Since the entire solar system inherits its heavy elements from supernovae unrelated to our star, I fail to understand why, while capturing most of said system's matter, the sun only contain light elements, especially hydrogen, selecting out heavy elements found in the rest of the system, especially rocky planets like earth.

EDIT: so reading the answer offered by G. Smith it appears my initial question title is wrong, because the Sun does contain heavier elements. Not sure if I should correct it afterwards or leave it for historical reasons.

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    $\begingroup$ curious.astro.cornell.edu/our-solar-system/53-our-solar-system/… $\endgroup$
    – G. Smith
    May 9, 2019 at 16:57
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    $\begingroup$ The better question is why the earth is not made of almost entirely lighter elements like most of the rest of the universe. $\endgroup$ May 9, 2019 at 18:36
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    $\begingroup$ It wouldn't be very good at being a star if it were made of dark elements, for one. $\endgroup$
    – 0xdd
    May 9, 2019 at 19:06
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    $\begingroup$ As XKCD says, there's more gold in the Sun than water in the Earth's oceans. $\endgroup$
    – PM 2Ring
    May 9, 2019 at 20:23
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    $\begingroup$ @PM 2Ring: thus the color yellow. (I know that's not true.) $\endgroup$
    – Winston
    May 9, 2019 at 20:32

1 Answer 1


The Sun didn’t “select out” heavy elements from the cloud. The planets selected out light elements because they don’t have enough gravity to hold on to their hydrogen and helium.

Source: http://curious.astro.cornell.edu/our-solar-system/53-our-solar-system/the-sun/composition/201-does-the-sun-have-any-heavy-elements-beginner

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    $\begingroup$ Thank you. That makes sense with Jupiter's ability to retain light elements as well. $\endgroup$
    – Winston
    May 9, 2019 at 17:06
  • $\begingroup$ Interesting, I never thought of it that way. So the protoplanetary disk may have had the same composition as the sun, at least for a while. So did all the planets originally have a composition similar to the gas giants, but over time the light elements left the atmosphere and were blown away by the solar wind? Where did they go? Is there a hydrogen layer at the heliopause? $\endgroup$ May 9, 2019 at 22:04
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    $\begingroup$ @PeterA.Schneider Well, not quite a hydrogen layer at the heliopause - after all, the heliosphere is an evacuated region of the interstellar medium. ISM outside of the solar system is much denser than inside. The heliopause is essentially where the pressure of the interstellar medium equals the pressure of the solar wind. The material thrown out thanks to the solar wind mixes easily with the ISM (with turbulent flow), and since it's no longer gravitationally bound to the Sun, the "leaked" hydrogen (and helium) has been dispersed over huge volumes of the galaxy in the billions of years. $\endgroup$
    – Luaan
    May 10, 2019 at 6:46

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