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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
FireHazardDate: Thursday, 28.11.2013, 07:45 | Message # 211
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So, I was checking out this Planet Making game after randomly searching "planet creator" (because why not) and found out it looks pretty cool. I made this little grouping and wondered if it was really possible:

First image, showing the system. The tiny ground clipping; just take it as some sort of tiny asteroid flying by the camera or something.

Second image, showing the system blurred, allowing for somewhat clearer view from the stars in the background. I could've just removed the stars, but why do that when you could have a fuzzy image?


There's two planets, both locked into spinning around eachother. Each has their own moon, the "main" planet having another habitable moon (both planets are habitable, by the way.) The "main" planet also has a thin set of rings, and is somewhat tilted, with large ring-like clouds going across it horizontally to it's poles. This planet's moon is fairly close and noticeably less than half it's own size. The "secondary" planet is about the same size as the "main" one, with it's own moon being quite small even in comparison to the other. These two planets orbit around a classic earth-like yellow star.

Although in the simulation you can't actually add secondary planets, you can add moons with textures of planets. Let's just assume that the habitable moon and "secondary" planet both have normally behaving clouds as a planet's clouds with oceans, deserts, ice caps, etc. would behave.

I warn you, I know nearly nothing about astronomical terms or if I've broken a law of physics or something, so stick with me here.

Added (28.11.2013, 10:54)
---------------------------------------------
Attached files on the thread are the images in their original size. It took me a bit to figure out how to get the images to work, I had to first download them from the website after taking them and then extract them from my computer. I got it eventually though. I'll go over them in a more explained way here: In the image, the eclipsed moon is the moon of the "main" planet, while the bright habitable planet in the background is the "secondary" with it's own tiny white dot as a moon. The planet textures are all different from Earth's, available in-game. I did, however, decide to stick with the Moon's texture for the tiny white dot as it is unreasonably bright to see the texture. Also, the little black ring near the bottom of the "main" planet is it's thin ring system, which is nearly invisible.

Attachments: 0191269.jpg(130Kb) · 4601993.jpg(67Kb)


Edited by FireHazard - Thursday, 28.11.2013, 07:53
 
WatsisnameDate: Thursday, 28.11.2013, 09:16 | Message # 212
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Howdy FireHazard, nice to have you!

Your system appears to be possible, at least as far as I can guess by the screenshots (to be precise you'd have to do some math). The moons should be close enough to their planets to be inside their spheres of influence, but at the same time not so close that they get torn apart by tidal forces. The positions as you have them seem to be okay but again that's pretty much me completely guessing. smile

Similarly, the planets themselves should also not be too far apart, or else their sun's gravity will separate them. You may read the wikipedia page on Hill Sphere's for more info.

One thing I can say for sure is that in the long term the orbits of the moons will not be stable. They will gradually spiral in and crash into their parent planets. The reason for this has to do with tidal effects and the fact that the two planets are tidally locked with one another.

So in a nutshell there is nothing that prevents a system like this from existing, but you wouldn't expect to find systems like this in nature very often because they won't last long (in the geological sense).

Hope that helps!





 
FireHazardDate: Thursday, 28.11.2013, 17:04 | Message # 213
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Awesome. Expect more of these from my curiosity, probably going to be making more crazy systems on this thread. I'll attempt to take more screenshots showing different angles next time, though, instead of just a scenic one. biggrin
 
FireHazardDate: Thursday, 28.11.2013, 18:19 | Message # 214
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I'm going to go ahead and post my unsure planetary systems that I've created on Planet Maker. Here's my first one, which has already been answered as to whether or not it's possible to exist: "Is this possible?"

And here's my second one, more will be arriving. I want to know if this could naturally occur:

There's a gas giant with rings, and over 10 moons (I only show 9 in model form, since the smallest of these are barely visible anyways.) It has a brown color to it and also bears brown rings. The largest 9 moons are of varying sizes, one of which is habitable with vegetation. One of the largest moons is closing in on the rings and (if I'm correct, at least [I don't know how this stuff works]) is slowly being sucked towards the giant in its orbit. The giant in question is at a reasonable distance from its star, much like Saturn is with the Sol system, the star is of about the same size as our own.

First image: It shows the smallest moons in an extra large size, while the largest of the nine are aligned.


Second image: Same thing from above.


Third image: Stars removed, showing the tiniest in their natural sizes. Try to make out the little dots if you can.


Fourth image: Shows the planet system in a natural time, no editing out the stars (or blurring like the last system.)


Attached files will show the original image sizes in case you want them to be in large.

Attachments: 3212074.jpg(79Kb) · 2979038.jpg(68Kb) · 1783002.jpg(41Kb) · 5742276.jpg(49Kb)


Edited by FireHazard - Thursday, 28.11.2013, 18:23
 
WatsisnameDate: Thursday, 28.11.2013, 21:18 | Message # 215
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Although these are cool, please don't fill this thread with fictitious systems and asking if they're all possible or not. I'll be happy to help you learn the principles so you can apply them yourself, but I'm not going to go through every system saying 'yes this works' or 'no this doesn't'. wink

Some basic ideas are:

-Objects should orbit within their parent bodies' Hill Sphere's, and not within their Roche limits. For giant planets it often makes sense to put rings inside their Roche limits.

-Object surfaces and composition should be consistent with their location in the system and expected surface temperatures due to sunlight. E.g. it wouldn't make much sense to have an earth-like planet in the same place as an ice moon.

-Don't have multiple large objects in nearby/similar/crossing orbits; these would be dynamically unstable.

-Don't give atmospheres to objects that are too small; their surface gravity has to be strong enough.

There's also free software such as Gravitation3D which can help you build and simulate n-body systems in 3D, to see what kind of orbital configurations are stable or not.





 
HarbingerDawnDate: Thursday, 28.11.2013, 21:31 | Message # 216
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Quote Watsisname ()
their surface gravity has to be strong enough.

Their overall mass is most important. Also, their temperature must be low enough.





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WatsisnameDate: Thursday, 28.11.2013, 22:20 | Message # 217
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Right, temperature matters, too. But thermal escape is directly related to surface gravity and indirectly related to mass, because it is the balance between the velocity of the molecules and the gravitational force pulling them down. Surface gravity is proportional to mass and inversely proportional to radius squared, or, equivalently, is proportional to radius and density.




 
HarbingerDawnDate: Thursday, 28.11.2013, 22:53 | Message # 218
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But let's say that you (hypothetically) had an object with a surface gravity of 0.01 g and a mass of 10 Solar masses. Would it not be able to retain an atmosphere much more readily than a smaller object with similar surface gravity - such as Pluto - at the same temperatures?




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WatsisnameDate: Thursday, 28.11.2013, 23:36 | Message # 219
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Ah, are we talking of amount of atmosphere that can be retained through outgassing, or, if we have these two objects, give them the same atmosphere to start with, then which holds on to that atmosphere more effectively?

In the latter case I'm inclined to think they would be the same. In the former, the more massive body has more outgassing potential, so if it can retain those gases then it can build a more substantial atmosphere than the less massive object, even though the ability to hold on to a certain gas is the same for both bodies.





 
HarbingerDawnDate: Thursday, 28.11.2013, 23:46 | Message # 220
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But wouldn't they have different escape velocities, therefore requiring more energy for an atom or molecule to escape the larger body than the smaller one?




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WatsisnameDate: Friday, 29.11.2013, 00:52 | Message # 221
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Wow, I'm glad you pushed me on this -- all this time I thought surface gravity and escape speed would not depend differently on the parameters of the object; but of course they do! In fact if the surface gravity is held constant then the escape speed grows as the fourth root of the mass. So you're right, there is a slight difference in this regard. smile




 
VoekoevakaDate: Friday, 29.11.2013, 01:13 | Message # 222
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The problem is the ring. I don't know if it is small or big, but the big moon should have made it decay.




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Rhysy27Date: Tuesday, 24.12.2013, 18:13 | Message # 223
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Our sun must have come from a star which went supernova. Could that star have had planets and if so, life? It fascinates me!




"It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring." - Carl Sagan
 
SpaceEngineerDate: Tuesday, 24.12.2013, 18:48 | Message # 224
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Quote Rhysy27 ()
Our sun must have come from a star which went supernova.

No. It comes from a lot of stars that exploded or get rid of their shell billions years ago. And Sun is made not only fro, matter ejected by these stars, it also have a lot of primordial hydrogen and helium created by the Big Bang.





 
WatsisnameDate: Tuesday, 24.12.2013, 18:56 | Message # 225
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Probably not, neat as that may be. smile

The solar nebula from which our system formed was of course seeded with elements from supernova explosions, perhaps with one of these events occurring only a few million years prior, based on isotopic abundance seen in primitive meteorites. But like SpaceEngineer said, most of the material came from first generation stars which would have only been made of primordial elements. Also, stars that end their lives by going supernova are more massive than our sun and go through their fuel much more rapidly. They probably do not stay on the main sequence long enough for life to develop on their planets.

So the stars that go supernova, and by doing so populate the universe with the elements necessary for life as we know it, were likely themselves uninhabited.





 
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