the collision.

Bad thing about n-body problem is that they have those.

Good thing about that is that you can exploit those singularities if they're not singularities for your plot-powered math. If one of system's suns is going to deviate too much and break everything, there could be some smaller deviation (like, planet's movement) that would be amplified to counteract sun trying to go off the leash.

On the other hand, it may happen that there does not exist smaller deviation to prevent some big deviation but your players would have hard time proving that, even if they try to.

Planet, in turn, can be nudged by something yet weaker - so that this nudge would be amplified at another "solved singularity". This nudge could be achieved through some atmospheric happening (which changes tidal picture a bit, which nudges the moon a bit, which nudges the planet a bit).

Atmospheric effects are ripe with similar stuff (singularities) too. The same means could be applied here to make everything work through weather control stations at several "balance" planets - uninhabitable planets that are mostly used for computing desired corrections and adjusting weather at specific points in a specific way to achieve that.

Think of it as employing a butterfly and super-super-computer to tell it exactly where and when should it flap its wings to divert a typhoon from densely-populated area to somewhere of lesser significance.

Of course, if those folks are exceptionally good they may be able to design planets with atmosphere that automatically reacts to changes in distances to suns with controlling nudges. However, that is harder and there would still be need for adjustments for stuff they didn't account for.

For example, there can be some rare-visiting comets, or some rogue celestial bodies. It's easier to spot those things from far away and account for them with total-wreck-preventing nudges, than secure a space where won't be any.

Also, for certain trajectories and/or masses of rogue celestial bodies it may be impossible to counteract effects of their passing, but that doesn't really make the system unstable.

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Please describe a solar system where the goldilocks zone planet(s) do not orbit a gas giant or sun

There's 1 such system and that's a binary star system, where the planet is placed between 2 stars and both stars are far enough from the planet to not burn its surface. The plausibility of such system is really low however, the stars would just suck all orbital debris that would allowed the formation of a planet.

I think that if stars are far enough, that planet could also have few satellites, regardi the tidal lock some expert could say that.

The answer to other answers is no.

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The key question here is: what is the definition of the goldilocks zone? Assuming the key is to maintain liquid water on a planet's surface, then there are many different parameters:

  1. The amount of energy hitting the planet from stars
  2. The thickness and composition of the planet's atmosphere
  3. Other characteristics of the planet (mass, composition of solids, presence/absence of geological cycles, internal heat sources, etc.)

There is also the possibility of maintaining liquid water somewhere other than a planet's surface. For instance, several Solar System bodies are thought to have long-lived subsurface oceans: Europa, Ganymede, and Ceres are the most promising.

The phrase "goldilocks zone" makes the assumption that the only relevant quantity is the orbital distance to one or more stars. But there is no need to be so restrictive.

Here are a few examples of situations that answer the question:

  1. A super-Europa with a rocky core and an ocean covered with a few miles-thick ice layer. Assuming an Earth-like abundance of lon-lived radionuclides such as Uranium, the ice layer acts as a thermal blanket to maintain the ocean in a liquid state. This planet can be free-floating in the galaxy, as it has no need for an external heat source.

  2. An Earth with a thick hydrogen atmosphere (10-100 bars works). In this case the hydrogen atmosphere acts as the thermal blanket that maintains liquid water on the planet's surface.

These two worlds are not "Earth-like" but they do maintain liquid water. With these two worlds there is no "goldilocks zone" of required orbits, there is just a zone that is disallowed too close to any stars. Basically, it can't get too hot.

FYI, see these two links for details about worlds 1 and 2: http://aeon.co/magazine/science/can-life-exist-on-a-planet-without-a-star/ https://planetplanet.net/2015/06/04/real-life-sci-fi-world-8-the-free-floating-earth/

  1. A Jupiter-mass black hole orbits a Sun-like star in the classical habitable zone, with an Earth-like "moon" orbiting the black hole.

  2. Earth orbiting a brown dwarf. Brown dwarfs don't burn hydrogen so they simply cool off in time. However, there is a set of orbits for which there is a billion-year window of goldilocks conditions (see here: https://planetplanet.net/2014/10/09/real-life-sci-fi-world-4-earth-around-a-brown-dwarf/)

  3. A planet in the habitable zone of a white dwarf. I suppose it's semantics whether a white dwarf counts as a star or not.

  4. It's a bit more speculative, but how about a planet that is free-floating within a star cluster that receives a pulse of energy every time it flies by some bright stars, then spends the next 10,000 years cooling off slowly. Whether this is viable would depend on the nature of the planet's atmosphere, how close it flies to what types of stars, etc. But not impossible.

To re-iterate my key point, the whole concept of the goldilocks zone is very limited. Earth itself -- with its current properties -- has at least 4 possible stable climates (see here: https://planetplanet.net/2016/04/06/no-livable-planets-without-life/). We are lucky to be in the goldilocks climate.

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They would be able to either be tidally locked or spinning on their own axis, depending when how long it's been stationary. If a planet was stationary it could not have a moon, having a moon would result in a binary orbit with each other, each orbiting around a common barycenter and neither stationary. A stationary planet would be little more than just a rouge planet what somehow lost its momentum, so it would lack a host star.

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  • $\begingroup$ @HenryTaylor no problem, seems like an interesting concept. $\endgroup$ – TrEs-2b Aug 14 '16 at 17:35
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Now this depends on the mass of the planet and the mass of the stars. The more mass an object has the more gravitational pull it has.

So if you want the sun and all the other planets to revolve around one planet, its mass would have to be greater than the stars mass.

Even then you would face a great danger in the early stages of this system. Some smaller planets would want to orbit the sun while also wanting to orbit the planet. Basically allot of planets crashing together and either combining mass or breaking off mass (kind of what scientists think happened to our moon).

Another important thing to take in mind is that if you did happen to gain enough mass to grow a gravitational pull greater than the Suns, that planet would become a sun. The more mass a planet has makes the gravity on the planet very high, creating lots of pressure. If we remember our 8th grade math course, we know pressure increases heat. In the end any atmosphere made of gas becomes plasma and the mass of the planet will slowly be eaten away and turned into more plasma.

For the planet to have gained this much mass it would have required lots of collisions. I do not believe a system revolving around a planet is possible. Sorry to say. Though you can theoretically have a three star system, however it will be extremely unstable.

I'll still answer the rest of your questions so you can have some ideas to write about:

1.potentially if we still go with the theory of which our new sun gained its mass from being impacted by other objects in space.

2.yes, but these moons would be slowly burned up over millions even billions of years.

3.as I mentioned earlier, they both could have their own non-stationary systems. Only problem is both would be causing hazards to the other.

  1. I'm guessing if we pretend it's a habitual planet and not a death ball of molten matter and plasma, we could compare the effect of it to being like night and day, as well as effect some sort of tides.

I hope this has helped out some.

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  • $\begingroup$ Thanks +1, but I wasn't trying to build a solar system with a planet in the center. I'm looking for a multi-star system where nothing orbits anything. Just two or more stars with a planet stuck at the intersection of their gravity wells. It is the feasibility and features of that situation which I am looking for. $\endgroup$ – Henry Taylor Aug 14 '16 at 17:42
  • $\begingroup$ So a two star system where there is a planet stuck in between them at the perfect point in their gravity to lose all motion? $\endgroup$ – XxCasualnessxX Aug 14 '16 at 17:45
  • $\begingroup$ That was the hope, but the other answers are beating it down a bit. $\endgroup$ – Henry Taylor Aug 14 '16 at 18:55
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    $\begingroup$ Well don't give up, space is vast and interesting. Just do a simple search like interesting systems. Another good thing to use is a steam game called universe simulator 2. You can create your own solo star system easily and and expirement with different types of systems. It's fairly accurate, as well. $\endgroup$ – XxCasualnessxX Aug 14 '16 at 22:36
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What you probably want is a binary planet.

The planets would orbit around their center of mass, which then in turn would orbit the sun within the Goldilocks zone. This should be stable and since the distance between planets would be comparatively small, both planets would be permanently in the Goldilocks zone and potentially habitable.

But please rewrite your question for the actual story, the combination of "in the Goldilocks zone" and "does not orbit a sun" annoys me for some reason.

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In some cases planets can bounce between the stars of a binary (see here for an animation: https://vimeo.com/81872631 and here for an article about the phenomenon: http://www.astronomynow.com/news/n1202/07exo/). A bouncing planet would not orbit one star or another but rather could bounce back and forth between the two (at least for millions of years, although I'm not sure if it's sustainable for billions of years).

Here is an example trajectory of a planet bouncing between two stars.
enter image description here

This setup does require some special conditions (e.g., several planets around one of the stars, and a binary star system with the right properties) but it is plausible. The planet would not be in a permanent goldilocks state but it could go in and out of a "habitable" setup.

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