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Silverblade5

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1 hour ago, Silverblade5 said:

Very possible. As star = sun, there are infinitely many combinations ;) 

Okay. Because that's very important for a universe I'm making, and I just wanted to know how close to possible it was.

Out of curiosity, what would the other planets' climates be like? What would the other planets look like to each other?

Edited by StrikerEZ
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32 minutes ago, StrikerEZ said:

Okay. Because that's very important for a universe I'm making, and I just wanted to know how close to possible it was.

Out of curiosity, what would the other planets' climates be like? What would the other planets look like to each other?

That... was a semantics pun. I honestly have no idea.

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Just now, Silverblade5 said:

That... was a semantics pun. I honestly have no idea.

Oh...my bad. :o

I usually have a hard time with understanding jokes/sarcasm across the internet unless it's practically screaming "Look at me! I'm a joke!"

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when you say "facing the sun" what do you mean?  do you want it to be tidally locked, so one side always faces the sun (think moon to earth or Taldain in the cosmere) or do you just mean that of the four, it is generally on the sun side the vast majority of the time (I assume the latter)?

the second option might be possible if the 4 planet configuration were itself tidally locked with the sun, so that the 4 planets revolve around their common center of gravity in sync with their revolution around the sun.  you'd have to have each planet individually rotating on its own axis within this configuration if you wanted day/night cycles, but that part at least doesn't seem unreasonable.  I have my doubts that such a configuration would be stable, since the planet closest to the sun would have a higher gravity acting on it than the further ones, but I certainly don't know enough physics to say for sure.  it also may not result in the sort of displays you might want, though I admittedly don't have any idea what you have in mind there.  it seems likely that, in this case, from the surface of one planet, the other 3 would always appear in the roughly same configuration, modulated a little bit by the system's elliptical orbit.  with their sizes determined mostly by distance, which mean looking at things like Roche limits to determine how far apart they would minimally need to be.

Edited by Dunkum
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23 hours ago, StrikerEZ said:

Okay, how possible would it be for four Earth-sized planets to share a common center of gravity, rotate around a Sun-sized star and still end up with one of them ending up facing the sun most of the time?

What exact kind of setup are you thinking of? Four planets locked in a giant plus symbol? Four planets orbiting a center of gravity like Pluto and Charon? A sketch and some elaboration would be very helpful.

In general though, it's very hard to get a large number of similar-sized astronomical bodies into a stable configuration when they are very close to each other. Our own Earth-Moon system is unstable on the scale of billions of years. Something like what your describing would probably only be stable on the scale of a few tens of thousands of years, like Roshar and its three moons. Each of the planets would also likely experience HUGE tidal forces. So yeah, of course it's possible, but getting it to work would probably require some insane geoengineering or shardic-level intervention.

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15 hours ago, Dunkum said:

when you say "facing the sun" what do you mean?  do you want it to be tidally locked, so one side always faces the sun (think moon to earth or Taldain in the cosmere) or do you just mean that of the four, it is generally on the sun side the vast majority of the time (I assume the latter)?

the second option might be possible if the 4 planet configuration were itself tidally locked with the sun, so that the 4 planets revolve around their common center of gravity in sync with their revolution around the sun.  you'd have to have each planet individually rotating on its own axis within this configuration if you wanted day/night cycles, but that part at least doesn't seem unreasonable.  I have my doubts that such a configuration would be stable, since the planet closest to the sun would have a higher gravity acting on it than the further ones, but I certainly don't know enough physics to say for sure.  it also may not result in the sort of displays you might want, though I admittedly don't have any idea what you have in mind there.  it seems likely that, in this case, from the surface of one planet, the other 3 would always appear in the roughly same configuration, modulated a little bit by the system's elliptical orbit.  with their sizes determined mostly by distance, which mean looking at things like Roche limits to determine how far apart they would minimally need to be.

Yeah, you guessed which one I meant. Sorry I wasn't clearer.

I wanted the planets to each believe the other three planets to be their moons, as that plays an important part in the storyline. 

3 hours ago, Glamdring804 said:

What exact kind of setup are you thinking of? Four planets locked in a giant plus symbol? Four planets orbiting a center of gravity like Pluto and Charon? A sketch and some elaboration would be very helpful.

In general though, it's very hard to get a large number of similar-sized astronomical bodies into a stable configuration when they are very close to each other. Our own Earth-Moon system is unstable on the scale of billions of years. Something like what your describing would probably only be stable on the scale of a few tens of thousands of years, like Roshar and its three moons. Each of the planets would also likely experience HUGE tidal forces. So yeah, of course it's possible, but getting it to work would probably require some insane geoengineering or shardic-level intervention.

It doesn't necessarily have to be a plus symbol, though that's the basic idea that pops in my head when I imagine these worlds. Whichever configuration would result with the least gravity problems would be best. I know the stability of these planets in this setup wouldn't last very long and wouldn't be natural, but that's the point. It wasn't natural, and it's sustained magically. Of course, the magic tries to make it work without constantly having to adjust so the planets don't collide.

Basically, what I need is these four planets to be able to have what they believe to be three moons. And, if one of them is closest to the sun more often the others, that would imply that one of them is farthest from the sun most of the time right? 

Sorry if I'm not being clear enough, I'm better at responding with details when I'm given questions.

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I'd look at what actually exists in real life, and try to tweak that to what you want. You could make your planets actually be moons. Have a black hole with the mass of Jupiter, and then you can have four 'moons' that are each the size of Jupiter's moons, which could easily be small planets. Jupiter's density doesn't matter, just its mass - so let's compress it down to an infinitesimally small point. I don't think Jupiter's moons would be close enough to see one another, but you could do a similar principle if you could figure out how to get a terrestrial planet with four relatively large moons. Or maybe you could base something on the Pluto planetary system, which has two large bodies and then more smaller bodies (if you're fine with having really small planets).

As far as tidally locked, our moon is basically 'tidally locked' towards the sun; although it goes around the Earth, it doesn't ever rotate, so the 'dark side' never sees the sun. So that concept is definitely possible. EDIT: So, that's fake news, apparently. You learn something new every day. But just because it isn't true doesn't mean it couldn't be true; the spin of a planet won't affect its orbit around a larger object. That's all I was getting at; I thought we had a real-life situation of what you're looking for, but this far, I guess not.

Edited by Pagerunner
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27 minutes ago, Pagerunner said:

As far as tidally locked, our moon is basically 'tidally locked' towards the sun; although it goes around the Earth, it doesn't ever rotate, so the 'dark side' never sees the sun. So that concept is definitely possible.

Er, not quite.  the moon is tidally locked with respect to Earth, so one side faces us at all times.  The dark side gets plenty of sunlight; it is 100% in the sun during a new moon for instance.  the moon rotates, but its rotational period is roughly equal to its revolutionary period.

 

2 hours ago, StrikerEZ said:

I know the stability of these planets in this setup wouldn't last very long and wouldn't be natural, but that's the point. It wasn't natural, and it's sustained magically. Of course, the magic tries to make it work without constantly having to adjust so the planets don't collide.

Ah, in that case I think that yes, something like that could conceivably work, though you would need a colossal amount of energy to create and maintain it, on the order of gods. that said, I am not sure about 1 planet getting more sun than the others...I don't have nearly the background to begin to contemplate the actual equations you would need to work this out, but I think you end up with a situation where one planet is always closest to the sun and the others don't really move much with respect to the sun, so planet 1 is always sunside, planet 2 is always on the far side of planet 1 from the sun, etc (what I described as having that whole planetary configuration being tidally locked with respect to the sun)...or you end up with a version where each planet spends roughly the same amount of time on the sun side.  you can stretch the period of that up a lot, so presumably you could have a version where one planet spends 10000 years on the sun side, but slowly revolves out of it to be replaced by the next planet.  maybe if you relax the size requirement a bit: if you have one planet much bigger than the others, so that the shared center of mass is much closer to it than to the others, then you could have a situation where it is almost like 3 smaller planets orbiting the one big one, but I don't think that fits the description of what you want.

do take all of this with a grain of salt, since my background in orbital mechanics is limited to entry level physics and astronomy courses, plus whatever I have picked up from hard sci-fi and pop science type publications.  I'm pretty sure everything I am saying is sound, but, as I mentioned, I wouldn't know how to model that at all.

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The only way to really get one planet to stay closer to the stars than the other would be to put them all in eachother's Lagrangian points. This would be stable without godly intervention for a few years, but it brings up some problems. The planets would all have to be in a line, meaning at least one planet would be blocked by another no matter which world you are on. The two middle planets would each have two "moons," and the outer planets would have only one. Also, the planets would be in fixed positions in the sky.

For your intents and purposes, I think you are better off having them orbit a common center of mass. As long as you are okay with having a powerful magic presence keep the system stable, you should be fine. Brandon does the same thing with Taldain in White Sand. As for one planet being closer to the sun than the others, there are some workarounds. Because they all orbit the same center of mass, then each planet would spend half it's time within the orbit of the CoM, and half it's time further out. As @Dunkum said, you could make one planet have a really long orbit. That would also require magical interference to make happen. If your intent is to make one planet hotter than the others, then there's other ways you could achieve that by tinkering with the biosphere. Water is a heat regulator, and planets with more water would have more stable temperatures. If you gave a planet low surface moisture, then it would have hot days and cold nights, like an actual desert.

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@Pagerunner @Dunkum @Glamdring804

Thanks everyone for the help. Honestly, astronomy has never been my strong suit (though I think it's cool) and I'm not even in physics yet, so I don't even understand a lot of what you're saying. But I think my idea could work, with some divine intervention.

The main reason I wanted one of the other planets to be closest to the sun is because the four planets all started with the same amount of water, but one of them loses a lot of its water, and the only way I could think of this happening is through it being closer to the sun. 

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12 hours ago, StrikerEZ said:

@Pagerunner @Dunkum @Glamdring804

Thanks everyone for the help. Honestly, astronomy has never been my strong suit (though I think it's cool) and I'm not even in physics yet, so I don't even understand a lot of what you're saying. But I think my idea could work, with some divine intervention.

The main reason I wanted one of the other planets to be closest to the sun is because the four planets all started with the same amount of water, but one of them loses a lot of its water, and the only way I could think of this happening is through it being closer to the sun. 

There are a number of other ways you could work around this. If a planet has a weaker magnetic field, then more high-energy radiation would strike the surface and atmosphere. Over millions and millions of years, water molecules in the air would be zapped apart, and the hydrogen, being an extraordinarily light gas, would be swept away into space. This is essentially what has happened to Venus, and it could have some interesting effects. When one planet is behind the planet leaking hydrogen, there would be heightened auroras on the outer planet due to the influx of hydrogen ions, though I'm not sure how noticeable the increase would be. Also, the people on the dry planet, if they've been their for a long amount of time, would naturally develop darker skin tones to accommodate the higher levels of ambient radiation.

Another way you could do it is have the water locked away in the planet's crust. Something similar happened to Mars. The surface of mars is orange because the crust has a moderately high iron content. The rocks absorbed a good portion of the planet's water, and essentially ended up rusting into their current color. The water is technically still there, but it's all been sequestered in the molecular structures of the rocks.

I'm not sure if either of these works for what you have in mind. I personally would use a combination of both of them. They would make an awfully beautiful surface, with sweeping landscapes of rusty red desert. Bear in mind that for your dry planet, you'll still need at least 10% of the surface covered in water in order to support enough photosynthetic life to sustain livable levels of oxygen in the atmosphere.

 

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8 minutes ago, Glamdring804 said:

There are a number of other ways you could work around this. If a planet has a weaker magnetic field, then more high-energy radiation would strike the surface and atmosphere. Over millions and millions of years, water molecules in the air would be zapped apart, and the hydrogen, being an extraordinarily light gas, would be swept away into space. This is essentially what has happened to Venus, and it could have some interesting effects. When one planet is behind the planet leaking hydrogen, there would be heightened auroras on the outer planet due to the influx of hydrogen ions, though I'm not sure how noticeable the increase would be. Also, the people on the dry planet, if they've been their for a long amount of time, would naturally develop darker skin tones to accommodate the higher levels of ambient radiation.

Another way you could do it is have the water locked away in the planet's crust. Something similar happened to Mars. The surface of mars is orange because the crust has a moderately high iron content. The rocks absorbed a good portion of the planet's water, and essentially ended up rusting into their current color. The water is technically still there, but it's all been sequestered in the molecular structures of the rocks.

I'm not sure if either of these works for what you have in mind. I personally would use a combination of both of them. They would make an awfully beautiful surface, with sweeping landscapes of rusty red desert. Bear in mind that for your dry planet, you'll still need at least 10% of the surface covered in water in order to support enough photosynthetic life to sustain livable levels of oxygen in the atmosphere.

 

I kind of like the first idea. It fixes the problem of having one planet dryer. I might think about using the part about the mars-like surface absorbing a lot of the water. Of course, there's still a lot of water left. But it's more like 35% of the surface, I think. I think these things work better for what I have in mind about the planets' creation, as this one of the four is kind of a failed experiment for trying to emulate something. 

Assuming the four planets are in a plus shape, and they all look a lot like Earth (lots of blue and green), what would the other planets look like from the dry planet? 

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41 minutes ago, StrikerEZ said:

I kind of like the first idea. It fixes the problem of having one planet dryer. I might think about using the part about the mars-like surface absorbing a lot of the water. Of course, there's still a lot of water left. But it's more like 35% of the surface, I think. I think these things work better for what I have in mind about the planets' creation, as this one of the four is kind of a failed experiment for trying to emulate something. 

Assuming the four planets are in a plus shape, and they all look a lot like Earth (lots of blue and green), what would the other planets look like from the dry planet? 

Depends on the water coverage. If they have surface water comparable to Earth (60% ~ 75%) then they would look mostly blue, with swirls of white clouds, and bits of brown and green underneath. Less water would mean more brown and perhaps less white, and more water would mean more blue.

Their relative sizes in the night sky would depend on how far apart they are. I would assume you will want them to be roughly the size of Earth's moon when viewed from the planet. I'll do some calculations here in a minute as to how far they would be. If they orbit in a giant plus formation, meaning they all are the same distance from the mutual center of gravity, then they would be fixed distances apart in the sky, specifically, each one would be 45 degrees away from the other.

Edited by Glamdring804
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1 hour ago, Silverblade5 said:

I'm going to update the OP with a list of go-to people for various subjects. So far, I've got @Glamdring804 for physics and @Chaos for math. Do we have anyone for biology or chemistry?

Interestingly, that's what just happened in a worldbuilding group I'm in :D

I'm gonna reap the benefit of speaking two languages to get two sets of opinions on my ideas :ph34r:

Edited by Oversleep
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