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Is this some kind of mathematical thing based on how orbits work, or is it more like natural selection, in that any moons that don't avoid each other just aren'
by jonplackett 7y ago
Is this some kind of mathematical thing based on how orbits work, or is it more like natural selection, in that any moons that don't avoid each other just aren't there anymore.
- FreeFull 7y agoIt is a mathematical thing based on how orbits work. Orbits that are very close to a resonance but not quite there will tend towards being even closer, so it's a stable system. If this wasn't the case, you wouldn't ever expect to observe anything like this, due to disturbances to the orbits (from other bodies tugging gravitationally on the objects) building up.
- mirekrusin 7y agoResonance is natural selection.
- lmilcin 7y agoNo, it is not. It would be if we saw many colliding orbits and only those that had resonance surviving in long run. But resonances are perfect ratios and no random orbits will ever have perfect ratios of orbit times. Instead what happens is that collisions seem to be extremely rare occurrence. Once two moons find themselves on close orbits they will tend to exchange energy until they find some kind of resonance that will keep true for a very long time until disturbed.
- mirekrusin 7y agoAnd what is your (absolute offset and) observation timeframe compered to the lifetime of the system?
- lmilcin 7y agoThere are simulations that show great deal of how and what is the likelihood of different systems forming.
- mirekrusin 7y agoYou simply cannot have long lived, same radius orbiting objects, they must stabilize on resonance to exist.
- patcon 7y agoIt might be more apt a metaphor than it seems...? Resonant orbits might not be natural selection, but they might participate in a form of thermodynamic selection: two simple forms and structures selecting for and reinforcing one another. They are both subsets of the same thermodynamic processes of structures/arrangements sticking arouns when they mutually support one another creating persistence in a chaotic system My understanding is that some folks believe there are similar mechanisms underlying the emergence of both -- a generalized form of selection between mutually reinforcing structures that encode elements of prediction of the chaotic environment they reside in, be that the periodicity of orbits (that "know* a stable path that will reasonably persist) or life itself (that have similar baked in prediction abilities we perceive subjectively as consciousness). Disclaimer: biochemist, technologist and armchair follower of complexity science
- gus_massa 7y agoThe idea is that the gravity of a moon affect the trajectory of the other moon and vice versa, until they are in resonance. It's a bad analogy, but it's closer to Lamarckism than Darwinism, but it's still a bad analogy. There are nothing similar to random mutations.
- mirekrusin 7y agoBy natural selection I meant that if you have two (or more) bodies on the same orbit they'll crash or they'll find stable orbit (resonance). Of course you see resonating ones because ones that wouldn't would collide millions of years ago.
- Aperocky 7y agoI agree that in principal most things are natural selection. The things that are not on a current time (a certain proportion of which bound to exist) frame are behaviors that will eventually be eliminated.
- kkylin 7y agoPresumably any moons that did not end up in a nice stable resonant orbit would have had a higher chance of being ejected or colliding with something.
- hcrisp 7y agoSo could two earth-sized planets be in resonant orbits around a sun that would otherwise intersect? If so, what does this mean for the definition of a planet as something which "clears the neighborhood"?
- thevsb_dnebbexj 7y agoI think it’s more along the lines of moons that don’t avoid each other merge.
- phkahler 7y agoYou may find this informative: https://en.m.wikipedia.org/wiki/Attractor https://en.m.wikipedia.org/wiki/Attractor
- kkylin 7y agoNot quite -- orbital mechanics are Hamiltonian, which means they conserve energy, phase space volume, and often a bunch of other things. Dynamical systems that conserve phase space volume cannot have "strange" attractors (attractors with zero volume) like the ones described in the article.
- kkylin 7y agoCorrection: by "article" I was referring to the Wikipedia one on attractors, not the original post.
- deleted 7y ago[deleted]
- chongli 7y agoResonance plays an incredibly large role in orbital mechanics [1]. All of the orbits of the moons of Jovian planets are in small fraction ratios of one another. [1] https://en.wikipedia.org/wiki/Orbital_resonance https://en.wikipedia.org/wiki/Orbital_resonance
- gorgoiler 7y agoGreat animation. Everything orbits everything. We are just trained as children to see the small things independently orbiting the big thing, but in reality all bodies orbit each other. What would this animation look like with one of the moons at the center with Jupiter in a fixed position?
- wongarsu 7y agoI often wonder if some of the simplifications we commonly teach do more harm than good. "Small thing orbits big thing" is one of them, "a thrown ball follows a parabola" is another one (it's true on a flat earth, but in reality you launch the ball into a highly elliptical orbit that just happens to intersect earth's surface after a few meters). These simplifications are often conceptually not that much simpler, they just have much simpler math. But saying "x is what's happening, but in these circumstances we can treat it as y" is an important skill in science and life, we should teach it more (and benefit from fewer misunderstandings caused by teaching only the simplification)