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Post by the light works on Apr 12, 2023 14:32:59 GMT
I'm currently reading a story in which the planet the story occurs on is tidally locked to the sun, and in an elliptical orbit. this results in a small human habitable area, essentially in the twilight zone, where the wobble of the planet results in a 24 hour day cycle, with the sun rising "sunward," staying low in the sky, and then setting in approximately the same place. the elliptical orbit creates a mild seasonal shift, with the dry and wet cycles as the planet gets closer and further. the author has set the orbital period at 720 days, with two years happening per orbit.
so the question is, does this fit in with our observed universe? I know all the individual elements are possible, but can the be put together like that? biggest question, of course, is whether the orbital period, the distance from the sun, and the tidal lock can all happen on the same planet.
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Post by the light works on Apr 12, 2023 14:34:11 GMT
secondary questions would be whether the planet could wobble on a 24 hour day/night cycle, and what kind of weather would happen on a tidally locked planet.
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Post by GTCGreg on Apr 12, 2023 14:54:21 GMT
I'm not sure about the scenario you present, but I recently read an article that many of the solar systems in our universe are actually binary star systems. Far more then first thought. Because the stars are so close together, we see them as a single star but there are really two. Any planet in a binary system has a very strange orbit. Sometimes not actually orbiting either star but locked in a fixed position between the two stars.
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Post by the light works on Apr 12, 2023 14:58:26 GMT
I'm not sure about the scenario you present, but I recently read an article that over half the solar systems in our universe are actually binary star systems. Because the stars are so close together, we see them as a single star but there are really two. Any planet in a binary system has a very strange orbit. Sometimes not actually orbiting either star but locked in a fixed position between the two stars. that might be represented by the Manticore system in David Weber's Honorverse. I don't recall the exact orbital structure of the system, but it's a binary system with three habitable planets - although one is only considered habitable by hardier individuals, being above average in gravity and length of year. with both wildfire season and frozen solid season lasting much longer than on earth. |
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Post by rmc on Apr 14, 2023 7:19:14 GMT
I'm currently reading a story in which the planet the story occurs on is tidally locked to the sun, and in an elliptical orbit. this results in a small human habitable area, essentially in the twilight zone, where the wobble of the planet results in a 24 hour day cycle, with the sun rising "sunward," staying low in the sky, and then setting in approximately the same place. the elliptical orbit creates a mild seasonal shift, with the dry and wet cycles as the planet gets closer and further. the author has set the orbital period at 720 days, with two years happening per orbit. so the question is, does this fit in with our observed universe? I know all the individual elements are possible, but can the be put together like that? biggest question, of course, is whether the orbital period, the distance from the sun, and the tidal lock can all happen on the same planet. From what I've read most planets throughout our galaxy (the ones we've currently found easily anyway... and "easily" is a relative term, of course) are close to their star, rapid orbital periods, tidally locked, orbit in eccentric, eliptic orbits... etc. Another recent report hypothesized that Earth's inner core and external plate tectonics got the way it is due to the specific way our moon formed. One planetary body colliding with early Earth such that both the moon formed and the inner core churned making plate tectonics possible. The ultimate result was a magnetosphere that protects our atmosphere due to a kind of dynamo effect created because of all that metal molten stuff moving around inside. Looking at all that, I'd guess that the "usual" exoplanet has a lot it must do or go through or have the luck of being situated just so in order to be conveniently livable. So it looks like most of what you listed is typical. However, 720 earth day orbits are not found too often... yet. And the perfect wobble... unknown, I'd guess at the moment anyway. As reliance on transit methods or star wobble techniques gives way to better instrumentation, like the JWST and others that might directly identify exoplanets, discovery of what the author has laid out might be found one day. Or, we may have already recorded such a planet, but the data is still just a bunch of numbers that need to be interpreted. Because long period orbits studied with wobble or transit methods require more observation time than rapid period orbits. It takes longer to tell what is happening watching slow motion than it does watching something quicker. |
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Post by the light works on Apr 14, 2023 12:38:07 GMT
I'm currently reading a story in which the planet the story occurs on is tidally locked to the sun, and in an elliptical orbit. this results in a small human habitable area, essentially in the twilight zone, where the wobble of the planet results in a 24 hour day cycle, with the sun rising "sunward," staying low in the sky, and then setting in approximately the same place. the elliptical orbit creates a mild seasonal shift, with the dry and wet cycles as the planet gets closer and further. the author has set the orbital period at 720 days, with two years happening per orbit. so the question is, does this fit in with our observed universe? I know all the individual elements are possible, but can the be put together like that? biggest question, of course, is whether the orbital period, the distance from the sun, and the tidal lock can all happen on the same planet. From what I've read most planets throughout our galaxy (the ones we've currently found easily anyway... and "easily" is a relative term, of course) are close to their star, rapid orbital periods, tidally locked, orbit in eccentric, eliptic orbits... etc. Another recent report hypothesized that Earth's inner core and external plate tectonics got the way it is due to the specific way our moon formed. One planetary body colliding with early Earth such that both the moon formed and the inner core churned making plate tectonics possible. The ultimate result was a magnetosphere that protects our atmosphere due to a kind of dynamo effect created because of all that metal molten stuff moving around inside. Looking at all that, I'd guess that the "usual" exoplanet has a lot it must do or go through or have the luck of being situated just so in order to be conveniently livable. So it looks like most of what you listed is typical. However, 720 earth day orbits are not found too often... yet. And the perfect wobble... unknown, I'd guess at the moment anyway. As reliance on transit methods or star wobble techniques gives way to better instrumentation, like the JWST and others that might directly identify exoplanets, discovery of what the author has laid out might be found one day. Or, we may have already recorded such a planet, but the data is still just a bunch of numbers that need to be interpreted. Because long period orbits studied with wobble or transit methods require more observation time than rapid period orbits. It takes longer to tell what is happening watching slow motion than it does watching something quicker. you can probably guess I haven't taken many classes on orbital mechanics. but it appears tidal locking happens when an orbiting body is quite close to what it is orbiting. and the best I could find on the libration of the moon implies that earthrise happens about once every 27 days; if you were at a point on the moon where the earth would rise and set. I don't even know how to ask to find an animation of what the pattern of earthrise and earthset would be. and of course, I don't know if the moon is necessarily representative of other tidally locked bodies. |
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Post by GTCGreg on Apr 14, 2023 15:08:00 GMT
It's said that Earth will become tidally locked in about 50 billion years. But I think we will have bigger problems long before that as the sun is expected to run out of fuel in "just" 5 billion years. Unless, of course, we pass a law banning Hydrogen and convert it to run on electricity.
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Post by the light works on Apr 14, 2023 15:31:08 GMT
It's said that Earth will become tidally locked in about 50 billion years. But I think we will have bigger problems long before that as the sun is expected to run out of fuel in "just" 5 billion years. Unless, of course, we pass a law banning Hydrogen and convert it to run on electricity. you're right. the solution is to subsidize fossil fuel extraction and encourage every city to run open gas fires at every street corner through the winter so people can be warm year around. or maybe we can have a thread that is about orbital physics instead of parroting those news outlets you don't trust. |
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Post by wvengineer on Apr 14, 2023 16:38:49 GMT
My understanding is that for something to be tidally locked, you need two things. 1. Relatively close to the main gravity body and 2. the smaller one will have a core that is not in the center, but is shifted towards the larger by a good amount. IIRC, the moon has a core that is about 1/3 of the moon diameter deep on the side facing earth. The earth's gravity combined with the off-center core results in sort of gravity anchor that hold the same side towards us. As the moon slowly drifts further from earth, the gravity holding the core off to the side drops. Eventually in a few billion years, the moon's core will be shift towards the center point and it will loose the tidal lock. To the planet in question, I have some issue. astronomy.com/magazine/ask-astro/2012/02/planetary-dynamicsAccording to this, for a star similar to SOL, for a planet to be close enough to get a tidal lock, it would have to be about 1/10 the orbital diameter as mercury. Mercury is so close to start with that it cannot naturally develop life as we know it. It is far too hot and the solar wind would strip off any atmosphere. Mercury would be a parade compared to what a tidally locked planet would be like. As far as the elliptical orbit, All planets have elliptical orbits to one degree or another, it's just most are close enough to a circle for all practical purposes. Earth varies by about 3 million miles between Aphelion and Perihelion. For us that isn't very noticeable. For a average orbit of 93 milliom miles from the sun, it isn't that noticeable. To get far enough away to case a "winter" but then get close enough for a "summer", that is such a narrow range to get the extremes on each end but not go too far that the would would be uninhabitable. I guess fire up the infinite improbability drive. |
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Post by GTCGreg on Apr 14, 2023 17:06:55 GMT
It's said that Earth will become tidally locked in about 50 billion years. But I think we will have bigger problems long before that as the sun is expected to run out of fuel in "just" 5 billion years. Unless, of course, we pass a law banning Hydrogen and convert it to run on electricity. you're right. the solution is to subsidize fossil fuel extraction and encourage every city to run open gas fires at every street corner through the winter so people can be warm year around. or maybe we can have a thread that is about orbital physics instead of parroting those news outlets you don't trust. My post was about orbital physics, but sorry to intrude on "your" thread. I blocked the thread to make sure it won't happen again. |
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Post by rmc on Apr 15, 2023 7:55:06 GMT
My understanding is that for something to be tidally locked, you need two things. 1. Relatively close to the main gravity body and 2. the smaller one will have a core that is not in the center, but is shifted towards the larger by a good amount. IIRC, the moon has a core that is about 1/3 of the moon diameter deep on the side facing earth. The earth's gravity combined with the off-center core results in sort of gravity anchor that hold the same side towards us. As the moon slowly drifts further from earth, the gravity holding the core off to the side drops. Eventually in a few billion years, the moon's core will be shift towards the center point and it will loose the tidal lock. To the planet in question, I have some issue. astronomy.com/magazine/ask-astro/2012/02/planetary-dynamicsAccording to this, for a star similar to SOL, for a planet to be close enough to get a tidal lock, it would have to be about 1/10 the orbital diameter as mercury. Mercury is so close to start with that it cannot naturally develop life as we know it. It is far too hot and the solar wind would strip off any atmosphere. Mercury would be a parade compared to what a tidally locked planet would be like. As far as the elliptical orbit, All planets have elliptical orbits to one degree or another, it's just most are close enough to a circle for all practical purposes. Earth varies by about 3 million miles between Aphelion and Perihelion. For us that isn't very noticeable. For a average orbit of 93 milliom miles from the sun, it isn't that noticeable. To get far enough away to case a "winter" but then get close enough for a "summer", that is such a narrow range to get the extremes on each end but not go too far that the would would be uninhabitable. I guess fire up the infinite improbability drive. I didn't realize the moon's core was shifted that amount! Yeah, that's cool about core shift. I think of a bicycle tire hung off the ground on an axle. If it has a heavy side causing it to be off balance you could spin it, but ultimately it will become "tidally locked to earth" heavy side down. That's one way to imagine tidal locking, I suppose. Thanks! I wonder to what degree each planet deals with core shift? |
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Post by the light works on Apr 15, 2023 13:39:41 GMT
in my limited reading about tidal lock, it mentioned that Earth and the moon both flex a little bit, and that flex, in the case of the moon, absorbed the moon's rotational inertia until it became tidally locked.
to use RMC's bike tire model, that would be a bike tire, with the hub slightly larger than the axle, or with a marble rolling free inside the tire. thus, the wheel is, for lack of a better term, less frictionless in its rotation.
this seems to me to mean even if it is in balance, it would still come to a stop more quickly than a body that isn't, again, for lack of a better term, close enough to share gravity.
that leaves me wondering whether there would be a measurable difference in weight between a known mass on a direct line on the earth side of the moon, and the same mass on the direct line on the far side of the moon. I assume there would be a difference, but my math skills are not up to the calculations.
as for the shape of the orbit, earth's elliptical orbit does have some effect on the weather - though it is the axial tilt that makes summer and winter by affecting the relative angle to the sun. it looks, in he course of the story, like the seasonal shifts are hot and dry, followed by rainy, followed by foggy, followed by cool and dry. then I think there must be more foggy and rainy seasons before getting back to hot and dry, but I haven't seen them described in the story, yet.
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Post by the light works on Apr 15, 2023 13:43:11 GMT
you're right. the solution is to subsidize fossil fuel extraction and encourage every city to run open gas fires at every street corner through the winter so people can be warm year around. or maybe we can have a thread that is about orbital physics instead of parroting those news outlets you don't trust. My post was about orbital physics, but sorry to intrude on "your" thread. I blocked the thread to make sure it won't happen again. or maybe just leave off the political sniping in threads that are about physics. |
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Post by the light works on Apr 15, 2023 13:54:18 GMT
I guess the next question would be if this was something that could happen in a star system where the star had entered the dwarf phase of its life. the long orbital period would seem to preclude that, though. close orbits are usually a shorter "year"
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Post by the light works on May 6, 2023 12:40:59 GMT
just an update: in that particular story, the planet was artificially influenced. I'm still not sure if the period of the wobble is possible, but the shape of the orbit and the tidal lock could be handwaved at that point.
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Post by wvengineer on May 10, 2023 1:19:26 GMT
that leaves me wondering whether there would be a measurable difference in weight between a known mass on a direct line on the earth side of the moon, and the same mass on the direct line on the far side of the moon. I assume there would be a difference, but my math skills are not up to the calculations. Since you asked... Mass person: 75 kg mass earth: 5.97E+24 kg mass moon: 7.34E+22 kg G 6.67E-11 m3/(kg*s^2) distance earth: 6371000 m (center of mass to surface) distance moon: 384400000 m F=G*m1*m2/r^2 So this gives me the following Weight on Earth: 736.498007 N (165.5713 lbs) Force from the moon: 0.002486545 N (0.000559 lbs) Net weight with Moon directly overhead 736.495520 (165.5708 lbs) So the moon only changes the weight by 5/10,000 of a pound. I don't think you could reliably measure that difference. |
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Post by the light works on May 10, 2023 14:04:08 GMT
that leaves me wondering whether there would be a measurable difference in weight between a known mass on a direct line on the earth side of the moon, and the same mass on the direct line on the far side of the moon. I assume there would be a difference, but my math skills are not up to the calculations. Since you asked... Mass person: 75 kg mass earth: 5.97E+24 kg mass moon: 7.34E+22 kg G 6.67E-11 m3/(kg*s^2) distance earth: 6371000 m (center of mass to surface) distance moon: 384400000 m F=G*m1*m2/r^2 So this gives me the following Weight on Earth: 736.498007 N (165.5713 lbs) Force from the moon: 0.002486545 N (0.000559 lbs) Net weight with Moon directly overhead 736.495520 (165.5708 lbs) So the moon only changes the weight by 5/10,000 of a pound. I don't think you could reliably measure that difference. i figured on earth it would be negligible to the point of not being measurable. otherwise, dieters would be weighing in on the full moon. I was curious if earth's gravity had a measurable effect on objects on the moon. - hence the extremes of being in the middle of earthside, and the middle of not-earthside. |
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