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Can the Earth sustain the weight of another Earth?

  1. Aug 3, 2015 #1
    Consider that earth was placed freely in space, away from the sun. Then another, but similar earth is brought carefully in contact with it, so that the two planets get locked in place by their mutual gravity fields. Now, would the earths suffer a structural collapse, or would they remain more or less in the same shape? And, would all the water be clumped around the contact point?
     
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  3. Aug 3, 2015 #2

    CWatters

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    Look up the structure of the earth. Is the earth mostly solid? Mostly liquid? Why is the earth a sphere?
     
  4. Aug 3, 2015 #3
    That's a nice answer to an extent. But the case is quite different here, right? The creation of earth was from a part of sun where the materials were at initial condition in molten state. That caused the heavy materials inside. But, here it is more a case of gravitation. Can both be considered from the same level?
     
  5. Aug 3, 2015 #4

    sophiecentaur

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    This scenario involves a truly vast amount of Potential energy, even when the two planets are placed 'gently' side by side. The forces in the area of contact would be enough to generate plenty of heat, during the initial settling. Just as rocks melt during tektonic movements, the parts of the mantle under such pressure would melt and the two halves would quickly (geologically quickly or even much faster) coalesc and 'melt together'.
    I guess a good supplementary question to ask would be 'How big could two rocky spheres be in order that they would melt together?" Afaik, the only objects we observe in space that are not pretty spheroidal are small in planetary terms.
    The presence of a large planet nearby is enough to generate enough tidal geological energy to melt its moons into roughly spherical shape.
     
  6. Aug 3, 2015 #5

    russ_watters

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    Consider that the definition of "planet" includes the ability to pull one's self into a sphere.
     
  7. Aug 3, 2015 #6

    A.T.

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    As opposed to back then, when gravitation didn't exist?
     
  8. Aug 3, 2015 #7

    sophiecentaur

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    Ha ha.
     
  9. Aug 3, 2015 #8
    I meant just gravitation cannot melt things so that it can be compared to how earth was initially created. Masses on earth dont get crushed in earth's surface anyhow.

    Well, two similar earth-like planets may get crushed, but how earth was created is still quite a different scenerio, specially to the answer of the question how materials will be in there afyerwards.
     
  10. Aug 3, 2015 #9

    DaveC426913

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    You might want to look up Earth's Roche limit. It will give you a good idea of how close that Earth II can get before you start having problems.
     
  11. Aug 3, 2015 #10

    phinds

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    Excuse me?
     
  12. Aug 3, 2015 #11

    Drakkith

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    They do if their mass is large enough. This is why mountains can only get so large.

    The crust of both planets would collapse under the immense weight and the two planets would mere into a single, larger planet.
     
  13. Aug 4, 2015 #12

    A.T.

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    The two Earths don't need to be "crushed", as they already are mostly fluid.
     
  14. Aug 4, 2015 #13

    sophiecentaur

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    The massive amount Energy available as heavy rocks move 'downwards' is counter intuitive because 'rock' is very hard and is difficult to melt in the lab. But it's to do with the actual numbers involved. It's all a matter of Energy available = Force times Distance and you are dealing with extremely high values for both quantities. I will mention, again, how rocks melt even under relatively mild conditions when tektonic plates squash and rub together at speeds of just a few cm/year.
    You have to ignore your initial reactions to such problems and wait until someone does some calculation, before coming to conclusions in Science.
     
  15. Aug 4, 2015 #14

    A.T.

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    One should visualize that most of it is already melted, while the crust is a relatively thin layer. Even without melting the crust, there is no rigid structure below it, to support another Earth.
     
  16. Aug 4, 2015 #15

    Drakkith

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    I don't think it matters if the interior of the Earth is still liquid or not. The two bodies are going to be 'crushed' together and form one body anyways, likely heating up significantly in the process.
     
  17. Aug 4, 2015 #16

    sophiecentaur

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    Yes. There would be a size of rock that, on its own, would not be molten (say the internal nuclear processes had died out long ago) but, when placed next to a similar one, would coalesc because there would be sufficient GPE to supply the necessary heat energy.
    But yer average 'intuitive' member of the public would need that to be explained in more words, probably. (Along with some visible evidence on Earth.
     
  18. Aug 5, 2015 #17
  19. Aug 5, 2015 #18

    sophiecentaur

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    That is only one theory. afaik. There are a number of different theories - each of which seems to fit with different classes of planet, apparently. One thing seems certain and that is based on the angular momentum of the Solar System. The planets and other stuff could not all have originated in a 'larger' Sun because the conserved total angular momentum would have needed the original Sun (in the model) to be spinning too fast to be stable.
    Here is one of many articles about the topic.
     
  20. Aug 5, 2015 #19

    phinds

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    Your statement did not say "solar nebula", it said "sun". You implied that the sun formed and then the planets broke off from it. As sophiecentaur has pointed out, that could not have happened.
     
  21. Aug 5, 2015 #20
    You're asking if the 12 mile crust of rock floating on 8000 miles of liquid has the structural integrity to hold up 6 sextillion tons? No, not even close.

    Think about this, why is the surface of the earth where it is? Gravity pulls it into the earth and buoyancy keeps it from sinking to the core. Hydrostatically balance, right? The force on the surface of the earth is 0 (gravity - outward pressure.) Now put another earth on top of it, what's the forces on the surface do? The force on earth's crust is now gravity[earth] - gravity[theta] - outward pressure. The two gravities cancel out, all you have left is outward pressure. Likewise on the opposite side of the planet, you suddenly have gravity[earth] + gravity[theta] - outward pressure, so you have extra forces pulling on it. In the core of the earth, there is a giant ball of solid iron suspended in a liquid, which is used to having a net force of zero on it. Now suddenly it's got a massive gravitational field pulling on it, it'll drift away from the exact centre of our planet and head towards the center of mass.
     
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