[Worldbuilding] I need help for the creation of a planet?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by NeptuneRise, Apr 13, 2010.

  1. NeptuneRise Worldbuilder Registered Senior Member

    Hi there! I'm new here

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    , and I was looking for some information, if people here can provide me with that?

    I'm working on a Worldbuilding project, where I'm creating a fictional universe, but I want the worlds that I and others would create, to be based on real scientific facts, with real astronomical data, and to be subject to our natural laws of physics, just like other worlds in our real universe.

    I need a planet that has a deep and thick atmosphere and that's 3 times the size of Jupiter.

    The atmosphere equals 2 thirds of the planet though. I need it to be that way because one of the many species on that planet live in the atmosphere, the rest being on the surface.

    Would the mass of this planet create extreme gravity in such a way that most of the life forms there are gigantic?

    This planet that I'm talking about, is in the 4th orbit around it's F5 main sequence star, and actually making it the last one in the orbital order. How distant should this planet be in order for this liquid water to be maintained, and not freeze over?

    Could 2.3 A.U. be ok?

    I need facts behind this. Since this is the forum for astronomy, and exobiology I thought I ask my question here

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    Any answers that remotely satisfy the information I need for these questions would be very appreciated. I also hope that this might also turn into an interesting discussion among those who are heavily into astronomy and astrophysics. Thank you

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    PS: Also, whoever feels like she/he can contribute to this Worldbuilding project in any way possible, or wants to be a part of it, please let me know. I take all kinds of people, with all kids of ideas and all kinds of advices/help they offer, well ... 99.99% of the time hehe :mrgreen:. As long as the project is still what the name suggests and does not turn into something else.
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  3. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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  5. Montec Registered Senior Member

    Hello NeptuneRise
    The planet would need to be hollow to keep gravity as low as possible. This is needed to keep the pressure and temperature differentials from surface to altitude within reason. (Also a good plot line) IE high pressure will increase the atmosphere's "green house" effect, especially with that much atmosphere. The F5 and 2.3 A.U. will work.

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  7. NeptuneRise Worldbuilder Registered Senior Member

    Thank you very much for that link, it has a lot of information that could help me

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    Yes, I was thinking of making my plane having huge "hollow pockets" inside its make up filled with either gas or maybe some liquids.

    And 80% of the life forms there are gigantic ( I mean, they evolve into gigantic size, they start as any life probably does - microbial size). Due to the gravity of the planet, which even though its low, it's still fairly extreme because of the size - 3 times the size of Jupiter.

    Although, you said low gravity. How low can I get the gravity to be (if Earth = 1G for an example in comparison) so it can still hold the atmosphere? I don't want the atmosphere going in space lol.

    Thanks for your input though

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  8. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    What Montec meant was that if the gravity is to be 1G (or thereabouts) then the planet would have to be hollow (or made of some extremely light materials).
    If it's 3 times the size of Jupiter then any "conventional" composition of the planet would make the gravity far higher than 1G.
  9. Montec Registered Senior Member

    I would not go lower than 0.8 g. A F5 is hotter than our sun and would likely eject particles (solar wind) at higher velocities. Solar wind will strip unprotected planets of the lighter gasses if their gravity is to low. However, a strong magnetic field will tend to protect planets from this loss. 2.5 AU would place your planet in the asteroid belt.
    As an example Mars at 1.5 AU and a gravity of 0.376g has very little atmosphere left.

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  10. NeptuneRise Worldbuilder Registered Senior Member

    Thank you for your comments, I really appreciate it.

    Ok, so this is what I came up with:

    F5V main sequence type of star

    Star Luminosity at Planet - 1.743470998203361 (Earth = 1)

    Star's Apparent Size 0.5811243331304294 (Sun viewed from Earth = 1)

    The planet is in 4th and last orbit around it.

    Distance: 2.5 A.U

    Planet Orbital Radius - 2.5763134657051983 A.U

    Gravity: 4.5G (Earth gravity = 1G)

    Metals: Lithium, Magnesium, Aluminium, Vanadium, Beryllium & Copper

    Atmosphere: Hydrogen, Nitrogen, Ammonia, Helium & Oxygen

    Stats sound ok?
  11. Giambattista sssssssssssssssssssssssss sssss Valued Senior Member

    Who built the hollow planet?
    I don't think those just come out of nowhere.
  12. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    Two points:
    1) your figures are way too "accurate". You don't need so many decimal places and
    2) using G=m/r[sup]2[/sup] transposed (a quick formula to find surface gravity in Earth values - all figures given in "Earths") I get a density that is 1.44x10[sup]-7[/sup] that of Earth. Since Earth is roughly 5.5 tonnes/ cu.m your planet would be 8x10[sup]-7[/sup] tonnes/ cu m, or 9000 times less dense than air (on average).
    Hardly gonna be any metals in there!
    If it's hollow you'll have to work out how thick the "shell" is. I haven't looked at that, but I suspect that it's not going to be very thick at all.
  13. Montec Registered Senior Member

    Take a look at the Jupiter wiki page. Particularly this part

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  14. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    Hollow planets - other than being tricky to come up with a reasonable method of formation - would also have no stored heat to keep the dark-side warm.
    All that it would have is whatever it can store in the crust / surface layer (and the atmosphere). I guess if this layer is thick enough you might be okay, but too thin and I'm sure the planet temp would drop too low at night to sustain life of any sort.

    Just look at mercury... the side facing the sun can reach 400-450 deg-C, but the night side drops to -170 deg-C despite being so close to the sun. I'm not too sure of the relative impact of the atmosphere and the planet on maintaining a planet's temperature, but i'd think the majority would be from the planet itself - and if the planet is too thin to store sufficient heat then the night-side would surely get problematic.

    Likewise the day-side... Would the crust of a hollow planet not get that much hotter that much more quickly (and lose it that much more quickly on the night-side)?

    Also - is a hollow planet able to generate a magnetic field to protect it?

    Anyhoo - just some thoughts.
  15. NeptuneRise Worldbuilder Registered Senior Member

    Nobody built it, it's suppose to be natural. And it's suppose to raise questions like that in the stories that are to unfold in this fictional universe. It's one of the things that puzzles the humans that discover this planet.

    And the Moon is hollow (or has shown such properties). Are you implying that our Moon is artificially built? Can't hollow objects (or planetary objects with "hollow pocket" internal structure) form naturally?

    lol, sorry. I just copied the results I got from computing certain stats in an online planet creation calculator of some sort.

    Here it is:


    Oh dear ... lol

    Thanks for making that calculation Dywyddyr, it seems I need to either change some stats, or think out the thickness of the interior.

    Maybe if I make the pockets larger as you go deeper inside the planet, I might make this more realistic? Like, for an example, starting with the large cavern systems found in South America, who people call 'hollow pockets', in the most upper layer of crust on this planet, and the pockets getting larger as you go deeper inside.

    Or maybe I should do the opposite? Larger hollow pockets near the surface of the planet, and they grow smaller as you progress deeper inside it? I dunno how much weight that would add, or would it change the density in any way. It's just a thought.

    If you have some ideas how I can fix this it would be very appreciated

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    Thanks Montec

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    But my planet is not a gas giant. Or does the same apply for other planet types as well?

    It says any gas giant larger then 3 times Jupiter's size would shrink etc.

    But mine is exactly 3 times the size. Maybe I will even make it 2.5 times, it doesn't matter, what I mean is - would it pose a problem for this type of world, or is it a case in gas giant exclusively?

    What do you propose for fixing that problem? I have excluded molten Moons orbiting the planet and giving it 'some' amount of heat since it's unrealistic. Isn't the distance enough for heat to come from the star? I mean, it's an F5 after all. I was actually worried if the star type would give out too much heat.

    What if liquids inside those pockets circulated around?

    Won't that create what we term geothermal heat?

    Also because of the elements I put out in the atmosphere, there would be frequent rainstorms. Some of the elements can ignite if they come in touch with electric discharge.

    I dunno, I'm just saying, if there is a way I can add a little more heat to the planet, I'm all ears. I don't need heat in the amounts we get from the Sun, since the lifeforms dwelling there don't need much heat. But it would be nice if you know a way I can add heat by introducing something plus, or just modifying a few things.

    Can a thick and deep atmosphere store heat? Then I think that would partially fix the problem. Wont also the elements contained in the atmosphere produce some sort of Green House Effect? Just throwing off some possibilities here.

    Yes it can. Or I think it can. Anyone knows this for sure?
  16. Search & Destroy Take one bite at a time Moderator

    I think the opposite is true actually.

    More energy would be required to rise vertically, making it less desirable. For gigantic organisms, rather than gravity you will need gigantic energy sources.

    Think about how oxygen content in the dino-period created basketball-sized bugs, and if there was 1000X the gravity they would all instantly do that wind-shield splat on the ground.
  17. Montec Registered Senior Member

    The thickness of the atmosphere is ,in part, what determines whether or not a planet is a gas giant or not. Also, if you look at Venus as an example, which has a thicker atmosphere than Earth, you will find the surface temperature and pressure much higher than Earth's. But at altitude where the pressure is 1 atmosphere (sea level pressure on Earth) the temperature is within the norms seen on Earth for the same pressure. So more atmosphere equals more pressure and higher temperatures for a given g-field. A 4.5 g-field and thick atmosphere will result in high pressure and temperature at the surface. So you will need to think up a reason for your hypothetical planet to exist outside known physics.

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    Last edited: Apr 16, 2010
  18. eburacum45 Valued Senior Member

    Take it from an old experienced world-builder; naturally occuring hollow planets are impossible.

    A planet more massive than Jupiter would be denser than Jupiter; it would not get any larger than Jupiter, unless the planet was very hot and near the star.

    Some gas giants are very hot and inflated. Here's Jupiter compared to an inflated gas giant, Hat-p-1b, which is very near its parent star, and is far too hot for human habitation.

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    this giant is only larger than Jupiter because it is much, much hotter, not because it is hollow.

    Empty bubbles inside a planet are not possible- the pressure is too great.

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