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Problem with the theories about the Sun and the planets

  1. Sep 8, 2007 #1
    I am not an astronomer or astrophysicist but lately, I have been reading a lot of books to upgrade my knowledge in cosmology.

    I have encountered two issues that I am baffled about and wonder if anyone can help me throw some light on them

    (1) If the planets are parts of the sun or came from the sun, why are the planets so different from the sun? Why are the planets not shining like the sun?

    (2) My idea is that if the earth were to move about 1 million miles closer to the Sun, not only would all the ice in the northern and southern poles melt and flood the whole planet and swallow up all the continents, but I also believe the earth would explode from the heat.

    If this could happen to earth, why is it that Mercury and Venus are so near to the Sun and yet they have not exploded?

    I would appreciate any explanation about these two issues.

    Thanks
    Scogos
     
  2. jcsd
  3. Sep 9, 2007 #2

    SpaceTiger

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    The planets have never been parts of the sun. It is true that the stuff that makes up planets and the sun came from the same cloud of gas, but the processes by which they formed were quite different. As for the reason that the planets don't shine, it has to do with their composition and central temperatures. The sun is powered by nuclear fusion, a process that requires temperatures and densities high enough to cause nuclei to merge. The planets aren't massive enough to keep these conditions in their core.

    On a side note, Jupiter is actually shining, but not brightly enough to be noticable over the sun's reflected light. It's not powered by nuclear fusion, but rather by the energy released in its slow collapse.


    Although the ice caps would melt, the earth would not explode if brought to Mercury's distance.
     
    Last edited: Sep 9, 2007
  4. Sep 9, 2007 #3

    Janus

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    For one thing, since the Earth's orbit aorund the Sun is not a perfect circle, it already does not keep a constant distance from the Sun. In fact, it varies by 3,000,000 miles; The Earth is 3,000,000 miles closer to the Sun in January than it is in July. You will notice that the Earth is actually closer to the Sun when it is summer in the Northern hemisphere than when it is summer. Since a three million mile variation causes very little actual change in temperature on the Earth, it is safe to say that you are over estimating how much change in temperature a 1 million mile difference will make.

    Second, even if the ice caps melted, the continents would not be swallowed up, the oceans would only rise a few hundred meters. Coastal areas would be flooded, but the vasrt majority of the land mass would remain above sea level.
     
  5. Sep 9, 2007 #4

    SpaceTiger

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    Good catch, I skimmed past the numbers. Janus is quite right, a change that small wouldn't even have a large impact on climate, though moving Earth to Mercury or Venus' distance certainly would.

    And I just realized this isn't cosmology...let's move it to general astro.
     
  6. Sep 9, 2007 #5

    russ_watters

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    You just debunked your own idea! Besides what Janus said, if the that didn't happen to the other inner planets, then the reason why is that your idea isn't right.

    Think about it this way: why, exactly, would a planet explode?
    You may have noticed that the inner and outer planets are quite different from each other. The outer planets are mostly hydrogen, not unlike the sun. The inner planets likely started forming with a lot of hydrogen around them, but it got lost when the sun ignited.
     
    Last edited: Sep 9, 2007
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