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Where do the heavier elements come from, such as those found in planets?

  1. Mar 30, 2012 #1
    Something similar to this came up in a lecture but it wasn't explained very well. From wikipedia it seems that our sun is made up of 74.9% Hydrogen and 23.8% Helium. The final 1.3% is made up of heavier elements such as oxygen, carbon, neon, and iron.

    If the the entire solar system condensed out of the same cloud of matter, how come the planets are composed of such different materials to the sun? Where do the other elements come from?

    I heard that heavier elements were thought to be made in supernovae, but then also heard that that was just a theory made to hide the fact that no one really knows. Does this mean that there would have been a previous star in this general area in space we occupy that went supernova, then our current solar system was created out of the remains?
  2. jcsd
  3. Mar 30, 2012 #2


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    Pretty much, yes. Sol is a recent Population I star. The heavier elements were fused in the supernovae of more ancient Population II stars. (larger number = earlier star)

  4. Mar 30, 2012 #3
    Good question. The answer is in planet formation---you couldn't make planets the size of earth ('terrestrial planets') with the same composition as the sun, because they wouldn't stay bound together. The 'gas-giants' are basically the smallest objects you can form in this environment that are gas dominated, but they still require a more dense core to have formed.

    Heavier elements are definitely produced in supernovae, and the numbers do work out quite well. That isn't to say that all of the details are worked out, for example, the exact contribution of different types of supernovae aren't perfectly worked out... This isn't my field of expertise, but I'm sure there are lots of details that need to be filled in.
  5. Mar 30, 2012 #4


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    The sun has plenty of heavy elements, but, captured the majority of the hydrogen and helium available in the primordial solar system. This gives it a higher fraction of these elements - especially compared to the terrestrial planets.
  6. Mar 31, 2012 #5
    Thank you. So should all the objects in the asteroid belts be composed of similar materials to the planets?
  7. Mar 31, 2012 #6


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    Welllll, similar, yes. They came from the same gas and dust that formed the solar system, but have been subjected to different processes.

    eg. the inner planets are all rocky, the outer planets are (mostly) gaseous due to these different processes too.

    But yes, the asteroids are thought to be a planetoid that might never have formed due to Jupiter's interference.
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