Can a body in space form a sphere?

  1. So this is some what of a silly question, I was bored and watching YouTube and there was a guy trying to say that the earth is hollow ( crazy people are funny to watch) but it got me thinking could a planet form so that it was hollow? Or could a something like a small moon be hollowed out? Im just curious and I dont know much about how planets form, im hoping you guys do know and can tell me. Thank you in advance for answering my ridicules question.
     
  2. jcsd
  3. Chronos

    Chronos 10,134
    Science Advisor
    Gold Member

    It would be a very odd situation. A hollow earth is pretty much out of the question. Plate tectonic would cause it to cave in like a poorly shored mine tunnel. Since planets and such are believed to form by accretion processes, a scenario where a hollow globe could form without collapsing under its own gravity is difficult to imagine.
     
  4. That is what I thought, but this guy was saying that when the planet was still liquid before it cooled that any gases traped inside would move to the core and the heavier elements would be pulled out by the rotation of the planet. Im not sure how gases would get trapped in a liquid but I guess its not unimaginable. What about hollowing out some thing like an asteroid on purpose? Is it doable or would its own gravity crush it?
     
  5. Drakkith

    Staff: Mentor

    That guy is incorrect. The heavier elements are drawn towards the core because they are more dense, while lighter elements and gases tend to rise towards the surface. In order for the rotation of the Earth to have the reverse effect, the Earth would have needed to spin so fast that it would have thrown itself apart during formation.



    Sure, as long as the asteroid is small enough. If it gets too big the weight of the upper layers gets too high to support and it caves in on itself.
     
  6. russ_watters

    Staff: Mentor

    That also wouldn't result in a sphere; it would be a disk.
     
  7. Well that answers my question, thank you guys.
     
  8. The guy who came up with the idea of a 'hollow Earth' is Neil Adams, he is a crack pot! There is no realm of science which isn't wrong based on his own 'Research'. The guys credentials are the creator of Marvel comics!


    Damo
     
  9. Wait wait wait... next your going to tell me that the queen of England isnt a lizard god! (Sarcasm) I know that most what is on the internet is complete nonsense, but it beats comedy central most days.
     
  10. Hollow Earth aside, the question is interesting.

    I can imagine a fluid in space, perfectly non-rotating, electrically charged and exhibiting some form of surface tension. The electric charge would try to expand the fluid while the surface tension would keep it in place. Would such setup form a hollow sphere?
     
  11. Thats kind of what I was thinking haael.
     
  12. Assuming the fluid didn't freeze couldn't you just "blow" a bubble? You would need just enough excess pressure to compensate for surface tension.

    Edit: the gas used could be created chemically?
     
  13. Yeah, but I don't seek for practical realisations, but for solving this theoretical puzzle.

    What interaction would admit a lowest-energy solution looking like a hollow sphere?

    Suppose we have a set of many tiny particles, interacting in some way. What the interaction should be for them to form a hollow sphere?

    What we already know:
    1. Infinite attracting interaction (gravity) would collapse them to a point.
    2. Infinite repelling interaction (electostatic) would scatter them throughout the universe.
    3. Infinite attracting interaction (gravity) plus short range repelling one (pressure) would result in a non-hollow ball with density increasing to the center, that means a star.

    Now I wonder: if we had infinite repelling interaction plus some short-range interaction that tries to reduce the surface in some sense - would it form a hollow sphere?
     
  14. Drakkith

    Staff: Mentor

    I know of no way for this to occur naturally.
     
  15. An interesting idea. I suppose it would happen if the inner core was made of a substance that shrunk as it cooled whereas the surface expanded as it cooled (like Ice?). But I think it would be inherently unstable.

    Another idea could be if there was an underground sea encircling the entire planet which evaporated somehow.

    Or... an icey asteroid that picked up lots of Earth dust encrusted on it's surface which formed a hard shell, then the asteroid passed close to the sun and it's inner core evaported.

    None of these things are likely. But you're welcome to use any in a science fiction story!
     
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